Segment connectivity, chain-length breathing, segmental stretch, and constraint release in reptation models. I. Theory and single-step strain predictions

A self-consistent reptation theory that accounts for chain-tube interaction s, segment connectivity, chain-length breathing, segmental stretch, and con straint release is proposed. Simulation results are compared semiquantitati vely to experimental observations in single-step strain hows. Since stochas tic simulation techniques are used, no approximations, such as independent alignment or consistent averaging are needed to obtain results. The simulat ion results show excellent agreement: with experimental trends in sheer and normal stress relaxations, including the second normal stress difference, well into the nonlinear regime. For most of these experiments, the original Doi and Edwards theory, which incorporates independent alignment or consis tent averaging, is not satisfactory. In the following companion paper, we s how how the model is capable of describing double-step-strain flows for all stress components. Subsequent papers show excellent agreement fur the ince ption of steady shear flow, and steady shear flow. (C) 1998 American Instit ute of Physics. [S0021-9606(98)52746-8].