Dynamics of entangled star-branched polymers

Abstract

The diffusion and longest-relaxation process of star molecules entangled in a fixed-obstacle matrix and in melts of a linear polymer are considered. The dynamics in a fixed matrix are considered in terms of a general diffusive motion in an ‘entropic’ potential field. The resulting diffusion coefficient D_s and longest relaxation time τ_s are calculated, and scale as D_s∝(1/N_b) exp (–αN_b), τ_s∝N_b exp (αN_b)(for a 3-arm star with N_b monomers per arm, where α is a constant). For the case of a linear melt matrix it is argued that ‘tube-renewal’ effects will dominate the dynamic behaviour above a certain N_b.

We report the first experimental study of the diffusion coefficient D(N) of 3-arm deuterated polybutadiene N-mer stars diffusing in a highly entangled melt of linear polyethylene. Our results provide strong support for the calculated form of the diffusion coefficient, at low values of N, and suggest that at high N values ‘tube’ renewal effects become important.