Ring‐Expansion Copolymerization of l‐Lactide and Glycolide

Abstract

1:1 Copolymerizations of glycolide (GL) and l‐lactide (LA) are performed in bulk at 100 C and at 160 C with four cyclic tin catalysts. The resulting copolyesters are characterized by size exclusion chromatography measurements, 1H and 13C NMR spectroscopy and by MALDI‐TOF mass spectrometry. At 160 °C and longer reaction time (22 h), nearly complete conversion of both monomers is achieved, and cyclic copolymers with nearly random sequences are formed. At shorter times (0.5–3.0 h, depending on catalyst) the conversion of LA is incomplete, and only cyclics having even numbers of lactyl units are obtained. At 100 C and 22 h again cycles mainly consisting of even numbered lactyl units are formed, but with even and odd numbers of glycolyl units. Copolymerization of lactide at 160 C with small amounts of GL show that formation of high Tm crystallites (Tm > 190 C) is hindered even when only >2% of GL is added. For polyglycolide containing a smaller amount of lactide complete solubility in hexafluoroisopropanol is only observed around and above 20 mol% of lactide.

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

“…Weidner et al reported similar behaviour for the preparation of cyclic PLGA via ring-expansion polymerisation using cyclic tin catalysts, whereby intracircular back-biting occurs predominately at the centre of the G dyads. 50…”

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][21][22][23][24][25][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, and hydrolytic degradation.…”

“…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.…”

Transformation of poly(l-lactide) crystals composed of linear chains into crystals composed of cycles

“…6 Second, the molecular mass can be controlled by the lactide/alcohol (LA/In) ratio, at least for LA/In ratios < 200/1. [8][9][10] Third, low dispersities (D < 1.3) can be achieved at polymerization temperatures around or below 120 °C, because in the case of primary alcohols the initiation step is faster than the propagation steps for steric and electronic reasons (Scheme 1). Fourth, the reactivity of the end group resulting from the incorporation of the initiator can be varied by the structure of the alcohol.…”