Random copolymerization with a large lactone enhances aliphatic polycarbonate crystallinity

Poly(carbonate-co-esters), were enzymatically synthesized (Novozyme-435) via polycondensation of diethylene carbonate, 1,4-butanediol and ω-pentadecalactone. Random poly(ω-pentadecalactone-co-butylene-co-carbonate) copolymers (PPBC) were obtained over a wide composition range (PDL content 10–75 mol%). Notwithstanding the high degree of compositional and microstructural disorder of the macromolecules, that are composed of randomly distributed ω-hydroxy acid (AB), carbonate (A2), and diol (B2) units, all (AB + A2 + B2) copolymers crystallize (crystallinity degree 30–66% by WAXS). When PDL content is ⩾20 mol%, PPBCs crystallize in the PPDL lattice. The copolymer with 10 mol% PDL shows a more complex crystallization pattern, that was investigated by combined DSC and T-controlled WAXS measurements. This copolymer develops three different types of crystals: two of them with lattice parameters matching those of PPDL and PBC homopolymers, the third one not being earlier reported in the literature. In this copolymer such new phase persists above melting of PPDL crystals, but it disappears before melting of PBC crystals. The new phase is attributed to a yet unknown metastable polymorph of PBC.