POLY(ORGANOPHOSPHAZENES) CONTAINING ALLYL SIDE-GROUPS - CROSS-LINKINGAND MODIFICATION BY HYDROSILYLATION

Poly(organophosphazenes) containing 4-(allyloxy)phenoxy and 4-[4'-(all yloxy)phenyl]phenoxy side groups were synthesized and modified by hydr osilylation reactions. A small-molecule model compound, taphenoxy[4-(a llyloxy)phenoxy]cyclotriphosphazene, underwent platinum-catalyzed hydr osilylation reactions with heptamethyltrisiloxane and dimethylethoxysi lane. The product of the second reaction, containing one dimethylethox ysilane group, underwent hydrolysis and self-condensation reactions in the presence of acid. Transposition of this chemistry to the high-pol ymer level was then accomplished. Thus, hydrosilylation of phosphazene high polymers with allylaryloxy side groups yielded poly(organophosph azenes) with dimethylsiloxane side group graft units. High siloxane lo adings were obtained without evidence of Si-O or Si-C bond cleavage. A series of polymers with 4-100% grafting of dimethylsiloxane segments (corresponding to 6.5-56.2% dimethylsiloxane by weight) were synthesiz ed and characterized by DSC, TGA, and GPC. Two polymers were further c haracterized by DMA. Glass transition temperatures of the siloxane-con taining polymers ranged from -79 to +20 degrees C, according to the am ount of siloxane grafting and the nature of the other groups attached directly to the phosphazene polymer backbone. The siloxane-containing polymers also showed a relaxation at approximately -120 degrees C. Thi s combined with SAXS data suggested that the dimethylsiloxane side gro up may exist in microphase-separated domains. Cross-linking of polymer s that contained unsaturated groups was achieved by ultraviolet irradi ation and gamma-irradiation. Poly(organophosphazenes) bearing 20 and 4 6 mol % dimethylethoxysilane groups cross-linked readily on exposure t o atmospheric moisture.