Rigid‐rod polymers with polysiloxane side chains. I. Synthesis and characterization of rigid‐rod polyimides with polysiloxane side chains and their compatibility with linear polysiloxanes

Abstract

Abstract Rigid‐rod aromatic polyimdies having polydimethylsiloxane side chains were prepared for the purpose of dispersing rigid‐rod molecules in silicone matrices for molecular reinforcement. The polyimides were obtained by imidizing the polyamide‐acids bearing the side chains either thermally or chemically, which were synthesized by reacting 4,4′‐diaminobiphenyl‐terminated polysiloxane macromonomers with pyromellitic dianhydride in THF. The polyamide‐acid films obtained by removing the solvent were soluble in THF, but the polyimides were insoluble in any common solvent. The polyimides showed no melting transition below 350°C on DSC analysis, at which temperature the side chain started decomposing. Although all the polyimides were anisotropic as observed by a polarizing microscope, x‐ray diffraction analysis suggested the presence of only limited chain organization. Blends with linear polydimethylsiloxanes were prepared by casting the THF solution containing the polyamide‐acid and the polydimethylsiloxane, followed by solvent evaporation and thermal imidization. With relatively longer side chains, the polyimides were proved to be compatibilized with polydimethylsiloxanes. © 1994 John Wiley & Sons, Inc.