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 6-valerolactone derivative, 5-（benzyloxy carbonylmethyl）-δ-valerolaetone （BVL） by the Baeyer-Villiger oxidation. Secondly, the ring-opening polymerization of BVL with ε-caprolactone was carried out in bulk using stannous octoate as the catalyst to produce poly（ε-caprolactone-co-δ-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 H2 using Pd/C as the catalyst to obtain poly（ε-caprolactone-co-δ-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 13C NMR spectra have clearly interpreted the sequence of ε-caprolactone and 5-（benzyloxycarbonylmethyl）-δ-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（ε-caprolactone-co-δ-valerolactone） might have great potential in biomedical fields.