On the dynamics of moderately and lightly crosslinked polymer networks

Abstract

The relaxation behavior of networks, where the entanglement density is comparable with the crosslink density, can be explained by a broad distribution of the lengths of the network chains. A stretched exponential behavior is obtained with a fractional exponent of 1/3. — In the case of lightly corsslinked systems the influence of entanglements on the dynamics of a tagged network chain is investigated. It is assumed that the entanglement dynamics can be viewed as a cooperative stochastic process. A mode coupling ansatz is ued which yields nonuniversal scaling behavior of the characteristic relaxation time of the form: τ _N =τ ₀ · N ^y, where the exponent γ depends on the averaged entanglement distance. Moreover, the relaxation function can be represented by a stretched exponential function: g(t) ∞ e ^{−(t/GtN) β}. The fractional exponent β also depends on the entanglement density.