Main-Chain Lyotropic Liquid-Crystalline Elastomers. 1. Syntheses of Cross-Linked Polyisocyanate Gels Acquiring Liquid-Crystalline Behavior in the Swollen State
نویسندگان
چکیده
Copolymers of n-hexyl and allyl isocyanates were successfully synthesized using an organotitanium(IV) catalyst initiated polymerization. Viscosity measurements indicated that molecular weight increased with decrease in monomer/initiator ratio. Monomer reactivity ratios were calculated using the copolymer composition equation, and the resulting values indicated relative randomness in the copolymer. The liquid-crystalline behavior of these copolymers was studied with regard to their molecular weight, composition, and concentration. Radical cross-linking was extensively studied but yielded only very brittle gels. Consequently, hydrosilation cross-linking was investigated and did yield networks suitable for orientation in a novel technique for increasing the mechanical properties of polymer films. All the hydrosilation cross-linked gels exhibited brilliant mesomorphic birefringence under a crosspolarized microscope at low cross-link density. In addition, the glass transition temperatures of the hydrosilation cross-linked networks were found to be lower than those of their constituent polymers.
منابع مشابه
Main-Chain Lyotropic Liquid-Crystalline Elastomers. 2. Orientation and Mechanical Properties of Polyisocyanate Films
Novel types of main-chain, lyotropic liquid-crystalline polymer networks consisting of polyisocyanate chains were prepared by hydrosilation cross-linking. The characteristic liquid-crystalline band texture generated by shearing these networks in the swollen state was found to persist much longer than in the case of solutions of the same polymer in the un-cross-linked state, suggesting preservat...
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