Crystallization and melting behavior of poly(ε-caprolactone-co--valerolactone) and poly(ε-caprolactone-co-L-lactide) copolymers with novel chain microstructures

Nuclear magnetic resonance spectroscopy (NMR) characterization of the statistical copolymers of this study showed that the poly(epsilon-caprolactone-co-L-lactide)s, with epsilon-caprolactone (epsilon-CL) molar contents ranging from 70 to 94% and epsilon-CL average sequence length (l(CL)) between 2.20-9.52, and the poly(epsilon-caprolactone-co--valerolactone)s, with 60 to 85% of epsilon-CL and l(CL) between 2.65-6.08, present semi-alternating (R2) and random (R approximate to 1) distribution of sequences, respectively. These syntheses were carried out with the aim of reducing the crystallinity of poly(epsilon-caprolactone) (PCL), needed to provide mechanical strength to the material but also responsible for its slow degradation rate. However, this was not achieved in the case of the epsilon-caprolactone-co--valerolactone (epsilon-CL-co--VAL). Non-isothermal cooling treatments at different rates and isothermal crystallizations (at 5, 10, 21 and 37 degrees C) were conducted by differential scanning calorimetry (DSC), and demonstrated that epsilon-CL copolymers containing -valerolactone (-VAL) exhibited a larger crystallization capability than those of L-lactide (L-LA) and also arranged into crystalline structures over shorter times. The crystallization enthalpies of the epsilon-CL-co--VAL copolymers during the cooling treatments and their heat of fusion (H-m) at the different isothermal temperatures were very large (i.e. H-c>53 Jg(-1)) and in some cases, unrelated to the copolymer composition. In some compositions, such as the 60 : 40, Wide Angle X-ray Scattering (WAXS) proved that that these two lactones undergo isomorphism and co-crystallize in a single cell. (c) 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42534.