(628f) Stochastic Simulation of the L,L-Lactide Ring-Opening Polymerization

In the present study, a comprehensive theoretical kinetic investigation of the homopolymerization of L,L-lactide in the presence of stannous octoate Sn(Oct)₂ as initiator for the synthesis of high-molecular weight polylactide is carried out using the stochastic Monte Carlo (MC) numerical method. The stochastic simulations proceed in complete conjunction with a detailed kinetic mechanism that involves, apart from the typical initiator activation, chain initiation, and propagation reactions, also chain transfer reactions (i.e., chain transfer to water, octanoic acid and monomer reactions), cyclization, esterification, transesterification and chain scission reactions as well as reactions leading to formation of specific end-groups. Via the implementation of the MC method, the dynamic evolution of a series of molecular properties (i.e., average molecular weights and molecular weight distributions) of the produced PLLA is accurately predicted. In addition, the effect of different polymerization conditions, such as the polymerization temperature and the monomer to initiator molar ratio on the final polymer properties is investigated. In this respect, it is found that the polymerization temperature and the monomer to initiator ratio display a significant effect on the polymerization rate and the molecular properties of the synthesized PLLAs.

The validity of the implemented kinetic model and the accuracy of the produced simulation results are assessed via a direct comparison with theoretical predictions of the average molecular properties by the method of moments as well with available experimental data. Among the novelties of the present work are the stochastic prediction of the detailed molecular characteristics of the polymer, the implementation of a comprehensive and detailed kinetic mechanism as well as the comparison of the theoretical prediction with experimental results of high purity and high molecular weight PLLA polymers.