About the Influence of (Non‐)Solvents on the Ring Expansion Polymerization of l‐Lactide and the Formation of Extended Ring Crystals. Issue 5 (7th December 2022)

• Record Type: Journal Article
• Authors: Kricheldorf, Hans R.; Weidner, Steffen M.; Meyer, Andreas
• Is Part Of: Macromolecular chemistry and physics. Volume 224:Issue 5(2023)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-12-07
• Subjects: crystallization -- cyclization -- poly(l‐lactide) -- ring‐expansion polymerization; Polymers -- Periodicals; Polymerization -- Periodicals; Synthetic products -- Periodicals; Macromolecules -- Periodicals; 547.7
• DOI: 10.1002/macp.202200385
• Languages: English
• ISSNs: 1022-1352

Abstract

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 (Δ H m 's up to 106 J g −1) ) are found confirming that Δ H m max, the Δ H m of a perfect crystal, is around or above 115 J g − 1 in contrast to literature data. Abstract : Addition of small amounts of suitable (non‐)solvents favors ring‐expansion polymerization of l ‐lactide, so that extremely high molecular weights, melting temperatures, and melting enthalpies can be achieved. The influence of chain‐folding on the thermodynamic optimization of crystalline cyclic poly(l ‐lactide)s is discussed.