Direct Methylenation of Carbonyl Group in Poly(ε-caprolactone) Chain Using Petasis Reagent and Further Functionalization

Abstract

To achieve addition of functional group to poly(ε-caprolactone) (PCL) chain, we conducted direct methylenation of PCL carbonyl group using the Petasis reagent. First, various methylenation reactions of benzyl-terminated PCL were carried out by changing the reaction temperature, reaction time, and the ratio of the reagent to the carbonyl groups of PCL. The results indicated that relatively shorter reaction times (1 h) and higher temperatures (120 ℃) are preferable for direct methylenation without cleavage of the polymer chains and undesired gelation. Thermal properties of the methylenated PCL were also studied to investigate their effect on crystallinity, compared with the initial PCL. It was found that increased methylenation leads to reduction in the crystallinity, while the polymer chain alignment in the polymer crystal could be disturbed by the addition of methylene groups. To confirm the functionalization of methylene groups in the PCL chain, the thiol-ene reaction model was applied using α,α’-azobisisobutyronitrile and thioglycolic acid under N₂ atmosphere. Successful carboxyl group attachment suggests that the methylene groups would be useful for further functionalization of the PCL chain for the design of new biodegradable aliphatic polyesters.