Issue 2, 2024

Polycondensations and cyclization of poly(l-lactide) ethyl esters in the solid state

Abstract

The usefulness of seven different tin catalysts, bismuth subsalicylate and titan tetra(ethoxide) for the polycondensation of ethyl L-lactate (ELA) was examined at 150 °C for 6 d. Dibutyltin bis(phenoxides) proved to be particularly effective. Despite the low reactivity of ELA, weight average molecular masses (Mw) of up to 12 500 were found along with partial crystallization. Furthermore, polylactides (PLAs) of similar molecular masses were prepared via ELA-initiated ROPs of L-lactide by means of the four most effective polycondensation catalysts. The crystalline linear PLAs were annealed at 140 or 160 °C in the presence of these catalysts. The results of the transesterification reactions in the solid PLAs were studied by means of matrix-assisted laser desorption/ionization (MALDI TOF) mass spectrometry, gel permeation chromatography (GPC), differential scanning calourimetry (DSC) and small-angle X-ray scattering (SAXS). The results indicate that polycondensation and formation of cycles proceed in the solid state via formation of loops on the surface of the crystallites. In summary, five different transesterification reactions are required to explain all results.

Graphical abstract: Polycondensations and cyclization of poly(l-lactide) ethyl esters in the solid state

Supplementary files

Article information

Article type
Paper
Submitted
06 Nov 2023
Accepted
24 Nov 2023
First published
27 Nov 2023
This article is Open Access
Creative Commons BY license

Polym. Chem., 2024,15, 71-82

Polycondensations and cyclization of poly(L-lactide) ethyl esters in the solid state

S. M. Weidner, A. Meyer, J. Falkenhagen and H. R. Kricheldorf, Polym. Chem., 2024, 15, 71 DOI: 10.1039/D3PY01232H

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