Polymer degradation mechanisms: New approaches

Discrete bond-weighted random scission of linear polymers

“…Previous isothermal studies with PMMA [16][17][18] have shown that there is a dependence of the observed degradation rate k obs on initial molecular weight which the pure ECS model does not predict, nor is it clear from Fig. 11 that this is the case.…”

“…For example, the model makes no distinction between a radical fragment and a molecule and so no termination processes are explicitly modelled. However, it has also been suggested, based on isothermal studies [15][16][17][18], that RS plays an increasingly important role in the thermal degradation of PMMA, depending on the temperature, and that this in turn affects the nature of the dependence of degradation rate on initial molecular weight. In order to investigate this situation, we now construct an approximation for k obs for the end-bond weighted case (17) above, which represents a degradation process involving a simultaneous mixture of RS and ECS.…”

“…It will also be used to analyse the case of simultaneous random and end-chain scission, which is thought to be important in the thermal degradation of PMMA [15][16][17][18]. The analysis of other scission mechanisms is also possible within this framework and the break-at-a-point model is briefly presented and investigated.…”

Degradation

“…If depolymerization is both chain-end and chain-scission initiated and termination is first-order then application of the steady-state assumption to the concentration of depolymerizing radicals leads to the following relation (14,15):…”

Infrared Spectroscopic Studies on Some Thermally Degraded Poly(methyl methacrylate) Doped with N,N,N´,N´- tetraoxaloyl Para Sulphanilamide

“…The degradation occurs in two main stages (43)(44)(45)(46)(47)(48)(49)(50)(51) . In the first stage, the radical chain unzipping reaction is initiated at unsaturated chain-ends.…”