Predicting the formation, structure and elastomeric properties of end-linked polymer networks

The molecular structures and macroscopic properties of network polymers dep end more closely on reactant structures (molar masses, functionalities, cha in flexibilities) and reaction conditions (dilution, proportions of differe nt reactants) than do those of linear polymers. To understand and predict e lastomeric properties, it is important to be able to model, statistically, the molecular growth leading to network formation. A new Monte-Carlo networ k polymerisation algorithm has been developed, using Flory-Stockmayer rando m-reaction statistics with intramolecular reaction allowed on a correctly w eighted basis. The algorithm simulates, as a function of extent of reaction , the formation of oil of the connections in a reaction mixture and counts all the ring structures. It also enables polymerisations and network struct ures to be simulated efficiently up to complete reaction. Comparisons of pr edictions from the algorithm with experimental data from end-linking polyme risations show the importance of accounting for the whole distribution of s izes of ring structure in determining reductions in elastic modulus. An imp ortant new factor, x, is introduced in the interpretation of experimental d ata. It is the fractional loss in elasticity per chain in loop structures l arger than the smallest.