Copolymers of omega-pentadecalactone and trimethylene carbonate from lipase catalysis: influence of microstructure on solid-state properties

Polycarbonate-polyesters were prepd. by Candida antarctica lipase B (Novozyme 435)-catalyzed ring-opening copolymn. of omega-pentadecanolactone (PDL) with trimethylene carbonate (TMC). Atypical solid-state properties were revealed by thermogravimetric anal., differential scanning calorimetry (DSC), and X-ray diffraction analyses. Thermal degrdn. of poly(PDL-TMC) occurs in two steps: the first well above the degrdn. range of poly(TMC) and the other at a temp. (430°C) comparable with that of poly(PDL) decompn. Thermal stability of the copolymers increases with randomization of comonomer distribution. All poly(PDL-TMC) investigated are highly cryst., even those with equimolar comonomer content and close-to-random distribution. This result indicates that PDL and TMC units cocrystallize. The copolymers show two melting processes: the higher one at about 90°C, i.e., close to poly(PDL) melting, and the other 30°C lower. The relative intensity of the two phenomena changes with copolymer microstructure. The X-ray diffraction patterns of poly(PDL-TMC) are practically identical to that of poly(PDL) in the range 10° < 2theta < 80°. Significant differences appear in the low-angle region below 2° = 10°, indicating in some copolymers the presence of crystals with higher periodicity than poly(PDL) along the chain direction. Comparison of DSC and X-ray results with copolymer microstructure shows that two crystal phases can develop in poly(PDL-TMC): poly(PDL) crystals and (whenever a significant amt. of heterodiads are present) another lower melting crystal phase, characterized by a larger fiber axis periodicity and possibly assocd. with crystn. of alternating PDL-TMC sequences.