POLYMER NANOCOMPOSITES :
MOLECULAR APPROACHES TO TAILORING SURFACES
Dr. S. SivaramNational Chemical Laboratory,
Pune-411 008, INDIA
Tel : 0091 20 2589 3030Fax : 0091 20 2589 3355
Email : [email protected] us at : http://www.ncl-india.org
Oklahoma State UniversityStillwater
May 24, 2010
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• Nano-composite is a hybrid material whose distinct
components are dispersed on a scale of nanometers.
• New class of fillers : nano-particles, nano-tubes / fibers
and nano-clays
• Typically < 5 % of the filler is required to obtain remarkable
WHAT ARE POLYMER NANOCOMPOSITES?
• Typically < 5 % of the filler is required to obtain remarkable
improvement in properties.
• Mechanical, thermal, electrical, optical, magnetic, barrier
and flame retardant properties are improved without
significant loss in toughness and clarity.
MACRO- AND NANO-COMPOSITES
MACROCOMPOSITES
• Short or long fibers dispersed in an organic polymer matrix
• Fibers: Glass, carbon,
NANOCOMPOSITES
• Multiphase material comprising of a matrix polymer and a dispersed inorganic phase
• Inorganics : clay, silica, • Fibers: Glass, carbon, boron
• Interfacial strength between the matrix and fiber determine properties
• Inorganics : clay, silica, mica, zeolites, molybdenum oxides/ sulfides
• Properties determined by the size of the dispersed inorganic phase (typically in nanometer sizes)
IIT-Madras 020905
FROM STRUCTURAL TO FUNCTIONAL MATERIALS
STRUCTURALMATERIALS
FUNCTIONALMATERIALS
MACROCOMPOSITES• Wetting and hydrophilic Interactions
BIOCOMPOSITES•Molecular self assembly•Hydrogen bondingInteractions
• Adhesive forces•Hydrogen bonding•Hydrophobic interactions
NANOCOMPOSITES•Intercalation and exfoliation•In-situ polymerization andpolymerization in constrained spaces•Hydrophobic interactions and electrostatic force
IIT-Madras 020905
Rigid rod fillers, polymer-polymer nanocomposites
Clays, Mica, Aluminosilicates
Macroscopically dispersed clays,
conventional inorganic fillers
POLYMER NANOCOMPOSITES :MOLECULAR HYBRIDS
1 D 2 D 0D/3D
POLYMER CLAY NANOCOMPOSITES SIMULTANEOUSLY EXHIBIT PROPERTIES OF BOTH 2D AND 3D HYBRIDS
STRUCTURE OF CLAYS
Montmorillonite Mx(Al4-xMgx)Si8O20(OH)4
Hectorite Mx(Mg6--xLix)Si8O20(OH)4
Saponite MxMg6Si8-xAlx) O20(OH)4
• Layered alumino silicates containing tetrahedral and octahedral sheets
• Stacked two dimensional oxy-anions are separated by hydrated cations
• The gallery cations can be replaced by soft organic cations,
examples, alkylammonium, alkyl phosphonium. This expands the inter-
gallery distances and also renders the gallery hydrophobic
STRUCTURE OF POLYMER CLAY NANO-COMPOSITES
• X-ray diffraction- most common technique to determine the
structure of nano-composites – shift in the d 001 peak
• Intercalated structures lead to well defined X-ray patterns
• Exfoliated structures show featureless XRD pattern due to
loss of ordered layered structures
• TEM offers the direct evidence for de-lamination of clay
platelets
• Rheological tools offer new insights into the structure of
nano-composites; In- situ techniques of structure
development during processing are also emerging as
powerful tools
TYPES OF NANOCOMPOSITES
PREPARATION OF NANOCOMPOSITES
• Melt intercalation
• In situ intercalative polymerization
• Solution Mixing d 001 peak
Reactive Modifiers
Ring opening Polymerization
CaprolactamCaprolactone
Radical Polymerization
Vinylbenzyl alkylammonium
cation
Olefin
IN SITU POLYMERIZATION AND REACTIVE MODIFIERS FOR CLAY
O N
N O11
O
BrBr
Thermoset Polymers
epoxy resins
Living or Controlled
Condensation Polymerization
PET, PBO, PU, PI
Olefin Polymerization
Catalyst on Clay
O
OO
N
N Cl
S
NS
NBr
HOO
N
NCl
Controlled Polymerization
POLYMER NANOCOMPOSITES : UNMET CHALLENGES
• Poor understanding of the nature of interface between the nano-particle and the polymer
- Surface modification of the nano-particle; compatibility and stability of the modifiers to polymer processing conditions
- Ability of polymer to wet the surface of the particle; nature of adsorption process of the macromolecule on the surface of the inorganics
- Inability to assess whether the nature of interface remains unchanged after thermal processing
• Inability to derive generalized rules of behavior for nano-composites
- PP-clay nano-composites show property enhancements, whereas, PE-clay nano-composites show no property improvement
- With PP , property enhancements are observed with higher MFI materials( lower MW), whereas, no enhancements are observed with lower MFI materials
- The relative roles of internal modifiers and externally added modifiers (compatibilizers) are inadequately understood
- Clays and nano-particles influence crystallization rates of semi-crystalline polymers. They are not just inert fillers.
POLYMER NANOCOMPOSITES : UNMET CHALLENGES
• Polymer nanocomposites predominantly restricted to polar polymers, e,g, Nylon, epoxy, poly(aniline)s . Polypropylene is the only widely studied non polar polymer. This is indicative of the difficulties in tailoring hydrophilic clay surfaces for compatibility with non polar polymers
• With clays, quarternary ammonium salts of long chain fatty acids are predominantly used as modifiers to render the inter layer gallery of clay somewhat hydrophobic. However, it is well known that such ammonium compounds are not very thermally stable and decompose below the melt processing temperatures of most polymers. Consequently, it is uncertain whether the structure of the clay remains in tact after melt processing.
TAILORING INTERFACES : TWO APPROACHES
� Use of organic modifiers which have reactive functionalities capable of becoming part of a polymer chain. This approach tethers the polymer chain within the interlayer gallery of the clay. The other end of the modifier molecule is bound to the clay The other end of the modifier molecule is bound to the clay surface through weak electrostatic forces
� Use of polymers with polar groups in the chain capable of interacting with the inter - gallery cations through electrostatic forces
SYNTHESIS OF POLYCARBONATE (PC) - CLAY NANOCOMPOSITES VIA IN-SITU POLYMERIZATION :
TAILORING INTERFACES THROUGH CHEMICAL TAILORING INTERFACES THROUGH CHEMICAL TETHERING OF POLYMER CHAINS
PC-NANOCOMPOSITES USING CLAY
MODIFIED WITH QUATERNARY ALKYL AMMONIUM SALTS
In-situ melt polymerization of bis- Phenol Awith diphenyl carbonate at 250°C resulted inthe formation of intercalated nanocomposite
Molecular weights of the polymer was low(Mn: ~9500)
Thermogravimetric analysis of the organoclay
Hoffmann degradation by ββββ- H elimination
N
C
R
R
CC
H 3
+
H O -
H
CC
+
NR
RH 3C
Ph3P+
Br-
N
N
CH3
CH3+
Br-
Hexadecyltriphenylphoshonium bromide (C16P)
Hexadecyl-1,2-dimethylimidazolium bromide (C16IMI)
THERMAL STABILITY OF PHOSPHONIUM AND
IMIDAZOLIUM MODIFIED CLAYS
bromide (C16IMI)
C16IMI-MMT
C16P-MMT
300 °C
17.8 Å
17.8 Å
21.5 Å
Entry no: 8
C16P-MMT
Inte
nsi
ty (
a.u
)PC/CLAY NANOCOMPOSITES WITH PHOSPHONIUM
CATIONS AS MODIFIERS
Ph3P
Br
2 4 6 8 10
17.8 Å
17.8 Å
Entry no: 6
Entry no: 7Inte
nsi
ty (
a.u
)
2 ThetaPC/C16P-MMT 3.6 wt% at different resolutions
Formation of phase separated nanocomposites
SYNTHESIS OF REACTIVE MODIFIERS
CH3
O
CH3
O
O O
CH3
O
O
OH10
CH3
O
OH10
CH3NaCl/H2O
DMSO
PhOH/HCl SHCOOH
OH
OH11
OH
Br11 CBr4/PPh3
OH Br10
NaOMe/MeOH
OHOH
PPh3
N
N
Br
OH
OH
11 PPh3
+Br
NN
OH
OH
11 +
BPAIMIBPAP
Entry Organoclay Catalyst a Wt % of MMT
Mole ratio (DPC: BPA: BPA
equivalents in organoclay)
Tg(°C)
Poly(carbonate)s b
Tg(°C)
Mn x 10-3 c
Mw/Mnc
1 - TMAH/NaOH - 108: 100: 0 146 - 22.1 2.31
2 BPAP-MMT TMAH/NaOH 1.8 108: 99.6: 0.45 124 122 4.4 1.93
3 BPAP-MMT - 1.8 108: 99.6: 0.45 145 144 24.5 1.74
PREPARATION OF PC/CLAY NANOCOMPOSITES
USING PHOSPHONIUM CATIONS AS MODIFIERS
4 BPAP-MMT - 3.6 108: 99.1: 0.91 144 138 20.7 2.26
5 BPAP-MMT - 5.3 108: 98.6: 1.36 145 134 25.0 2.77
6 C16P-MMT - 1.8 108: 100: 0 141 144 15.0 1.81
7 C16P-MMT - 3.6 108: 100: 0 143 142 16.5 1.76
8 C16P-MMT - 5.3 108: 100: 0 142 143 18.8 1.69
a TMAH: 10-4 mmol/mol of BPA, NaOH: 10-6 mmol/mol of BPA b obtained from the nanocomposite after ion exchange with LiCl
c by GPC in CHCl3 and calculated with respect to polystyrene standards
THERMAL STABILITY OF ORGANOCLAYS MODIFIED WITH THE REACTIVE MODIFIERS
R
OHR
240 °C
300 °C The first step in degradation of BPAP-MMT and BPAIMI-MMT is likely due tothe decomposition of the bis-phenolmoiety. However, such degradation isless likely once the bis-phenol moietyis incorporated into a polymer chain
OH
OH
+OH
PC- NANOCOMPOSITES WITH CLAYS MODIFIED WITH THE REACTIVE MODIFIERS
Exfoliated structures result using clays with modifiers containing reactive functionalities while only intercalated structures are
obtained when the clays used do not have a reactive functionality
3.6 %
PC/CLAY NANOCOMPOSITES WITH REACTIVE MODIFIERS BEARING PHOSPHONIUM CATIONS
PPh311
HO Br
5.3 %Good dispersion of the clay
indicative of exfoliated structures.
OH
1.8 %
0
400
800
1,200
1,600
2,000
2,400
Entry no: 1
Entry no: 3Entry no: 4Entry no: 5
E' (
MP
a)
0
400
800
1,200
1,600
2,000
Entry no: 1
Entry no: 6
Entry no: 7
Entry no: 8
E' (
MP
a)
Ph3P
Br
PPh311
OH
HO Br
DYNAMIC MECHANICAL BEHAVIOR
0 40 80 120 160 200Temperature (°C)
0 40 80 120 160 200Temperature (°C)
• Increase in storage modulus is higher for exfoliated nanocomposites obtained using reactive modifiers
• Relatively slower relaxation behavior for the exfoliated nanocomposites is attributed to the restricted mobility of polymer chains anchored to the clay surface.
Entry Organoclay Catalyst a Wt % of
MMT
Mole ratio (DPC: BPA: BPAequivalents in organoclay)
Tg(°C)
Poly(carbonate)s b
Tg (°C) Mn x 10-3 c
Mw/Mnc
9 BPAIM-MMT TMAH/NaOH 3.6 108: 99.1: 0.91 128 132 8.3 1.91
10 BPAIM-MMT - 3.6 108: 99.1: 0.91 126 131 8.2 1.94
11 C16IM-MMT - 3.6 108: 100: 0 132 138 10.3 2.05
PREPARATION OF PC/CLAY NANOCOMPOSITES USING IMIDAZOLIUM CATIONS AS MODIFIERS
a TMAH: 10-4 mmol/mol of BPA, NaOH: 10-6 mmol/mol of BPA a TMAH: 10-4 mmol/mol of BPA, NaOH: 10-6 mmol/mol of BPA b obtained from the nanocomposite after ion exchange with LiCl c by GPC in CHCl3 and calculated with respect to polystyrene standards
• Extensive depolymerization was observed resulting in low molecular weight PC.
• This is indicative of decomposition of the modifier during polymerization resulting in free imidazole formation.
• Imidazoles in high concentration are known to be efficient depolymerization agents for PC
N NR'
R
OH
HO R
OH
O
N N
R'
2 4 6 8 10
0
5000
10000
15000
20000
23.0 Å
Entry no: 10
BPAIM-MMT
Inte
nsi
ty (
a.u
)
2 Theta
PC/CLAY NANOCOMPOSITES WITH IMIDAZOLIUM
CATIONS AS MODIFIERS
Exfoliated structures using modifiers with reactive functionality
2 4 6 8 10
5000
10000
15000
27.6 Å
18.5 Å
Entry no: 11
C16IM-MMT
Inte
nsi
ty (
a.u
)
2 Theta
Intercalated structures using modifiers with no reactive functionality
CONCLUSIONS
Modified clay
reactive groupNo reactive group
ExfoliatedIntercalated
SYNTHESIS OF Syndiotactic - POLYSTYRENE (s PS) -CLAY NANOCOMPOSITES :
TAILORING INTERFACES THROUGH USE OF TAILORING INTERFACES THROUGH USE OF SULFONATED POLYSTYRENE IONOMERS AS MODIFIERS
HCH2C CH2
HC
x y
SO3H
CH2HC
n
H3C C O SO3H
O
C2H2Cl4/ CHCl3
HCH2C CH2
HC
x y
SO3- M+
M OH/MeOH
Where M+ = Na+, K+ or Rb+
70 °C/3 hours
PREPARATION OF SULFONATED s-PS IONOMERS
sPS was sulfonated to different levels (0.5, 2.0, 3.2 and 3.8 mol%) and neutralized with alkali salts (NaOH, KOH, RbOH)
STRUCTURE OF s-PS/ORGANOCLAY NANOCOMPOSITES
• In the nanocomposite, s-PS penetrates into a fraction of the clay galleriesand the gallery expands to 21.0 Å.
• The peak at around 2θ = 6.8° in the sPS and sPS/organoclay nanocomposite isdue to the 1 1 0 reflection of the αααα crystalline form.
• The organoclay tactoids remain in tact without any substantial intercalationdue to limited interaction of s-PS with the organoclay layers in view of the lowsurface energy of the sPS.
STRUCTURE OF SULFONATED S-PS IONOMER/ORGANOCLAY
NANOCOMPOSITES
Sulfonation level (%)
Clay gallery height (Å)
H+ Na+ K+ Rb+
0.5 18.4 19.0 26.3 27.2
2.0 22.0 29.4 * *
3.2 26.0 31.5 * *
Degree of dispersion of the organoclay in the polymer matrix improves with anincrease in the degree of sulfonation.
Increase in the size and polarizability of the cation (Na+<K+<Rb+) result inhigher degree of dispersion even at low degrees of sulfonation.
3.2 26.0 31.5 * *
3.8 29.0 34.0 * *
STRUCTURE OF SULFONATED SPS IONOMER -CLAY NANOCOMPOSITES
SsPS 3.8 mol % NaSsPS 3.8 mol %
SsPS and NaSsPS/ organoclay nanocomposites showintercalated structures whileKSsPS and RbSsPS formexfoliated structures.
KSsPS 3.8 mol % RbSsPS 3.8 mol %
Stronger ion-dipole interaction with higher polarizable (softer) cations act as bridge between negatively charged clay layers and the
polyanions.
Sulfonation level (%)
Crystallization temperature (oC)
Without clay Nanocomposite
H+ Na+ K+ Rb+ H+ Na+ K+ Rb+
0.5 234 233 233 232 234 236 236 236
2.0 225 199 189 193 228 209 218 223
3.2 222 183 183 194 222 205 215 222
CRYSTALLIZATION BEHAVIOR OF SULFONATED s-PS IONOMER/ORGANOCLAY NANOCOMPOSITES
3.8 212 * * * 212 163 184 198
* Do not crystallize on cooling from the melt
• TCC decreases with increasing degree of sulfonation indicating inhibition ofcrystallization. Crystallization was further inhibited when the H+ ion was replaced bydifferent cations like Na+, K+ and Rb+.
•Organoclay layers reduce the tendency of ions to aggregate causing thecrystallization rate to increase.
• Exfoliated nanocomposites show better crystallization rate than the intercalated onesbecause of the uniformly dispersed clay layers in the polymer matrix .
CONCLUSIONS
� Exfoliated sPS ionomer/organoclay nanocomposites were prepared viasolvent casting.
� Higher degree of sulfonation leads to better interaction with the polar silicatesurface of the organoclay resulting in better dispersion.
� Increase in the size and polarizability of the cation (Na+<K+<Rb+) result inhigher degree of intercalation/exfoliation even at low degrees of sulfonation.
� Nanocomposites prepared using more thermally stable 1-hexadecyl-2,3-dimethylimidazolium cation modified clay are amenable to being processed attemperatures upto 300 °C without any appreciable degradation.
� The dispersed silicate clay layers partially restores the reduced crystallizationrates of sPS ionomers by disrupting the ionic aggregation.
THANK YOU
Synthesis of Polyurethane Clay Nanocomposites via In-situ Polymerization
Objectives
• To prepare fully exfoliated PU-clay nanocomposite
• To improve the interaction of the polymer with clay by tethering the polymer chain on to the clay surface tethering the polymer chain on to the clay surface
• To tether the PU chain on the clay surface by choosing a suitable modifier for the clay
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HO-R-OH Organoclay
(hydrophobically modified)
Organoclay (short chain
hydroxy amines)Prepolymer
(OCN-R-NCO )
Chain extension
diolOCN-R-NCO
Cured
Solvent casting
PU- Nanocomposites - Literature
PU Organoclay
(hydrophobically modified)
Solvent casting
Above methods results in only intercalated nanocomposites
+NH3
OH
OH
2,3-dihydroxypropylammonium ion(2 OH Mont)
+NH3
(CH2)11
CH3
Dodecyl ammonium ion(12 CH3 Mont)
Literature
The modifier having small chain diols show very little intercalation, whereas the modifier with a long alkyl chain shows better intercaltion as seen from increase in the d-spacing from 1.6 nm of the organoclay to 2.4 nm in the nanocomposite
- Tien YI, Wei KH, Macromolecules, 34, 9045 (2001)
Reaction of Organoclay with Isocyanate
30
60
TR
AN
SM
ITT
AN
CE
C30B/PI C25A/PI
1710 cm-1
3310 cm-1
Bis(hydroxyethyl)ditallowammonium ionTH
TH
NOOH H
+
N
TH
H3C+
CH
(1)
Closite 30B
Closite 25A
3000 2000
WAVENUMBER
Dimethyltallow-(2-ethylhexyl)ammonium ion
CH3
(2)
Closite 25A
where TH = tallow group
Organoclay containing the modifier with hydroxyl group reacts with isocyanate to form urethane linkage
Closite 30B
NCO
Bis(hydroxyethyl)ditallowammonium ionTH
TH
NOOH H
+
(1)TH
TH
NOOC C
O ON N
H H+
PU-Nanocomposites in toluene medium
OHN
OH
TH
TH
+
N O
CH3
OCN
H
O
O N
O
H
CH3
NCO
+THO O
NCO content 9 % Closite 30B
Intercalated nanocomposite
OH
OH
+N
THOO N
HNH
CH3 CH3
OHN
OH
TH
TH
+
N O
CH3
OCN
H
O
O N
O
H
CH3
NCO
NCO content: 9 %
PU-Nanocomposites in DMF medium
OH OHTH
+N
TH
THOO N
HNH
O O
CH3 CH3
NCO content: 0 %
As the organoclay is mixed with prepolymer all the NCO is consumed
Effect of amount of TMP on nanocomposite structure
OH
OH
OH
OHN
OH
TH
TH
++
N O
CH3
OCN
H
O
O N
O
H
CH3
NCO
+ OH
OH
As the amount of TMP increases, the extent of intercalation increases
Effect of introduction of branch points in the polymer on nanocomposite structure
As the mol % of the branching agent (trimethylol propane)increases , the amount of intercalation increased as seen fromthe shift in the 001 peak towards lower 2 theta
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60°C/ 6 h
Nanocomposite by In-Situ Polymerization
Intercalated
HO
OH
CH3
NCO
NCO
+
2-ethyl-1,3-hexanediol 2,4-Toluenediisocyanate
Structure of modifiers Intercalated
Closite 30B
Bis(hydroxyethyl)ditallowammonium ionTH
TH
NOOH H
+
(1)
Closite 25A
where TH = tallow group
Dimethyltallow-(2-ethylhexyl)ammonium
N
TH
H3C+
CH3
NOO
H
HH H
+
Bishydroxyethylammonium ion
OC
Structure of modifiers
d) Closite 25A/PUe) Closite 30B
f) Closite 30B/PU
Nanocomposites by In-Situ Polymerization
a) OC
b) OC/PUc) Closite 25A
When the organoclay is mixed with the monomers and then polymerized, only intercalated nanocomposites are formed
Synthesis of PU-Nanocomposites
NOC
Bis(hydroxyethyl)dihydogenatedtallowammonium ion
H3C N
H
C
O
O H3C
N
N
H
C
O
O
COPrepolymer terminated with diisocyanate
NCO content 8.1%
Closite 30B
TH
TH
NOOH H
+
TH
NOOC C
O ON N
H H+
TH
NOOC CN N
OH
OH
PU-Nanocomposite
NCO content 6.4%
NOOH H
H
H+ +
HH NOO
TH
TH
Bis(hydroxyethyl)ditallBis(hydroxyethyl)ammonium ion (OC) Bis(hydroxyethyl)dihydrogenated tallow ammonium ion
(Closite 30B)
Effect of long alkyl chain
Presence of hydroxyl groups along with the hydrophobic group improves the extent of intercalation as seen from the increase in d-spacing from
Presence of long alkyl chain in the modifier along with the hydroxyl groups improved the extent of intercalation of polymer in to the clay gallery
from the increase in d-spacing from 18.0 Å for the organoclay to 35.0 Å for the nanocomposite.
When there is no hydrophobic group, the nanocomposites formed shows very little intercalation as seen from the increase of d-spacing from 13.4Å for the organoclay to 16.4 Å for the nanocomposite.