SELF-SIMILAR RELAXATION BEHAVIOR AT THE GEL POINT OF A BLEND OF A CROSS-LINKING POLY(EPSILON-CAPROLACTONE) DIOL WITH A POLY(STYRENE-CO-ACRYLONITRILE)

Novel polymer properties can be achieved by blending high molecular we ight linear chains into a cross-linking system of short linear chains. This study is concerned with the rheological properties that are domi nated at first by the highly entangled linear chains. However, with in creasing extent of cross-linking, the short chains connect into a netw ork structure and begin to dominate the theology. The material here co nsists of cross-linking poly(epsilon-caprolactone) diol (PCL) and up t o 40% of linear poly(styrene-co-acrylonitrile) (SAN) of high molecular weight. The blend was molecularly mixed before crosslinking. Three co mpeting processes determine the structure of the system, (1) chemical cross-linking of the low molecular weight species into a sample spanni ng network of interpenetrating chains, (2) fluctuations in composition due to phase separation at increasing extents of reaction, and (3) cr ystallization of the PCL, which we tried to suppress as much as possib le. At the gel point, systems with low SAN content show the typical sc aling behavior of the critical gel with a self-similar relaxation spec trum, H(lambda) = G(o)/Gamma(n) (lambda/lambda)(-n), lambda > lambda(o ), at low probing frequencies, omega < 1/lambda(o). However, for the s ystems with high concentrations of the inert component, the self-simil ar region did not develop, possibly due to the phase separation induce d by the cross-linking. The relaxation exponent, n, decreased with inc reasing concentration of the highly entangled linear component. The re sults suggest that dynamic mechanical methods are applicable for deter mination of the gel point for homogeneous semi-IPN systems.