Modelling the elastic behaviour of real chains in polymer networks

Monte‐Carlo simulations of the elastic behaviour of PDMS networks, using a realistic (R‐I‐S) network‐chain model, are able to reproduce experimentally observed deviations from Gaussian network behaviour in uniaxial extension. The finite extensibility of the network chains is shown to cause non‐affine deformation of the mean‐square network‐chain end‐to‐end distance, even at moderate sample deformations (λ≈1.5). An increase in the proportion of fully‐extended chains with increasing macroscopic strain gives rise to a steady decrease in the rate of network free‐energy change, causing a reduction in the network modulus at moderate macroscopic strains. There is no need to invoke a transition from affine to phantom chain behaviour as deformation increases.