Raman structural analysis of L-lactide/ε-caprolactone copolymers and poly(L-lactide)/poly(ε-caprolactone) blends

We present Raman study of the L-lactide/ε-caprolactone (PLCL) copolymers with the L-lactide (LLA) content from 10 to 90 mol %. The copolymers were synthesized by bulk ring-opening polymerization. As additional method, we used the wide-angle X-ray scattering analysis to obtain the crystallinity degree of the poly(L-lactide) (PLLA) and poly(ε-caprolactone) (PCL) blocks. We extend the previously proposed method of determination of the crystallinity degree of PLLA areas in the PLCL copolymers up to the ε-caprolactone (CL) content of 50 mol %. The method includes analysis of the ratio of the peak intensities of the PLLA bands at 411 and 874 cm^-1. We also suggest for the first time using the PCL bands at 958 and 1110 cm^-1 to evaluate the crystallinity degree of PCL blocks in the PLCL copolymers. Besides, we extend the previously proposed method of evaluation of the relative contents of the comonomers in the PLCL copolymers to the whole range of the CL content as well as to analysis of melt-mixed PLLA/PCL blend. The method is based on the measurement of the ratio of the peak intensities of the PLLA band at 2947 cm^-1 and the PCL band at 2914 cm^-1.