Developments in understanding the formation, structure and properties of polymer networks

Abstract

AbstractTwo areas of networks modelling are described. The first is concerned with the application of a Monte‐Carlo (MC) algorithm to account fully for loop formation in RA2 + R′B3 and RA2 + R′B4 polymerisations. The resulting interpretation of experimental elastic moduli of HDI‐based polyurethane (PU) networks prepared at different dilutions shows it is essential to account for elastic losses in loop structures of all sizes. An important parameter, x, is introduced, namely the average fractional loss of elasticity per larger loop structure relative to the loss per smallest loop structure. Application of the MC calculations to the formation and resulting structures of MDI‐based PU networks and poly(dimethyl siloxane) (PDMS) networks shows the competing effects of loop structures and chain interactions (PU) or topological entanglements (PDMS) on the modulus. The second area of networks modelling is the MC simulation of the elastic behaviour of chains in networks using realistic rotational‐isomeric‐state chain models. Stress‐strain and stress‐optical properties can be modelled quantitatively. In stress‐strain behaviour, an increase in the proportion of fully extended chains with increasing macroscopic strain causes a reduction in network modulus at moderate macroscopic strains. There is no need to invoke a transition from affine to phantom chain behaviour as deformation increases. For stress‐optical properties, the MC method gives, in agreement with experiment, values of stress‐optical coefficient that are dependent upon both deformation ratio and network‐chain length. Applications of the method to the quantitative modelling of the stress‐strain properties of PDMS networks and the stress‐optical properties of polyethylene and poly(ethylene terephalate) networks are described.