Modeling of molecular weight distribution in ring-opening polymerization of l, l -lactide

The molecular weight distributions of poly(lactic acid) produced by ring-opening polymerization of l,l-lactide in bulk melt are measured and compared with the ones predicted using a kinetic model accounting for reversible catalyst activation, reversible propagation, reversible chain transfer to cocatalyst, and intermolecular transesterification. The same values of the model parameters as evaluated in previous works are used without any adjustment; i.e. The model is used in a fully predictive way. In order to calculate the complete molecular weight distribution, the model equations are solved through two different numerical methods, "direct integration" of the population balances at all values of chain length, and "fractionated moments", where the chains are artificially classified into two different categories, depending upon the experienced reaction steps. The accuracy of the molecular weight distributions calculated in the latter case is evaluated by comparison with those computed by solving the model equations with the "direct integration" method. It is found that the "fractionated moments" method provides enough accuracy and much smaller computational effort, thus representing an optimal tool for most modeling applications. Finally, the model predictions are compared with the experimental molecular weight distributions measured experimentally in bulk melt at 130 °C and various initial concentrations of catalyst and cocatalyst. The generally good agreement verified between model and experiment after correcting for peak broadening represents a convincing confirmation of the model's reliability. © 2014 American Chemical Society.