Progress in Organic Coatings 62 (2008) 393–399

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Progress in Organic Coatings

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Phase morphology and surface properties of moisture cured polyurethane-urea(MCPU) coatings: Effect of catalysts

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S.K. Rath, A.M. Ishack, U.G. Suryavansi, L. ChandrasNaval Materials Research Laboratory, Shil-Badlapur Road, Addl. Ambernath, Ambernath

a r t i c l e i n f o

Article history:Received 20 November 2007Received in revised form 13 February 2008Accepted 19 February 2008

Keywords:Moisture curePolyurethane-ureaPhase morphologySurface property

a b s t r a c t

Effect of catalysts on curipolyurethane-urea (MCPUnated polybutadiene (HTPurethane catalysts at 30 ◦Cwas used to monitor theinduced shortening of indphase morphology of theand differential scanningdistance of hard segmentsevaluated by FTIR-ATR anddeconvolution of the FTIRwith increasing efficiencysurface energy changes of

1. Introduction

Moisture cured polyurethane-ureas contain NCO-terminated

polyurethane prepolymer [1], which on curing in the presenceof atmospheric moisture produce highly crosslinked networks.MCPUs are widely used in the high performance coating appli-cations as well as reactive hot melt adhesive industries. Theadvantages of one component polyurethane-urea systems havebeen summarized by Gardner [2]. First of all they can be man-ufactured as one package system and their application is easier.Secondly since the reactant is water, the formulations have less VOCthan two component systems. In comparison to two componentpolyurethanes, the MCPUs have good adhesion, abrasion resistance,thermal stability, hardness, chemical and solvent resistance [3]. Fur-ther these materials adhere well to visibly damp surfaces as theypenetrate into pores and tight crevices, where moisture is present.In order to obtain adequate modulus and strength development, thecure of NCO-terminated polyurethane prepolymer with moisturerequires a careful control of processing conditions. The parametersaffecting the cure process are relative humidity, isocyanate contentin the prepolymer and catalyst type [4,5].

Phase morphology of segmented polyurethanes has been stud-ied extensively by researchers [6–10]. The factors which influence

∗ Corresponding author. Tel.: +91 251 2620401x337; fax: +91 251 2620604.E-mail address: mrpatri@rediffmail.com (M. Patri).

0300-9440/$ – see front matter © 2008 Elsevier B.V. All rights reserved.doi:10.1016/j.porgcoat.2008.02.004

ar, M. Patri ∗

6, Maharashtra, India

haviour, phase morphology and surface properties of a moisture cureding has been studied. The prepolymer, prepared by capping hydroxy termi-th isophorone diisocyanate (IPDI), was cured with moisture using differentrelative humidity of 60%. Fourier transform infrared spectroscopy (FTIR)g process. Gel fraction studies through solubility method, show catalystn period for gelation and increase in gel fraction. Effect of catalysts onwas evaluated by X-ray diffraction, small angle X-ray scattering (SAXS)

imetry (DSC). The results show that the heat of fusion and interdomainnfluenced by the choice of catalysts. The effect on surface properties wasact angle goniometry. The type of H-bonding interaction was identified bytra. The results show that the surface polar group concentrations increasee catalysts. Consequently there is a clear observation of catalyst inducedCPU.

© 2008 Elsevier B.V. All rights reserved.

phase separation include segmental polarity difference [11], seg-mental length [12], crystallizability of either segment [13], intra-and intersegment interactions such as hydrogen bonding [13,14].overall composition and molecular weight [11]. Extensive phasemixing of soft and hard segments of PTMG/IPDI based MCPUs andtheir effect on surface properties are reported [15]. In compari-

son to segmented polyurethanes, the phase morphology studieson MCPUs have been relatively scanty.

The behaviour of the MCPUs at the surface and interfaces hasa significant effect on various properties and plays a vital role incoating applications. The surface composition of multicomponentMCPUs during cure progress has been studied in detail by manyresearchers [16–18]. XPS studies have shown the enrichment in softsegments on the air-side surface of polyurethanes [19–21].

In the present study, hydroxy terminated polybutadiene cappedwith isophorone diisocyanate has been used as the prepolymerfor MCPU formation. Effect of catalysts on curing, thermal proper-ties, phase morphology and surface properties of MCPU have beenstudied.

2. Experimental

2.1. Materials

Isophorone diisocyanate (IPDI) from E-Merck was used asreceived. Hydroxy terminated polybutadiene (HTPB) (functional-ity 2.4, OH value 50) was purchased from ORION Chem Ltd., India.

rganic

394 S.K. Rath et al. / Progress in O

Dibutyltin dilaurate (DBTDL) was purchased from Fluka and used asreceived. Ferric chloride and triethyl amine (TEA) were purchasedfrom S.D. Fine Chemicals, India. Trietheyl amine was vacuum dis-tilled before use.

2.1.1. Synthesis of prepolymerThe prepolymer from IPDI and HTPB was synthesized at 60 ◦C in

a three-necked R.B. flask equipped with a mechanical stirrer. Themolar ratio of NCO to OH groups was 2:1. The reaction was car-ried without use of any catalysts under a dry nitrogen blanket untilthe desired isocyanate content is obtained. Isocyanate content inthe prepolymer was determined by titration with diethyl amine[22]. The NCO value was 3.48% compared to the theoretical valueof 3.64%.

2.2. Preparation of films

The prepolymer was mixed with different catalysts (0.05 wt%)and the films were cast on a Teflon mould. The films were cured withmoisture at 30 ◦C and 60% RH. The progress of curing was monitoredby monitoring the decay of the isocyanate band by FTIR spectra. Thetime for complete cure for various catalysts were found to be 1120 h(unanalysed), 1080 h (FeCl3), 930 h (TEA) and 820 h (DBTDL).

2.3. Characterization techniques

2.3.1. FTIR analysisFTIR spectra of the samples were recorded using a PerkinElmer

1650 FTIR spectrophotometer with a resolution of 4 cm−1 and 32scans. Crosslinking for the one component system was followed bymonitoring the disappearance of isocyanate band. In the FTIR anal-ysis, integrated intensities of the absorbance bands were correctedfor sample thickness differences using the CH2 stretching band near2980 cm−1 as normalising factor.

For calculating the degree of curing it is assumed that there areno side reactions [11]. From the isocyanate conversion the degreeof curing was calculated as follows

Isocyanate conversion (p) = 1 − At − A∞A0 − A∞

Where A0 is the normalised area of absorption at the initial time,At is the normalised area of absorption at a certain time duringthe cure process, and A∞ is the final normalised area of absorption

at infinite time. For a completely cured system A∞ will be zero,because no NCO functionality will be available for IR absorption insuch a case.

2.3.2. Determination of sol and gel fractionThe sol and gel fraction of the MCPUs with progress of cure was

evaluated by soxhlet extracting the MCPUs with toluene. The solfraction was determined using the following equation

Sol fraction (%) =(

W − W1

W1

)× 100

where W is the initial weight and W1 is the weight of the sampleafter extraction

Gel fraction (%) = 100 − sol fraction (%)

2.3.3. TGAThe thermal stability of the polymer film with progress of cure

was studied in Nitrogen environment using TA instruments Hi Res2950 Thermogravimetric Analyser. The measurements were carriedout from 30 to 800 ◦C at a heating rate of 10 ◦C/min.

Coatings 62 (2008) 393–399

2.3.4. Wide-angle X-ray diffractionThe crystallinity of the MCPUs was evaluated by using Cu K� ray

of wavelength 1.54 A between 10 and 30◦ at 0.2◦/10 s in a PhilipsX-ray diffractometer.

2.3.5. SAXSSmall angle X-ray scattering, SAXS (Ariton Paar, Austria) exper-

iments was performed on moisture cured polymer films using anX-ray source having wavelength 1.54 A. The samples were scannedfor 15 min at 25 ◦C. The scattering patterns were recorded using thecollimation technique. The scattering patterns were integrated togenerate an I(q) versus q curve, where I(q) is the intensity of thescattered X-rays and q is the scattering vector.

2.3.6. DSCCalorimetric measurements of the completely cured MCPUs

were carried out using TA instruments DSC Q-100, from −80 ◦C to120 ◦C at a heating rate of 5 ◦C/min under nitrogen atmosphere. Theinstrument was calibrated with Indium standards before measure-ments.

2.3.7. FTIR-ATRAttenuated total reflectance (ATR) analysis was carried out in

a Thermocom Nicholet 5700 spectrometer with a horizontal flatplate ATR accessory. The ATR crystal was diamond with an end-face angle of 45◦. The substrate-facing side of the polymer film wasplaced against the crystal and clamped into position. Each sam-ple was scanned 100 times at a resolution of 4 cm−1 and the scanswere signal averaged. In ATR the depth of penetration for a non-absorbing medium, defined as the distance required for the electricfield amplitude to fall to e−1 of its value at the surface, has beengiven by Harrick [23].

dp = �

2�n1(sin � − (n1/n2)2)0.5

Where n1 is the refractive index of the sample and n2 is the refrac-tive index of the ATR element. Micebella and Harrick [24] has shownthat sampling depth for polymeric materials is about three times dp.

2.4. Surface energy analysis through goniometry

The surface free energies of polymer samples were deter-mined by contact angle goniometer using a Kruss G10 goniometry

interfaced to image capture software. The surface energy systemmeasures and averages contact angles of various liquids and cal-culates the surface energy. Advancing (�A) contact angles weremeasured for droplets (2–10 �L) of double distilled water anddiidomethane using the movable protractor scale of the goniome-ter. The spatial size probed (in the plane of the surface) was 1–2 mmin diameter. The images of three droplet liquids of each test liquidare taken by a CCD camera and the contact angles were determinedusing automated image analysis.

3. Results and discussion

3.1. Cure behaviour of MCPUs

Hydroxy terminated polybutadiene with a functionality of 2.4has been used for prepolymer synthesis. Hence during the cureprocess a three dimensional network is formed without the aid ofan external crosslinker. The evidence of a crosslinked network isapparent from the evaluation of the gel fraction by extraction ofthe MCPUs with toluene. Fig. 1 shows the effect of catalysts on curetime dependant gel fractions of the MCPU. From the results it is seen

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S.K. Rath et al. / Progress in Or

Fig. 1. Dependence of gel fraction on curing time of MCPU cured with various cat-

alysts.

that the induction period for gel formation is longer for uncatalysedMCPU. With introduction of catalysts the induction period for gela-tion decreases and the gel fraction content increases. However, ina crosslinked network, still some unreacted functional groups existat the end of the curing process, some chains with low molecularweight are entrained in the network and rendered inactive [25].The possibility of entrainment of unreacted chains decreases withthe efficiency of the catalyst, hence the lower sol fraction.

The curing reaction of moisture cured polyurethane-ureas(MCPUs) involves a series of polyaddition reactions which dependsupon the curing conditions. Water vapour from the atmospherediffuses into the MCPU, and the nucleophilic attack of water onNCO-terminated prepolymer results in an irreversible reaction,which produces carbamic acid. The carbamic acid is unstable atroom temperature and decomposes into CO2 and a primary amine.The primary amine is reactive with the NCO-terminated prepoly-mer and produces urea. The cure progress was monitored by FTIR,monitoring the disappearance of the –NCO peak. Fig. 2 illustrates

Fig. 2. FTIR spectra of HTPB/IPDI, showing the decay of NCO group at a cure time of760 h (film thickness 0.15 mm).

Coatings 62 (2008) 393–399 395

the FTIR spectrum (corresponding to the isocyanate band) of theMCPUs after 760 h of cure time. From the figure it is seen that theintensity of unreacted isocyanate peak is of the order: no cata-lyst > FeCl3 > triethyl amine > DBTDL. At this cure time the DBTDLcatalysed system has approached 92% completion of the cure,whereas without catalyst only 33% completion of cure has beenaccomplished. Complete curing of uncatalysed prepolymer tookplace in 1120 h, whereas the DBTDL catalysed system cured in 820 h.From the FTIR results, it is clear that use of catalysts hastens thecure process and DBTDL is found to be the most efficient catalystfollowed by triethylamine and ferric chloride.

Now we discuss the gel fraction and curing process resultsvis a vis the reactivity of IPDI towards various catalysts. Amongdiisocyanates, IPDI possesses a primary aliphatic and a secondarycylcoaliphatic isocyanate group leading to four isomers from cisand trans conformation [26]. An unequal reactivity between theprimary and secondary NCO groups is usually reported. Depend-ing on the reaction conditions of temperature and catalyst type,the reactivity difference ratio between the secondary and the pri-mary isocyanates is reported to be in the range 0.2:1–12:1 [26].Lamolder et al. [27] showed that catalyst nature had a dramaticeffect on the selectivity of IPDI in the urethane reaction. FurtherBurel et al. [26] studied the effect of catalyst concentration andtemperature on kinetics of urethane reactions. They found that theselectivity decreases and tends towards a plateau as DBTDL con-tent increases. In the present study the catalyst concentration hasbeen fixed for all the compositions. Moreover, the curing processleads to formation of urea functional groups instead of urethanes.Based on the observations of Burel et al. [26] we presume that inthe capping reaction the primary aliphatic isocyanates of IPDI areinvolved (in absence of any catalyst) owing to their higher reactiv-ity compared to secondary isocyanate functional group. Thus, thesecondary cycloaliphatic isocyanates are expected to participate inurea formation. The longer curing times observed for the uncatal-ysed system provide evidence to our presumption. Moreover, sincethe curing process was carried out at room temperature and sameconcentration of catalyst (0.05 wt%) for all the systems, selectivityof the isocyanates is not expected to be altered.

It must be noted that the composition of the MCPUs is same,except for the nature of catalysts. The hard and soft segmentconcentration of the completely cured MCPUs were calculated asfollows.

Hard segment concentration (%) = MOH + Miso + Mce × 100

Mtotal

where MOH is the molecular mass of hydroxyl group of polyol, i.e.HTPB, Miso is the molecular mass of isocyanate compound used, i.e.IPDI, Mce is the molecular mass of chain extender, i.e. water, Mtotalis the total molecular mass. The calculations were carried out basedon the 2:1 molar ratio of IPDI/HTPB used in the capping reaction andaccordingly the amount of water required for complete curing.

Soft segment concentration (%)

= 100 − hard segment concentration (%)

3.2. TGA

The weight loss versus temperature plot of the MCPU curedby using different catalysts is shown in Fig. 3. The tests were car-ried out after a cure time of 760 h which corresponds to differentdegree of cure with different catalysts. From the figure it is seenthat the DBTDL catalysed MCPU shows slightly higher thermal sta-bility compared to other systems. Enhancement of thermal stabilitycould be attributed to the progress of cure for the samples. Further

396 S.K. Rath et al. / Progress in Organic Coatings 62 (2008) 393–399

Fig. 3. TGA thermogram of moisture cured polyurethane-ureas catalysed with dif-ferent catalysts at a cure time of 760 h.

it is seen that the degradation pattern of the MCPU for all the cat-alysts is similar, with a two-step decomposition profile. The initialdecomposition temperature is 285 ◦C for the DBTDL catalysed sys-tem at the given cure time. The other systems differ only marginallyin the order TEA > FeCl3 > uncatalysed reflecting the cure progress.This result is in line with our FTIR results of DBTDL being the mostefficient catalyst in the cure process followed by TEA, FeCl3.

3.3. Morphology studies

3.3.1. Wide-angle X-ray diffraction (WAXD)It has been previously reported [28,29] that polyureas exhibit

crystallinity. In this study, the crystallinity of the MCPUs wasexamined by WAXD. Fig. 4 shows the diffraction patterns of theMCPUs. From the figure it is seen that the diffraction patterns inall cases exhibit a dominant amorphous halo indicating absence ofcrystalinity. These results are in agreement with previous studiesthat shown that polyureas containing nonsymmetrical structureare amorphous and that introduction of chemical crosslinks inpolyurethanes disrupts the crystallinity [30]. From the gel frac-tion studies it is already evident that the MCPUs are crosslinked,

Fig. 4. Wide-angle X-ray diffraction of moisture cured polyurethane-ureas catalysedwith different catalysts.

Fig. 5. SAXS plot (I vs. q) of moisture cured polyurethane-ureas catalysed withdifferent catalysts.

although the extent varies with nature of catalysts. Hence it is likelythat this same situation is produced in the MCPU synthesized in thisstudy.

3.3.2. SAXSThe polybutadiene based polyurethane networks are reported to

exhibit a pronounced two-phase structure [31,32] As follows fromFig. 5 an interference maximum is observed in the scattering vec-tor range 0.7–1 nm−1 for all the curves (SAXS experiments were

performed only on uncatalysed, DBTDL and TEA catalysed MCPUs).This type of SAXS curve could be attributed to a two-phase struc-ture. In the MCPU system, first phase, the soft one, is formed bythe butadiene component of the network, while the urea and ure-thane form hard segments, the second phase. This structure modelof the moisture cured polyurethenae-ureas is quite similar to theones studied by others for polybutadiene based networks [31].

In the tracking of morphological changes, one of the key exper-imentally determined parameters is the interdomain spacing fromSAXS. The interdomain distance (L) defined as the average distancebetween two hard domains can be obtained from the SAXS intensityprofiles by the application of Bragg’s equation: L = 2�/qmax, whereqmax is defined as the first-order scattering maximum. The interdo-main values obtained from the SAXS plots are presented in Table 1.From the results it is seen that catalysts affect the interdomain dis-tance. It is well established that the interdomain distance dependson the hard and soft segment composition of a phase separatedmaterial. The hard segment concentration of the present MCPU is20.1%. On investigating a series of polyurethane elastomers withvaried hard segment concentration, Abouzhar et al. [33] proposed

Table 1Effect of catalysts on the interdomain distance and enthalpy of fusion of MCPU

Catalyst Interdomain distance (nm) Enthalpy of fusion (J/gm)

None 8.3 0.246FeCl3 – 0.203TEA 8.6 0.051DBTDL 8.5 *

* A base line shift is observed instead of an endotherm.

S.K. Rath et al. / Progress in Organic Coatings 62 (2008) 393–399 397

3.4. Surface properties

3.4.1. FTIR-ATRFig. 7 shows the FTIR-ATR spectra (for the polar urethane and

urea groups) of the fully cured MCPU cured with different catalysts.A spectral range from 1600 to 1750 cm−1 was chosen to emphasizethe carbonyl region which contributes to the polarity of the surface.The sampling depth for the ATR analysis at various wave numbersin the carbonyl region was found to be 3–3.7 �m. The refractiveindex of the MCPU was found to be 1.5156 from Abbe refractome-ter and does not change with nature of the curing catalysts. Hencethe sampling depths in the analysis did not vary with the nature ofthe catalyst. From the spectra a complex band envelope is observed

Fig. 6. DSC thermogram of fully cured poly urethane-ureas cured with differentcatalysts.

an interconnected hard segment morphology at relatively higherhard segment concentration (>25 wt%). They suggested that ran-domly dispersed micro domains existed in the polyol matrix whenthe hard segment concentration is less then 25 wt%. We cannottherefore conclusively comment on the effect of catalysts on distri-bution of hard segments from the present data at a hard segmentconcentration of less then 25 wt%, as the results do not show anyparticular trend of interdomain distance with introduction of cat-alysts. However, DSC results give additional information regardingthe hard segments, which is discussed later.

3.3.3. DSCFig. 6 shows the DSC thermogram of HTPB and the fully cured

MCPU cured with various catalysts. From the figure it is seen thatHTPB has a sub-room temperature transition at−26.2 ◦C, which cor-responds to the glass transition temperature. The MCPU show twotransitions for all the catalysts. The low temperature transition cor-responds to the soft segment, the polybutadiene segment, whereasthe high temperature transition at 53–55 ◦C corresponds to thehard segment, i.e. transition associated with breakdown of hydro-gen bonding between hard segments of urethane/urea groups. Twotransitions clearly suggest that the MCPUs are phase separatedas found from SAXS studies. Very recently Daniel Da-Silva et al.

[34] showed the evidence of phase separation in moisture curedpolyurethane-ureas by means of modulated differential scanningcalorimetry. Through irreversible heat flow measurements, theyfound the location of the broad endotherms in the range 60–100 ◦C.In the present study we observe mild endotherms (through con-vention DSC measurement) attributable to the lower hard segmentcontent of the MCPUs. The enthalpy of fusion of the hard segmentsis given in Table 1. From the results it is seen that the uncatalysedMCPU has the highest �H value, suggesting bigger hard domainsizes. The �H value decreases with catalysts. Interestingly enough,with increase in catalytic activity of the catalysts, the enthalpy offusion decreases. This provides evidence to our speculation thatrapid aggregation behaviour decreases the hard domain size. TheDSC results by Kwei [35] on segmented polyurethanes showed thatthe phase separation of soft and hard segments was relatively fasterwhile the ordering of hard segments took a longer time. Further Liet al. [36] argued that hard segment mobility and system viscos-ity are the main controlling factors for the phase behaviour of thepolyurethanes. The same reasoning holds well for the present study.Further the observation of domain formation could be attributedto the large difference in the reactivity of the cycloaliphatic sec-

Fig. 7. FTIR-ATR spectra of the air-side surface of fully cured polyurethane-ureascatalysed with different catalysts.

ondary isocyanate and the primary aliphatic isocyanates. As alreadymentioned in the discussion on curing studies, the less reactivesecondary isocyanates are involved in the urea formation, whichcontributes to the ordered domain formation. The slower reactiv-ity of the secondary isocyanates provides ample time for formationof ordered domains of ordered urea hydrogen bonds involving theurea functional groups as discussed in the FTIR-ATR analysis. Withcatalysts the system viscosity builds up and hence the hard segmentmobility is hindered. Thus, the ordering of hard segments would beincomplete even in otherwise fully cured MCPU.

in this region of urea and urethane carbonyls in different environ-ments. Hence to identify the underlying component bands in theC O zone deconvolution of the peaks were performed. The spec-tra of MCPU (uncatalysed) were chosen for display to identify thecomponent bands. Fig. 8 shows the deconvoluted spectra of theuncatalysed MCPU. The band assignments of the C O zone is illus-trated in Table 2. The degree of phase separation was evaluated bythe area analysis of the free and bonded urea and urethane peaks.

Table 2Infrared stretching band assignments of the carbonyl group in the MCPUs as seenfrom the deconvoluted FTIR-ATR spectra

Functional group Wavenumber (cm−1) Band assignment

�(C O) urethane 1740–1730 Free urethane1730–1725 H-bonded urethane

�(C O) urea 1700–1690 Free urea1690–1650 Monodentate urea (less ordered

H-bonded urea)1650–1640 Bidentate urea (ordered urea

H-bonded urea)

398 S.K. Rath et al. / Progress in Organic Coatings 62 (2008) 393–399

d FTIR-ATR spectra of unctalyzed MCPU.

TR spe

)/At

Fig. 8. Representative deconvolute

Table 3Fraction of free and bonded, urea and urethane carbonyl from deconvoluted FTIR-A

Sample A (urea C OH-bonded)/At A (urea C O free

Uncatalysed 0.46 0.54FeCl3 0.42 0.58TEA 0.39 0.61DBTDL 0.34 0.66

At is the total area encompassing the carbonyl peak.

From the results in Table 3, it is seen that the bonded urethane andurea fractions decrease with increasing catalytic activity. That is thefree carbonyl fraction for both urea and urethanes increase. Sincethe unsatisfied bonding potential of the free carbonyl is larger com-pared to bonded ones, it can be concluded that the free energy of thesurface increases with increasing catalytic activity of the catalysts.

3.4.2. Surface energySurface energies were evaluated using the surface tension-

component theory. According to this approach, the surface tensionof a phase could be divided up into independent components suchas London dispersions contribution �d and polar contribution �p,as represented below.

� = �d + �p

For a drop of liquid at equilibrium with a solid surface, theliquid–solid contact angle (�) is given by the following equation

�L(1 + cos �)

2(�dL )

1/2= (�P

S )1/2

(�pL �d

L )1/2 + (�d

S )1/2

Where �L is the surface tension of the liquid and subscript S = solidand L = liquid. �L, �d

L , �pL can be found in literature [37]. In this study

diiodomethane and water were used as the probing liquids. Forwater �L = 72.8 mJ/m2, �p

L = 51.0 mJ/m2 and �dL = 21.8 mJ/m2. For

diidomethane �L = 50.76 mJ/m2, �pL = 0 mJ/m2, �d

L = 50.76 mJ/m2

at 20 ◦C. Hence by measuring the contact angle for two well char-acterized liquids two equations with two unknowns, i.e. �d

S and �pS

are generated. The surface energy �S = �dS + �p

S can be obtained.

ctra

A (urethane C O H-bonded)/At A (urethane C O free)/At

0.39 0.610.36 0.640.33 0.670.29 0.71

Table 4Effect of catalysts on the surface energy of MCPU

Catalyst Surface energy(�, mJ/m2)

Dispersecomponent (�d,mJ/m2)

Polarcomponent (�p,mJ/m2)

None 34.6 ± 0.58 32.2 ± 0.32 2.4 ± 0.09FeCl3 37 ± 0.69 34.1 ± 0.38 2.9 ± 0.14TEA 38.9 ± 0.73 35.3 ± 0.39 3.7 ± 0.19DBTDL 40.4 ± 0.79 35.8 ± 0.42 4.6 ± 0.22

The variation of surface energy of the MCPUs with differentcatalysts is shown in Table 4. It must be noted that because ofthe observed variation in surface roughness between samples,the reported values do not represent the true surface energy ofthe materials and are presented for reasons of comparison only.From the results it is seen that the surface energy of the unac-talyzed MCPU is 34.6 ± 0.58 mJ/m2 with a polar component of2.4 ± 0.09 mJ/m2. It is observed that with introduction of cata-lysts the surface energy increases. Further with increasing catalyticactivity the surface energy of the MCPUs increase. The polar com-ponent contribution to the surface energy is also found to followthe same trend. With introduction of catalysts the viscosity of theMCPUs increases, thus the diffusion of the hard segments towardsthe bulk away from the air interface is hindered. This in turn causeslocalization of the polar segments compared to unanalysed MCPUs.This trend is supported by the findings from FTIR-ATR analysis thatthe fraction of free carbonyl content with increasing catalytic activ-ity as observed in FTIR-ATR.

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[[[[[[[

S.K. Rath et al. / Progress in Or

4. Conclusion

Prepolymer based on hydroxy terminated polybutadienecapped with IPDI was cured with moisture to form crosslinkedMCPU by use of various catalysts, without the aid of any exter-nal crosslinker. The MCPU showed a phase separated morphologyfor different catalysts, found from SAXS studies. The interdomain

distance was influenced by the choice of catalysts. DSC results fur-ther confirm the biphasic morphology of the MCPUs. Further withincreasing strength of the catalysts, the enthalpy of fusion corre-sponding to the hard segment decreased, confirming the decreasein size of the hard segments. FTIR-ATR was used to study the sur-face concentration of urea and urethane groups for MCPUs curedwith various catalysts. Goniometry results showed increase in sur-face energy as well as the polar component of the surface energy,with increasing catalytic activity of the catalysts used. Thus, thechoice of catalysts seems to affect both the phase morphology andthe surface properties of the MCPUs.

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