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Kinetic parameters estimation of ring-opening poly(lactic acid) polymerization by modeling and simulation

Abstract The modeling of ring-opening polymerization of lactide to poly(lactic acid) (PLA) has been carried out. Carothers first synthesized PLA in 1932. Since then, hundreds of research papers and patents have appeared in the literature. However, there is a lack of data concerning the rate constants for initiation, propagation and termination steps of PLA polymerization, except some data about the apparent rate constant. This work investigates, theoretically, the individual rate constants using a simple numerical technique. The progress of lactide polymerization can be modeled by assuming a ring opening reaction mechanism comprising chain initiation, chain propagation, and chain termination. The simulator developed, based on the solutionof differential equations corresponding to the above-mentioned kinetic scheme, Generates a detailed molecular weight distribution that can be used to estimate average molecular weights (or average degree of polymerization) vs. polymerization time curves. These simulated curves, on matching with the reported experimental data (for different catalysts), yield the absolute values of rate constants. The values have been determined for zinc lactate. Rate constants could be determined by using the molecular weight and the polydispersity vs. polymerization data. This methodology offers greater opportunity for capturing high, non-equilibrium polymer yield through appropriately timed termination of the polymerization reaction.