Predicting molecular weight distribution by deterministic modeling and Monte Carlo simulations of radical polymerization with branching and scission allowing for multiradicals and gelation in various reactor configurations

Modeling of the molecular weight distribution (MWD) under circumstances of low-density polyethylene (ldPE) has been carried out for a tubular reactor under realistic non-isothermal conditions and for a series of CSTR's (Yaghini and Iedema, in press). The model allows for the existence of multiradicals and the occurrence of gelation. This model is based on a Galerkin finite element approach (FEM) and employs the pseudo distribution concept to address the number of radical sites per chain as the second dimension next to chain length. For reference, Monte Carlo (MC) simulations have been carried out for the same reactor configurations. Assuming 'topological scission', accounting for the highly branched character of the system, good agreement was found between the multiradical model and MC simulations. As conditions of ldPE polymerization lead to broad MWD and are close to gelation, allowing for gel turns out to be crucial. Not allowing for gel leads to extremely broad bimodal MWD, which with the present set of models we could now identify as an artefact.