Ring-opening copolymerization thermodynamics and kinetics of gamma-vaIeroIactone/epsilon-caprolactone

The general misconception that gamma-lactones are not thermodynamically polymerizable has limited the development of all gamma-lactone-based copolymers. A few studies have reported copolymerization of these five-membered cyclic esters with more reactive monomers, yet a systematic investigation of kinetics and thermodynamics is still lacking. To explore the feasibility of the reaction, we combined equilibrium and non-isothermal syntheses for the copolymerization of gamma-valerolactone with epsilon-caprolactone, initiated with methoxy polyethyleneglycol and catalyzed by Tin(II) 2-ethylhexanoate. Here, we present the polymerization kinetic and thermodynamic parameters for different monomer ratios in the reaction feed. We observed the dependency of enthalpy and entropy of polymerization upon monomer ratio changes, and estimated a linear increase in the activation energy by increasing the gamma-valerolactone fraction in the starting monomer mixture. Our data demonstrate that gamma-valerolactone can copolymerize with epsilon-caprolactone, but only under specific conditions. The reaction parameters determined in this study will enable preparation of additional gamma-valerolactone-based copolymers and development of a family of degradable materials with improved properties in respect to commonly used polyesters.