RHEOLOGY OF LONG-CHAIN RANDOMLY BRANCHED POLYBUTADIENE

The rheology of a series of long-chain randomly branched polybutadiene s (PBDs) has been investigated. Branched samples were made through a h ydrosilation reaction between a small difunctional crosslinker and the 1,2 groups distributed on the backbone of near-monodisperse PBD (M(w) = 56 000, 137 000; M(w)/M(n) = 1.04). The resulting samples have both dispersity in molecular weight and architecture. The species distribu tion has been studied using size exclusion chromatography and has been found to agree with the Flory-Stockmayer distribution for the random branching of monodisperse chains. Sinusoidal oscillation and creep/cre ep recovery experiments were done to determine dynamic moduli, zero sh ear viscosity, and equilibrium creep compliance. The observation that branching is random allows structural parameters to be calculated such as weight fractions and average molecular weights of free chains, arm s, and interior chains. These parameters are used in existing rheology models whose results are compared to experimental observation. In par ticular, qualitative agreement is found for eta(0) as a function of br anching content by applying the model proposed by McLeish and O'Connor [Polymer 34, 2998-3003 (1993)] for star/linear blends. (C) 1996 Socie ty of Rheology.