Castor Oil PolyurethaneAcrylic or Vinyl Polymer Interpenetrating

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27 Castor Oil Polyurethane-Acrylic or Vinyl Polymer Interpenetrating Polymer Networks Cured at Room Temperature H. Q. Xie, C . X. Zhang, and J. S. Guo Department of Chemistry, Huazhong University of Science and Technology, Wuhan, 430074, People's Republic of China

During the formation of simultaneously grafted interpenetrating polymer networks (IPNs), the relative formation rates of castor oil polyurethane and poly(methyl methacrylate) are compared by IR spectrophotometry. The formation rate of the polyurethane network is higher than the graft polymerization rate of methyl methacrylate. The time of gelation decreases with increasing polyurethane content. The rate of gel formation in the IPN that contains poly(methyl acrylate) is higher than in the IPN that contains polystyrene. A maximum tensile strength of the IPNs occurs when the polyurethane content is about 50%. Transmission electron micrographs indicate that the polyurethane exists as domains in the continuous phase of polyacrylate. A broad glass-transition temperature occurs in the dynamic mechanical spectrum of the IPN.

INTERPENETRATING POLYMER NETWORK

(IPN) is a combination of two polymer networks that interpenetrate each other (1, 2). The study of IPNs has aroused great interest because most IPNs exhibit better mechanical properties than their individual networks due to a synergistic effect induced by forced compatibility of the components. Castor oil is a fine candidate for making IPNs because it is a triglyceride of ricinoleic acid, which contains three hydroxyl groups and three double bonds.

AN

0065-2393/94/0239-0557S06.00/0 © 1994 American Chemical Society

In Interpenetrating Polymer Networks; Klempner, D., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1994.


558

N I TERPENETRATING POLYMER NETWORKS

Yenwo et al. (3) were first to utilize castor oil to synthesize IPNs. To obtain sequential IPNs, Yenwo et al. first reacted the castor oil with sulfur or diisocyanate to cross-link it. Cross-linking was followed by swelling with a plastic-forming monomer, such as styrene plus cross-linker, and in situ polymerization. Electron microscopy shows that the polystyrene phase size of the castor oil urethane-polystyrene I P N decreases with increased cross-lin king of the castor oil component and increases with increasing polystyrene content. Dynamic mechanical spectroscopy studies show extensive but incomplete molecular mixing of the two networks (4). The glass-transition temperature of the IPNs gradually merges from two distinct transitions into one broad transition at an intermediate temperature as the cross-link level of the castor oil component is increased. The stress-strain results indicate that at low polystyrene content the IPNs behave like reinforced elastomers, whereas at high polystyrene content the IPNs exhibit decreased elongation and behave like toughened plastics. Toughened plastics materials show well developed yield points, stress whitening, and necking. The tensile strength and Young's modulus are enhanced as the polystyrene content or cross-link level of the polyurethane is increased. The impact strength of the materials is approxi mately two or three times that of polystyrene. The best materials are materials with compositions in the range of 40-60% castor oil urethane. The materials prepared at an N C O - O H ratio of 0.95 have the best impact properties. Instead of sequential IPNs, Devia et al. (5) studied the synthesis of simultaneous interpenetrating networks based on elastomeric polymers de rived from castor oil and cross-linked polystyrene. The elastomers included the cross-linked polyester of castor oil and sebacic acid, cross-linked polyure thane with 2,4-toluene diisocyanate (TDI), and cross-linked polyester-polyurethane from castor oil, sebacic acid, and T D I . The polystyrene phase was cross-linked with 1 % divinylbenzene, and 0.4% benzoyl peroxide was used as the initiator for the styrene polymerization at 80 °C. Experimental data on the extent of the reaction at the gel point agreed remarkably well with prediction based on the Flory-Stockmayer equation for the castor oil-sebacic acid system as a function of C O O H - O H ratio in the mixture. Two kinds of materials with elastomer component compositions of 10 and 40% behaved as toughened plastics and reinforced elastomers, respectively. Devia et al. later reported the morphology and glass-transition behavior of the preceding simultaneous IPNs based on electron microscopy and dynamic mechanical spectroscopy techniques (6). A two-phase morphology was revealed. With 10% elastomer composition, the use of vigorous stirring during the early stages of the reaction resulted in materials that had crosslinked polystyrene in the continuous phase and elastomer domains as the dispersed phase. The elastomer domains contained a polystyrene cellular structure. Materials that had 40% elastomer showed a continuous castor oil



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elastomer phase and the polystyrene displayed a bimodal size cellular struc ture. A 40:60 castor oil polyurethane:polystyrene sequential I P N exhibited greater dual network continuity and smaller, less well-defined phases than the simultaneous I P N counterpart. The higher formation rate of the elastomer network relative to the plastic network could lead to a morphology where the elastomer is the continuous phase. The bimodal distribution of domain sizes in these systems suggests that phase separation occurs at several different stages. Dynamic mechanical spectroscopy studies showed two well-defined glasstransition temperatures near respective homopolymer glass transitions, but shifted inward to greater or lesser extent. This shift indicates some molecular mixing between the two polymers. Devia et al. (7) also investigated the stress-strain and impact loading behavior of the simultaneous IPNs. These materials proved to be tougher than their corresponding homopolymer networks. The castor oil polyester elastomer-toughened plastics yielded the greatest improvement in impact resistance. In a succeeding paper, these authors (8) also indicated that the tough ness of the simultaneous IPNs increased with decreasing domain size of the polystyrene dispersed phase. The use of a prepolymer for elastomer network synthesis promoted the formation of larger polystyrene domains. The impact resistance of the simultaneous IPNs increased with total elastomer content. Properly cross-linked and post-cured compositions developed impact energy of ~ 60-70 J/m. The simultaneous IPNs based on castor-oil-derived elas tomers and cross-linked polystyrene formed engineering materials that com pared satisfactorily to commercial polymers in terms of mechanical behavior. Jordhamo et al. (9) studied phase continuity and inversion in the simultaneous IPNs of castor-oil-based polyester-polyurethane elastomers and divinylbenzene cross-linked polystyrene by optical microscopy. The simulta neous IPNs were prepared by adding a proper amount of the oil prepolymer and styrene to the reactor and then adding T D I to react with the remaining O H groups. Early in the reaction all the components formed a clear solution, but at a critical concentration, phase separation occurred. Eventually, the polystyrene phase reached a critical volume fraction and phase inversion occurred when polystyrene became the continuous phase. The phase inver sion process was bordered on one side by phase separation and on the other by polystyrene gelation. Xie and Tan (10) synthesized simultaneous IPNs at room temperature from castor oil polyurethane and copolymers of vinyl monomers (including styrene, methyl methacrylate, and acrylonitrile) using redox initiator without cross-linking agent. These studies differed from the former studies by Devia et al. (5), where the authors used benzoyl peroxide as an initiator, higher polymerization temperature, and divinylbenzene as a cross-linking agent. Xie and Tan showed that benzoyl peroxide-dimethylaniline acted as a better



560


redox initiator at room temperature than cyclohexanone peroxide-cobalt naphthenate. The simultaneous IPNs exhibited high tensile strength, good resilience, high abrasion resistance, and good chemical resistance to hydroly sis, acid, base, and oil. Kumar et al. (II) prepared several simultaneous IPNs of castor-oil-based polyurethane and divinylbenzene-styrene copolymer under conditions where the free radical polymerization of styrene and divinylbenzene and the crosslinking reaction of castor oil and T D I progressed at comparable rates. Comparison of the mechanical properties and cross-link density of the I P N and individual networks indicated a marginal increase in tensile strength and cross-link density from polyurethane to 60:40 polyurethane:polystyrene I P N . I P N samples prepared with higher polystyrene content showed a steady decrease in the foregoing properties. This reversal of the expected trend was attributed to the possibility of greater molecular interpénétration achieved due to similar gelation times and the resultant extension of chains and increase in free volume between cross-links. This hypothesis was further confirmed by thermogravimetric data on the initial stage of decomposition of the I P N . Patel and co-workers (12) investigated simultaneous IPNs prepared from radical copolymerization of liquid prepolyesters that were obtained from castor oil and dibasic acids, such as oxalic acid, malonic acid, and succinic acid, with acrylamide initiated with benzoyl peroxide. When the polyester content was greater than 45 wt%, I P N formation was impossible due to the fact that acrylamide exclusively homopolymerized. Differential scanning calorimetry (DSC) results showed that the IPNs had two glass-transition temperatures and thermograms revealed that the I P N was more stable than the individual components. The I P N was insoluble in acetone, dimethylformamide, dimethylsulfone, and dimethylacetamide. Patel and Suthar (13) also reported simultaneous IPNs from castor oil polyurethane and cross-linked poly(methyl methacrylate). Isocyanate termi nated prepolymers obtained from castor oil and T D I with N C O - O H ratios of 1.6:2.0 were reacted with a mixture of methyl methacrylate, 1 % ethylene glycol dimethacrylate, and 0.5% benzoyl peroxide at 60 °C for 24 h and then at 120 °C for 4 h to form the IPNs. The results indicated that, due to experimental difficulties, IPNs with more than 45 w t % prepolymer are not possible. The thermal study revealed that the IPNs were stable up to 300 °C and then started losing weight. A n increased chance for physical interaction was postulated to occur between networks containing urethane groups in the polyurethane and the ester groups of poly(methyl methacrylate). Recently Patel and Suthar published a series of papers concerning the synthesis of sequential IPNs composed of castor-oil-based polyurethane and various polyacrylates. The polyurethane was first prepared from castor oil and methyl diisocyanate, hydroxymethyl diisocyanate T D I , or isophorone diiso cyanate with a varying N C O - O H ratio and then swollen in methyl methacry-



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late (14), methyl acrylate (15), butyl acrylate (16), or ethyl acrylate (17) that contained ethylene glycol dimethacrylate as cross-linking agent. The mixtures were subsequently polymerized by radical polymerization initiated with ben zoyl peroxide to given I P N films via the transfer molding technique. These IPNs were characterized by chemical resistance, mechanical properties, and thermal behavior. The morphology was shown by scanning electron mi croscopy (SEM) and dielectric properties were measured at different temper atures. L i u et al. (18) synthesized simultaneous IPNs and AB-cross-hnked poly mers based on castor oil polyurethane and poly(butyl methacrylate-divinyl benzene). Studies of the dynamic mechanical properties showed that the I P N exhibited a broader loss tangent (tan δ) peak with two glas s-transition relax ations than did the AB-cross-linked polymer, which showed only a single glass-transition relaxation. Natchimuthu and co-workers (19) reported that semi-IPNs (SIPNs) made by castor oil polyurethane and cellulose nitrate showed some degree of miscibility at 30% cellulose nitrate content. Enhanced miscibility was ob served by partial replacement of cellulose nitrate with vinyl chloride-vinyl acetate copolymer. The ternary IPNs of cellulose nitrate, vinyl chloride-vinyl acetate copolymer, and polyurethane based on castor oil showed increased tensile strength and decreased flammability as compared to polyurethanecellulose nitrate IPNs alone. Xie et al. (20) studied the formation kinetics of simultaneous interpene trating polymer networks obtained from castor oil, T D I , and vinyl or acrylic monomer without cross-linking agent at room temperature using redox initiator. Each component of the redox initiator, either benzoyl peroxide or dimethyl aniline, can accelerate formation of the polyurethane network. Castor oil not only reacted with toluene diisocyanate in the formation of the polyurethane network, but also took part in the formation of vinyl copolymer grafts via unsaturation. Heat evolved during the formation of the polyurethane favored the copolymerization of vinyl monomers with castor oil. The final I P N did not dissolve in any solvent, which indicates that the I P N was a grafted SIPN. Had the vinyl monomer not taken part in the formation of grafts with the double bonds of castor oil in the polyurethane network, a SIPN would have been obtained and the resultant vinyl polymer chains would dissolve in solvent. Dynamic mechanical studies of the grafted SIPNs showed two glass-transition temperatures for the I P N that contained polystyrene or poly(methyl methacrylate), but only one glass-transition temperature for the I P N that contained polyacrylonitrile. This observation indicates more molecu lar mixing in the polyacrylonitrile I P N . The grafted SIPN with vinyl or acrylic terpolymer exhibited two glass-transition temperatures. The second or higher glass-transition temperature was lowered when more acrylonitrile and less styrene were present in the I P N . This result again indicates more interpéné tration.



562


The room temperature cured castor oil polyurethane-acrylic or vinyl polymer grafted SIPNs exhibited good properties, including high strength, good resilience, anticorrosion, oil and solvent resistance, and high abrasion resistance (10, 20). These features make them candidates for room tempera ture cured coating materials or adhesives on iron or steel without rust removal and also for reinforced rubber, toughened plastics, or damping materials cast at room temperature. Further study of these grafted SIPNs is warranted. The present work compares the formation rates of polyurethane network and poly(methyl methacrylate) grafts via infrared spectrophotometry (IR), the relationship between gel point and gel content of IPNs with different compositions, and the mechanical properties and dynamic mechanical prop erties of the IPNs as well as the morphology generated under different conditions. These comparisons will further our understanding of the reaction kinetics of the parallel reactions and the gelation during grafted I P N forma tion as well as the specific morphologies of the grafted IPNs. This knowledge will allow us to improve the mechanical properties and damping properties of the grafted IPNs by variation of the compositional components.

Experimental Details Materials. Chemically pure castor oil was dried by azeotropic distillation with chemically pure toluene. Dimethylaniline (DMA), dibutyltin dilaurate (DBTDL) and all the monomers were chemically pure and used as received. Benzoyl peroxide (BPO) was dried in a vacuum desiccator. 2,4-Toluene diiso cyanate (TDI) was analytical grade. Synthesis of Simultaneous IPN. Synthesis was carried out as follows: Castor oil was first reacted with T D I at a molar ratio of N C O : O H = 2.2 at room temperature while stirring for 1 h. The resultant prepolymer was mixed with vinyl or acrylic monomer, castor oil, D B T D L (as catalyst), and BPO and D M A (as redox initiators) for 10 min, then poured into a mold and cured at room temperature for 24 h. Comparison of Formation Rates of Polyurethane Network and Polydnetnyl methacrylate) Graft. The formation rates of polyurethane (PU) network and poly(methyl methacrylate) (PMMA) graft were compared by coating a mixture of the prepolymer, castor oil, methyl methacrylate (MMA), BPO, D M A , and D B T D L with molar ratio of N C O : O H = 1 and weight ratio of P U : P M M A = 60:40 onto K B r disks and measuring with an IR spectrophotometer (PE-580B) in the range of 400-4000 c m " at time intervals. 1

Gelation. The time of gelation was determined by observation of the fluidity of a reaction mixture of the prepolymer, castor oil, methyl acrylate (MA) or styrene (ST), BPO, D M A , and D B T D L in a dried capped bottle at room temperature. The fluidity of the reaction mixture was lost when it reached the gel point. The time interval from mixing of the components to the gel point was


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Castor Oil PU-Acrylic IPNs


recorded as the gelation time. The gel content was determined by weighing the dried insoluble residue of the sample that was removed from the reaction mixture and placed into toluene for 48 h. Testing and Characterization. The mechanical properties of IPN speci mens that had been cured at room temperature for 72 h were measured on a tensile tester ( X Q - 2 5 0 ) with a stretching rate of 2 5 0 mm/min. Dynamic mechani cal spectra were measured on viscoelastometer apparatus (Rheovibron model DDV-III-EA) with a heating rate of 3 °C/min at 3 5 Hz in the temperature range of —50 to + 1 5 0 °C. Transmission electron micrographs of the IPNs were taken with a transmission electron microscope (Phillips 300). The IPN sample was first stained with O s 0 vapor and cut with a microtome. 4

Results and Discussion Comparison of the Formation Rates of Castor O i l Polyurethane and Poly(methyl methacrylate). The spectra in Figure 1 show the change of IR absorption for the IPN-forming reaction mixture at differ ent time intervals. A n absorption peak at 2 2 7 8 c m represents the N C O group, whereas an absorption peak at 9 6 5 c m " represents the double bonds - 1

1

Figure 1. Change of IR spectrum of the reaction mixture during synthesis of the grafted semi-IPN. Reaction times for curves 1, 2, 3, and 4 are 2, 10, 20, and 45 min, respectively.


564


in M M A . The spectra in Figure 1 reveal that the rate of disappearance of the N C O peak at 2278 cm"" is higher than the rate of the double bond peak at 965 c m . This observation indicates that the formation rate of the polyurethane network is higher than the formation rate of the P M M A graft. This difference is the result of an induction period of the free radical polymerization of M M A , which was then accelerated by the heat of formation of the castor oil polyurethane network (20). Because the final product contained over 95% gel content, M M A was not merely homopolymerized, but copolymerized with the double bonds of castor oil to form grafts. Because caster oil reacted with T D I to form the P U network, the grafts do not dissolve in toluene and remain in gel form. 1


- 1

G e l Point and G e l Content. The time of gelation changed in relation to monomer content in the I P N formation (Figure 2). Increased gelation time corresponded to increased styrene content especially above 60% styrene content. This relationship also demonstrates that the formation

100

20

1

Styrene content, $ 40 60 80

100

2 3 4 Polymerization time, h

Figure 2. Gelation time vs. vinyl content in the reaction mixture (·) and gel content vs. reaction time for synthesis of IPNs: PU:PS = 60:40 (A) and PU.PMA = 60:40 (A).


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rate of the polyurethane network is higher than the rate of free radical polymerization of styrene. The rate of gel formation is higher in the P U - P M A I P N than in the PU-polystyrene (PS) I P N (Figure 2). This difference is probably due to the greater steric hindrance of styrene compared with M A . The gel content at the gel point (P ) for different grafted IPNs with different N C O - O H ratios was compared with the predicted value from the Carother equation (21):


C

P = 0.5 + ( f f ) " c

0

(1)

1

or the Flory-Stockmayer equation (21):

Κ = [r(/ - 1 ) Γ 0

(2)

1/2

where f is the hydroxyl functionality of the castor oil (equal to 2.7) and r is the N C O - O H ratio. Table I indicates that the experimental value of P for P U - P S IPNs agrees better with the value predicted from the Flory-Stockmayer equation than with the Carothers equation. This preferential agreement is probably because the Flory-Stockmayer equation is based on a statistical approach, whereas the Carothers equation assumes that gelation takes place when the number average molecular weight approaches infinity. The experimental value for P U - P M A IPNs lies between the values predicted by the two equations. Q

C

Effect of Different Compositions on the Tensile Strength of IPNs. Figure 3 shows that both monomer and polyurethane content affect the tensile strength of the IPNs. A l l the I P N samples were prepared at a N C O : O H = 1.5 molar ratio. Most of the IPNs exhibit a maximum tensile strength with P U content of about 50% that may be attributed to the maximum interpenetrating degree and enhanced compatibility at equal weights of polyurethane and acrylic or vinyl polymer, which results in a synergistic effect. For PU-poly(vinyl acetate) (PVAc) IPNs the maximum tensile strength occurred at a P U content of about 35%. Table I. Comparison of the Experimental and Predicted Values of Gel Content at Gel Point IPN PU-PMA PU-PMA PU-PS PU-PS

NCO.OH

Exp.

Eql

Eq 2

1.1 1.0 1.1 1.0

0.780 0.805 0.740 0.760

0.837 0.870 0.837 0.870

0.731 0.767 0.731 0.767



566


5 I 0

ι

«

20

»

»

«

ι

ι

ι

40 60 80 Polyurethane content

11

Figure 3. Tensile strength of the IPNs with different compositions: O, methyl acrylate; · butyl acrylate; A, vinyl acetate; A, acrylonitrile. The maximum tensile strength of IPNs that contain different acrylic or vinyl polymers decreases in the following order: poly(vinyl acetate) > poly( acrylonitrile) = poly(butyl acrylate) > poly( methyl acrylate) Morphology of the I P N s . Transmission electron micrographs of the P U - P M A I P N stained with O s 0 show that castor oil polyurethane exists as dark domains (the unreacted double bonds of castor oil can be stained with O s 0 ) and P M A grafts exist as a bright continuous phase (Figure 4a). This morphology can be explained by the fact that P U formed earlier and exhibited higher viscosity in the reaction mixture than P M A and, thus, tended to form domains. Preliminary reaction of the prepolymer with castor oil for 20 min and then addition of M A to the reaction mixture results in larger polyurethane domains as shown in Figure 4b. Use of methacrylic acid (MAA) as one of the monomers significantly changes the morphology; almost no domains except cocontinuous phases can be observed (Figure 4c). This change occurs because M A A can react with the N C O groups of the prepoly4

4


XIE ET AL.


567


27.

Figure 4. Micrographs of the PU-PMA IPN (20,000 x): a, simultaneous reactions; h, MA added after 20 min of reaction; c, MAA added with MA at the beginning of the reaction.


568



mer and, thus, the P M A - P M A A graft can also cross-link with the P U network. Dynamic Mechanical Properties of the IPNs. The dynamic mechanical spectrum of the P U - P M A I P N shows a broad glass-transition temperature, as illustrated in Figure 5, that is due to the partial compatibility between P M A and P U and the enhanced compatibility due to the interpene trating network. Table II indicates the temperature range for tan δ > 0.3 and the maximum tan δ in the dynamic mechanical spectra of different IPNs, all of which show a broad glass-transition temperature. In the case of the I P N that contains P M A , the temperature range above tan δ = 0.3 is only 50 °C, whereas for the I P N that contains poly(butyl acrylate-butyl methacrylate) the temperature range is wider and the maximum tan δ higher. The inclusion of acrylic acid in the monomers in the formation of IPNs causes the tempera-

E6 -50

+50 T.C

+100

10.01 +150

Figure 5. Dynamic mechanical spectrum of the PU-PMA IPN. (PU.PMA = 60:40 wt%).


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Table II. Damping Properties of the IPNs Composition of IPN

Temperature Range at tan δ > 0.3 (°C)

Max. tan δ

-2

to + 5 0

52

0.61

BA:BMA = 1

-10

to + 65

75

0.78

MA:BA:AA = 5:5:2

+10

to + 85

75

0.65

PU:PMA = 60:40 PU:PBA-PBMA = 60:40; P U : P M A - P B A - P A A = 60:40;


AT(°C)

ture range to shift to higher temperatures. This shift may be attributed to the cross-linking reaction of acrylic acid units in the grafts with some N C O groups of the castor oil prepolymer used to form the P U network during I P N synthesis.

Conclusion During the formation of simultaneous castor oil polyurethane-acrylic or vinyl polymer grafted I P N , IR spectrophotometry analysis showed that the forma tion rate of the polyurethane network was higher than the graft polymeriza tion rate of methyl methacrylate. The time of gelation increased with i n creased styrene content and the higher rate of gel formation in the P U - P M A I P N compared with the P U - P S I P N agreed well with the rate predicted from the Flory-Stockmayer equation. The maximum tensile strength of the I P N occurred when the polyurethane content was about 50%. Transmission electron micrographs indicated that the polyurethane existed as domains in the continuous phase of poly(methyl acrylate). When methacrylic acid was used with methyl acrylate in the formation of IPNs, almost no domains except cocontinuous phases could be observed. The dynamic mechanical spectrum of the I P N that contained poly(butyl acrylate-butyl methacrylate) showed a broad glass-transition temperature with a temperature range above tan 5 = 0.30 from —10 to + 65 °C and with a maximum tan δ of 0.78.

Acknowledgment Financial support from the National Natural Science Foundation Committee of China is gratefully acknowledged.

References 1. Klempner, D. Angew. Chem. 1978, 90, 104. 2. Sperling, L. H . Interpenetrating Polymer Networks and Related Materials; Plenum: New York, 1981. 3. Yenwo, G. M . ; Manson, J. Α.; Pulido, J.; Sperling, L. H . J. Appl. Polym. Sci. 1977, 2 1 , 1531.



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4. Yenwo, G. M.; Sperling, L. H.; Pulido, J.; Manson, J. Α.; Conde, A. Polym. Eng. Sci. 1977, 17, 251. 5. Devia, N.; Manson, J. Α.; Sperling, L. H.; Conde, A. Macromolecules 1979, 12, 360. 6. Devia, N . ; Manson, J. Α.; Sperling, L. H.; Conde, A. Polym. Eng. Sci. 1979, 19, 869. 7. Devia, N.; Manson, J. Α.; Sperling, L. H . Polym. Eng. Sci. 1979, 19, 878. 8. Devia, N.; Manson, J. Α.; Sperling, L. H.; Conde, A. J. Appl. Polym. Sci. 1979, 24, 569. 9. Jordhamo, G. M.; Manson, J. Α.; Sperling, L. H . Polym. Mater. Sci. Eng. 1984, 50, 362. 10. Xie, H . Q.; Tan, P. W. China Synth. Rubber Industry 1984, 7, 180. 11. Kumar, V. G.; Rao, M . R.; Guruprasad, T. R.; Rao, Κ. V. C. J. Appl. Polym. Sci. 1983, 34, 1803. 12. Patel, M . Patel, P.; Suthar, B. Makromol. Chem. 1986, 187, 525. 13. Patel, M.; Suthar, B. Angew. Makromol. Chem. 1987, 149, 111. 14. Patel, M.; Suthar, B. J. Polym. Sci., Polym. Chem. Ed. 1987, 25, 2251. 15. Patel, M.; Suthar, B. Eur. Polym. J. 1987, 23, 399. 16. Patel, P.; Suthar, B. Polym. Eng. Sci. 1988, 28, 901. 17. Patel, P.; Suthar, B.; Patel, M . Brit. Polym. J. 1988, 20, 525. 18. Liu, J. J. Liu, W. Z.; Zhou, U . R. China Synth. Rubber Industry 1989, 12, 395. 19. Natchimuthu, W.; Rajalingam, P.; Radhakrishnan, G.; Francis, D. J. J. Appl. Polym. Sci. 1990, 41, 3059. 20. Xie, H . Q.; Tan, P. W.; Guo, J. S. In Advances in Interpenetrating Polymer Networks; Klempner, D.; Frisch, K. C., Eds.; Technomic: Lancaster, PA, 1991; Vol. 3, p 187. 21. Odian, G. P. Principles of Polymerization; McGraw-Hill: New York, 1970; p 99. ;

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RECEIVED for review November gust 12, 1992.

11, 1991.

ACCEPTED revised manuscript A u


Castor Oil PolyurethaneAcrylic or Vinyl Polymer Interpenetrating

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