NMR INVESTIGATION OF INTERPHASES IN DIMETHYLSILOXANE-STYRENE BLOCK-COPOLYMERS - INFLUENCE OF BLOCK MOLECULAR-WEIGHT

H-1 n.m.r. relaxation data, determined via either wide-line H-1 n.m.r. or high-resolution solid-state C-13 n.m.r., were used to analyse the existence and extent of interphasic regions in dimethylsiloxane-styren e block copolymers. Results thus obtained have shown that copolymers h aving very short blocks possess relatively large interphases character ized by intermediate mobility. In addition, some styrene units are tra pped in the dimethylsiloxane soft microphase. With increasing block mo lecular weights, the extent of the phase of intermediate mobility, as well as the percentage of styrene units trapped in the dimethylsiloxan e soft microphase, decrease. In agreement with the conclusions previou sly deduced from d.s.c. experiments, and within the sensitivity of the n.m.r. technique, the samples with the longest blocks are sharply pha se-separated.