Thermally Initiated Trans-esterification in Poly(ε-caprolactone) and Its Dependence on Molecular Weight

Abstract

Biodegradability and biocompatibility of poly(e-caprolactone) (PCL) are the prime properties which advanced the use of this polymer in fields of tissue engineering and biomedicals. Being an aliphatic polyester, PCL is prone to undergo trans-esterification which is one of the mechanisms reported for its degradation besides being used in making its copolymers. Trans-esterification occurs both, inter- and intra-molecularly and in this work we report that the mechanism of trans-esterification depends on the molecular weight of the polymer when it is subjected to 160 °C for time up to 24 h. For low molecular weight PCL (Mp = 10,000 g/mol) inter-molecular trans-esterification is the predominant mechanism while for the high molecular weight PCL (Mp = 80,000 g/mol) it is intra-molecular. A mid molecular weight PCL (Mp = 43,000 g/mol) showed presence of both, inter- as well as intra-molecular trans-esterification, when heated at 160 °C for 24 h. A decrease in relative crystallinity for all the samples showed reduction in crystalline component of the polymer confirming occurrence of trans-esterification at chosen conditions. An increase in tensile strength and modulus is observed after treatment at 160 °C for 24 h due to formation of more entangled network of polymer chains as a result of trans-esterification reactions.