Computer Simulation of Polymer Chain Scission in Biodegradable Polymers

Abstract

Biodegradable polymers degrade due to the hydrolysis (chain scission) of the polymer chains. Two theories of hydrolysis are that 1) scissions occur randomly at any bond in chains, and 2) scissions occur in the final bond at chain ends. In this study, a simulation tool was developed to simulate both random chain scission and chain end scission. The effect of each type of scission was analysed. Random scissions were found to have over 1000 time's greater impact on molecular weight reduction than end scissions. For the degradation of poly lactic acid by random scission, it was found that M n must reduce to <5000 g/mol in order for a polymer to exhibit significant mass loss due to the diffusion of water-soluble short chains. In contrast, end scission was able to produce a significant fraction of water-soluble chains with little or no effect on M n . The production rate of water-soluble chains was linearly related to end scission but increase in an accelerated manner due to random scission. Molecular weight distributions were fitted to experimental data for the degradation of poly D-lactic acid.

Lifetime prediction of biodegradable polymers

“…By contrast, Gleadall and Pan used a Monte Carlo approach to simulate molecular weight distributions for a PDLA at different times of degradation. They adjusted the kinetics by applying a scission rate, with the model results being successfully compared with experimental data from an earlier publication [139]. Random scissions were found to have over 1000 times greater impact on molecular weight reduction than end scissions, which were able to produce a significant fraction of water-soluble chains with little or no effect on Mn.…”

A kinetic scission model for molecular weight evolution in bioresorbable polymers

“…[36][37][38][39][40][41][42] Gleadall et al [43] explored the effects of different hydrolysis mechanisms, determining both mid-and end-chain scissions are necessary to result in mass loss and molecular weight reduction, respectively. Scission models have been proposed to describe how chain cleavages affect the molecular weight distribution of a polymer, with both mid-and end-chain scissions considered, [20,44] but these have failed to incorporate the effect of autocatalysis on the degradation behavior. Kinetic Monte Carlo approaches have been developed, providing predictions for the temporal evolution of the molecular weight distribution.…”

“…In contrast, for the latter method, all chains would have an equal chance of being selected, with a bond in a short chain having a greater chance of being chosen than a bond in a long chain, e.g., a chain of length 100 has the same chance of being selected as a chain of length 1000, but there are 10 times more bonds available to break in the longer one. Previous scission models kept S end and S mid fixed throughout the simulation, [44,47,48] making it difficult to relate results to time, with degradation being a non-linear process. To overcome this, we update the model to allow S end and S mid to vary during the simulation, as described in the following section.…”

Influence of the polymer degradation on enhanced oil recovery processes

“…In order to simulate the degradation, an exponential decay law will be assumed in the average molecular weight. This law was selected based on degradation experiments presented in the literature as well as numerical models developed to consider the degradation of polymer chains in porous media [61][62][63][64][65][66] . This yields,…”