ROP of L‐lactide and ε‐caprolactone catalyzed by tin(ii) and tin(iv) acetates–switching from COOH terminated linear chains to cycles

Abstract

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 SnAc2 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. SnAc4 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: SnAc2 > SnAc4 > Bu2SnAc2 ~ Oct2SnAc2.

The role of transesterifications in reversible polycondensations and a reinvestigation of the Jacobson–Beckmann–Stockmayer experiments

“…The first critique of the JS theory was published by the first author in 2003 11 and 2014, 12 but did not suffice to rebut the widely accepted JS-theory. However, recently, the authors could demonstrate that reversible, like irreversible, polycondensations involve end-to-end (ete) cyclization, the existence of which was denied by J + S. 13,14 The existence of ete-cyclization has the consequence that all condensation products must be cycles regardless of the monomer structure and reaction conditions. Even more recently, the authors have found that reversible polycondensations exist, which proceed without the contribution of back-biting up to high conversions (98 ± 1%).…”

“…The experimental work presented by the authors was based on cyclic monomers and various tin catalysts. 13–15 However, the experimental work of Jacobson, Beckmann and Stockmayer (JBS) differs largely from that, because it is based on the polycondensations of 1,10-decanediol and adipic acid, and because toluene sulfonic acid (TSA) was used as the catalyst ((a) in Scheme 1). However, proton-catalyzed esterification and transesterification mechanisms (Scheme 1) and tin-carboxylate or phenoxide-catalyzed transesterification mechanisms (coordination–insertion mechanism) are quite different.…”

Effect of chain architecture and comonomer ratio on the biodegradability and thermal stability of biodegradable copolymers of l-lactide and δ-valerolactone

“…Kricheldorf and colleagues demonstrated that several tin catalysts could synthesize high molecular weight cyclic polymers within a short reaction time of less than 4 hours. 20–26 However, it should be noted that cyclic polymers obtained through REP typically exhibit a large polydisperse index compared to those obtained through LRC due to potential chain transfer reactions. 19…”

“…Until now, there have been limited studies on the physical properties such as molecular weight, intrinsic viscosity, and thermal properties 10,18–41 and hydrolytic degradation. 29,42 of cyclic polyesters.…”

Influence of polymerisation conditions on the kinetics of poly(lactic-co-glycolic acid)-b-poly(ethylene glycol)-b-poly(lactic-co-glycolic acid) triblock synthesis and the occurrence of transesterification side reactions

“…The synthesis of PEG-PLGA block copolymers via ROP, and more generally PLGA and polylactones, has been conducted thermally in the absence of catalysts 25,26 as well as using salt, 9,11,27,28 organometallic, 29 and organic catalysts. 23,30,31 While organocatalysts typically provide superior control over the polymerisation, generating polymers with expected molecular weights and narrow Đ values, 30,32 many display relatively high toxicities and may not be suitable for large or industrial scale production.…”