Effect of ionic liquids on the structural, thermal and in vitro degradation properties of poly(ε-caprolactone) synthesized in the presence of Candida antarctica lipase B

The study provides detailed information on the differences in the structural, thermal and degradation properties of poly(e-caprolactone) synthesized in two different ionic liquids, 1-butyl-3-methylimidazolium hexafluorophosphate [bmim][PF6] and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [bmim][NTf2], regarding its further usage in the pharmaceutical field. The polymer structure confirms the presence of both linear polymer chains with end-functional hydroxyl groups allowing covalent coupling of the therapeutic agents, and cyclic macromolecules, both affecting the degree of crystallinity of polymer. The highest macrocyclic content (64%) after 7 days of polymerization at 80 8C was observed for [bmim][NTf2]. For [bmim][PF6], the macrocyclic content value was not dependent on the reaction time and remained at a similar level (10–14% at 80 8C). The results of degradation test revealed that hydrolytic degradation of ester bonds is more pronounced for PCLs synthesized in [bmim][NTf2], due to their lower degree of crystallinity compared with PCLs obtained in [bmim][PF6]. A high purity, low polydispersity index of the obtained polymers and high yield of the process (ca., 90%) indicate that ionic liquids seem to be promising solvents for the synthesis of biomedical polymers