On the entanglement-based mechanism in thermal degradation of vinyl polymers

In thermal degradation of the main-chain-scission type of vinyl polymers as a polymer reaction in melt, we propose that each subsequent elementary reaction of terminal macroradicals generated by the initiation is significantly influenced by entanglement constraint of molten polymer chain which is a reaction field. First, the intermolecular hydrogen abstraction followed by beta-scission occurs dominantly at other molecules forming the entanglement constraint tube. As a result, the reaction field becomes rapidly drop in the molecular weight M of molten polymer to the region of M< M-c (characteristic molecular weight) and furthermore M < M-e (entanglement molecular weight). Thus, in the reaction field constituted by isolated random coil chain that the entanglement is disentangled and entanglement constraint is released, the intramolecular hydrogen abstraction occurs predominantly because it is controlled by the activation energy and the frequency factor. On the other hand, the direct beta-scission (depolymerization) of the macroradicals also takes place in tubes independent of entanglement constraints. (C) 2019 Elsevier Ltd. All rights reserved.