Novel synthesis of polyimide-polyhybridsiloxane block copolymers via polyhydrosilylation: Characterization and physical properties

The insertion of soft polysiloxane segments into a polyimide backbone intro duces changes in its properties (processability, low surface tension, gas p ermeability, and lower dielectric constant). Generally, these polyimide-pol ysiloxane copolymers are synthesized by the condensation of a dianhydride w ith an aromatic diamine and an amine telechelic polysiloxane, or by transim idization between an aminopyridine-terminated oligoimide and an amine end-c apped oligosiloxane. This study investigated another route to obtain perfec tly alternating polyimide-polyhybridsiloxane (PI-PHSX) block copolymers. Th e hydrosilylation, widely studied previously, was performed to elaborate co polymers from an allyl telechelic polyimide and a hydrosilane telechelic po lyhybridsiloxane. The use of a telechelic polyhybridsiloxane as a soft segm ent brought better thermostability and better chemical resistance in compar ison with an oligosiloxane based on Si(CH3)(2)-O- units. Using the same all yl telechelic polyimide moiety but varying the size of the hybrid siloxane part, we obtained different PI-PHSX block copolymers, leading to thermoplas tic elastomers (TPE). We investigated the effect of the soft-segment length on the thermal resistance, activation energy of thermal degradation, mecha nical behavior, and surface properties of a series three PI-PHSX block copo lymers containing 36, 54, and 75 wt % polyimide. (C) 2001 John Wiley & Sons , Inc.