Preparation of high-molecular-weight poly(1,4-butylene carbonate-co-terephthalate) and its thermal properties

Condensation copolymerizations of 1,4-butanediol (BD), dimethyl carbonate (DMC), and dimethyl terephthalate (DMT) were conducted by a two-step procedure using sodium alkoxide (0.1–0.2 mol%) as a catalyst with a variable [DMT]/[BD] feed ratio. In the first step, oligomers bearing almost equal numbers of hydroxyl and methoxycarbonyl end-groups were generated, which were polycondensed mostly by the elimination of methanol at 190–210 °C under reduced pressure. By this procedure, high-molecular-weight poly(1,4-butylene carbonate-co-terephthalate)s (PBCTs) were easily prepared with Mw 60 000–200 000 in a reasonably short reaction time (∼8.5 h) and even on a large scale (110 g polymer per batch) in a 250 mL glass reactor. The PBCTs prepared at a high [DMT]/[BD] feed ratio 0.30–0.50 were semi-crystalline polymers with fast crystallization rates and melting temperatures in the range 95–146 °C, which were adjustable by the [DMT]/[BD] feed ratio. The glass transition temperatures were rather high around 0 °C. These thermal properties were comparable to those of commercialized compostable polyesters such as PLA, PHA, PBAT, and PBSA.