Synthesis and characterization of perfectly alternating segmented copolymers comprised of poly(dimethylsiloxane)s and engineering thermoplastics

Abstract

Novel perfectly alternating segmented copolymers containing imide junction points were synthesized via terminal amine-anhydride coupling from poly(dimethylsiloxane)s and either poly(arylene ether)s or polyimides. The copolymers were characterized in solution and the solid state. The -(-A-B-)-n architecture and molecular design of these linear systems afforded thermodynamically microphase separated systems which gave rise to interesting copolymer properties. Each controlled molecular weight oligomeric segment, or homopolymer, was initally synthesized with reactive endgroups and fully characterized prior to copolymerization. Thus, anhydride-terminated poly(dimethylsiloxane)s were prepared via cationic ring-opening polymerization in the presence of a "monofunctional" bis-norbornane anhydride disiloxane endcapping species. Aromatic amine-terminated engineering thermoplastics were synthesized through either nucleophilic aromatic substitution in the presence of a “monofunctional” aminophenol endcapper (as for poly(arylene ether ketone)s and poly(arylene ether sulfone)) or by solution imidization using a controlled excess of the diamine monomer. A solution imidization method was developed for the segmented copolymerization that simplified the typically two-step, two-solvent method into a one-step approach with a single solvent. Thus, a previously described condensation catalyst, 2-hydroxypyridine, was utilized which was demonstrated to be essential in obtaining high molecular weight copolymers. These segmented copolymers generally were fibrous and highly soluble in many common organic solvents. Creasable, transparent, solution-cast films were readily prepared. Thermal and morphological analyses demonstrated that the copolymers exhibited phase separation, and displayed lower and upper Tg's as a result of the two components employed. At short hard block lengths, uper Tg's were somewhat depressed, implying partial miscibility.