The synthesis of simultaneous interpenetrating networks (SIN's) based on elastomeric polymers derived from castor oil and cross-linked polystyrene was studied. The elastomers employed included the cross-linked polyester of castor oil and sebacic acid, the cross-linked polyurethane with 2, 4-tolylene diisocyanate, and the cross-linked poly(ester-urethane) from castor oil, sebacic acid, and 2, 4-tolylene diisocyanate. The polystyrene phase was cross-linked with 1% divinylbenzene (55% solution), and 0.4% benzoyl peroxide was used as the initiator for the styrene polymerization. This paper describes the synthesis, kinetics, chemical characteristics of the systems involved, and effect of each on the resulting two-phase morphology. Solubility and kinetic considerations showed that either a monomer or prepolymer mixture can be employed for the synthesis of polyurethane SIN's, while a polyester prepolymer was required for the polyester SIN's. Two main compositions having 10 and 40% of the elastomer component were studied. Such materials behaved as tough plastics and reinforced elastomers, respectively. The morphology of the SIN's was found to be sensitive to synthetic details, such as the reaction time with stirring and time of pouring into the mold, after which the reaction was continued without stirring. A definite “window” was shown to exist, controlled by the time required for phase inversion on one side and the time to reach gelation on the other. Morphology studies throughout the course of the polymerization revealed that with proper stirring a phase inversion occurs for compositions up to about 15% castor oil elastomer content. The polystyrene phase cannot be made the continuous phase by mechanical stirring above 15% castor oil elastomer content. A detailed description is given of the morphological stages of the reaction mixture during polymerization, as well as a discussion of the roles of the relative polymerization rates, and polymer I/polymer II compatibility throughout the synthetic process. © 1979, American Chemical Society. All rights reserved.
