Ring-opening copolymerization thermodynamics and kinetics of γ-valerolactone/ϵ-caprolactone.

Mariacristina Gagliardi,Angelo Bifone,Andrew C Marr

doi:10.1371/journal.pone.0199231

Abstract

The general misconception that γ-lactones are not thermodynamically polymerizable has limited the development of all γ-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 γ-valerolactone with ϵ-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 γ-valerolactone fraction in the starting monomer mixture. Our data demonstrate that γ-valerolactone can copolymerize with ϵ-caprolactone, but only under specific conditions. The reaction parameters determined in this study will enable preparation of additional γ-valerolactone-based copolymers and development of a family of degradable materials with improved properties in respect to commonly used polyesters.

Highlights

Degradable polymers are attracting increasing attention for their application in the fields of green chemistry, food packaging, agriculture and nanomedicine [1]
We demonstrated that ring-opening copolymerization of γ-valerolactone and -caprolactone is feasible under specific conditions of temperature and composition of the starting feed
The combination of results from equilibrium, low-conversion and non-isothermal polymerizations enabled analyses of all major aspects related to kinetics and thermodynamics of this specific copolymerization process by varying the starting γ-valerolactone copolymerization monomer feeds

Summary

Introduction

Degradable polymers are attracting increasing attention for their application in the fields of green chemistry, food packaging, agriculture and nanomedicine [1]. Hydrolyzable materials are interesting for their short half-life, complete degradation and favorable clearance of degradation products. Aliphatic polyesters are the most widespread hydrolizable polymers due to their favorable characteristics [2], and cyclic esters lactones are starting reactants for their synthesis. The majority of short-chain (four-, six- and seven-membered) cyclic esters are useful monomers that polymerize via Ring-Opening Polymerization (ROP). The ability of lactones to react via ROP is determined by the ring stability and their aptitude to shift the monomer/polymer equilibrium to the product side.

Methods

Results

Conclusion