Monte Carlo study of structure and kinetics of formation of end-linked polymer networks

The kinetics of formation and structural properties of end-linked polymer networks were studied by Monte Carlo simulations on a three-dimensional cubic lattice. Networks were generated from the solutions of linear polymer chains with functional end groups and tetrafunctional cross linkers. Systems of 10-, 20-mer precursor polymer chains with values of the ratio of cross linkers to polymer chains end groups r ranging from 0.9 to 1.4 were studied. Polymer volume fraction ϕ was varied from 0.1 to 0.5. Different ways of polymer network formation are possible, namely, gel creation process can proceed as homogeneous gelation as well as microgel separation. In addition to those limiting ways of polymerization process, intermediate cases were observed. All varied parameters (length of precursor polymer chains N, r and ϕ) influence the kinetics of the cross-linking. An algorithm to determine the soluble fraction in solution and the amount of loops and pendent structures in the polymer network was proposed. In agreement with experimental observations, simulations show that networks with lower soluble fractions which are more defect-free result from long precursor polymer chains (N=20) for approximately polymer melt densities (ϕ≈0.4) at higher than stoichiometric r values (r≈1.2).