A Monte Carlo study of the structural properties of end-linked polymer networks

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Abstract
The formation and structural properties of end-linked polymer networks were studied in the framework of the bond fluctuation model on a three-dimensional simple cubic lattice. Only excluded volume interactions were considered between repeat units (monomers and cross-links). Networks were created with a wide range of the ratio of cross-link sites to precursor polymer chain ends, r, to test the experimental observation that a nonstoichiometric ratio generates a more perfect network. Systems of 10-, 20-, and 50-mer precursor polymer chains with values of r ranging from 0.9 to 1.6 were studied. An algorithm was developed to determine the soluble fraction and the amount of loops and pendent structures. The network properties were evaluated at the same number of Monte Carlo steps per repeat unit for each chain length independent of r value. In agreement with experimental observations, the simulation results show that the optimum r values are nonstoichiometric, increase with increasing chain length of the precursor polymer chain, and increase with side reaction.