Reactive Polymers Fundamentals and Applications || Polyurethanes

2

Polyurethanes

Polyurethanes consist basically of two components, an isocyanate compo-nent and a diol component. The diol component can be a polyether end-capped diol or a polyester end-capped diol. The urethane structure may beidentified as the esters of carbamic acid or ester amides of a carbonic acid.The urethane formation is achieved by the addition of a tertiary amine andan organometallic compound.

There are many monographs on the topic,1–11 the most recent ofW. Dias Vilar12 and Klempner.13 Polyurethanes also find use in medicalapplications.14, 15 They are used to a large extent as adhesives16 and ascoatings.

2.1 HISTORY

Polyurethane was first described by Bayer∗ in 1937.17 The first poly-urea was composed from hexane-1,6-diamine and hexane-1,6-diisocyan-ate. Two diisocyanates used at that time, diphenylmethane-4,4′-diisocyan-ate and naphthalene-1,5-diisocyanate, are still key products in polyureth-ane chemistry. Besides O. Bayer, H. Rinke, A. Hoechtlen, P. Hoppe andE. Meinbrenner contributed significantly to the development of polyureth-anes.

In 1940, toluene diisocyanate was introduced. From the beginningpolyurethanes were utilized as foams, coatings, and cast elastomers.

∗Otto Bayer, born in Frankfurt/Main 1902, died 1982

69

70 Reactive Polymers Fundamentals and Applications

R NH2 C

Cl

ClO R N C O+

Figure 2.1: Synthesis of Isocyanates

2.2 MONOMERS

Monomers for the synthesis of polyurethanes consist of two types, i.e.,diisocyanates and polyols.

2.2.1 Diisocyanates

The basic synthesis of isocyanates is shown in Figure 2.1. The synthesisstarts with an amine, aliphatic or aromatic and phosgene. The isocyanateis formed by the elimination of two molecules of HCl.

Phosgene Route. The synthesis route via phosgene was invented in 1884by Hentschel, although isocyanates had been discovered in 1848 by Wurtz.The synthesis runs via two basic steps, i.e.

1. Formation of the carbamic chloride,2. Elimination of hydrochloric acid.

The industrial synthesis has to minimize the various side reactionsthat may occur, as shown in Figure 2.2.

Phosgene-free Route. There is also a phosgene-free synthesis route,because of the hazards of handling phosgene. The route is shown in Figure2.3. The synthesis starts with nitrobenzene; from that the ethyl urethaneis directly formed with carbon monoxide and ethanol. The urethane isdimerized by a carbonylation reaction. Finally, by heating the urethane isdecomposed into the isocyanate and the alcohol.

Typical diisocyanates are shown in Table 2.1. Aromatic diisocyan-ates are shown in Figure 2.4. The highly volatile isocyanates are very toxic.

During curing there is also an emission of the unreacted isocyanate.The emission also depends on the reactivity of the particular isocyanate, as

Polyurethanes 71

C

Cl

ClO C O

N

N

H

H

R

R

R NH2

R NH2

R NH2 HCl R NH3 Cl

C O

N

N

H

H

R

R

+

+

R N C O

N R

H

H

+

Figure 2.2: Side Reactions in Isocyanate Synthesis: Salt Formation with HClgenerated, Formation of Urea from Amine and Isocyanate, Formation of Ureafrom Amine and Phosgene

NH C

O

HNC

O

CH2

O O

CH2CH2

CH3 CH3

CH2 NCOOCN

CHO

NO2 NH C

O

O CH2

CH3

CO +CH

3CH2OH

Figure 2.3: Phosgene-free Synthesis of Diisocyanates


CH2 NCOOCN

4,4'-Diphenyl methane diisocyanate

CH2 NCO

NCO

2,4'-Diphenyl methane diisocyanate

OCN

NCO

Naphthalene 1,5-diisocyanate

NCO

NCO

CH3

Toluene 2,4-diisocyanate

NCO

CH3

OCN

Toluene 2,6-diisocyanate

Figure 2.4: Aromatic Diisocyanates

Polyurethanes 73

Table 2.1: Isocyanates for Polyurethanes

Isocyanate Remarks

Hexamethylene diisocyanate Color-freeIsophorone diisocyanate Color-freeDicyclohexylmethane-4,4′-diisocyanate4,4′-Diisocyanato dicyclo hexylmethane2,4-Toluene diisocyanate A mixture of 65% 2,4 isomer and

35% 2,6 isomer is most com-mon

2,6-Toluene diisocyanate1,5-Naphthalene diisocyanate4,4′-Methylene diphenyl diisocyanate Lower volatile then TDI4,4-Methylene biscyclohexyl diisocyanate(HMDI)

1,2-Bis(isocyanate)ethoxyethane(TEGDI)

Extremely soft18

Macromonomers See Ref.19

Lysine-diisocyanate Biodegradable formulations20

detected in a mixture of 2,4′-methylene diphenyl diisocyanate (2,4′-MDI)and 4,4′-methylene diphenyl diisocyanate (4,4′-MDI). Because of the highreactivity with moisture, the analysis requires special techniques; less than5 ng/m3 can be detected.21

2.2.1.1 Toluene diisocyanate

In technical applications, toluene diisocyanate (TDI) is used either as pure2,4-isomer or as a blend of the 2,4- and 2,6-isomers. Two blend qualitiesare available, TDI-80/20 and TDI-65/35, which means 80% 2,4-isomerwith 20% 2,6-isomer, and 65% 2,4-isomer with 35% 2,6-isomer, respec-tively. The two isocyanate groups have unequal reactivity; the isocyanategroup at the p-position is more reactive.

Toluene diisocyanate is synthesized from toluene via dinitrotoluene,reduction of the nitro group with hydrogen (c.f. Figure 2.5) and phosgena-tion as shown in Figure 2.1.

The nitration of toluene is achieved in a two-step procedure. In thefirst step a mixture of the ortho, para, and meta isomers (63% o-isomer,33% p-isomer, 4% m-isomer) is obtained. The isomers can be separatedby distillation. When p-nitrotoluene is used in the second nitration step, a


CH3

HNO3/H2SO4

CH3

NO2O2N

CH3

NH2H2N

CH3

NCOOCNC

O

Cl Cl

H2

Figure 2.5: First Steps of the Synthesis of Toluene diisocyanate

100% 2,4-dinitrotoluene is obtained. The nitration of o-nitrotoluene finallyyields the TDI-65/35 quality. If the blend obtained from the first step isdirectly reacted, the TDI-80/20 quality will be obtained.

2.2.1.2 Diphenylmethane diisocyanate

Diphenylmethane diisocyanate (MDI) has a lower vapor pressure and istherefore less toxic than TDI. The synthesis of MDI starts with the conden-sation of aniline with formaldehyde as shown in Figure 2.6 for the ortho

adducts. In fact, 2,2′- and 2,4′- and 4,4′-isomers are formed, the yield ofthe dimer of 4,4′-diphenylmethane diamine being in an amount of ca. 50%.The isocyanates are obtained then in the usual way by phosgenation. Thecrude mixture can be directly used. However, the mixture can be separatedor otherwise modified in order to obtain products with more convenientproperties.

4,4′-MDI has a melting point around 38°C. It forms insoluble dimerswhen stored above the melting point. Further, it tends to crystalize. Amixture of 2,4′-MDI and 4,4′-MDI shows a lowering of the melting pointwith a minimum of 15°C at 50% p-isomer.

2.2.1.3 Aliphatic Diisocyanates

A disadvantage of aromatic diisocyanates is that they become yellow todark brown when they are cured. This limits the fields of applications.

Polyurethanes 75

NH2

CH2 CH2 CH2

NH2 NH2

CH2 O

NH2

CH2 NH2H2N

+

Figure 2.6: Condensation of Aniline with Formaldehyde

Aliphatic diisocyanates are colorless, but have other disadvantages. In par-ticular, the mechanical properties of the final products, such as such aselongation, tensile strength and flexibility, are inferior. However, aliphaticisocyanates find important applications in coating formulations. Aliphaticdiisocyanates include 1,6-hexane diisocyanate (HDI), isophorone diiso-cyanate (IPDI), dicyclohexylmethane-4,4′-diisocyanate, i.e., hydrogenatedMDI, c.f. Figure 2.7.

In general, aliphatic are less reactive than aromatic isocyanates. Dueto steric hinderance, the affinity of m-tetramethylxylene diisocyanate towater is so small that it can be dispersed in water without reacting.

2.2.1.4 Modified Diisocyanates

The isocyanates can be modified in several ways, i.e. by dimerization,oligomerization with diols, or capping the isocyanate group.

Dimerization. Diisocyanates can be dimerized, by splitting off carbondioxide, to the respective carbodiimides. The carbodiimide can react fur-ther with an excess of isocyanate to a uretonimine, c.f. Figure 2.8. Such


CH2 CH2 CH2 CH2 CH2 CH2 CH2 NCOOCN

Hexamethylene diisocyanate

CH2

H3C

CH3

NCO

NCO

Isophorone diisocyanate

C CH3H3C

NCO

C

H3C

CH3

NCO

m-Tetramethylxylene diisocyanate

Figure 2.7: Aliphatic Diisocyanates: 1,6-Hexane diisocyanate, Isophorone diiso-cyanate, m-Tetramethylxylene diisocyanate

compounds have now three isocyanate groups in the molecule, i.e., theyhave a functionality of three.

The properties of MDI can be varied in wide ranges, and conse-quently can be used for different applications. The crude MDI is used forrigid foams. Pure 4,4′-MDI is used, among other applications, for shoesoles and also for thermoplastic polyurethanes.

Biuret Reaction. Water hydrolyzes the isocyanate group very quickly.Therefore it is essential to store the isocyanate material moisture-free. Onthe other hand, the action of water can be purposefully used to modifyisocyanates. A biuret is formed by the reaction of a substituted urea withisocyanate, as shown in Figure 2.9. The substituted urea itself can be ob-tained by the reaction of water with isocyanate. An amine is formed in thecourse of hydrolysis that condenses immediately with water to the substi-tuted urea. The substituted urea is the reagent for the biuret reaction asexplained above.

Prepolymers. If a glycol or a glycol ether is reacted with an excessof a diisocyanate, then a prepolymer is formed. In this reaction one diolcouples two molecules of diisocyanate, as schematically shown in Figure2.10. Also, branched alcohols, like 1,1,1-trimethylolpropane, can be used.

Polyurethanes 77

CH2

NCO

N

C

N

CH2

NCO

CH2

NCO

NCO

CH2

NCO

NCO

CH2

NCO

N

C

N

CH2

NCO

N

C

O

CH2

NCO

Figure 2.8: Formation of Uretonimine

R N C O

N C OH

R N R’

R N C O

H

N C O

R’NR

Figure 2.9: Biuret Formation of Isocyanates


CH2 NOCN

H

C

O

O

CH2

CH2

O

CH2

CH2

O

C

O

N

H

CH2OCN

+

CH2 NCOOCN

CH2 CH2 O CH2 CH2 OHHO

Figure 2.10: Formation of Prepolymers

Polyurethanes 79

In this case ideally a trifunctional isocyanate is formed.When the stoichiometric ratio of isocyanate groups to alcohol groups

is more then two, appreciable amounts of unreacted diisocyanate is left be-hind, which causes an increased toxicity. If the diisocyanate is sufficientlyvolatile, the unreacted residual diisocyanate can be removed by distillationunder vacuum. Such mixtures are liquids at room temperature. Because oflarger structure the prepolymers are less volatile and therefore less toxic.

Toluene diisocyanate and isophorone diisocyanate possess two iso-cyanate groups with different reactivities. When forming the prepolymer,the more reactive group is reacted. The less reactive group is left unreacted.

The properties of the final product can be adjusted by the selectionof the components and the amounts making the prepolymer. For example,prepolymers based on poly(ethylene oxide) or poly(propylene oxide) willbe used for hydrophilic gels, whereas hydrophobic polyols will result inhydrophobic polyurethanes. For hydrophobic polyurethanes, polyols withvery nonpolar backbones, e.g., hydroxyl functional poly(butadiene), canbe used to introduce the hydrophobicity.22

By choosing the stoichiometric ratio of NCO to OH groups, the con-tent of free isocyanate groups can be adjusted from 2% to 20%.

Viscosity is an important parameter for the processability of the rawmaterials. The viscosity increases with molecular weight and decreaseswith the content of unreacted isocyanate. The viscosity also increases withincreasing allophanate formed, because this is a crosslinking reaction. Theallophanate formation is favored at temperatures above 60 to 80°C and cat-alyzed by alkaline residues in polyether polyols, if any is present. There-fore, to increase the storage time of the prepolymer, acid stabilizers such asbenzoyl chloride, acetyl chloride, or p-toluenesulfonic acid can be added.

End-capped Diisocyanates. The reaction of the isocyanate group withalcohols to form the urethane functionality is thermoreversible. At elevatedtemperatures the urethane decomposes into the isocyanate. This reactionis utilized at the phosgene-free route of synthesis of isocyanates. On theother hand, the reversibility can be used in the preparation of end-capped,or blocked diisocyanates.

The isocyanate group is allowed to react with compounds containingacidic hydrogen atoms. In this way the isocyanate group is masked and notaccessible for other reactants. At elevated temperatures the retro reactiontakes place, the isocyanate group is set free, and in presence of amines the


urethane can be formed. A necessary condition for the concept to workproperly is that the unblocking reaction takes places at lower temperaturesthan the thermal decomposition of the urethane group.

The temperatures for the retro reaction of unblocking are between 90and 160°C. Aromatic isocyanates are less stable than aliphatic isocyanates.The temperature of unblocking decreases in the following order for thetypes of blocking agents: alcohols > lactams > ketoximes > active meth-ylene groups containing compounds. Suitable blocking agents are phenol,ethyl acetoacetate, ε-caprolactam, methylethylketoxime, diethyl malonate,and 3,5-dimethylpyrazole.

N,N′-Carbonylbiscaprolactam (CBC), c.f. Figure 2.11, offers an iso-cyanate-free route to new families of thermosets and reactive resins withcaprolactam-blocked isocyanates. CBC reacts with primary amines intoblocked isocyanates at 100 to 150°C. The reaction is also suitable forhighly functional amine dendrimers and polymers.

With polyols, a ring-opening of the caprolactam occurs. Catalystsinclude zirconium alcoholates, magnesium bromide or dibutyltin dilaurate(DBTDL). N-carbamoyl caprolactam end groups are formed by a nucleo-philic attack of the hydroxy group at one of the CBC caprolactam rings andsubsequent ring opening. Thus, the corresponding blocked ester-functionalisocyanates are formed.

The CBC derivatives are attractive crosslinking agents and inter-facial coupling agents for adhesives and coatings. Further, due to thenon-toxic CBC-intermediates and polyesterurethanes, they are also suit-able for medical applications.23, 24 When the ring opening reaction is donewith poly(propylene oxide)-based triols, then crosslinked polyurethanesare obtained.25 Thus, 1,2-bis-[2(2-hydroxy-5-methylphenyl)-5-benzotri-azolyl]-ethane (BHMBE) reacts with the phenolic hydroxyl groups and isthus a reactive UV-absorber.26 The synthesis starts from 4,4′-diaminodi-benzyl in several steps. The structure is shown in Figure 2.12.

Isocyanurate. The formation of an isocyanurate is in fact a trimeriza-tion of an isocyanate (Figure 2.13). Trimers from toluene diisocyanate andhexamethylene diisocyanate are available. Such isocyanate isocyanuratestructures are trifunctional, i.e., they have three isocyanate groups pend-ing. They can be modified to become more hydrophilic, if one isocyanategroup is allowed to be coupled with a polyglycol, e.g., poly(ethylene ox-ide) or poly(propylene oxide).

Polyurethanes 81

N C

OO

N

HX

O

R

+ RXHN

O

C

OO

N

N

O

HC

OO

NXR +

Figure 2.11: Reaction of N,N ′-Carbonylbiscaprolactam with a Nucleophile RXH.Top: ring elimination with formation of caprolactam. Bottom: ring opening reac-tion.23

CH2 CH2N

N

N N

N

N

H3C CH3

OH HO

Figure 2.12: 1,2-Bis-[2(2-hydroxy-5-methylphenyl)-5-benzotriazolyl]-ethane26


3 R NCON

N

N

O

O

O

R

R

R

Figure 2.13: Trimerization: Formation of an Isocyanurate Structure

Macromonomers. A macromonomer is a polymer that contains reac-tive groups, here isocyanate groups. A macromonomer from 2-(dimethyl-amino)ethyl methacrylate that bears a 1-(isopropenylphenyl)-1,1-dimeth-ylmethyl isocyanate group has been synthesized. However, 2-(dimeth-ylamino)ethyl methacrylate (DMAEMA) reacts with 2-mercaptoethanolpreferably in an addition reaction that acts as chain transfer agent in radicaltelomerization. In this way, an adduct of the methacrylate and the mer-capto compound is formed. The structure of the adduct and the productof functionalization are shown in Figure 2.14. The oligomers can be thenfunctionalized with 1-(isopropenylphenyl)-1,1-dimethylmethyl isocyanate(TMI), resulting in macromonomers.19

α,α′-Dihydroxyl-poly(butyl acrylate) prepared by atom transfer rad-ical polymerization (ATRP) has been used as a macromonomer with twohydroxyl groups at one end. This macromonomer was used for chain ex-tension of diphenyl-methane-4,4-diisocyanate to obtain comb-like oligoisocyanates, as shown in Figure 2.15. These materials have potential in-terest as pressure-sensitive adhesives (PSA).27

In a completely different way rodlike macromonomers were ob-tained. In a first step, the N=C bond n-hexyl isocyanate was polymerizedby titanium catalysts in a living polymerization. The living chain end wasdeactivated by methacryloyl chloride to result in a methacrylic-terminatedpoly(n-hexyl isocyanate.28

Block copolymers from n-hexyl isocyanate and isoprene have beenobtained by a living polymerization technique.29 The living anionic poly-merization proceeds very fast and therefore low temperatures −98°C, arerequired to control the selectivity. 3,5-Bis(4-aminophenoxy)benzoic acid,c.f. Figure 2.16, is a monomer from the type AB2. It can be polycondensedto form dendritic polymers. These polymers contain pendant amino groupsthat can be crosslinked with diisocyanates.30

Polyurethanes 83

CH2 CH2

CH3

C

O

O

CH2

CH2

N

CH3H3C

S

CH2

CH2

H2CH

CH3

C

CH3

CH3

C NH

O

C O

CH2 CH2

CH3

C

O

O

CH2

CH2

N

CH3H3C

S

CH2

CH2

OH

CH2 CH

CH3

C

O

O

CH2

CH2

N

CH3H3C

S

CH2

CH2

OH

H

Figure 2.14: Adduct from 2-(dimethylamino)ethyl methacrylate and 1-(isoprop-enylphenyl)-1,1-dimethylmethyl isocyanate19

CH2 CH

C O

O CH2 CH2 CH2 CH3

NCOCH2

CH3

H3C C

O C

O

CH2 HH

N N

O O

C CO OCH2 CH2

CH3

CH2

C

CH3CH2CH2CH2O

OC

CHCH2

Figure 2.15: Comb-like Oligo Isocyanates27


C

O

OH

O

O

H2N

H2N

Figure 2.16: 3,5-Bis(4-aminophenoxy)benzoic acid

2.2.1.5 Enzymatic Synthesis of Polyurethanes

Polyurethanes have been synthesized using the enzyme Candida antarcticalipase B. The use of enzymatic methods offers the possibility to reverse theconventional process by creating the urethane first and then using a lowtemperature enzymatic polyester synthesis to build the polymer. A novelseries of biscarbamate esters and polyesters also could be obtained.31

2.2.1.6 Synthesis of Urethanes via Carbonate Esters

The synthesis of urethanes avoiding handling of isocyanates is also pos-sible by the reaction of amines or diamines with ethylene carbonate. Thescheme is shown in Figure 2.17. Urethane dimethacrylates suitable fordental fillers have been synthesized in this way. For example, ethylenecarbonate in two-fold excess was reacted with 1,6-hexane diamine to ob-tain a urdiol. This was reacted with methacrylic anhydride.32

2.2.2 Polyols

Polyols are the second basic component beside diisocyanates. There aretwo types of polyols,

1. Polyether polyols,2. Polyester polyols.

2.2.2.1 Polyether Polyols

Most widely used are polyether polyols. Monomers commonly used forpolyether polyols are listed in Table 2.2.

Polyurethanes 85

NHC

O

O(CH2)2OHHO(CH2)2O

O

C HN

NH2

H2N

CH2

CH2O

O

O

O

O

OH2C

H2C

Figure 2.17: Reaction of Ethylene Carbonate with 1,6-Hexane diamine

Table 2.2: Monomers for Polyether Polyols

Monomer Remarks

Propylene oxideEthylene oxide As copolymer with propylene oxideButylene oxideTetrahydrofuran In fibers and elastomers


R OH B R O

R O CH2 CH2

CH3

OO

CH3

CH2CH2OR

+

+

Figure 2.18: Initial Steps of the Formation of Polyether polyols

Anionic Ring Opening. Polyols with a molecular weight between 1,000and 6,000 Dalton and a functionality between 1.8 and 3.0 are used in flex-ible foams and elastomers. Polyols with a molecular weight below 1,000Dalton and high functionalities result in high crosslinked rigid chains andare used in rigid foams and high performance coatings.

The polymerization is initiated with an alcohol and a strong base.The base is usually potassium hydroxide that forms initially the monomericalcoholate. The alcoholate anion is subjected to a series of ring opening re-actions of the epoxide or the cyclic ether. The basic mechanism is sketchedin Figure 2.18.

In the case of nonsymmetric epoxides the alcoholate anion attacksthe less hindered carbon atom of the epoxide, as shown in Figure 2.18.

Therefore, polyols composed exclusively from propylene oxide bearsecondary hydroxyl groups as end groups. Secondary hydroxyl groups areless reactive than primary hydroxyl groups.

To get polyols with the more reactive primary hydroxyl groups, thepolymerization is started with propylene oxide, and in the final stage eth-ylene oxide is added. Ethylene oxide improves the water solubility of thepolyol.

Due to the mechanism of polymerization without termination in pre-paring polyether polyols, the molecular weight distribution of the polyolsexhibits a Poisson distribution. This is narrower than the distribution ofpolyester polyols. Instead of alcohols, amines can also be used. Typicalinitiator alcohols are propylene glycol, glycerol, trimethylolpropane, tri-ethanolamine, pentaerythritol, sorbitol, or sucrose.

Sucrose results in highly branched polyols suitable for rigid foams,whereas the alcohols with a lower functionality are used for flexible ma-terials. Amines include ethylene diamine, toluene diamine, 4′,4′-diphenyl-

Polyurethanes 87

methane diamine, and diethylenetriamine. The resulting polyols exhibit ahigher basicity than the polyols with an alcohol as initiator and are there-fore more reactive with isocyanates.

A side reaction of the base in polymerization is the isomerizationreaction. For example, propylene oxide isomerizes to allyl alcohol. As aconsequence, vinyl-terminated monofunctional polyols are formed. Suchmonofunctional polyols are addressed as monols. Such compounds havenegative influence on the mechanical properties of the final products.

The formation of monols can be suppressed by using special cata-lysts, e.g., zinc hexacyanocobaltate. This type of catalyst is referred to asdouble metal cyanide catalyst.

Grafted Polyols. Copolymer polyols are obtained by grafting styreneor acrylonitrile to poly(propylene oxide). The radicals attack the tertiaryhydrogen sites (−CH2CHtert(−CH3)−O) in the poly(propylene oxide) asa transfer reaction to the poly(propylene oxide). Originally pure acrylo-nitrile was used for grafting, but the so formed copolymer polyols causediscoloration problems in slabstock flexible foams. For this reason styr-ene/acrylonitrile copolymer polyols were developed.

Vinyl Functionalized Polyols. Another method is to functionalize thepolyols with a vinyl moiety. This is achieved by reaction of the polyolswith maleic anhydride, or methacryloyl chloride. Of course the function-ality of the polyols must be greater than two with respect to the hydroxylgroup, because hydroxyl groups are lost. If to the vinyl functionalizedpolyol a polymerizing vinyl monomer mixture is added, the pendent vinylgroup polyols take part in the polymerization reaction. With respect to thevinyl polymer a comb-like structure is formed, the teeth of the “comb” be-ing the polyol moieties. The styrene is hydrophobic, and at higher conver-sion the backbone of the comb may collapse to yield a spherical structure.The polyol chains are at the surface of the sphere.

Polyurea-modified Polyols. Urea urethane polyols and polyurea-modi-fied polyols are another type of polyols. They are synthesized in a two-stage reaction.

1. In the first stage a diamine or an amino alcohol is allowed to re-act with an excess of diisocyanate. The amine groups react with


the isocyanate group to form urea groups, whereas the hydroxygroups react with the isocyanate group to form urethane groups.The excess of isocyanate causes the formation of an isocyanateend-capped prepolymer. In the case of a diamine, isocyanates areformed that contain exclusively urea groups in their backbone. Inthe case of amino alcohols isocyanates containing urea and ureth-ane in the backbone are formed. Suitable diamines are hydrazine,ethylene diamine, etc.

2. In the second stage a diol or a polyol in molar excess with respectto the unreacted isocyanate groups is added. The pending isocyan-ate groups react with the hydroxy groups to form chain-extendedpolymeric polyols. The reaction of diamines with isocyanates pro-ceeds fast in comparison to the reaction of polyols with isocyan-ates.

Autocatalytic Polyols. The alkylamine group can be introduced in apolyol chain by using N-alkylaziridine or N,N-dialkyl glycidylamine asa comonomer with ethylene oxide or propylene oxide. Since the aminegroups in the chain catalyze the reaction of the hydroxyl groups with theisocyanate, this type of polyol is called autocatalytic.33

Autocatalytic polyols require less capping with primary hydroxyls,that is, less ethylene oxide capping to obtain the same performance in flex-ible molded foam than conventional polyols when used under the sameconditions. Moreover, low emission polyurethane polymers can be madewith autocatalytic polyols.

2.2.2.2 Polyester Polyols

Typical monomer combinations for polyester polyols are shown in Ta-ble 2.3.

Polyesters from Acid and Alcohols. The polyesters are produced by pre-heating the diol to ca. 90°C and adding the acid into it. The reaction tem-perature is raised gently up to 200°C to completion. Inert gas or vacuumis used to remove the water. The condensation is an equilibrium reaction,and a Schulz-Flory distribution of the molecular weight is obtained.

The condensation is catalyzed by acids, bases, and transition metalcompounds. However, catalysts should be used with care, because they

Polyurethanes 89

Table 2.3: Monomers for Polyester Polyols

Acid Alcohol Components Uses

Adipic acid, diethylene glycol, 1,1,1-trimethylol-propane

Flexible foam

Adipic acid, phthalic acid, 1,2-propylene glycol, gly-cerol

Semi-rigid foam

Adipic acid, phthalic acid, oleic acid, 1,1,1-trimeth-ylolpropane

Rigid foam

Adipic acid, ethylene glycol, diethylene glycol Shoe solesAdipic acid, ethylene glycol, 1,4-butanediol Elastomersε-caprolactone, various diols Ring opening condsa-

tionCastor oil, glycerol, trimethylolpropane Transesterification

could have undesirable effects on the subsequent curing reaction. Con-densation catalysts based on tin and other transition metals added only inthe ppm range did not show negative effects on the later procedures andproperties.

The hydroxyl numbers increase from flexible foams to rigid foamsfrom 60 mgKOH/g up to 400 mgKOH/g. Acids for soft foams are ali-phatic acids, such as adipic acid, whereas phthalic anhydride increases therigidity.

Terephthalic acid or isophthalic acid are used in high performancehard coatings and adhesives. Such foams are improved to be flame re-sistant. Foams based on aromatic polyester polyols show charring uponexposure to flame.

Polyesters based on terephthalic acid are manufactured by transes-terification of dimethyl terephthalate. Also poly(ethylene terephthalate)waste materials, such as polyester fibers or soft drink bottles, can be recy-cled by glycolysis to obtain suitable polyols.

Triols, such as glycerol and 1,1,1-trimethylolpropane, will resultin branched polyesters. Alcohols for flexible foams are ethylene glycol,diethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, etc.Longer chains result in a greater hydrolytic stability, simply because thereare fewer ester groups in the structure.

Polyesters from a single acid component and a single alcohol com-ponent are crystalline. The crystallinity can be reduced by using mixturesof diols or mixtures of different polyesters.


Mixed polyesters from waste acids of the production of nylon con-tain adipic acid, glutaric acid, and succinic acid. The acids can be alsohydrogenated to obtain the respective diols that can be used in the conden-sation.

The ester group in polyester polyols is sensitive to hydrolysis at-tack. The hydrolysis stability can be improved with additives that reactwith carboxylic and alcoholic groups, which are formed during the hydro-lysis. These additives include oxazolines, epoxy compounds, and carbodi-imide structures. In particular, polyester polyols can be stabilized by theaddition of 1 to 2% of hindered aromatic carbodiimides. These compoundsare scavengers for the acid generated by ester hydrolysis. The acid wouldcatalyze further hydrolysis.

Polyester polyols can contain 10 to 20% of vinyl polymers. Thevinyl polymers improve the hydrolysis stability, hardness and the form sta-bility.

ε-Caprolactone based polyesters. Another synthesis route for aliphaticpolyester polyols is the ring opening polymerization of ε-caprolactone withvarious glycols.

These include diethylene glycol, 1,4 butanediol, neopentyl glycol, or1,6-hexanediol. Branched products are obtained by adding 1,1,1-trimeth-ylolpropane or glycerol to a bifunctional alcohol. Higher branched polyes-ters utilize pentaerythritol. The poly(ε-caprolactone)-containing polyestersexhibit a greater hydrolysis resistance and lower viscosity than comparablepolyadipate glycols.

2.2.3 Other Polyols

2.2.3.1 Hydrocarbon Polyols

Hydrocarbon polyols can be obtained by living anionic polymerization ofbutadiene initiated by sodium naphthalene, which is the common route topolymerize butadiene. However, the living chains are finally terminated byadding ethylene oxide or propylene oxide. By adding water a poly(butadi-ene) with primary and secondary hydroxyl groups is obtained.

Hydroxy-terminated poly(butadiene) is also accessible by free-radi-cal polymerization of butadiene, initiated by hydrogen peroxide. The ma-jor advantage of hydrocarbon polyols is the high chemical resistance. Thelow glass transition temperature keeps its elastomeric properties down to

Polyurethanes 91

extremely low temperatures. The double bonds in the chain or pendentdouble bonds open the possibility of further reactions, like vulcanizationand other chemical reactions. The functionality of these diols is two, there-fore they can be used for thermoplastic polyurethanes.

2.2.3.2 Polythioether Polyols

Polythioether polyols include products obtained by condensing thiodigly-col either alone or with other glycols, alkylene oxides, dicarboxylic acids,formaldehyde, amino-alcohols, or aminocarboxylic acids.

2.2.3.3 Polyacetal Polyols

Polyacetal polyols are prepared by reacting glycols such as diethylene gly-col, triethylene glycol, or hexanediol with formaldehyde. Suitable polyac-etals may also be prepared by polymerizing cyclic acetals.

2.2.3.4 Acrylic Polyols

Acrylic polyols are obtained by copolymerization of acrylic monomers,such as ethyl acrylate, n-butyl acrylate, acrylic acid, methyl methacrylate,or styrene with minor amounts of 2-hydroxyethyl acrylate or 4-hydroxy-butyl acrylate. Styrene, if added, makes the acrylic polyol more hydropho-bic. Acrylic polyols are used in two-component coating systems. Theyexhibit good chemical resistance and weatherability.

2.2.3.5 Liquefied Wood

Liquefied wood can be obtained by the liquefaction of benzylated woodwastes using dibasic esters as solvent with hydrochloric acid as catalyst.The reaction is completed at 80°C after 3 hours. Liquefied wood acts asa diol component for, e.g., TDI, IPDI, and HDI. Polyurethane resins fromliquefied wood have a higher thermal stability than the traditional polyur-ethane resins.34

2.2.4 Polyamines

The amine functionality reacts with the isocyanate group to a urea moiety.In this way an amine group corresponds to a hydroxy group that reacts withthe isocyanate group to a urethane moiety.


Hydroxyl end groups in polyether polyols can be converted into am-ine end groups by reductive amination. This type of compound is called anamine-terminated polyether, or simply polyetheramine. Polyetheraminesare suitable for soft segments of polyurea resins.

2.2.5 Chain Extenders

Chain extenders, curing agents, and crosslinkers are low molecular com-pounds for improving properties of the final products. Examples are shownin Table 2.4. Chain extenders are difunctional compounds. Glycols areused in polyurethanes. Diamines or hydroxylamines are used in polyureasand mixed polyurethane ureas. Low-molecular weight polyamines reactwith the isocyanate group very fast, and can be used in reactive injectionmolding, where short cycles are essential.

2,2′-Pyromellitdiimidodisuccinic anhydride (DA) can act as a chainextender for isocyanates in the presence of polyols. In a first stage, thepolyol is allowed to react with the isocyanate compound to get isocyanate-terminated oligomers. In the second stage, the 2,2′-pyromellitdiimidodi-succinic anhydride reacts with the oligomer, splitting off carbon dioxide toresult in a poly(urethane-imide-imide). This class of polyurethane has ahigher thermal stability than conventional polyurethanes.35

Chain extenders with the triazene structure are photosensitive com-pounds.36 They are used together with another extender as a coextender.Because the resulting triazene polyurethanes become crosslinked by expo-sure to UV irradiation, they have a potential use as negative-resist poly-mers.

2.2.6 Catalysts

Catalysts are necessary to obtain the desired end products. The final prop-erties depend strongly on the content of urethane, urea, allophanate, biuret,and isocyanurate bonds. Therefore, catalysts govern the final properties ofthe materials. The nature of the catalysts also greatly influences the re-action time and the properties of the final product. The catalysts can beclassified into three main categories:

1. Catalysts for blowing,2. Catalysts for gelling, and3. Catalysts for crosslinking.

Polyurethanes 93

Table 2.4: Chain ExtendersCompound Remarks

Ethylene glycolDiethylene glycolPropylene glycolDipropylene glycol1,4 Butanediol2-Methyl-1,3-propylene diolN,N ′-bis(2-hydroxypropylaniline)Water1,4-Di(2-hydroxyethyl)hydroquinoneDiethanolamineTriethanolamine1,1,1-TrimethylolpropaneGlycerolDimethylol butanoic acid (DMBA) Waterborne chain ex-

tender37

HydrazineEthylene diamine (EDA)1,4-Cyclohexane diamineIsophorone diamine4,4′-bis(sec-Butylamine)dicyclohexylmethane4,4′-bis(sec-Butylamine)diphenylmethaneDiethyltoluene diamine Both isomers4,4′-Methylene bis(2-chloroaniline)4-Chloro-3,5-diamino-benzoic acid isobutylester3,5-Dimethylthio-toluene diamine Both isomersTrimethylene glycol-di-p-aminobenzoate4,4′-Methylene bis(3-chloro-2,6-diethylaniline)1-(α-Naphthyl)-3,3-di(2-hydroxyethyl)-triazene-1 (NT-D)

Photosensitive36

1-Phenyl-3,3-di(2-hydroxyethyl)-triazene-1 (PT-D)

Photosensitive36


Table 2.5: Catalysts Classified According to the Reaction

Reaction Catalyst Type

Trimerization Strong bases, quaternary ammonium salts, phos-phines

Dimerization Phosphorous compoundsPolymerization Alkaline metal hydroxidesAddition to alcohols Tertiary amines, organometals, metal saltsReaction with water Tertiary aminesAddition to urethane Metal saltsAddition to amines Tin and zinc salts

From the chemical view, catalysts for producing polyurethanes can be di-vided into two general types: tertiary amines and organo-tin compounds.

Organometallic tin catalysts predominantly favor the gelling reac-tion, while amine catalysts exhibit a more varied range of blow/gel bal-ance. A lot of catalysts have been described and reviewed.6, 38 The choiceof the catalyst depends on which reaction and which structure is to be fa-vored. Table 2.5 lists types of catalysts that are suitable for the individualreactions.

It is important to tune the kinetics of the individual reactions prop-erly. For example, if the blowing reactions take place significantly beforethe sufficient progress of gelling (crosslinking), the viscosity of the react-ing material is low, causing the carbon dioxide to escape, and will not yielda foam.

On the other hand, if the gelling (or crosslinking reaction) occurs toofast, the blowing gas cannot expand the material. Thus, it is necessary tobalance the individual reactions. This balance can be readily controlled bythe nature and quantity of the catalyst used.

2.2.7 Blowing

Chemical blowing is effected by the reaction of isocyanate and water. Therate of blowing increases with the catalyst and water content.39 As anintermediate, carbamic acid is formed. The carbamic acid is not stable; itdecomposes into an amine and carbon dioxide. Carbon dioxide expandsthe polyurethane into a foam.

There are also physical blowing agents available. In this case thefoam is generated by the evaporation of the blowing agent supported by

Polyurethanes 95

external heating but also by the temperature rise due to the formation of thepolyurethane from the diisocyanate and the polyol. Suitable reagents forphysical blowing were previously fluorocarbons and chlorofluorocarbons.The latter class of substance has been removed because of its ozone deple-tion potential. Pentane is a substitute for chlorofluorocarbons. The releaseof the physical blowing agents occurs in three ways when a foamed mate-rial is recycled or shredded:40

1. The instantaneous release from cells split or damaged by the shred-ding,

2. The short-term release from cells adjacent to the cut surface , and3. The long-term release by normal diffusion processes.

Formic acid has been proposed as a chemical blowing agent.41, 42

Formic acid can behave either as an acid or an aldehyde. In contrast towater that yields exclusively carbon dioxide, formic acid upon contact withan isocyanate group reacts to initially liberate carbon monoxide and furtherdecomposes to form an amine with a release of carbon dioxide, accordingto the following reaction:

2Φ−NCO+HCOOH → CO+CO2 +Φ−NH−CO−NH−Φ (2.1)

Aside from its zero ozone depletion potential, a further advantage of usingformic acid is that 2 mol of gas are released for every mole of formic acidpresent, whereas a water-isocyanate reaction results in the release of only1 mol of gas per mol of water. In both the water-isocyanate and the formicacid-isocyanate reactions, the isocyanate is consumed and one must add aproportionate excess of isocyanate to compensate for the loss. However,since formic acid is a more efficient blowing agent than water, the numberof moles of formic acid necessary to produce the same number of moles ofgas as a water-isocyanate reaction is greatly reduced, thereby reducing theamount of excess isocyanate and leading to a substantial economic advan-tage.43

It is believed that liberation of carbon monoxide and subsequentlycarbon dioxide in the reaction Eq. 2.1 proceeds at a slower rate than therelease of carbon dioxide in a water-isocyanate reaction for two reasons:

1. The anhydride is more stable than the carbamic acid formed ina water-isocyanate reaction and, therefore, requires more thermalenergy to decompose, and


2. The reaction is a two-step reaction rather than the one-step reactionpresent in a water-isocyanate reaction.

The exothermic reaction in a polyol composition containing formic acidproceeds in a more controlled manner than in an all water blown reaction.

Formic acid in combination with hydrochlorofluorocarbons improvesthe mechanical and thermal properties. It exhibits a delayed action andthus a prolonged gel time. Rigid foams produced with formic acid possessexcellent dimensional stability at low densities.43 However, the generationof carbon monoxide during the curing and corrosion problems are evidentdrawbacks.

2.2.7.1 Gelling and Crosslinking

Gelling reactions are discussed as curing reactions that do not blow, butyield linear urethanes. These reactions are similar to crosslinking reac-tions, from the chemical view. The technical term “curing” is not commonin polyurethanes, except for unsaturated polyester technology, epoxies,etc., because the resulting final products are often not hard, e.g., flexiblefoams.

The basic reactions in the course of polyurethane formation are shownin Figure 2.19. These include the reaction of isocyanate with a polyolto yield a polyurethane, the formation of urea from an isocyanate and anamine, and the blowing reaction. Other reactions are the formation of abiuret, c.f. Figure 2.9 and the trimerization, c.f. Figure 2.13.

The action of a catalyst can be studied conveniently with model com-pounds. Suitable experimental techniques are liquid chromatography,in-frared spectroscopy, and nuclear magnetic resonance spectroscopy. In-frared spectroscopy conveniently monitors the disappearance of the iso-cyanate group.

Raman spectroscopy is advantageous in two ways. Since the Ramaneffect is a scattering process, samples of any shape or size can be examined.Moreover, Raman spectroscopy measurements can be conducted remotelyusing inexpensive, communications grade, fused-silica optical fibers.44

Nuclear magnetic resonance spectroscopy suffers from the disad-vantage that the spectroscopic shifts of the urethane, urea, allophanate, andbiuret linkages are very similar.

Rheological techniques are also suitable for monitoring the progressof curing.45–47 The dynamic viscosity has been measured as a function of

Polyurethanes 97

R N C O

H O R’

R N C O

H R’O

R N C O

H N R’

R N C O

H R’N

R N C O

H O H

R N C O

H HO

CO2R NH

H

R N C O

N C O

R’O

H

R

R N C O

H

N C O

R’OR

Figure 2.19: Basic Reactions in Polyurethane Formation: Reaction of Isocyanatewith a Polyol; Formation of Urea from Isocyanate and Amine; Chemical Blowingwith Water; Allophanate formation


time and found to be independent of the shear rate.47 A simple technique ofthis kind is to drop metal ball bearings consecutively into a growing foam.The position of the ball bearings in the final foam reflects the viscosityprofile. The simultaneous measurement of the height of the foam givesinformation of the degree of expansion.

The gel times can be used to evaluate the activity of catalysts. In par-ticular, it was found that the activity of catalysts, among them organometal-lic catalysts, decreases in the order Bi > Pb > Sn > triethylamine > .. ..46

The rheological properties determined by dynamic mechanical tech-niques can be sensitive to the rate of mechanical deformation. The rate ofexpansion or possibly the rate of foam rise can be used characterizing theactivity of certain catalysts.

A combined measurement of the expansion and the weight loss per-mits characterizing the mass of CO2 trapped within a foam, the mass ofCO2 lost, and the total mass of CO2 generated during curing.

There are three major classes of catalysts: tertiary amines, organicsalts, and organometallics. Often the chemical nature of the catalysts isnot disclosed in the patent literature. However, a compilation of chemicalstructures of commercially available catalysts useful in the manufacture offlexible foams is available.48 Nevertheless, it is often difficult to establishstructure-property relationships because of the unavailability of informa-tion.

2.2.7.2 Tertiary Amine Catalysts

Commercially used amines are summarized in Table 2.6 and shown in Fig-ure 2.20. Amine catalysts are often delivered as a solution in dipropyleneglycol. This makes the dosage of small quantities easier.

Tertiary amines are used most commonly to catalyze the urethaneformation. They catalyze both gelling and blowing reactions but not theformation of isocyanurate. Tertiary amines are often formulated with org-anotin compounds.

As the basicity increases, the crosslinking is favored. A known prob-lem is volatility that causes odor. Further, the migration of amine catalystscan cause a discoloration when the final polyurethane is used with poly-(vinyl chloride) (PVC). This problem emerges in the automotive industryand is addressed as “vinyl staining”.

The discoloration of poly(vinyl chloride) bound to polyurethane has

Polyurethanes 99

Table 2.6: Tertiary Amine Catalysts

Amine Remarks

1,4-Diazabicyclo[2.2.2]octane (DABCO) Widely employedBis(2-dimethylaminoethyl)ether (BDMAEE) High-resiliency

foams, heavy blow-ing catalyst

N-Ethylmorpholine Polyester slabstockfoam

N-Methylmorpholine Polyester slabstockfoam

N′,N′-dimethylpiperazine High vapor pressure,improves skin forma-tion in molded foam

Triethylamine Highly volatile curecatalyst

N,N-dimethylethylamine Low odorSubstituted pyridines Uretdiones2-Azabicyclo[2.2.1]heptaneN-(3-Dimethylaminopropyl)-2-ethylhexanoic acidamide

49

N,N,N ′,N ′,N ′′-pentamethyldiethylene triamine Heavy blowingcatalyst

N,N-dimethylcyclohexylamine Odorous liquidN,N-dimethylbenzylamine Polyester flexible

foamsN,N-Dimethylethanolamine Polyether flexible

foams3-Hydroxy-1-azabicyclo[2.2.2]octane Reactive catalyst2-(2-N,N-Diethylaminoethoxy)ethanol Reactive catalyst5-Dimethylamino-3-methyl-1-pentanol Reactive catalyst, low

odor50

1-(2-hydroxypropyl)imidazole Reactive catalyst1-(3′-Aminopropyl)imidazole Reactive catalyst51

1-(3′-(Imidazolinyl)propyl)urea 51

Bis(3-(N,N-dimethylamino)propyl)amine,chain-extended with polyol and polyisocyanate

52


CH2 CH2 O CH2 CH2 NNH3C

H3C

CH3

CH3

Bis(2-dimethylaminoethyl)ether

N-Ethylmorpholine

N

O

CH2 CH3

CH2 CH2

N NCH2CH2

CH2CH2

1,4-Diazabicyclo[2.2.2]octane

NCH3

CH2

2-Methyl-2-azabicyclo[2.2.1]heptane

NH3C

H3CCH2 CH2 OH

N,N-Dimethylethanolamine

Figure 2.20: Tertiary Amine Catalysts: 1,4-Diazabicyclo[2.2.2]octane, N-Ethyl-morpholine, Bis(2-dimethylaminoethyl)ether, 2-Azabicyclo[2.2.1]heptane, N,N-Dimethylethanolamine

Polyurethanes 101

been attributed to the catalyzed dehydrochlorination of the PVC by theresidual amine catalyst.53 Amine-free catalyst systems based on carboxyl-ates are helpful to avoid this phenomenon.54, 55

The activity of amines increases with increasing basicity. Howev-er, the activity is negatively influenced by steric hindrance. The urethaneformed by the reaction catalyzes further formation of urethane. Amines ofthe general structure RR′N(CH2)nOR′′ are effective blowing catalysts atn = 2, but good gelling catalysts at n = 3.

Triethylene diamine is a synonym for 1,4-diazabicyclo[2.2.2]octane,which is both an excellent gelling and blowing catalyst. It is the most usedtertiary amine in the production of polyurethanes. The unusual high ac-tivity of 1,4-diazabicyclo[2.2.2]octane emerges from a lack of steric hin-drance in spite of its moderate basicity. Its complex with boric acid exhibitsa reduced odor.

Bis(2-dimethylaminoethyl)ether is used to produce high-resiliencyfoam, because it promotes the reaction of the isocyanate with water. Itis often used together with triethylene diamine. N-ethylmorpholine and N-methylmorpholine have lower activity and are therefore used in the produc-tion of polyester slabstock foam, where only catalysts with lower activityare needed. N-Methylmorpholine, N-ethylmorpholine and triethylaminebelong to the group of skin cure catalysts. These are tertiary amines withhigh vapor pressure. They volatilize from the developing foam to the foammold surface, thus promoting an additional reactivity there.

Substituted hexahydro-s-triazines, like 1,3,5-tris(3-dimethylamino-propyl)-s-hexahydrotriazine and hexamethylenetetramine56 and alkylatedimidazoles, like 1-methylimidazole or 1,2-dimethylimidazole57–60 (Figure2.21) are also used in both high resiliency and rigid foams. An amidinecontains a chemical structure as presented in Eq. 2.2.

CN

N (2.2)

Certain bicyclic amidines (Fig. 2.22) exhibit a high gelling activity cou-pled with low volatility. However, these materials are sensitive to heat,light, and oxygen. 1,8-Diazobicyclo[5.4.0]undec-7-ene or 1,5-diazobicy-clo[4.3.0]non-5-ene in combination with primary amines can catalyze thereaction of phenol blocked isocyanates.61 The bicyclic catalyst is capa-


N

N

NCH2

CH2 CH2 CH2

CH2 CH2 N

N

H2CH2CH2CN

H3C

H3C

CH3

CH3

CH3

CH3

1,3,5-Tris(3-dimethylaminopropyl)-s-hexahydrotriazine

N

H2CN

CH2

NCH2

H2C

N

CH2

Hexamethylenetetramine

N

N

CH3

1-Methylimidazole

Figure 2.21: 1,3,5-tris(3-dimethylaminopropyl)-s-hexahydrotriazine, hexameth-ylenetetramine, 1-methylimidazole

ble of unblocking phenol blocked isocyanate groups, and can effect curingwithin an hour at ambient temperature. Among the amidines the bicyclicamidines have greater activity than the monocyclic amidines.62 Alkylam-ino amides, i.e. secondary amides with a pendent tertiary amine with thebasic structure [(CH3)2N(CH2)3]2NCOR are odorless and have a high re-sistance to hydrolysis.63 For example, formaldehyde can be condensedwith N,N-bis(3-dimethylamino-n-propyl)amine. Ammonia is evolved toyield N,N-bis[3-(dimethylamino)propyl]formamide.

N

N

1,8-Diazobicyclo [5.4.0] undecene-7

N

N

1,5-Diazobicyclo [4.3.0] non-5-ene

Figure 2.22: 1,8-Diazobicyclo[5.4.0]undec-7-ene, 1,5-Diazobicyclo[4.3.0]non-5-ene

Polyurethanes 103

These types of compounds are strong gelling catalysts. Combinationof the latter compound with a weak blowing catalyst, such as methoxyeth-ylmorpholine has been described.64

Formamide-type catalysis can be used to replace the highly volatiledimethylpiperazine. The use of N,N-Bis[3-(dimethylamino)propyl]form-amide as the sole catalyst produces a tight foam. Blends with methoxyeth-ylmorpholine or optionally with 2,2′-oxybis(N,N-dimethylethanamine) arestrong blowing catalysts. They improve flow, skin cure, and de-mold timesin flexible molded polyether foams.64

Still less volatile catalysts can be prepared using bifunctional oxalicesters instead of formic acid derivatives.65 This class is addressed as alkyl-amino oxamides. An aqueous catalyst mixture is obtained to form the saltsby, e.g., salicylic acid. Alternative catalysts have cyclic structures, e.g.,bis[N-(3-imidazolidinylpropyl)]oxamide, or bis[N-(3-morpholinopropyl)]-oxamide. Headspace gas chromatography was applied to measure the fugi-tivity. The oxalic acid amide adducts were not volatile under the conditionsof analysis.

To combine good in-mold flowability and fast curing, delayed-actioncatalysts were developed. Reduced reactivity in reactive injection moldingis sometimes desirable so that large molds could be filled completely beforecure. The activity of an amine catalyst can be delayed by adding acids, suchas formic acid, 2-ethylhexanoic acid, or amino acids.66 The amine salt isless active then the free amine. As the curing proceeds the temperaturerises. At elevated temperatures the amine salt dissociates to the free amineand acid.

Zwitterionic salts from triethylene diamine and tetra-n-butylammon-ium chloroacetate also delay the reaction. The effect of controlled catalysismay be realized in improved reactivity profiles, for instance, delayed initi-ation or accelerated cure.67, 68

A disadvantage in the usage of amine salts is the possibility of cor-rosion, a negative influence on the long-term properties of the final prod-uct. Half esters of diethylene glycol with maleic anhydride or phthalicanhydride can be used to neutralize, or block amines, such as bis(2-di-methylaminoethyl)ether (BDMAEE). Such types of blocked amines arenoncorrosive, delayed-action catalysts for flexible foams.69 The reactioncan be performed in one stroke, allowing phthalic anhydride to react withBDMAEE in diethylene glycol.

Acid-blocked amine catalysts have an unpleasant odor associated


with their use, especially when the polyurethane mixtures are cured inan oven at temperatures above 120°C. This unpleasant odor also remainsin the final product, making these catalysts unsuitable for some applica-tions.70

The incorporation of active hydrogens, such as primary and sec-ondary hydroxyl groups and amino groups, into the catalyst structure issuitable to reduce odors and emissions.

2.2.7.3 Mechanisms of Tertiary Amine Catalysts

Two basic mechanisms for tertiary amine-catalyzed formation of urethaneare under discussion. The first mechanism deals with the formation ofan isocyanate-amine complex followed by reaction with an alcohol. Thismechanism suggests that the nucleophilicity of the amine is the dominantfactor. The second mechanism postulates an amine-alcohol complex thatreacts with the isocyanate. According to this mechanism, the amine basic-ity is the dominant factor.

The mechanism based on an isocyanate-amine complex seems to bemore generally accepted. It is suggested that Lewis bases are activating thealcohols.71

2.2.7.4 Reactive Catalysts

If the catalysts are modified with a group that reacts with isocyanates, thenthe catalysts can be incorporated into the polyurethane material. For exam-ple, triethanolamine has three hydroxy functions and is at the same time atertiary amine. Other compounds include an adduct of glycidyl diethylam-ine with 2(di-methylamino)ethanol.72, 73

A hydroxy functional tertiary amine can be produced by a Michaeltype reaction followed by reductive amination of the cyano group, as exem-plified with 1-(3-dimethylaminopropoxy)-2-butanol in Figure 2.23. Sincethe butanol can attack the acrylonitrile either with the primary hydroxylgroup or with the secondary hydroxyl group, in fact an isomeric mixturewill be obtained.74 In the same way an adduct with 1-methylpiperazine canbe obtained.

Reactive catalysts typically show a high activity in the initial stageof polymerization and then a reduced activity when they are included inthe growing polymer.

Polyurethanes 105

H2C CH C N

CH2 CH CH2 CH3

OH

O H

H2C CH C N

HO

OH

CH3CH2CHCH2

H2C CH CH2 N

HO

OH

CH3CH2CHCH2

CH3

CH3

1-(3-Dimethylaminopropoxy)-2-butanol

CH3 N CH3

+ H2 - NH3

Figure 2.23: Synthesis of a Hydroxy Functional Tertiary Amine: 1-(3-Dimethyl-aminopropoxy)-2-butanol

2-Dimethylaminoethyl urea or N,N′-Bis(3-dimethylaminopropyl)urea contains the ureido group which enables the catalysts to react intothe polyurethane matrix. These reactive catalysts can be used as gellingcatalysts or blowing catalysts with complementary blowing or gelling co-catalysts, respectively, which may or may not contain reactive functionalgroups to produce polyurethane foam materials. The reactive catalysts pro-duce polyurethane foams which have no amine emissions.75

Examples for reactive catalysts include 3-quinuclidinol (3-hydroxy-1-azabicyclo[2.2.2]octane),76, 77 propoxylated 3-quinuclidinol, 3-hydroxy-methyl quinuclidine,78 and 2-(2-N,N-diethylaminoethoxy)ethanol.

Propoxylated 3-quinuclidinol is a liquid, which is soluble in diprop-ylene glycol, whereas 3-quinuclidinol is a high melting solid. 3-Meth-yl-3-hydroxymethyl quinuclidine may be prepared by reacting ethylpyr-idine with formaldehyde to afford 2-methyl-2-(4-pyridyl)-1,3-propanediolwhich is hydrogenated to 2-methyl-2-(4-piperidyl)-1,3-propanediol whichin turn is cyclized to the quinuclidine product.78 2-(2-N,N-diethylamino-ethoxy)ethanol is superior with regard to vinyl staining.

Combinations of a nonreactive catalyst and a reactive catalyst, e.g.,N,N-bis(3-dimethylaminopropyl)formamide and dimethylaminopropylur-ea, have been proposed for foams for interior components of automo-


biles.79 Such low-volatility catalysts do not emit vapors over time or underthe effects of heat which would otherwise cause nuisance fogging of wind-shields, and also reduce the chemical content of the air inside vehicles towhich a driver and passengers are otherwise exposed.

2.2.7.5 Anionic Catalysts

Anionic catalysts favor the isocyanurate formation. Isocyanurate units arebuilt by trimerizing an isocyanate. The isocyanurate group improves prop-erties such as thermal resistance, flame retardancy, and chemical resistance.

In quaternary ammonium carboxylates, alkali metal carboxylatesand substituted phenols such as 2,4,6-tris(dimethylaminomethyl)phenol,the active species is the anion. This is different from amine salt catalystswhere the active species is the free amine.

Examples for quaternary ammonium carboxylates are benzylamm-onium carboxylate,80 tetramethylammonium pivalate, and methyldioctyl-decylammonium pivalate (C8H17)2(C10H21)(CH3)N+−O2CC(CH3).81

Tetraalkylammonium fluorides and cesium fluoride are extremelyselective catalysts for the formation of isocyanurate.82

The trimerization of diisocyanates produces not only the trimer, i.e.,monoisocyanurate, but also higher oligomers. The viscosity of the de-monomerized polyisocyanate increases as the oligomer content increases.

The deactivation of the catalyst is necessary in order to terminate thetrimerization and to ensure the storage stability of the polyisocyanate. Thedegree of trimerization can be controlled by the addition of a catalyst in-hibitor. After adding the catalyst inhibitor, the trimerization stops.83 Suit-able catalyst inhibitors are compounds which enter into chemical reactionswith quaternary ammonium fluorides. Examples include calcium chlorideor alkyl chlorosilanes such as ethyl chlorosilane, or substances which ad-sorptively bind quaternary ammonium fluorides, such as silica gel. Furtherorganic acids or acid chlorides deactivate the catalysts.

Potassium octoate and tertiary phosphines are other catalysts usefulfor the dimerization and trimerization of isocyanates. Carboxylic acidsfavor the formation of urea bond compounds.84, 85 Potassium acetate is ageneral purpose catalyst.

2.2.7.6 Organometallic Catalysts

Commonly used organometallic catalysts are shown in Table 2.7. It is

Polyurethanes 107

Table 2.7: Organometallic Catalysts

Compound Remarks

Dibutyltin dilaurate (DBTDL) Standard CompoundStannous octoate Polyether-based slabstock foamsDibutyltin diacetateDibutyltin dimercaptideLead naphthenateLead octoateDibutyltin bis(4-hydroxyphenylacetate)Dibutyltin bis(2,3-dihydroxypropylmer-captide)

Hydrolytically stable

Ferric acetylacetonate Elastomers

believed that the catalytic action occurs by a ternary complex of the iso-cyanate, hydroxyl, and the organometallic compound. A Lewis acid-iso-cyanate complex is formed followed by complexation with the alcohol.71

For gelling reactions, organometallic catalysts are more selectivethan tertiary amines. Some organotin compounds lose their activity in thepresence of water or at high temperatures. As in the case of amine cata-lysts, the activity decreases in sterically hindered compounds. Also, sol-vent effects are observed. The solvent effect is relevant for solvent-basedcoating formulations. Dialkyltin dimercaptides, such as dibutyltin dilaurylmercaptide, exhibit good storage times when admixed with other catalystcomponents.86

Dibutyltin dilaurate catalyzes the formation of urethane suppressingthe formation of allophanates and isocyanurates.87 With high resiliencyfoams (HR), where more reactive polyols are generally employed, veryfew tin catalysts can be used because the foam cell walls are less proneto rupture than with conventional foams, and this can result in shrinkageproblems.56 Bis(2-acyloxyalkyl)diorganotins exhibit only a small activityat room temperature. However they decompose at elevated temperaturesinto diorganotin dicarboxylates, which are the active species and olefins.For this reason they are also referred to as latent catalysts. This effect canbe used to tailor catalysts. One advantage of the latent catalysts of the for-mula like Figure 2.24 is, therefore, to be able to mix the starting materialswith the latent catalyst without catalysis of the reaction taking place andto initiate the catalysis of the reaction by heating the mixture to the de-composition temperature of the latent catalyst. 2-Acetoxyethyl-dibutyltin


CH2CH2CH2Bu = CH3

Sn

Bu

Bu

Cl

CH3

OC

O

CH2CH2Sn

Bu

Bu H

ClCH

O

C O

CH3

CH2

hν

∆

Figure 2.24: Synthesis of 2-Acetoxyethyl-dibutyltin chloride from Chlorodibut-yltin hydride and Vinyl acetate

chloride is prepared from chlorodibutyltin hydride and vinyl acetate, c.f.Figure 2.24, and it is decomposed by heat at 90°C within one hour.88, 89

Another latent tin catalyst consists of the adduct of a tin carboxylateor other tin compound with a sulfonylisocyanate, such as dibutyltin dilau-rate or dibutyltin methoxide and tosyl isocyanate.90 Tin alkoxides or tinhydroxides have a far higher catalytic activity than the tin carboxylates.These additional compounds are extremely sensitive to hydrolysis, alcoho-lysis and are decomposed by the presence of water.

Moisture can be supplied by the substrate, the atmosphere or bycompounds containing reactive groups toward isocyanate, in particular hy-droxyl groups, with release of the catalysts. Before hydrolytic or alco-holytic decomposition of the addition compounds takes place, these com-pounds are completely inert towards isocyanate groups. They give rise tono side reactions which would impair the storage stability of organic poly-isocyanates. Combinations of organotin catalysts and hydrogen chlorideextend the pot-life time in coating compositions without changing the curetime.91 Bismuth neodecanoate and combinations of bismuth and zircon-ium carboxylic acid salts also exhibit longer pot-life times combined withrapid curing.92 However, catalysts based on bismuth are water sensitiveand deactivate in the presence of moisture.

Polymeric metal catalysts are less prone to migrate. They can besynthesized by reacting a diorganotin dichloride or dibutyltin oxide witha hydroxymercaptan, such as 3-mercapto-1,2-propanediol with water re-moval. A viscous polymeric material is obtained.93

Dibutyltin bis(4-hydroxyphenylacetate) and dibutyltin bis(2,3-dihy-droxypropylmercaptide) are hydrolytically particularly stable. The hy-

Polyurethanes 109

droxy functionality allows an incorporation in the polyurethane chain.94

A low odor and migration resistant organotin catalyst consists ofthe reaction products of dibutyltin oxide and aromatic aminocarboxylicacids, e.g., 3,5-diaminobenzoic acid to result in tin-di-n-butyl-di-3,5-am-ino benzoate.95

2.3 SPECIAL ADDITIVES

Chemical formulations of polyurethane foams are based on the followingingredients:

1. Polyol,2. Isocyanate,3. Catalysts,4. Water,5. Blowing agent,6. Surfactant,7. Pigment,8. Additives.

2.3.1 Fillers

2.3.1.1 Rectorite Nanocomposites

Rectorite (REC) is a clay mineral with a 1:1 regular interstratification ofa dioctahedral mica and a dioctahedral smectite. Rectorite has been usedto yield intercalated or exfoliated thermoplastic polyurethane rubber nano-composites by melt processing intercalation.

X-ray diffraction and transmission electron microscopy clarified thatthe composites with lower amounts of clay are intercalation or part exfo-liation nanocomposites. The mechanical properties of the composites aresubstantially enhanced.96

2.3.1.2 Zeolite

Zeolite has been used for modifying the structure of polyurethane mem-branes and to improve their properties. Membranes with zeolite contentbetween 10 and 70%, have been prepared. The preparation method in-duces an anisotropy in the membranes. The membranes have therefore an


asymmetric structure consisting of the top skin, i.e., the active layer, thesubstructure, and the bottom skin.97

2.3.1.3 Iron Particles

The sound absorption characteristic within a certain frequency bandwidthof a flexible polyurethane foam can be changed, when 2 to 5 µm carbonyliron particles are incorporated, when constant intensity magnetic fields areapplied.98

2.3.2 Reinforcing Materials

2.3.2.1 Nanosilica Particles

Polyurethane ionomers in an aqueous emulsion were reinforced with hy-drophobic nanosilica to give composites. The aqueous emulsion was stableand the particle size increased as the content of hydrophobic nanosilica wasincreased. The reinforcing effects of nanosilica on the mechanical proper-ties were examined in various tests. The composites showed an enhancedthermal and water resistance.99

Nanosized SiO2 particles can be prepared via the sol-gel process.In a sol-gel process, the inorganic mineral is formed and deposited in-situin the organic polymer matrix, for example, aqueous emulsions of cationicpolyurethane ionomers, mixed with tetraethoxysilane, hydrolyze by the ac-tion of acid. In this way, silica nanocomposites, based on poly(ε-caprolac-tone glycol) as soft segment, and isophorone diisocyanate as hard segment,and 3-dimethylamino-1,2-propanediol as chain extender were prepared.100

Mechanical properties are improved by the incorporation of the par-ticles. The particles do not essentially affect the low temperature-resistantproperties, but improve the heat-resistance of the resin.101 The dispersionof the particles can be enhanced by a surface modification with (3-amino-propyl)triethoxysilane.102

Polyurethane/filler composites also can be prepared by mixing thepolyol with a solution of the silica in methylethylketone, then strippingthe methylethylketone. This solution is then reacted with a diisocyanate,and then chain-extended with 1,4-butanediol. Atomic force microscopyrevealed that the filler particles were evenly distributed in the hard and softphases.103

Polyurethanes 111

Table 2.8: Flame Retardants for Polyurethanes

Compound Reference

Expandable graphite 105

Triethyl phosphate 106

Ammonium polyphosphate 107

Melamine cyanurate 107

Poly(epichlorohydrin) (PECH) 108

3-Chloro-1,2-propanediol, reactive 109

2.3.2.2 Layered Silicate Nanocomposites

High performance nanocomposites that consist of a polyurethane elastomer(PUE) and an organically modified layered silicate have been described.104

The polyurethane is based on poly(propylene glycol), 4,4′-methylene bis-(cyclohexyl isocyanate) and 1,4-butanediol. The tensile strength and strainat break for these PUE nanocomposites increases more than 150%. Anisocyanate index of 1.10 results in the best improvement in stress and elon-gation at break.

Polyurethane/organophilic montmorillonite (PU/OMT) nanocompos-ites have an enhanced tensile strength and improved thermal properties, incomparison to unmodified polyurethane.110 An amphiphilic urethane pre-cursor with hydrophilic poly(ethylene oxide) (PEO) was used to preparenanocomposites containing Na+-montmorillonite.111

2.3.2.3 Nanoclays

Waterborne polyurethane/poly(methyl methacrylate) hybrid materials werereinforced with exfoliated organoclay. The size of the particles in the emul-sion increased when the contents of PMMA or organoclay was increased.X-ray measurements showed an effective exfoliation of the silicate layer inthe polymer matrix.112

2.3.3 Flame Retardants

Flame retardants, recently described, are summarized in Table 2.8.


2.3.3.1 Poly(epichlorohydrin)

Poly(epichlorohydrin) (PECH) was phosphorylated by the reaction the P-Hbond of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO)with the pendent chloromethyl groups of PECH. A phosphorus-containingPECH with hydroxyl terminal groups is thus obtained.108 From this com-pound a phosphorous-containing polyurethane is obtained by the reactionwith 2,4-toluene diisocyanate. The polymers are useful as multifunctionalmodifiers for epoxy resins and for improving the toughness and flame re-tardancy.

2.3.3.2 Expandable Graphite

The protective shield in a polyurethane expandable graphite (EG) systemconsists of expanded worms of graphite embedded in the tarry degradedmatrix of polyurethane.105

The expansion of EG is due to a redox process between H2SO4,intercalated between graphite layers, and the graphite itself that originatesthe blowing gases according to the reaction:

C+2H2SO4 → CO2 +2H2O+2SO2 (2.3)

Expandable graphite can be used in poly(isocyanurate) polyureth-ane foams in order to improve fire behavior of such foams. In order toobtain a completely halogen-free material, water blown foams must beprepared thus avoiding the use of hydrochlorofluorocarbons or hydroflu-orocarbons. The limiting oxygen index of the material without expandablegraphite is at 24% and reaches 30.5% in presence of 25% of expandablegraphite.113 Triethyl phosphate shows a synergistic effect with expand-able graphite.106 Further expandable graphite or triethyl phosphate do notworsen the mechanical properties. Ammonium polyphosphate, melaminecyanurate, and expandable graphite were tested in a comparative study.Expandable graphite showed the best results.107

2.3.3.3 Charring Agents

In the case of ammonium polyphosphate, the blowing effect is less impor-tant105 than in expandable graphite. Ammonium polyphosphate, melaminecyanurate and expandable graphite are compounds that form char layersthat provide a thermal isolation.

Polyurethanes 113

Table 2.9: Global Production/Consumption Data of Important Monomersand Polymers115

Monomer Mill. Metric tons Year Reference

Phosgene 5 2002 116

Toluene diisocyanate 1.3 2000 117

p,p′-Methylene diphenyl diisocyanate (MDI) 2.4 2000 117

Ethyleneamines 0.248 2002 118

Phthalic anhydride 3.2 2000 119

Maleic anhydride 1.3 2001 120

1,4-Butanediol 1 2003 121

Polyurethane foams (flexible and semi-rigid) 2.3 2001 122

Polyurethane foams (rigid) 1.6 2001 122

Polyurethane elastomers 0.581 2001 123

Urethane surface coatings 1.5 1999 124

However, the action takes place in different ways. Ammonium poly-phosphate leads to the formation of a char layer through a series of pro-cesses consisting of initial peroxide formation, decomposition to alcoholsand aldehydes, formation of alkyl-phosphate esters, dehydration and sub-sequent char formation.114 Thermogravimetric studies showed that the ad-dition of ammonium polyphosphate accelerates the decomposition of thematrix but leads to an increase in the amount of high-temperature residue,under an oxidative or inert atmosphere.

This stabilized residue acts as a protective thermal barrier duringthe intumescence fire retardancy process. The resulting char consists ofan aromatic carbonaceous structure which condenses and oxidizes at hightemperature. In the presence of ammonium polyphosphate, a reaction be-tween the additive and the polymer occurs, which leads to the formation ofa phosphocarbonaceous polyaromatic structure.125

Melamine cyanurate acts in an endothermic decomposition and givesoff ammonia. Still nitrogen-containing polymers form then a char layer.107

2.3.4 Production Data

Global Production Data of the most important monomers used for unsatur-ated polyurethane resins are shown in Table 2.9.


2.4 CURING

The isocyanurate formation and isocyanate degree of conversion can bemeasured simultaneously by means of FT-IR spectroscopy.126

The curing behavior of polyurethanes based on modified methylenediphenyl diisocyanate and poly(propylene oxide) polyols has been stud-ied using isothermal Fourier-transform infrared (FTIR) spectroscopy , di-fferential scanning calorimetry (DSC) and adiabatic exothermic experi-ments. Increasing the concentration of the catalyst, i.e., dibutyltin dilau-rate (DBTDL) or decreasing the molecular weight of the polyol raises therate of reaction and shifts the DSC exothermic peak temperature to lowertemperatures.

However, the heat of reaction remains constant. A marked increasein reaction rate is observed when an ethylene oxide end-capped polyolis used instead of a standard propylene oxide end-capped polyol. Theconversion of isocyanate for several concentrations of dibutyltin dilaurate(DBTDL) fits a second-order kinetics. The activation energy of curing isindependent of the molecular weight of the hydroxy compound.127 How-ever, the activation energy depends on the extent of conversion.47

With isocyanate reactive hot-melt adhesives an autocatalytic effectwas observed. The autocatalysis is not dependent on the structure of diolsbut on the isocyanates.128

2.4.1 Recycling

2.4.1.1 Solvolysis

In recycling, catalysts can effect a reduction of the time required to recyclepolyurethanes via hydrolysis and glycolysis. The products of polyurethanerecycling are a complex mixture of alcohols and amines. Useful catalystsfor recycling include titanium tetrabutoxide, potassium acetate, sodium hy-droxide or lithium hydroxide. uncatalyzed polyurethane recycling is alsopossible.

The recovery and purification of the polyol-containing liquid prod-ucts can be achieved by the distillation of the glycolysis products. Theamount of recoverable products by distillation reaches a maximum of 45%,when a process temperature of 245 to 260°C is applied.129

Polyurethanes 115

2.4.1.2 Ultrasonic Reactor

High resiliency polyurethane foam has been recycled by the application ofhigh-power ultrasound in a continuous ultrasonic reactor. The foam hasbeen decrosslinked at various screw speeds and various ultrasound ampli-tudes, then blended at different ratios with the virgin polyurethane rubberand then cured. In comparison to the ground recycled samples, the blendsof the decrosslinked samples are easier to mix and exhibit enhanced prop-erties.130

2.4.1.3 Polyacetal-modified Polyurethanes

Polyacetals are thermally stable but undergo a degradation by treatmentwith aqueous acid even at room temperature. Therefore, polyacetals arecandidates for degradable polymers for chemical recycling. Polyurethaneelastomers with degradable polyacetal soft segments have been synthes-ized.131 The polyurethanes were synthesized from polyacetal glycol and4,4-diphenylmethane diisocyanate. 1,4-Butanediol was used as a chainextender. For comparison, samples containing a polyether glycol insteadof the polyacetal glycol were prepared. Acid treatment indicated that thedegradation took place.

2.4.1.4 Production Wastes

Waste residue from the production of toluene diisocyanate was used as amodifier in making improved waterproofing bitumen. The degree of im-provement of the softening point could be correlated with the blend mor-phology.132

2.5 PROPERTIES

2.5.1 Mechanical Properties

Copolymers of propylene oxide and ethylene oxide are used for softerfoams in comparison with polyols obtained exclusively from propyleneoxide.

In comparison with polyether polyurethanes, polyester polyureth-anes are more resistant to oil, grease, solvents, and oxidation. They exhibitbetter mechanical properties. On the other hand, polyester polyurethanesare less chemically stable and are also sensitive to microbiological attack.


2.5.2 Thermal Properties

Additives, in particular nanocomposites, have a positive effect on the ther-mal properties. On heating up to degradation, the urethane structure under-goes a retro reaction into isocyanates. Therefore, highly poisonous prod-ucts can be formed. The isocyanates yield depends greatly on the specificcombustion conditions selected, such as temperature, ventilation, and fuelload.

The mechanism of thermal degradation has been sketched.133 Poly-urethane undergoes a depolycondensation. Volatile diisocyanate and iso-cyanate-terminated fragments are formed.134

In laboratory combustion experiments, isocyanates could be detectedin the gaseous effluent. They were analyzed using impinger flasks contain-ing 1-(2-methoxyphenyl)piperazine (MOPIP) as derivatizing reagent. Thederivatives were analyzed by high performance liquid chromatography andtandem mass spectrometry. Isocyanic acid, aliphatic isocyanates, alkenylisocyanates, and other derivatives were found.135

Heavy metals influence the thermal degradation. Manganese, cobalt,and iron ions favor the polyurethane degradation. Chromium and cop-per ions reduce the initial thermal stability of the polyurethane and have acatalytic effect on the second stage of its decomposition, but enhance thethermal stability of its intermediate decomposition products. By the mod-ification of polyurethanes with these transition metal ions, changes in thedecomposition mechanism of the polyurethane are induced.136

2.5.3 Weathering Resistance

In aliphatic polyurethane-acrylate (PUA) resins, usually used for coatings,the urethane linkage is the most sensitive bond type with respect to photo-degradation. The materials exhibit good weathering properties.137

2.6 APPLICATIONS AND USES

2.6.1 Casting

Cold casting and hot casting systems are available. A polyurethane/poly-(styrene-co-divinylbenzene) system can be cured at room temperature, ina one-step process.138

Polyurethanes 117

Table 2.10: Interpenetrating Polymer Networks

Polyurethane Further Component Reference

Castor oil-basedpolyurethane

Poly(acrylonitrile),unsaturated polyester resin

139

Polyurethane–poly(ethylene oxide)

Poly(acrylonitrile) 140

Polyurethane Vinylester resin 141

Polyurethane Poly(styrene) 142

Polyurethane ionomer Poly(vinyl chloride) 143

Polyurethane Poly(acrylate) latex 144, 145

Polyurethane Poly(methacrylate) 146–148

Polyurethane Poly(butyl methacrylate) 149

Polyurethane Poly(acrylamide) 150

Polyurethane Nitrokonjac glucomannan 151

Polyurethane Epoxy resin 152, 153

Polyurethane Poly(vinylpyrrolidone) 154

Polyurethane Poly(benzoxazine) 155

Polyurethane Poly(allyl diglycol carbonate) 156

2.7 SPECIAL FORMULATIONS

2.7.1 Interpenetrating Networks

Several types of interpenetrating networks with polyurethanes have beenprepared and characterized. These types are summarized in Table 2.10.

In a tricomponent interpenetrating polymer network composed ofcastor oil, toluene diisocyanate, acrylonitrile, ethylene glycol diacrylate,and an unsaturated polyester resin, it was found that the tensile strength ofthe unsaturated polyester (UP) matrix was decreased and flexural and im-pact strengths were increased upon incorporating polyurethane/polyacrylo-nitrile (PU/PAN) networks.139

Poly(methyl methacrylate-co-2-methacryloyloxyethyl isocyanate) canbe crosslinked with various diols that result in polyurethane structures. Thecrosslinking kinetics of diols, such as ethylene glycol (EG), 1,6-hexane-diol, and 1,10-decanediol (DD) has been investigated, and second-orderkinetics was observed. The rate constants decreased from EG to DD.146

The addition of nanosized silicon dioxide can improve compatibility,damping and phase structure of interpenetrating networks.152


CH2

CH3

CH3

H3C

NCO

NH

C O

O

NH

OH

CH2OH

O

CH2

CH3

CH3

H3C N C O

NCO

O

CH2OH

OH

NH2

O

n n

Figure 2.25: Reaction of Chitosan with Isophorone

2.7.2 Grafting with Isocyanates

2.7.2.1 Chitosan

Chitosan is a linear polysaccharide obtained from the N-deacetylation ofchitin. The amino group in chitosan can be reacted with an isocyanate,as shown in Figure 2.25, exemplified with isophorone diisocyanate. If inaddition a polyol is present, then the second isocyanate group in isophoronecan react with the polyol and longer pendent polyurethane chains can beformed.157

2.7.3 Medical Applications

2.7.3.1 Siloxane-based Polyurethanes

Polyurethane elastomers are used for medical implants. Deficiencies ofconventional polyurethanes include deterioration of mechanical propertiesand degradation by hydrolysis reactions. Polyurethanes with improvedlong-term biostability are based on polyethers, hydrocarbons, poly(carbon-ate)s, and siloxane macrodiols. These components are intended to replacethe conventional polyesters and polyethers. Siloxane-based polyurethanesshow excellent biostability.158

Polyurethanes 119

2.7.3.2 Blood Compatibility

Polyurethanes are widely used as blood-contacting biomaterials becausethey exhibit good biocompatibility and further due to their mechanicalproperties. However, the blood compatibility is not adequate for certainapplications. Modification of the surface is an effective way to improvethe blood compatibility.

Sulfonic and carboxyl groups can effectively improve the blood com-patibility of polyurethane. Films of polyurethane containing acrylic acidwere exposed to a sulfur dioxide plasma to graft sulfonic acid group on itssurfaces. During the preparation of the films by dissolution, acrylic acidpolymerizes to some extent.159

Carboxybetaine has been grafted onto polyurethane. A three-stepprocedure was used. First, the film surfaces were treated with hexameth-ylene diisocyanate in presence of DBTDL. Then, N,N-dimethylethyleth-anolamine (DMEA) or 4-dimethylamino-1-butanol (DMBA), respectively,was allowed to react in toluene with the pendent isocyanate groups. Fi-nally, carboxybetaines were formed in the surface by ring opening involv-ing the tertiary amine of DMEA or DMBA and β-propiolactone (PL).160

Similarly, sulfobetaines can be formed on the surface by the reaction of1,3-propanesulfone (PS) instead of PL.161, 162

A polyurethane containing a phosphorylcholine structure has im-proved blood compatibility. The phosphorylcholine moiety consists of(6-hydroxy)hexyl-2-(trimethylaminonio)ethyl phosphate (HTEP). A seg-mented polyurethane (SPU) containing the phosphorylcholine structurewas synthesized from diphenylmethane diisocyanate, soft segment poly-tetramethylene glycol (PTMG), and HTEP, with 1,4-butanediol (BD) as achain extender.163 The phosphorylcholine structure on the surface of theSPU was proven by attenuated total reflectance Fourier transform infraredspectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS) andwater contact angle measurements.

2.7.3.3 Degradable Polyurethanes

Longitudinal lesions in the meniscus are frequent orthopedic problems ofthe knee. The repair by simple techniques is limited to the vascular partof the meniscus. For the repair of the avascular part of the meniscus, ascaffold consisting of polyurethane foam has been developed. The scaffoldis intended to assist the body in the formation of new meniscus cell tissue.


A segmented polyurethane with poly(ε-caprolactone) as the soft seg-ment and 1,4-butanediisocyanate and 1,4-butanediol as uniform hard seg-ments was chosen.164 The material has a micro phase separated morphol-ogy and excellent mechanical properties. Foams were prepared for a por-ous scaffold. The scaffold was tested by implantation in the knees of bea-gles. It was found that meniscus-like tissue had been formed in the scaf-fold.

Another biodegradable, sponge-like polyurethane scaffold consistsof lysine-diisocyanate (LDI) and glycerol. Ascorbic acid (AA) was co-polymerized with LDI-glycerol.20

The cytocompatibility of polyurethane porous scaffolds is improvedby photo grafting of methacrylic acid or poly(2-hydroxyethyl acrylate)onto the surface.165, 166

Polyurethanes can be degraded by esterase. This may contributeto the failure of medical implants. A strong dependence on the enzymeconcentration for polyurethanes with different hard segment chemistry wasestablished.167

2.7.3.4 Prevention of Polyurethane Heart Valve Cusp Calcification

The calcification of polyurethane prosthetic heart valve leaflets is highlyundesirable. Polyurethane valves modified with covalently linked bispho-sphonate groups are resistant to calcification, but the highly polar bispho-sphonate groups on the polyurethane surface attract sodium counter ion,therefore, water absorption is increased. However, attaching diethylam-ino groups to the bisphosphonate-modified polyurethane will reduce waterabsorption.168

2.7.4 Waterborne Polyurethanes

Waterborne polyurethanes are used mainly for coatings, but also for com-posites and nanocomposites. They are covered briefly, with special atten-tion to their chemistry. Water dispersable paints can be produced frompolyester polyol, isophorone diisocyanate and hydrophilic monomers suchas dimethylol propionic acid (DMPA) and tartaric acid (TA).169 Phos-phorus-containing flame retardant water-dispersed polyurethane coatingswere also synthesized by incorporating a phosphorus compound into thepolyurethane main chain.170

Polyurethanes 121

Table 2.11: Composites Made From Waterborne Polyurethane Materials

Second Compound Reference

Starch 174

Carboxymethyl konjac glucomannan (CMKGM) 175

Casein 176

Carboxymethyl chitin 177, 178

Soy flour 179

Bis(4-aminophenyl)phenylphosphine oxide (BAPPO) was obtainedfrom bis(4-nitrophenyl)phenylphosphine oxide by the reduction of the ni-tro groups.171

The stability of waterborne dispersions can be improved by using acontinuous process of preparation.172 Acetone addition has a large effecton the particle diameter.173

Waterborne anionomeric polyurethane-ureas can be made from di-methylol terminated perfluoropolyethers, isophorone diisocyanate, dimeth-ylol propionic acid, and ethylene diamine. The materials are obtained asstable aqueous dispersions.

Surface properties and chemical resistance were estimated by themeasurement of contact angles and spot tests with different solvents. Thesurface hydrophobicity was not affected by the composition. Water-sorp-tion behavior is however sensitive to the content of carboxyl groups in thepolymer.180

Another type of waterborne polyurethane-urea anionomers consistsof isophorone diisocyanate, poly(tetramethylene ether) glycol, dimethylolbutanoic acid (DMBA), and hydrazine monohydrate (HD). Ethylene di-amine (EDA), 1,4-butane diamine (BDA) are chain extenders. The pen-dent carboxylic groups are neutralized by ammonia/copper hydroxyde ortriethylamine (TEA).181

Table 2.11 summarizes composites made from waterborne polyur-ethane materials. Composite materials were prepared by blending carboxy-methyl konjac glucomannan (CMKGM) and a waterborne polyurethane(WPU). A blend sheet with 80% CMKGM exhibited good miscibility andhigher tensile strength (89.1 MPa) than that of both of the individual ma-terials, i.e. waterborne polyurethane sheets (3.2 MPa) and CMKGM (56.4MPa) sheets. With an increase of CMKGM content, the tensile strength,Young’s modulus, and thermal stability increased significantly, attributed


to intermolecular hydrogen-bonding between CMKGM and WPU.175

Waterborne polyurethane and casein have been prepared by blendingat 90°C for 30 min, and then crosslinking with ethanedial. Water resistanceof the materials proved to be quite good.176

2.7.5 Ceramic Foams

Organic polymers can be used in the manufacture of ceramic components.The organic polymers are admixed with the inorganic ceramic components,either to ceramic powder or to an inorganic monomer, as processing aids.Such a mixture can be processed in injection molding machines or by othertechniques. The organic polymer supports the process of shaping a greenpart. Subsequently it is volatilized by pyrolysis or oxidation during heat-ing. Ceramic foams can be produced with polyurethane and ceramic pow-der mixtures.182

2.7.6 Adhesion Modification

In order to increase the compatibility between polyamide 6 and thermo-plastic polyurethane, the polyurethane was reactively modified.183

2.7.7 Electrolytes

Polymer electrolytes are used as solid electrolyte materials in rechargeablelithium batteries and electrochromic devices.

Solid polymer electrolytes (SPE) have been introduced since the di-scovery of poly(ethylene oxide)electrolytes.184–186

In polyethers, the dissociation of alkali-metal salts occurs by the for-mation of transient crosslinks between the ether oxygen groups in the hostpolymer and alkali-metal cations. The anion is usually not solvated. Themain deficiency of polyether-type electrolytes is the high degree of crys-tallization of the polyether.

Thermoplastic polyether polyurethanes (TPU), doped with variousalkali metal salts, have also been studied as polymer electrolytes. TPUexhibits good mechanical properties, a tough crystallinity of the polyethersegments is reduced.

Polyurethanes can be modified with chelate groups in order to en-hance the electrical properties. ((3-(4-(1-(4-(3-(Bis-carboxymethylamino)2-hydroxy-propoxy) phenyl)-1-methyl-ethyl) phenoxy) 2-hydroxypropyl)

Polyurethanes 123

C

CH3

CH3

O OCH2 CH2

CH CH

CH2 CH2

HO OH

N N

CH2H2C H2C

C C CO O O

CH2

C O

OHOHHO HO

Figure 2.26: ((3-(4-(1-(4-(3-(Bis-carboxymethylamino) 2-hydroxy-propoxy)phenyl)-1-methyl-ethyl) phenoxy) 2-hydroxypropyl) carboxy methylamino) ac-etic acid

carboxy methylamino) acetic acid (EPIDA), c.f. Figure 2.26, is such achelate. The molecule bears hydroxyl functions, which are basically reac-tive with isocyanate groups. Therefore, it can be built into a polyurethanechain.187 These electrolytes, due to the chelating groups, exhibit a sig-nificant interaction of the Li+ ions. A change in polymer morphology isalso observed. An increase in the glass transition temperature of the softsegment occurs.

Porous polymers, based on polyurethane/polyacrylate, can be pre-pared by emulsion polymerization. During the production, no organic sol-vent is used. The synthesis proceeds in four steps, listed here.188

1. A prepolymer is prepared from 2,4-toluene diisocyanate and poly-(propylene glycol). 2,4-toluene diisocyanate is in a two-fold ex-cess.

2. 2-Hydroxyethyl methacrylate (HEMA) is added to the prepolymer.The hydroxyl groups react with the residual isocyanate groups.

3. Again poly(ethylene glycol) is added in order to react with the re-maining isocyanate groups. A macromonomer with pendant dou-ble bonds is obtained.

4. The macromonomer is emulsified and polymerized by the additionof 2,2′-azobis(isobutyronitrile).

The ionic conductivity is about 10−3 Scm−1 at room temperature.This conductivity is useful for many practical electrochemical applications.

A light-emitting electrochemical cell (LEC) is composed of a blend


of semiconducting polymer and polymer electrolyte mixture.An electrochemical cell was built from poly(p-phenylene vinylene)

(PPV), as light-emitting material and lithium ion conducting waterbornepolyurethane ionomer as solid electrolyte.189 The polyurethane was pre-pared from a poly(ethylene glycol), α,α′-dimethylol propionic acid andisophorone diisocyanate.

REFERENCES

1. E. N. Doyle. The development and Use of Polyurethane Products. McGraw-Hill, New York, 1971.

2. R. M. Evans. Polyurethane Sealants. Technology and Applications. Tech-nomic Publ., Lancaster, PA, 1993.

3. C. Hepburn. Polyurethane Elastomers. Elsevier Applied Science, London,1992.

4. G. Oertel and L. Abele. Polyurethane Handbook. Chemistry - Raw Materi-

als - Processing - Application. Hanser, München, Wien, 1994.5. D. Randall and S. Lee. The Polyurethanes Book. Huntsman International,

Everberg, 2002.6. J. H. Saunders and K. C. Frisch. Polyurethanes. Chemistry and Technology.

1. Chemistry, volume 16 of High polymers. Interscience Publ., New York,NY, 1962.

7. M. Szycher. Szycher’s Handbook of Polyurethanes. CRC Press, Boca Ra-ton, 1999.

8. K. Uhlig. Polyurethan-Taschenbuch. Hanser, München, Wien, 1998.9. G. Woods. The ICI Polyurethanes Book. Wiley, New York, NY, 1987.

10. P. Wright. Solid Polyurethane Elastomers. Maclaren, London, 1969.11. D. Klempner and K. C. Frisch, editors. Carl Hanser Verlag, München, 1991.12. W. D. Vilar. Chemistry and Technology of Polyurethanes. Vilar Consultoria

Técnica Ltda, Lagoa, Rio de Janeiro, RJ, Brazil, 3rd edition, 2002.13. D. R. Klempner and V. Sendijarevic, editors. Hanser Gardner Publications,

München, Cincinnati, 2004.14. P. Vermette, H. J. Griesser, G. Laroche, and R. Guidoin, editors. Biomed-

ical Applications of Polyurethanes, volume 6 of Tissue Engineering Unit.Landes Bioscience, Georgetown, TX, 2001.

15. N. M. K. Lamba, K. A. Woodhouse, and S. L. Cooper. Polyurethanes in

Biomedical Applications. CRC Press, Boca Raton, FL, updated edition edi-tion, 1998.

16. K. C. Frisch. Chemistry and technology of polyurethane adhesives. InA. V. Pocius, editor, Surfaces, Chemistry and Applications, volume 2 ofAdhesion Science and Engineering, pages 759–812. Elsevier Science BV,Amsterdam, 2002.

Polyurethanes 125

17. O. Bayer, W. Siefken, H. Rinke, L. Orthner, and H. Schild. A process forthe production of polyurethanes and polyureas [Verfahren zur Herstellungvon Polyurethanen bzw. Polyharnstoffen]. DE Patent 728 981, assigned toIG Farbenindustrie AG, December 7 1937.

18. K. Kojio, T. Fukumaru, and M. Furukawa. Highly softened polyurethaneelastomer synthesized with novel 1,2-bis(isocyanate)ethoxyethane. Macro-

molecules, 37(9):3287–3291, May 2004.19. C. Boyer, G. Boutevin, J. J. Robin, and B. Boutevin. Synthesis of a new

macromonomer from 2-(dimethylamino)ethyl methacrylate bearing 1-(iso-propenylphenyl)-1,1-dimethylmethyl isocyanate group. Macromol. Chem.

Phys., 205(5):645–655, March 2004.20. J. Y. Zhang, B. A. Doll, E. J. Beckman, and J. O. Hollinger. A biodegradable

polyurethane-ascorbic acid scaffold for bone tissue engineering. J. Biomed.

Mater. Res., Part A, 67A(2):389–400, November 2003.21. M. Wirts, D. Grunwald, D. Schulze, E. Uhde, and T. Salthammer. Time

course of isocyanate emission from curing polyurethane adhesives. Atmos.

Environ., 37(39-40):5467–5475, December 2003.22. K. W. Haider, J. C. Chan, E. H. Jonsson, U. W. Franz, and R. P. Taylor. Hy-

drophobic light stable polyurethane elastomer with improved mechanicalproperties. US Patent 6 780 957, assigned to Bayer Polymers LLC (Pitts-burgh, PA), August 24 2004.

23. S. Maier, T. Loontjens, B. Scholtens, and R. Mülhaupt. Carbonylbiscapro-lactam: A versatile reagent for organic synthesis and isocyanate-free ureth-ane chemistry. Angew. Chem.-Int. Edit., 42(41):5094–5097, 2003.

24. S. Maier, T. Loontjens, B. Scholtens, and R. Mülhaupt. Isocyanate-freeroute to caprolactam-blocked oligomeric isocyanates via carbonylbiscapro-lactam- (CBC-) mediated end group conversion. Macromolecules, 36(13):4727–4734, July 2003.

25. J. Zimmermann, T. Loontjens, B. J. R. Scholtens, and R. Mülhaupt. Theformation of poly(ester-urea) networks in the absence of isocyanate mono-mers. Biomaterials, 25(14):2713–2719, June 2004.

26. E. Scortanu, C. Priscariu, and A. A. Caraculacu. Study of the mechani-cal properties of dibenzyl-based polyurethane containing a molecularly dis-persed UV absorber. High Perform. Polym., 16(1):113–121, March 2004.

27. A. Baron, E. Cloutet, H. Cramail, and E. Papon. Relationship between ar-chitecture and adhesive properties of macromolecular materials, 1 - studyof comb-like polyurethane-based copolymers. Macromol. Chem. Phys.,204(13):1616–1620, September 2003.

28. K. Se and K. Aoyama. Preparation and characterization of graft copoly-mers of methyl methacrylate and poly(n-hexyl isocyanate) macromono-mers. Polymer, 45(1):79–85, January 2004.

29. J.-H. Ahn, Y.-D. Shin, S.-Y. Kim, and J.-S. Lee. Synthesis of well-de-fined block copolymers of n-hexyl isocyanate with isoprene by living an-


ionic polymerization. Polymer, 44(14):3847–3854, June 2003.30. A. S. Nasar, M. Jikei, and M.-A. Kakimoto. Synthesis and properties

of polyurethane elastomers crosslinked with amine-terminated AB2-typehyperbranched polyamides. Eur. Polym. J., 39(6):1201–1208, June 2003.

31. R. W. McCabe and A. Taylor. Synthesis of novel polyurethane polyestersusing the enzyme Candida antarctica lipase B. Green Chem., 6(2):151–155,2004.

32. H. J. Assumption and L. J. Mathias. Photopolymerization of urethane di-methacrylates synthesized via a non-isocyanate route. Polymer, 44(18):5131–5136, August 2003.

33. S. Waddington, J.-M. L. Sonney, R. J. Elwell, F. M. Casati, and A. Storione.Low emission polyurethane polymers made with autocatalytic polyols. USPatent 6 762 274, assigned to Dow Global Technologies Inc. (Midland, MI),July 13 2004.

34. Y. P. Wei, F. Cheng, H. P. Li, and J. G. Yu. Synthesis and properties ofpolyurethane resins based on liquefied wood. J. Appl. Polym. Sci., 92(1):351–356, April 2004.

35. H. Yeganeh and M. A. Shamekhi. Poly(urethane-imide-imide), a new gener-ation of thermoplastic polyurethane elastomers with enhanced thermal sta-bility. Polymer, 45(2):359–365, January 2004.

36. E. C. Buruiana, V. Niculescu, and T. Buruiana. New polyurethanecationomers with naphthyl and phenyltriazene pendants: Synthesis andproperties. J. Appl. Polym. Sci., 92(4):2599–2605, May 2004.

37. Z. Y. Ren, H. P. Wu, J. M. Ma, and D. Z. Ma. FTIR studies on the modelpolyurethane hard segments based on a new waterborne chain extender di-methylol butanoic acid (DMBA). Chin. J. Polym. Sci., 22(3):225–230, May2004.

38. A. L. Silva and J. C. Bordado. Recent developments in polyurethane cata-lysis: Catalytic mechanisms review. Catal. Rev.-Sci. Eng., 46(1):31–51,2004.

39. K. H. Choe, D. S. Lee, W. J. Seo, and W. N. Kim. Properties of rigidpolyurethane foams with blowing agents and catalysts. Polym. J., 36(5):368–373, 2004.

40. P. Kjeldsen and C. Scheutz. Short- and long-term releases of fluorocarbonsfrom disposal of polyurethane foam waste. Environ. Sci. Technol., 37(21):5071–5079, November 2003.

41. M. Modesti, N. Baldoin, and F. Simioni. Formic acid as a co-blowing agentin rigid polyurethane foams. Eur. Polym. J., 34(9):1233–1241, September1998.

42. M. A. O’ Neill, W. D. Kirk, S. C. Simmons, P. Trudeau, and J. W. Bremmer.System and method of forming composite structures. US Patent 6 627 018,assigned to Advance USA, LLC (Old Lyme, CT), September 30 2003.

Polyurethanes 127

43. T. B. Lee, T. L. Fishback, and C. J. Reichel. Polyol composition havinggood flow and formic acid blown rigid polyurethane foams made therebyhaving good dimensional stability. US Patent 5 770 635, assigned to BASFCorporation (Mt. Olive, NJ), June 23 1998.

44. S. Parnell, K. Min, and M. Cakmak. Kinetic studies of polyurethane poly-merization with Raman spectroscopy. Polymer, 44(18):5137–5144, August2003.

45. J. V. McClusky, R. E. O’ Neill, R. D. Priester, Jr., and W. A. Ramsey. Vibrat-ing rod viscometer. a valuable probe into polyurethane chemistry. Journal

of Cellular Plastics, 32(2):224–241, 1996.46. J. W. Britain and P. G. Gemeinhardt. Catalysis of the isocyanate hydroxyl

reaction. J. Appl. Polym. Sci., 4(11):207–211, 1960.47. F. Dimier, N. Sbirrazzuoli, B. Vergnes, and M. Vincent. Curing kinetics and

chemorheological analysis of polyurethane formation. Polym. Eng. Sci.,44(3):518–527, March 2004.

48. R. Herrington and K. Hock. Flexible Polyurethane Foams. Dow Chemical,Midland, 1991.

49. J. J. Burdeniuc. Tertiary amino alkyl amide polyurethane catalysts derivedfrom long chain alkyl and fatty carboxylic acids. US Patent 6 762 211, as-signed to Air Products and Chemicals, Inc. (Allentown, PA), July 13 2004.

50. A. Ishikawa, M. Sakai, and M. Morii. Process for producing polyureth-ane. US Patent 6 767 929, assigned to Kao Corporation (Tokyo, JP), July 272004.

51. T. Masuda, H. Nakamura, and Y. Tamano. Catalyst for production of a poly-urethane resin and method for producing a polyurethane resin. US Patent6 723 819, assigned to Tosoh Corporation (Yamaguchi-ken, JP), April 202004.

52. P. Haas, D. Wegener, and H. Grammes. Activators for the production ofpolyurethane foams. US Patent 6 759 363, assigned to Bayer Aktienge-sellschaft (Leverkusen, DE), June 6 2004.

53. R. L. Zimmerman and T. M. Austin. Factors affecting the discolorationof vinyl that has been molded against urethane foam. Journal of Cellular

Plastics, 24(3):256–265, 1988.54. E. Huygens, B. Eling, and A. Christfreund. Amine-free catalyst systems for

automotive instrument panels. Journal of Cellular Plastics, 28(2):160–174,192.

55. A. Christfreund, E. Huygens, and B. Eling. Amine-free catalyst systems forautomotive instrument panels. Cell. Polym., 10(6):452–465, 1992.

56. O. M. Baker, F. E. Critchfield, and P. M. Westfall. Process for producingflexible polyurethane foam using hexahydro-s-triazine catalysts. US Patent4 814 359, assigned to Union Carbide Corporation (Danbury, CT), March21 1989.


57. S. Spertini. Process for making flexible foams. US Patent 5 266 604, as-signed to Imperial Chemical Industries PLC (London, GB2), November 301993.

58. H. Yoshimura, Y. Tamano, and S. Arai. Process for producing flexible poly-urethane foam having high air flow property. US Patent 5 306 738, assignedto Tosoh Corporation (Shinnanyo, JP), April 26 1994.

59. Y. Tamano, S. Okuzono, M. Ishida, S. Arai, and H. Yoshimura. Process forproducing rigid polyurethane foam. US Patent 5 100 927, assigned to TosohCorporation (Shinnanyo, JP), March 31 1992.

60. H. Yoshimura, S. Okuzono, and S. Arai. Process for producing high re-silience polyurethane foam. US Patent 5 104 907, assigned to Tosoh Corpo-ration (Shinnanyo, JP), April 14 1992.

61. S. L. Hannah and M. R. Williams. Catalyzed fast cure polyurethane sealantcomposition. US Patent 4 952 659, assigned to The B. F. Goodrich Com-pany (Akron, OH), August 28 1990.

62. D. Katsamberis and S. P. Pappas. Catalysis of isocyanate-alcohol andblocked-isocynante-alcohol reactions by amidines. J. Appl. Polym. Sci.,41(9):2059–2065, 1990.

63. J. Blahak, H. Hubner, J. Koster, H. J. Meiners, and H. Thomas. Odorlesscatalysts for the synthesis of polyurethanes. US Patent 4 348 536, assignedto Bayer Aktiengesellschaft (Leverkusen, DE), September 7 1982.

64. E. L. Rister, Jr., R. A. Grigsby, Jr., and R. L. Zimmerman. Catalyst sys-tems for polyurethane polyester foams. US Patent 6 534 555, assigned toHuntsman Petrochemical Corporation (Austin, TX), March 18 2003.

65. R. M. Gerkin, K. K. Robinson, and E. J. Dererian. Alkylamino oxamidesas low odor, non-fugitive catalysts for the production of polyurethanes. USPatent 6 600 001, assigned to Crompton Corporation (Middlebury, CT), July29 2003.

66. M. T. Pence and K. G. McDaniel. Rim compositions using amino acid saltcatalysts. US Patent 5 157 057, assigned to Arco Chemical Technology, L.P.(Wilmington, DE), October 20 1992.

67. J. D. Nichols, A. C. L. Savoca, and M. L. Listemann. Quaternary ammon-ium carboxylate inner salt compositions as controlled activity catalysts formaking polyurethane foam. US Patent 5 240 970, assigned to Air Productsand Chemicals, Inc. (Allentown, PA), August 31 1993.

68. H. E. Ghobary and L. Müller. Process for preparing polyurethane foam.US Patent 6 395 796, assigned to Crompton Corporation (Middlebury, CT),May 28 2002.

69. S. H. Wendel and R. Fard-Aghaie. Acid-blocked amine catalysts for theproduction of polyurethanes. US Patent 6 525 107, assigned to Air Productsand Chemicals, Inc. (Allentown, PA), February 25 2003.

70. J. W. Rosthauser, H. Nefzger, R. L. Cline, and G. C. Erhart. Delayed actioncatalysts for carpet backing and air frothed foam. US Patent 6 140 381,

Polyurethanes 129

assigned to Bayer Corporation (Pittsburgh, PA), October 31 2000.71. L. Thiele and R. Becker. Catalytic mechanisms of polyurethane formation.

Adv. Urethane Sci. Technol., 12:59–85, 1993.72. R. Kopp and H.-A. Freitag. Process for the production of optionally cellular

polyurethanes. US Patent 4 510 269, assigned to Bayer Aktiengesellschaft(Leverkusen, DE), April 9 1985.

73. H. Peter, B. Johannes, M. Werner, and K. Manfred. Verfahren zur Herstel-lung von Polyurethankunststoffen. DE Patent 2 732 292, assigned to BayerAG, February 1 1981.

74. J. P. Casey, R. V. C. Carr, G. J. Wasilczyk, and R. G. Petrella. Tertiary aminecatalysts for polurethanes. US Patent 5 091 583, assigned to Air Productsand Chemicals, Inc. (Allentown, PA), February 25 1992.

75. L. A. Mercando, M. L. Listemann, and M. J. Kimock. Reactive catalystcompositions for improving water blown polyurethane foam performance.US Patent 6 232 356, assigned to Air Products and Chemicals, Inc. (Allen-town, PA), May 15 2001.

76. A. C. L. Savoca and M. L. Listemann. 3-Quinuclidinol catalyst composi-tions for making polyurethane foams. US Patent 5 143 944, assigned to AirProducts and Chemicals, Inc. (Allentown, PA), September 1 1992.

77. A. C. L. Savoca and M. L. Listemann. 3-Quinuclidinol catalyst composi-tions for making polyurethane foams. US Patent 5 194 609, assigned to AirProducts and Chemicals, Inc. (Allentown, PA), March 16 1993.

78. M. L. Listemann, K. E. Minnich, B. E. Farrell, L. A. Mercando, M. J. Ki-mock, and J. D. Nichols. Hydroxymethyl quinuclidine catalyst composi-tions for making polyurethane foams. US Patent 5 710 191, assigned to AirProducts and Chemicals, Inc. (Allentown, PA), January 20 1998.

79. H. H. Humbert and R. A. Grigsby, Jr. Advances in urethane foam cata-lysis. US Patent 6 458 860, assigned to Huntsman Petrochemical Corpora-tion (Austin, TX), October 1 2002.

80. S. Kohlstruk, I. Bockhoff, M. Ewald, and R. Lomoelder. Catalyst and pro-cess for preparing low-viscosity and color-reduced polyisocyanates contain-ing isocyanurate groups. US Patent 6 613 863, assigned to Degussa AG(Duesseldorf, DE), October 2 2003.

81. L. E. Katz, E. A. Barsa, B. W. Tucker, and P. V. Grosso. Catalyst andprocess for producing isocyanate trimers. US Patent 5 691 440, assigned toArco Chemical Technonogy, L.P. (Greenville, DE), November 25 1997.

82. T. Endo and Y. Nambu. Catalyst for isocyanate trimerization. US Patent5 264 572, assigned to Asahi Denka Kogyo K.K. (Tokyo, JP), November 231993.

83. H. J. Scholl and J. Pedain. Process for the production of polyisocyanatescontaining isocyanurate groups and their use. US Patent 4 960 848, assignedto Bayer Aktiengesellschaft (Leverkusen, DE), October 2 1990.


84. Y. Watabe, M. Ishii, and Y. Iseda. New catalysts in urethane formation I ef-fect of catalyst on molecular weight of polyureaurethane and determinationof the minimum demolding time. J. Appl. Polym. Sci., 25:2339–2745, 1980.

85. Y. Watabe, M. Ishii, and Y. Iseda. New catalysts in urethane formation IIcatalytic activity of carboxylic acids. J. Appl. Polym. Sci., 25:2747–2754,1980.

86. R. Carswell. Blends of alkylene glycols and relatively high equiva-lent weight active hydrogen compounds containing additives. US Patent5 057 543, assigned to The Dow Chemical Company (Midland, MI), Octo-ber 15 1991.

87. S. W. Wong and K. C. Frisch. In K. C. Frisch and D. Klempner, editors,Advances in Urethane Science and Technology, volume 10, page 49. Tech-nomic, Lancaster, 1987.

88. J.-M. Frances, V. Gouron, B. Jousseaume, and M. Pereyre. Optionally chel-ated tin(iv) compounds useful as latent catalysts. US Patent 5 075 468, as-signed to Rhone-Poulenc Chimie (Courbevoie, FR), December 24 1991.

89. J.-M. Frances, V. Gouron, B. Jousseaume, and M. Pereyre. Tin (iv)compounds. US Patent 5 084 543, assigned to Rhone-Poulenc Chimie(Courbevoie, FR), January 28 1992.

90. R. Richter, H. P. Müller, W. Weber, R. Hombach, B. Riberi, R. Busch, andH.-G. Metzinger. Polyisocyanate preparations containing latent tin catalystsand a process for their preparation. US Patent 5 045 226, assigned to BayerAktiengesellschaft (Bayerwerk, DE), September 3 1991.

91. J. W. Rosthauser, E. P. Squiller, and P. H. Markusch. Rapid curing,light stable, two-component polyurethane coating compositions. US Patent5 154 950, assigned to Miles Inc. (Pittsburgh, PA), October 13 1992.

92. D. A. Sciangola. Latent catalysts comprising bismuth carboxylates and zir-conium carboxylates. US Patent 5 064 871, assigned to Essex SpecialtyProducts, Inc. (Clifton, NJ), November 12 1991.

93. J. D. Nichols and J. B. Dickenson. Cationic electrodepositable composi-tions of partially-blocked polyisocyanates and amine-epoxy resins contain-ing polymeric diorganotin catalysts. US Patent 4 981 925, assigned to AirProducts and Chemicals, Inc. (Allentown, PA), January 1 1991.

94. J. E. Dewhurst and J. D. Nichols. Polyurethane rim elastomers obtainedwith hydroxyl-containing organotin catalysts. US Patent 5 256 704, as-signed to Air Products and Chemicals, Inc. (Allentown, PA), October 261993.

95. V. Ullrich and C. Schudok. Polyurethane catalysts. US Patent 5 155 248,assigned to Rhein Chemie Rheinau GmbH (Mannheim, DE), October 131992.

96. X. Y. Ma, H. J. Lu, G. Z. Liang, and H. X. Yan. Rectorite/thermoplasticpolyurethane nanocomposites: Preparation, characterization, and proper-ties. J. Appl. Polym. Sci., 93(2):608–614, July 2004.

Polyurethanes 131

97. M. G. Ciobanu and M. Bezdadea. SAPO-5 zeolite-filled polyurethanemembranes. 1. preparation and morphological characterisation. Rev. Chim.,55(3):140–143, March 2004.

98. F. Scarpa, W. A. Bullough, and P. Lumley. Trends in acoustic properties ofiron particle seeded auxetic polyurethane foam. Proc. Inst. Mech. Eng. Part

C-J. Eng. Mech. Eng. Sci., 218(2):241–244, February 2004.99. B. K. Kim, J. W. Seo, and H. M. Jeong. Properties of waterborne polyur-

ethane/nanosilica composite. Macromol. Res., 11(3):198–201, June 2003.100. Y. Zhu and D. X. Sun. Preparation of silicon dioxide/polyurethane nano-

composites by a sol-gel process. J. Appl. Polym. Sci., 92(3):2013–2016,May 2004.

101. J. Shen, Z. H. Zhang, and G. M. Wu. Preparation and characterization ofpolyurethane doped with nano-sized SiO2 derived from sol-gel process. J.

Chem. Eng. Jpn., 36(10):1270–1275, October 2003.102. S. Chen, J. Sui, and L. Chen. Positional assembly of hybrid polyureth-

ane nanocomposites via incorporation of inorganic building blocks into or-ganic polymer. Colloid Polym. Sci., 2004. Only online at July 2004: DOI:10.1007/s00396-004-1093-4.

103. Z. S. Petrovic, Y. J. Cho, I. Javni, S. Magonov, N. Yerina, D. W. Schaefer,J. Ilavsky, and A. Waddon. Effect of silica nanoparticles on morphology ofsegmented polyurethanes. Polymer, 45(12):4285–4295, May 2004.

104. M. Song, D. J. Hourston, K. J. Yao, J. K. H. Tay, and M. A. Ansarifar.High performance nanocomposites of polyurethane elastomer and organ-ically modified layered silicate. J. Appl. Polym. Sci., 90(12):3239–3243,December 2003.

105. S. Duquesne, R. Delobel, M. Le Bras, and G. Camino. A comparative studyof the mechanism of action of ammonium polyphosphate and expandablegraphite in polyurethane. Polym. Degrad. Stabil., 77(2):333–344, August2002.

106. M. Modesti, A. Lorenzetti, F. Simioni, and G. Camino. Expandable graphiteas an intumescent flame retardant in polyisocyanurate-polyurethane foams.Polym. Degrad. Stabil., 77(2):195–202, August 2002.

107. M. Modesti and A. Lorenzetti. Flame retardancy of polyisocyanurate-poly-urethane foams: use of different charring agents. Polym. Degrad. Stabil.,78(2):341–347, November 2002.

108. C. S. Wu, Y. L. Liu, and Y. S. Chiu. Preparation of phosphorous-containingpoly(epichlorohydrin) and polyurethane from a novel synthesis route. J.

Appl. Polym. Sci., 85(10):2254–2259, September 2002.109. K. Pielichowski and D. Slotwinska. Flame-resistant modified segmented

polyurethanes with 3-chloro-1,2-propanediol in the main chain–thermoan-alytical studies. Thermochim. Acta, 410(1-2):79–86, February 2004.

110. L. Song, Y. Hu, B. G. Li, S. F. Wang, W. C. Fan, and Z. Y. Chen. A studyon the synthesis and properties of polyurethane/clay nanocomposites. Int.


J. Polym. Anal. Charact., 8(5):317–326, September–October 2003.111. J. Y. Kim, W. C. Jung, K. Y. Park, and K. D. Suh. Synthesis of

Na+-montmorillonite/amphiphilic polyurethane nanocomposite via bulkand coalescence emulsion polymerization. J. Appl. Polym. Sci., 89(11):3130–3136, September 2003.

112. H. M. Jeong and S. H. Lee. Properties of waterborne polyurethane/PMMA/-clay hybrid materials. J. Macromol. Sci.-Phys., B42(6):1153–1167, 2003.

113. M. Modesti and A. Lorenzetti. Improvement on fire behaviour of waterblown pir-pur foams: use of an halogen-free flame retardant. Eur. Polym.

J., 39(2):263–268, February 2003.114. K. Kishore and K. Mohandas. Mechanistic studies on the action of am-

monium phosphate on polymer fire retardancy. Combust. Flame, 43(2):145–153, November 1981.

115. R. Gubler, editor. Chemical Economics Handbook (CEH). SRI Consult-ing, a Division of Access Intelligence, Menlo Park, CA, 1950–to present.(Internet: http://ceh.sric.sri.com/).

116. M. Malveda. Report “Phosgene”. In Chemical Economics Handbook

(CEH). SRI Consulting, a Division of Access Intelligence, Menlo Park, CA,August 2003. (Internet: http://ceh.sric.sri.com/).

117. H. Chinn, W. Cox, and A. Kishi. Report “Diisocyanates and Polyisocyan-

ates”. In Chemical Economics Handbook (CEH). SRI Consulting, a Di-vision of Access Intelligence, Menlo Park, CA, February 2003. (Internet:http://ceh.sric.sri.com/).

118. M. Malveda, T. Kaelin, and A. Kishi. Report “Ethyleneamines”. In Chemi-

cal Economics Handbook (CEH). SRI Consulting, a Division of Access In-telligence, Menlo Park, CA, July 2003. (Internet: http://ceh.sric.sri.com/).

119. S. Bizzari. Report “Phthalic Anhydride”. In Chemical Economics Hand-

book (CEH). SRI Consulting, a Division of Access Intelligence, MenloPark, CA, April 2004. (Internet: http://ceh.sric.sri.com/).

120. E. Greiner and M. Yoneyama. Report “Maleic Anhydride”. In Chemical

Economics Handbook (CEH). SRI Consulting, a Division of Access Intelli-gence, Menlo Park, CA, August 2002. (Internet: http://ceh.sric.sri.com/).

121. K.-L. Ring, T. Kaelin, and K. Yokose. Report “1,4-Butanediol”. In Chemi-

cal Economics Handbook (CEH). SRI Consulting, a Division of Access In-telligence, Menlo Park, CA, June 2004. (Internet: http://ceh.sric.sri.com/).

122. H. Chinn, A. Kishi, and U. Loechner. Report “Polyurethane Foams”.In Chemical Economics Handbook (CEH). SRI Consulting, a Divisionof Access Intelligence, Menlo Park, CA, November 2002. (Internet:http://ceh.sric.sri.com/).

123. H. Chinn, U. Loechner, and M. Yoneyama. Report “Polyurethane Elas-

tomers”. In Chemical Economics Handbook (CEH). SRI Consulting, aDivision of Access Intelligence, Menlo Park, CA, April 2003. (Internet:http://ceh.sric.sri.com/).

Polyurethanes 133

124. E. Linak, F. Dubois, and A. Kishi. Report “Urethane Surface Coat-

ings”. In Chemical Economics Handbook (CEH). SRI Consulting, a Di-vision of Access Intelligence, Menlo Park, CA, September 2000. (Internet:http://ceh.sric.sri.com/).

125. S. Duquesne, M. Le Bras, S. Bourbigot, R. Delobel, G. Camino, B. Eling,C. Lindsay, T. Roels, and H. Vezin. Mechanism of fire retardancy of poly-urethanes using ammonium polyphosphate. J. Appl. Polym. Sci., 82(13):3262–3274, December 2001.

126. M. Modesti and A. Lorenzetti. An experimental method for evaluatingisocyanate conversion and trimer formation in polyisocyanate-polyurethanefoams. Eur. Polym. J., 37(5):949–954, May 2001.

127. A. E. Mayr, W. D. Cook, G. H. Edward, and G. J. Murray. Cure and proper-ties of unfoamed polyurethanes based on uretonimine modified methylene-diphenyl diisocyanate. Polym. Int., 49(3):293–301, March 2000.

128. Y. J. Cui, L. Hong, X. L. Wang, and X. Z. Tang. Evaluation of the curekinetics of isocyanate reactive hot-melt adhesives with differential scanningcalorimetry. J. Appl. Polym. Sci., 89(10):2708–2713, September 2003.

129. C.-H. Wu, C.-Y. Chang, C.-M. Cheng, and H.-C. Huang. Glycolysis ofwaste flexible polyurethane foam. Polym. Degrad. Stabil., 80(1):103–111,2003.

130. S. Ghose and A. I. Isayev. Continuous process for recycling of polyurethanefoam. J. Cell. Plast., 40(3):167–189, May 2004.

131. T. Hashimoto, A. Umehara, M. Urushisaki, and T. Kodaira. Synthesis ofa new degradable polyurethane elastomer containing polyacetal soft seg-ments. J. Polym. Sci. Pol. Chem., 42(11):2766–2773, June 2004.

132. B. Singh, H. Tarannum, and M. Gupta. Use of isocyanate production wastein the preparation of improved waterproofing bitumen. J. Appl. Polym. Sci.,90(5):1365–1377, October 2003.

133. T. Gupta and B. Adhikari. Thermal degradation and stability of HTPB-based polyurethane and polyurethaneureas. Thermochim. Acta, 402(1-2):169–181, June 2003.

134. H. H. G. Jellinek, editor. Degradation and Stabilization of Polymers, vol-ume 1. Elsevier, New York, 1983.

135. M. Boutin, J. Lesage, C. Ostiguy, J. Pauluhn, and M. J. Bertrand. Ident-ification of the isocyanates generated during the thermal degradation of apolyurethane car paint. J. Anal. Appl. Pyrolysis, 71(2):791–802, June 2004.

136. G. Moroi. Influence of ion species on the thermal degradation of polyureth-ane interaction products with transition metal ions. J. Anal. Appl. Pyrolysis,71(2):485–500, June 2004.

137. C. Decker, F. Masson, and R. Schwalm. Weathering resistance of water-based UV-cured polyurethane-acrylate coatings. Polym. Degrad. Stabil.,83(2):309–320, February 2004.


138. G. Z. Liang, J. R. Meng, and L. Zhao. Casting polyurethane modified bypoly(styren-co-divinyl benzene) via one-step process at room temperature.Polym.-Plast. Technol. Eng., 43(2):341–355, 2004.

139. S. Guhanathan, R. Hariharan, and M. Sarojadevi. Studies on castor oil-based polyurethane/polyacrylonitrile interpenetrating polymer network fortoughening of unsaturated polyester resin. J. Appl. Polym. Sci., 92(2):817–829, April 2004.

140. P. Basak and V. S. Manorama. Poly(ethylene oxide)-polyurethane/poly-(acrylonitrile) semi-interpenetrating polymer networks for solid polymerelectrolytes: vibrational spectroscopic studies in support of electrical be-havior. Eur. Polym. J., 40(6):1155–1162, June 2004.

141. C.-L. Qin, W.-M. Cai, J. Cai, D.-Y. Tang, J.-S. Zhang, and M. Qin. Dampingproperties and morphology of polyurethane/vinyl ester resin interpenetrat-ing polymer network. Mater. Chem. Phys., 85(2-3):402–409, June 2004.

142. T. T. Alekseeva, S. I. Grishchuk, Y. S. Lipatov, N. V. Babkina, and N. V.Yarovaya. Kinetic parameters of formation of interpenetrating polyureth-ane-polystyrene polymer networks and their thermophysical and viscoelas-tic properties. Polym. Sci. Ser. A, 45(8):721–728, August 2003.

143. S. N. Jaisankar, Y. Lakshminarayana, and G. Radhakrishnan. Semi-inter-penetrating polymer networks based on polyurethane ionomer/poly(vinylchloride). Adv. Polym. Technol., 23(1):24–31, 2004.

144. S. Chen and L. Chen. Structure and properties of polyurethane/polyacryl-ate latex interpenetrating networks hybrid emulsions. Colloid Polym. Sci.,282(1):14–20, December 2003.

145. L. Chen and S. Chen. Latex interpenetrating networks based on polyureth-ane, polyacrylate and epoxy resin. Prog. Org. Coat., 49(3):252–258, April2004.

146. T. Kiguchi, H. Aota, and A. Matsumoto. Crosslinking polymerizationleading to interpenetrating polymer network formation. II. polyadditioncrosslinking reactions of poly(methyl methacrylate-co-2-methacryloyloxy-ethyl isocyanate) with various diols. J. Polym. Sci. Pol. Chem., 41(21):3243–3248, November 2003.

147. J. Culin, Z. Veksli, A. Anzlovar, and M. Zigon. Spin probe study of semi-in-terpenetrating polymer networks based on polyurethane and polymethacryl-ate functional prepolymers. Polym. Int., 52(8):1346–1350, August 2003.

148. S. Vlad, A. Vlad, and T. Oprea. Interpenetrating polymer networks (IPN)based on polyurethane and polymethylmethacrylate. Rev. Roum. Chim.,47(6):571–576, June 2002.

149. V. D. Athawale and P. S. Pillay. Sequential interpenetrating polymer net-works synthesized from polyester based polyurethane and poly(butyl meth-acrylate). Bull. Chem. Soc. Jpn., 76(6):1265–1271, June 2003.

150. S. H. Baek and B. K. Kim. Synthesis of polyacrylamide/polyurethane hy-drogels by latex IPN and AB crosslinked polymers. Colloids and Sur-

Polyurethanes 135

faces A: Physicochemical and Engineering Aspects, 220(1-3):191–198,June 2003.

151. S. J. Gao, L. N. Zhang, and Q. L. Huang. Effect of the synthesis route on thestructure and properties of polyurethane/nitrokonjac glucomannan semi-in-terpenetrating polymer networks. J. Appl. Polym. Sci., 90(7):1948–1954,September 2003.

152. H. W. Zhang, B. Wang, H. T. Li, Y. Jiang, and J. Y. Wang. Synthesisand characterization of nanocomposites of silicon dioxide and polyurethaneand epoxy resin interpenetrating network. Polym. Int., 52(9):1493–1497,September 2003.

153. C. N. Cascaval, D. Rosu, L. Rosu, and C. Ciobanu. Thermal degradation ofsemi-interpenetrating polymer networks based on polyurethane and epoxymaleate of bisphenol A. Polymer Testing, 22(1):45–49, February 2003.

154. L. V. Karabanova, G. Boiteux, O. Gain, G. Seytre, L. M. Sergeeva, E. D.Lutsyk, and P. A. Bondarenko. Semi-interpenetrating polymer networksbased on polyurethane and polyvinylpyrrolidone. II. dielectric relaxationand thermal behaviour. J. Appl. Polym. Sci., 90(5):1191–1201, October2003.

155. Y. J. Cui, Y. Chen, X. L. Wang, G. H. Tian, and X. Z. Tang. Synthesisand characterization of polyurethane/polybenzoxazine-based interpenetrat-ing polymer networks (IPNs). Polym. Int., 52(8):1246–1248, August 2003.

156. S. Dadbin and M. Frounchi. Effects of polyurethane soft segment and cross-link density on the morphology and mechanical properties of polyurethane/-poly(allyl diglycol carbonate) simultaneous interpenetrating polymer net-works. J. Appl. Polym. Sci., 89(6):1583–1595, August 2003.

157. S. S. Silva, S. M. C. Menezes, and R. B. Garcia. Synthesis and character-ization of polyurethane-g-chitosan. Eur. Polym. J., 39(7):1515–1519, July2003.

158. P. A. Gunatillake, D. J. Martin, G. F. Meijs, S. J. McCarthy, and R. Adhikari.Designing biostable polyurethane elastomers for biomedical implants. Aust.

J. Chem., 56(6):545–557, 2003.159. Q. Lv, C. B. Cao, and H. S. Zhu. Blood compatibility of polyurethane

immobilized with acrylic acid and plasma grafting sulfonic acid. J. Mater.

Sci. -Mater. Med., 15(5):607–611, May 2004.160. Y. Jiang, J. Zhang, J. Zhou, Y.-L. Yuan, J. Shen, and L. Si-cong. Platelet ad-

hesion onto segmented polyurethane surfaces modified by carboxybetaine.J. Biomater. Sci., Polym. Ed., 14(12):1339–1349, 2003.

161. Y. Jiang, Y.-L. Yuan, J. Shen, S. cong Lin, W. Zhu, and J. lin Fang. Graftingof sulfobetaine onto a polyurethane surface to improve blood compatibility.Chin. J. Polym. Sci., 21(4):419–425, July 2003.

162. Y. Jiang, B. Rongbing, T. Ling, S. Jian, and L. Si-Cong. Blood compat-ibility of polyurethane surface grafted copolymerization with sulfobetainemonomer. Colloids and Surfaces B: Biointerfaces, 36(1):27–33, July 2004.


163. L. Chen, L. Wang, Z. M. Yang, J. Shen, and S. C. Lin. Synthetic studies onblood compatible biomaterials 13: A novel segmented polyurethane con-taining phosphorylcholine structure: Synthesis, characterization and bloodcompatibility evaluation. Chin. J. Polym. Sci., 21(1):45–50, January 2003.

164. R. G. J. C. Heijkants, R. V. Van Calck, J. H. De Groot, A. J. Pennings, A. J.Schouten, T. G. Van Tienen, N. Ramrattan, P. Buma, and R. P. H. Veth.Design, synthesis and properties of a degradable polyurethane scaffold formeniscus regeneration. J. Mater. Sci. -Mater. Med., 15(4):423–427, April2004. Special Issue: Selected papers from the 18th European Conferenceon Biomaterials (ESB2003), Stuttgart, Germany, 2003.

165. C. Y. Gao, X. H. Hu, Y. Hong, J. J. Guan, and J. C. Shen. Photografting ofpoly(hydroxylethyl acrylate) onto porous polyurethane scaffolds to improvetheir endothelial cell compatibility. J. Biomater. Sci., Polym. Ed., 14(9):937–950, 2003.

166. Y. B. Zhu, C. Y. Gao, J. J. Guan, and J. C. Shen. Engineering porous poly-urethane scaffolds by photografting polymerization of methacrylic acid forimproved endothelial cell compatibility. J. Biomed. Mater. Res., Part A,67A(4):1367–1373, December 2003.

167. Y. W. Tang, R. S. Labow, and J. P. Santerre. Enzyme induced biodegrada-tion of polycarbonate-polyurethanes: dose dependence effect of cholesterolesterase. Biomaterials, 24(12):2003–2011, May 2003.

168. I. Alferiev, S. J. Stachelek, Z. B. Lu, A. L. Fu, T. L. Sellaro, J. M. Connol-ly, R. W. Bianco, M. S. Sacks, and R. J. Levy. Prevention of polyurethanevalve cusp calcification with covalently attached bisphosphonate diethyl-amino moieties. J. Biomed. Mater. Res., Part A, 66A(2):385–395, August2003.

169. G. Gunduz and R. R. Kisakijrek. Structure-property study of waterbornepolyurethane coatings with different hydrophilic contents and polyols. J.

Dispersion Sci. Technol., 25(2):217–228, March 2004.170. F. Celebi, L. Aras, G. Gunduz, and I. M. Akhmedov. Synthesis and charac-

terization of waterborne and phosphorus-containing flame retardant polyur-ethane coatings. J. Coat. Technol., 75(944):65–71, September 2003.

171. F. Celebi, O. Polat, L. Aras, G. Gunduz, and I. M. Akhmedov. Synthesisand characterization of water-dispersed flame-retardant polyurethane resinusing phosphorus-containing chain extender. J. Appl. Polym. Sci., 91(2):1314–1321, January 2004.

172. M. Keyvani. Improved polyurethane dispersion stability via continuous pro-cess. Adv. Polym. Technol., 22(3):218–224, Fall 2003.

173. C. Chinwanitcharoen, S. Kanoh, T. Yamada, S. Hayashi, and S. Sugano.Preparation of aqueous dispersible polyurethane: Effect of acetone on theparticle size and storage stability of polyurethane emulsion. J. Appl. Polym.

Sci., 91(6):3455–3461, March 2004.

Polyurethanes 137

174. X. D. Cao, L. N. Zhang, J. Huang, G. Yang, and Y. X. Wang. Structure-properties relationship of starch/waterborne polyurethane composites. J.

Appl. Polym. Sci., 90(12):3325–3332, December 2003.175. G. Yang, Q. Huang, L. Zhang, J. Zhou, and S. Gao. Miscibility and prop-

erties of blend materials from waterborne polyurethane and carboxymethylkonjac glucomannan. J. Appl. Polym. Sci., 92(1):77–83, April 2004.

176. N. G. Wang, L. Zhang, Y. S. Lu, and Y. M. Du. Properties of crosslinkedcasein/waterborne polyurethane composites. J. Appl. Polym. Sci., 91(1):332–338, January 2004.

177. M. Zeng, L. N. Zhang, N. G. Wang, and Z. C. Zhu. Miscibility and prop-erties of blend membrane of waterborne polyurethane and carboxymethyl-chitin. J. Appl. Polym. Sci., 90(5):1233–1241, October 2003.

178. M. Zeng, L. Zhang, and Y. Zhou. Effects of solid substrate on structure andproperties of casting waterborne polyurethane/carboxymethylchitin films.Polymer, 45(10):3535–3545, May 2004.

179. Y. Chen, L. N. Zhang, and L. B. Du. Structure and properties of compositescompression-molded from polyurethane prepolymer and various soy prod-ucts. Ind. Eng. Chem. Res., 42(26):6786–6794, December 2003.

180. S. Turri, M. Levi, and T. Trombetta. Waterborne anionomeric polyureth-ane-ureas from functionalized fluorovolvethers. J. Appl. Polym. Sci., 93(1):136–144, July 2004.

181. Y. S. Kwak, S. W. Park, and H. D. Kim. Preparation and properties of water-borne polyurethane-urea anionomers - influences of the type of neutralizingagent and chain extender. Colloid Polym. Sci., 281(10):957–963, October2003.

182. T. Takahashi, H. Munstedt, M. Modesti, and P. Colombo. Oxidation resis-tant ceramic foam from a silicone preceramic polymer/polyurethane blend.J. Eur. Ceram. Soc., 21(16):2821–2828, December 2001.

183. J. Nagel, M. B. Brauer, B. Hupfer, D. Lehmann, and K. Lunkwitz. Ad-hesion modification of thermoplastic polyurethane and chemical influenceson the adhesion in composites with pa 6. Kautsch. Gummi Kunstst., 57(5):240–247, May 2004.

184. B. Scrosati, A. Magistris, C. M. Mari, and G. Mariotto, editors. Fast Ion

Transport in Solids : [Proceedings of the NATO Advanced Research Work-

shop on Fast Ion Transport in Solids, Belgirate, Italy, September 20 - 26,

1992]. NATO ASI series : Series E, Applied sciences. Kluwer AcademicPublishers, Dordrecht, 1993.

185. W. A. V. Schalkwijk and B. Scrosati, editors. Advances in Lithium-Ion

Batteries. Kluwer Academic Publishers, Dordrecht, 2002.186. B. Scrosati, editor. Application of Electroactive Polymers. Chapman and

Hall, London, 1993.187. S.-M. Lee, C.-Y. Chen, C.-C. Wang, and Y.-H. Huang. The effect of EPIDA

units on the conductivity of poly(ethylene glycol)-4,4′-diphenylmethane


diisocyanate-EPIDA polyurethane electrolytes. Electrochim. Acta, 48(6):669–677, February 2003.

188. X. Huang, T. Ren, and X. Tang. Porous polyurethane/acrylate polymerelectrolytes prepared by emulsion polymerization. Mater. Lett., 57(26-27):4182–4186, September 2003.

189. H.-L. Wang, A. Gopalan, and T.-C. Wen. A novel lithium single ion basedpolyurethane electrolyte for light-emitting electrochemical cell. Mater.

Chem. Phys., 82(3):793–800, December 2003.

Documents

Reactive Polymers Fundamentals and Applications || Polyurethanes