Branched poly[1,4-butylene carbonate-co-terephthalate]s (PBCTs) have been synthesized by the addition of a small amount of trifunctional or tetrafunctional alcohol monomers [glycerol propoxylate (1) or pentaerythritol (2)] in the polycondensation of 1,4-butanediol, dimethyl carbonate, and dimethyl terephthalate and their thermal, mechanical and rheological properties have been investigated. The branched PBCT exhibited more pronounced toughness in tensile test while providing the advantage of processibility at high shear rates due to the pronounced shear thinning in melt. To avoid gel formation, the feed amount of 1 or 2 was carefully controlled at below 0.5 mol% for 1 and below 0.3 mol% for 2. When feed of 1 or 2 was used, a high-molecular-weight melt state (Mw ~180,000 g/mol) was reached in a total reaction time of 5.5?6.5 h with a yield higher than 90%. The generated PBCTs were a semicrystalline polymer (Tg ~5 °C and Tm ~120 °C) when the terephthalate content (F[TPA]) was 45?50 mol%. The crystallization rate increased with increasing F[TPA] and branch content (F[1 or 2]); PBCT composed of F[TPA] = 49 mol% and F[1] = 0.44 mol% was crystallized completely in a short time, ~3 min, at a crystallization temperature of 50 °C. The branched PBCT exhibited more pronounced toughness in tensile test while providing the advantage of processibility at high shear rates due to the pronounced shear thinning in melt. It was also found that the branched PBCTs were biodegradable by a buffer solution containing a lipase.
