Deformation behavior of tetramethyl-p-silphenylenesiloxane (TMPS)-dimethylsiloxane (DMS) block copolymer spherulitic films

Abstract

A study of the morphology of uniaxially drawn spherulites of TMPS-DMS block copolymers with TMPS contents ranging from 90 to 30 wt % was made especially by electron and optical microscopy. For the entire range of polymer compositions, the copolymers, like the TMPS homopolymer, form negatively birefringent spherulites when crystallized from solution, or from the supercooled melt. A banded spherulitic morphology is observed. The deformability of copolymer spherulites increases as the DMS amorphous component increases. The DMS component coexists with, but is physically excluded from the ordered TMPS “crystalline” phase. In samples having the higher TMPS compositions, deformation occurs through crack formation, mechanical slip, tilting and/or twisting of the lamellae that help comprise the spherulites. At high DMS contents this “soft” component is undoubtedly responsible for the flexible character of these copolymers. Sample clarity also increases with DMS content as the crystallinity decreases.