effect of initial molecular weight distribution in polyethylene melts on degradation process at high temperatures*

The molecular weight distribution of synthetic polymers is an important factor to consider when synthesizing, processing, and manufacturing industrial plastics. The breadth of this distribution, or dispersity, is determined by the ratio of the number average molecular weight to weight average molecular weight, and is correlated with material properties. While most theoretical studies consider uniform polymer melts, monodispersity is not practically achieved in experiments. There is a pressing need to explore the effect of initial dispersity on the degradation process. We use dissipative particle dynamics (DPD) to probe the effects of initial molecular weight distribution on random scission in linear polymer melts. To capture the effects of entanglements in melts, we use modified segmental repulsive potential (mSRP) formulation of DPD. We consider melts with initial dispersities of 1.05 to 1.3. We use the Schulz-Zimm initial distribution of chains, which is known to be an accurate predictor of the distribution of polymer chains in polyethylene. We track weight fraction, number fraction, and dispersity of polymer fragments during random scission at high temperatures and quantify the effects of initial dispersity.