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

ABSTRACT Nuclear magnetic resonance spectroscopy (NMR) characterization of the statistical copolymers of this study showed that the poly(ε‐caprolactone‐co‐L‐lactide)s, with ε‐caprolactone (ε‐CL) molar contents ranging from 70 to 94% and ε‐CL average sequence length (lCL) between 2.20–9.52, and the poly(ε‐caprolactone‐co‐δ‐valerolactone)s, with 60 to 85% of ε‐CL and lCL between 2.65–6.08, present semi‐alternating (R→2) and random (R∼1) distribution of sequences, respectively. These syntheses were carried out with the aim of reducing the crystallinity of poly(ε‐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 ε‐caprolactone‐co‐δ‐valerolactone (ε‐CL‐co‐δ‐VAL). Non‐isothermal cooling treatments at different rates and isothermal crystallizations (at 5, 10, 21 and 37°C) were conducted by differential scanning calorimetry (DSC), and demonstrated that ε‐CL copolymers containing δ‐valerolactone (δ‐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 ε‐CL‐co‐δ‐VAL copolymers during the cooling treatments and their heat of fusion (ΔHm) at the different isothermal temperatures were very large (i.e. ΔHc > 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. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42534.