Polylactones, 47 A-B-A triblock copolyesters and random copolyesters of trimethylene carbonate and various lactones via macrocyclic polymerization

2,2-Dibutyl-2-stanna-1,3-dioxepane (DSDOP)-initiated copolymerizations of t rimethylene carbonate (TMC) with beta-D,L-butyrolactone (beta-D,L-BL), delt a-valerolactone (delta-VL), epsilon-caprolactone (epsilon-CL) or L-lactide (Lac) were performed in chlorobenzene at 80 degrees C. When equimolar mixtu res of TMC and a lactone were copolymerized, copolyesters having nearly ran dom sequences were obtained in the case of beta-D,L-BL, delta-VL and epsilo n-CL, whereas an almost perfect homopolymerization was observed for L-lacti de. Furthermore, a series of sequential copolymerizations was conducted so that the TMC was polymerized first. After removal of the Bu2Sn group with 1 ,2-dimercaptoethane, telechelic A-B-A triblock copolymers having free OH en dgroups were obtained from all four lactones. In another series of sequenti al copolymerizations, the lactones were used as the first monomer. Again a telechelic triblock copolyester was obtained with beta-D,L-BL, whereas copo lyesters with largely randomized sequences were isolated, when delta-VL or epsilon-CL were used as first monomer. With L-lactide as the first monomer an almost perfect homopoly(L-lactide) was obtained and most of the TMC rema ined unreacted, in close analogy to the attempted random copolymerizations.