Aliphatic Polyester Carbonate Copolymers: Enzymatic Synthesis and Solid-State Characterization

Abstract

Candida antarctica Lipase B (CALB), immobilized on Lewatit (Novozym 435), was used as catalyst to prepare a series of poly(butylene carbonate-co-butylene succinate) [poly(BC-co-BS)] copolymers. The polymers were synthesized by copolymerizations of diethyl carbonate (DEC), 1,4-butanediol (BD), and diethyl succinate (DES) at 70-80 °C under 2.0 mmHg pressure. Poly(BC-co-BS) with Mw up to 21 000 and polydispersity between 1.6 and 1.9 were obtained. By changing the monomer feed ratio, proportions of carbonate-to-ester repeating units in polymers were varied from 18:82 to 86:14. For example, poly(BC-co-14 mol% BS) and poly(BC-co-82 mol% BS) were prepared by using DEC/DES/BD feed ratios of 1.6:0.2:1 and 0.4:0.8:1, respectively. NMR analysis shows that copolymer carbonate and ester repeat units are randomly distributed along polymer chains. TGA, DSC, and WAXS were used to investigate the thermal properties and crystal structures of these copolymers. The synthesized, random, poly(BC-co-BS) copolymers are more thermally stable than poly(butylene carbonate) (PBC, decomposition temperature 338 °C), but less stable than poly(butylene succinate) (PBS, decomposition temperature 391 °C). Depending on composition, poly(BC-co-BS) copolymers vary from semicrystalline to near completely amorphous. The semicrystalline copolymers show only one crystal phase (either of the PBC-type or the PBS-type), indicating the inability of either crystal lattice to host foreign comonomer units. At particular copolymer compositions (~70 mol% BC units), neither BC units nor BS units are able to organize into a crystal structure.