Synthesis and Characterization of Poly(ε-caprolactone-co-δ-valerolactone) with Pendant Carboxylic Functional Groups

In this paper, aliphatic polyesters functionalized with pendant carboxylic groups were synthesized via several steps. Firstly, substituted cyclic ketone, 2-(benzyloxycarbonyl methyl) cyclopentanone (BCP) was prepared through the reaction of enamine with benzyl-2-bromoacetate, and subsequently converted into the relevant functionalized delta-valerolactone derivative, 5-(benzyloxy carbonylmethyl)-delta-valerolactone (BVL) by the Baeyer-Villiger oxidation. Secondly, the ring-opening polymerization of BVL with epsilon-caprolactone was carried out in bulk using stannous octoate as the catalyst to produce poly(epsilon-caprolactone-co-delta-valerolactone) bearing the benzyl-protected carboxyl functional groups [P(CL-co-BVL)]. Finally, the benzyl-protecting groups of P(CL-co-BVL) were effectively removed by H-2 using Pd/C as the catalyst to obtain poly(epsilon-caprolactone-co-delta-valerolactone) bearing pendant carboxylic acids [P(CL-co-CVL)]. The structure and the properties of the polymer have been studied by Nuclear Magnetic Resonance (NMR), Fourier Infrared Spectroscopy (FT-IR) and Differential Scan Calorimetry (DSC) etc. The NMR and FT-IR results confirmed the polymer structure, and the C-13 NMR spectra have clearly interpreted the sequence of epsilon-caprolactone and 5-(benzyloxycarbonylmethyl)-delta-valerolactone in the copolymer. When the benzyl-protecting groups were removed, the aliphatic polyesters bearing carboxylic groups were obtained. Moreover, the hydrophilicity of the polymer was improved. Thus, poly(epsilon-caprolactone-co-delta-valerolactone) might have great potential in biomedical fields.