About the Influence of (Non‐)Solvents on the Ring Expansion Polymerization of l‐Lactide and the Formation of Extended Ring Crystals

Abstract

Ring-expansion polymerizations (REPs) catalyzed by two cyclic tin catalysts (2-stanna-1.3-dioxa-4,5,6,7-dibenzazepine [SnBiph] and 2,2-dibutyl-2-stanna-1,3-dithiolane [DSTL]) are performed at 140 °C in bulk. Small amounts (4 vol%) of chlorobenzene or other solvents are added to facilitate transesterification reactions (ring-ring equilibration) in the solid poly(l-lactide)s. In the mass range up to m/z 13 000 crystalline PLAs displaying a so-called saw-tooth pattern in the MALDI-TOF mass spectra are obtained indicating the formation of extended-ring crystals. The characteristics of extended-ring crystallites and folded-ring crystallites are discussed. Furthermore, extremely high melting temperatures (T m 's up to 201.2 °C) and melting enthalpies (𝚫H m 's up to 106 J g −1) ) are found confirming that 𝚫H m max, the 𝚫H m of a perfect crystal, is around or above 115 J g −1 in contrast to literature data.

Syntheses of high molecular mass polyglycolides via ring‐opening polymerization with simultaneous polycondensation (ROPPOC) by means of tin and zinc catalysts

“…Yet, similarly high values were obtained in a recent study dealing with ring‐expansion polymerization of glycolide 33 . M n and M w data reported previously for polylactides prepared via ring‐expansion polymerization (REP) or with SnOct 2 and BuSnPhF were likewise high with M n 's up to 200,000 and M w 's up to 425,000 37,38 …”

“…33 M n and M w data reported previously for polylactides prepared via ring-expansion polymerization (REP) or with SnOct 2 and BuSnPhF were likewise high with M n 's up to 200,000 and M w 's up to 425,000. 37,38 From a review of this work and previous publications, the authors have learned that many polymer scientists expect the M n of cyclic polyesters to be parallel to the monomer/initiator ratio. This expectation is not justified for the following reasons.…”

Stereochemical Heterogeneity Analysis of Polylactides by Multidimensional Liquid Chromatography

“…19 Additionally, cyclic oligomers and polymers were achieved via ring expansion polymerization in a small amount of chlorobenzene using 2-stanna-1.3-dioxa-4,5,6,7-dibenzazepine [SnBiph] as a catalyst. 20 The applied characterization techniques provided average structural characteristics rather than their distributions. In order to evaluate both the SCC and compositional distribution of these complex polymers after synthesis, processing, and over time, efficient and accurate methods are of high relevance.…”

“…and observed ROP/reversible polycondensation reaction (ROPRPC), which formed predominantly cyclic PLAs (4d) . Additionally, cyclic oligomers and polymers were achieved via ring expansion polymerization in a small amount of chlorobenzene using 2-stanna-1.3-dioxa-4,5,6,7-dibenzazepine [SnBiph] as a catalyst …”

“…Aliphatic polyesters, such as poly­(lactic acid) (PLA), are continuously gaining interest in biomedical applications, thanks to their ability to degrade into nontoxic metabolites (CO 2 and H 2 O). These classes of polymers are also gaining interest in academic and industrial research due to their eco-friendly properties, making them a potential replacement for traditional petroleum-based plastics used in applications such as packaging, medical implants, and drug delivery systems. − …”