Synthesis and properties of new block copolymers based on polydimethylsiloxane and tetraphenylethylene‐containing polyimide

New polydimethylsiloxane (PDMS)‐polyimide block copolymers were synthesized by the solution polycondensation of aminopropyl‐terminated polydimethylsiloxane, 1,1‐bis(4‐aminophenyl)‐2,2‐diphenylethylene, and 3,3′,4,4′‐benzophenonetetracarboxylic dithioanhydride in pyridine. New 1,3‐bis(3‐aminopropyl)tetramethyldisiloxane (BADS)‐based random copolyimides were also prepared. The inherent viscosities of all the random and block copolyimides were in the range of 0.13–0.90 dL/g in N‐methyl‐2‐pyrrolidone. These copolymers were soluble in N,N‐dimethylacetamide, N‐methyl‐2‐pyrrolidone, and m‐cresol. All the BADS‐based random copolymers and PDMS‐containing copolymers with PDMS content above 42 wt % were soluble in tetrahydrofuran and chloroform. Transparent or somewhat cpaque films were prepared by casting from the reaction solutions. The BADS‐based random copolyimides had one glass transition temperature (Tg) in the whole composition ranges, which showed single phase nature of the copolymers. On the other hand, the PDMS‐polyimide block copolymers had double TgS, indicating phase‐separated morphology. The block copolymers containing PDMS content above 73 wt % behaved like a high temperature elastomer.