Ring-expansion polymerization of meso-lactide catalyzed by dibutyltin derivatives

Meso-Lactide was polymerized in bulk at 60, 80, and 100 degrees C by means of three different types of catalysts: dibutyltin sulfides (2,2-dibutyl-2-stanna-1,3-dithiolane and 2,2-dibutyl-2-stanna-1,3-dithiane), dibutyltin derivatives of substituted catechols (BuCa, CyCa, and BzCa), and dibutyltin derivatives of 2,2dihydroxybiphenyl (SnBi) and 2,2-dihydroxy-1,1-binaphthyl (SnNa). Only the latter two catalysts were active at 60 degrees C. The architecture of the resulting polylactides depends very much on the structure of the catalyst and on the temperature. At the lowest temperature (60 degrees C), SnBi and SnNa mainly yielded even-numbered linear chains, but SnNa also yielded even-numbered cycles at 100 degrees C and short reaction times. In contrast, BuCa, CyCa, and BzCa mainly yielded odd-numbered cycles, although the same catalysts yielded even-numbered linear chains when benzylalcohol was added. (c) 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 749-759