Modeling of the molecular weight distribution (MWD) of low-density Polyethylene (IdPE) has been carried out for a tubular reactor under realistic non-isothermal conditions and for a series of CSTR's. The model allows for the existence of multiradicals and the occurrence of gelation. The deterministic model is based on a Galerkin finite element approach (KM) and employs the pseudo distribution concept to address the number of radical sites per chain as the second dimension next to chain length. The Galerkin method is shown to allow a straightforward and compact formulation of the series of CSTR's using a repetitive matrix structure with connective elements. The 'topological scission' model is utilized as the closest approximation of random scission in deterministic modeling accounting for the highly branched character of the system As conditions of IdPE polymerization lead to broad MWD and are close to gelation, allowing for gel turns out to be crucial. It was observed that a broad MWD in a single CSTR becomes narrower as the number of CSTR's in series increases and is narrowest in the batch reactor. (C) 2015 Elsevier Ltd. All rights reserved.