SYNTHESIS AND PROPERTIES OF NEW MULTIBLOCK COPOLYMERS BASED ON POLY(DIMETHYLSILOXANE) AND N-PHENYLATED POLYUREAS

A new class of multiblock copolymers having well-defined structures was synthesized starting from poly(dimethylsiloxane) (PDMS) and N-phenylated polyureas by the solution polyaddition technique. Three synthetic methods, i.e., one-step, two-step, and chain-extension methods, were adopted for the synthesis of PDMS-polyurea multiblock copolymers with wide ranging compositions. In the two-step method, α,ω -diisocyanate-terminated polyurea oligomers, which were preformed from, α, α′ -dianilino-p-xylene (DAX) and 4,4′ -methylenebis(phenyl isocyanate) (MBI) in anisole, were reacted with α,ω-bis(3-aminopropyl)- poly(dimethylsiloxanes) (PDMS-diamines) in the same flask leading to the formation of multiblock copolymers. In the one-step method, three reaction components, DAX, MBI, and a PDMS-diamine, were reacted all together in anisóle. In the chain-extension method, PDMS-diamines were reacted first with MBI giving α,ω-diisocyanate-terminated PDMS oligomers, which were subjected to reaction with DAX in anisóle forming multiblock copolymers. These polyadditions afforded multiblock copolymers having inherent viscosities of 0.2-0.7 dL·g1. They are readily soluble in a variety of solvents such as chloroform, tetrahydrofuran, m-cresol, and N,N dimethylacetamide (DMAc). Transparent, ductile, and elastic films were obtained by casting from the chloroform solutions or directly from the reaction solutions just prepared. Calorimetric measurements showed that the films of the multiblock copolymers prepared by the two-step method has the best defined, microphase-separated morphology, and the films by the chain-extension method had the second best, compared with films by the one-step method. The multiblock copolymers obtained by the two-step method afforded films with the most balanced mechanical properties. The film mechanical properties were highly dependent on the PDMS content; at low PDMS levels the materials behave as rubber-toughened plastics, while at higher PDMS contents the materials are analogous to elastomers. © 1990, American Chemical Society. All rights reserved.