Molecular weight/branching distribution modeling of low-density-polyethylene accounting for topological scission and combination termination in continuous stirred tank reactor

We present a comprehensive model to predict the molecular weight distribution (MWD),1 and branching distribution of low-density polyethylene (ldPE),2 for free radical polymerization system in a continuous stirred tank reactor (CSTR).3 The model accounts for branching, by branching moment or pseudo-distributions. The common free radical polymerization reactions including chain scission have been considered in the model. Non-linear or the so-called topological scission has been modeled using approximate fragment length distributions derived from scission, applied to branching topologies. To model the distributions, the Galerkin-FEM method based on the same principles as PREDICI® has been applied and implemented in MATLAB©. The fundamental numerical problem arising from topological scission has been solved. Thus, the model provides more accurate results, allowing a precise comparison to earlier results and to Monte Carlo simulations.