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ROP of L‐lactide and ε‐caprolactone catalyzed by tin( ii ) and tin( iv ) acetates–switching from COOH terminated linear chains to cycles
Author(s) -
Kricheldorf Hans R.,
Weidner Steffen M.
Publication year - 2021
Publication title -
journal of polymer science
Language(s) - English
Resource type - Journals
eISSN - 2642-4169
pISSN - 2642-4150
DOI - 10.1002/pol.20200866
Subject(s) - tin , chemistry , catalysis , lactide , monomer , caprolactone , polymer chemistry , nuclear chemistry , medicinal chemistry , polymerization , organic chemistry , polymer
The catalytic potential of tin(II)acetate, tin(IV)acetate, dibutyltin‐bis‐acetate and dioctyl tin‐bis‐acetate was compared based on polymerizations of L‐lactide conducted in bulk at 160 or 130°C. With SnAc 2 low‐Lac/Cat ratios (15/1–50/1) were studied and linear chains having one acetate and one carboxyl end group almost free of cyclics were obtained. Higher monomer/catalyst ratios and lower temperatures favored formation of cycles that reached weight average molecular weights (Mw's) between 100,000 and 2,500,000. SnAc 4 yielded mixtures of cycles and linear species under all reaction conditions. Dibutyltin‐ and dioctyl tin bis‐acetate yielded cyclic polylactides under most reaction conditions with Mw's in the range of 20,000–80,000. Ring‐opening polymerizations performed with ε‐caprolactone showed similar trends, but the formation of COOH‐terminated linear chains was significantly more favored compared to analogous experiments with lactide. The reactivity of the acetate catalysts decreased in the following order: SnAc 2 > SnAc 4 > Bu 2 SnAc 2 ~ Oct 2 SnAc 2 .