Viscoelasticity of randomly crosslinked polymer networks relaxation of dangling chains.

Viscoelastic relaxation of concentrated polymer systems requires the disentanglement of the polymers. In a crosslinked rubbery network only dangling chains, branches singly attached to the network, can disentangle. Just part of any applied stress is relaxed, and this quite slowly. The relaxation of polymer branches by contraction in the effective tube formed by the remaining polymer was quantified in the earlier Pearson-Helfand theory, which described the relaxation of star-shaped macromolecules. The theory is here extended to account for the polydispersity of network branches, a factor which plays a major role in determining the law of elastomer relaxation.