MODELING KINETIC PATHWAYS FOR ENZYME CATALYZED SYNTHESIS OF POLY(ε-CAPROLACTONE)

Peter M. Johnson, Santanu Kundu, Kathryn L. Beers

Enzyme-based catalysis has been promoted as a green synthesis route for industrial scale degradable plastics, replacing current routes which use toxic metal catalysts.  Enzyme catalysts have further advantages over metal catalysts, such as milder processing conditions and improved regioselectivity.  Progress on determining the optimal enzyme for polymerization has been made, but the lack of knowledge about the controlling parameters of the synthesis route limits industrial use.  In particular, the polymerization kinetics has a number of equilibrium reactions that occur with the potential to reduce reaction rates or the molar mass of end products.   Since only the ring opening step can be monitored in situ, the remaining kinetic pathway is difficult to deconvolute.  Recent experimental work has shown both the water concentration and enzyme degradation reactions during polymerization are key steps to controlling the molar mass distribution.  We present a comprehensive kinetic model for enzyme catalyzed polymerization that captures trends seen in literature and provides a better understanding of the roles each component on the polymerization kinetics.  Both enzyme catalyzed polymerization and degradation experiments were performed to refine the model and determine key reaction conditions necessary to form high molar mass products.  Model results will be presented verifying experimental results and demonstrating how to improve the polymerization by modulating water and oligomer concentrations to shift the reaction kinetics to higher molar mass species.