A new family of high-molecular-weight poly(isosorbide carbonate-co-butylene terephthalate)s (PICBTs) partially based on renewable isosorbide (Is) were prepared by incorporating 1,4-butanediol (BD) and dimethyl terephthalate (DMT) into poly(isosorbide carbonate) (PIC), via a two-step bulk condensation polymerization. The incorporation of BD and DMT was developed to compensate for the low reactivity of Is and improve the molecular weight and processability of PIC, while retaining the rigidity and hence high glass transition temperature (Tg) of PIC. The resulting copolymers showed high number-average molecular weights ranging from 30600 to 52300 g mol−1 and tunable Tg values from 69 to 146 °C. The molecular structure of the novel poly(ester carbonate)s was confirmed using 1H, 13C, 2D-COSY and 2D-HSQC NMR techniques. 1H NMR analysis revealed the random sequence distributions of the PICBTs. A systematic study on the structure–property relationship revealed that the thermal, dynamic mechanical and mechanical properties of the PICBTs strongly depended on their composition, which would enable molecular design of material properties with the desired balance of material rigidity, ductility, and biobased content.

A designed synthetic strategy to overcome the low reactivity of isosorbide (Is) and terephthalic acid (TPA) is developed for the preparation of engineering polycondensates. This method contained substitution of unreactive end groups of Is and TPA by reacting with dimethyl carbonate and 1,2-alkanediol or 1,3-alkanediol respectively, followed by transesterification, cyclization of an alkylene carbonate unit, and polycondensation. Is and TPA were temporarily linked by an unstable alkylene carbonate unit and then underwent cyclization with the elimination of five- or six-membered cyclic carbonate at elevated temperature, leading to a family of poly(isosorbide carbonate-co-isosorbide terephthalate)s with high Tg (169–193 °C) and high number-average molecular weights (22700–28500 g mol−1). The molecular structure of the copolymer was confirmed using 1H, 13C and 2D NMR techniques. GC-MS, 1H NMR and 13C NMR were used to monitor the molecular structure evolution during the combinatorial polymerization process and a mechanism was proposed. Furthermore, the structure–thermal properties relationship study was also conducted on a range of relevant polyesters.

To improve the crystallization ability of poly(butylene carbonate) (PBC), a monomer with a linear long chain as a biobased derivative of castor oil was randomly introduced into the PBC main chain. A series of aliphatic copolycarbonates poly(butylene-co-decamethylene carbonate)s (PBDCs), with weight-average molecular weights of 125000 to 202000 g mol−1, were synthesized from dimethyl carbonate, 1,4-butanediol, and 1,10-decanediol via a two-step polycondensation process, using sodium acetylacetonate as the catalyst. The PBDCs, being statistically random copolymers, showed a single Tg over the entire composition range. The DSC results testified that the introduction of a decamethylene carbonate (DC) unit can significantly enhance the crystallization rate of PBC. The PBDC copolycarbonates had a minimum melting point in the plot of melting point versus composition. Wide-angle X-ray diffraction patterns showed that the copolycarbonates with up to 20 mol% DC units formed PBC type crystals, while those with higher DC unit content crystallized in poly(decamethylene carbonate) (PDC) type crystals. This indicates that the PBDC copolycarbonates show isodimorphic cocrystallization. The thermal stability, crystalline morphology, and enzymatic degradation of the PBDC copolycarbonates were also studied.

Thermal degradation behaviors of poly(hexamethylene carbonate) (PHC) were investigated by means of thermogravimetric analysis (TGA), proton nuclear magnetic resonance (1H NMR), gel permeation chromatography (GPC) and pyrolysis–gas chromatography/mass spectrometry (Py-GC/MS). Six types of PHC samples with different end groups and molecular weights were synthesized to systematically investigate the thermal degradation mechanism. Thermal degradation behaviors of the PHC samples were examined under both isothermal and non-isothermal conditions. The PHC samples showed distinct thermal degradation behaviors from other aliphatic polycarbonates (poly(propylene carbonate), poly(trimethylene carbonate) and poly(butylene carbonate)). The results indicated that the chain-end structure makes a slight effect on the thermal stability of PHC regardless of the molecular weight. During the non-isothermal degradation of PHC, four main reactions were illustrated: unzipping, intramolecular transesterification, β-H transfer and decarboxylation reactions. Intramolecular transesterification reaction dominantly occurs below 300 °C accompanying with unzipping reaction which can only be induced by hydroxyl end group, and releasing cyclic hexamethylene carbonate monomer and dimer. Above 300 °C, the four degradation reactions take place simultaneously.