Polymer networks: principles of formation, structure and properties

This paper discusses the results of two types of theoretical investigations into the formation, structure and properties of polymer networks. First, to predict the value of the initial elastic modulus, it is important to be able to model, statistically, the molecular growth leading to network formation. A Monte-Carlo network polymerization algorithm has been developed. It uses Flory-Stockmayer random-reaction statistics with intermolecular reaction allowed on a correctly weighted basis. The algorithm simulates, as a function of extent of reaction, the formation of all of the connections in a reaction mixture and counts all the ring structures. It also enables polymerizations and network structures to be simulated efficiently up to complete reaction. Comparisons of predictions from the algorithm with experimental data from end- linking polymerizations show the importance of accounting for the whole distribution of sizes of ring structure in determining reductions in elastic modulus. The second type of investigation shows that Monte-Carlo simulations of the elastic behaviour of chains in networks, using realistic (R-I-S) network- chain models, are able to reproduce experimentally observed deviations from Gaussian network behaviour in uniaxial extension. (Example: polyurethane.)