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

Abstract

Meso‐Lactide was polymerized in bulk at 60, 80, and 100 °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 2,2′dihydroxybiphenyl (SnBi) and 2,2′‐dihydroxy‐1,1′‐binaphthyl (SnNa). Only the latter two catalysts were active at 60 °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 °C), SnBi and SnNa mainly yielded even‐numbered linear chains, but SnNa also yielded even‐numbered cycles at 100 °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. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 749–759

Transesterification in Alcohol‐Initiated ROPs of l‐ and meso‐Lactide Catalyzed by Sn(II) and Sn(IV) Compounds at Low Temperatures

“…SnOct 2 was purchased from Aldrich Co. (Steinheim, Germany) and used as received in the form of a 1 m solution in dry toluene. Syntheses and characterization of several dibutyl tin catalysts used in this work were reported previously . The syntheses of those catalysts not reported before are described below.…”

“…Syntheses and characterization of several dibutyl tin catalysts used in this work were reported previously. [14][15][16][17] The syntheses of those catalysts not reported before are described below. The starting materials dibutyltin oxide, di-octyltin oxide salicylic acid, 4-chloroacetylcatechol, and 4-cyanocatechol were purchased from Aldrich Co. (Steinheim, Germany).…”

“…Nonetheless, these findings support the conclusion that the cyclization tendency of poly(m-lactide) is higher than that of poly(l-lactide). This conclusion is supported by a previous study of SnNa-catalyzed REPs. [16] When meso-and l-lactide were polymerized for 2 h at 102 °C in bulk, l-lactide yielded a product with a strong predominance of even-numbered cycles, whereas the poly(m-lactide) prepared under identical conditions was fully equilibrated, meaning that a much larger fraction of odd-numbered cycles was formed by intracircular back-biting. Hence, it may be concluded that the nearly random stereo sequence of a poly(meso/rac.-lactide) entails conformations that favor formation of loops and cycles more than the isotactic stereo sequence of poly(l-lactide).…”

Spirocyclic bisphenoxides of Ge, Zr, and Sn as catalysts for ring‐expansion polymerizations of l‐ and meso‐lactide

“…Quite recently, the authors of this work have reported that the cyclic dibutyltin derivatives outlined in Scheme catalyze ring‐expansion polymerizations (REPs) at temperatures >100 °C . Since all active species exclusively involve covalent bonds and no ions, these REPs proceed without racemization even at 180 °C and weight‐average molecular weights in the range of 100,000–150,000 g mol −1 were obtained in numerous experiments.…”

About formation of cycles in Sn(II) octanoate‐catalyzed polymerizations of lactides

“…2), 19 and 2,2 0 -dihydroxybipheny and -binaphthyl. 20 As an example, the simplified mechanism of a ring-expansion SCHEME 1 Simplified mechanism of the alcohol-initiated and SnOct 2 -catalyzed ROP of lactide. Table 1.…”