POLYMER SEGMENTAL DYNAMICS AND ENTANGLEMENT CONSTRAINT

The relaxation time (T-e) associated with the transition from liquid-l ike behaviour to pseudo solid-like behaviour for polybutadiene and pol yisoprene, as observed in simple Bloch decay n.m.r. experiments, is sh own to be linearly dependent upon the polymer molecular weight. This t ransition begins at the critical molecular weight, M-c, as classically defined by a variety of rheological experiments. The linear dependenc e of T-e upon molecular weight, using a simple diffusion model, requir es the length scale over which the relaxation is operative to be indep endent of total polymer molecular weight. The experimental results ide ntify the length scale associated with this relaxation time to be the length scale represented by the critical molecular weight (M-c); this process is observed to utilized are found to be sensitive to chain dyn amics on the length scale corresponding to the critical molecular weig ht, not the total polymer molecular weight. (C) 1997 Elsevier Science Ltd.