High Tm Poly(l‐lactide)s by Means of Bismuth Catalysts?. Issue 8 (7th March 2021)

• Record Type: Journal Article
• Authors: Kricheldorf, Hans R.; Meyer, Andreas; Weidner, Steffen M.
• Is Part Of: Macromolecular chemistry and physics. Volume 222:Issue 8(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-03-07
• Subjects: annealing -- crystallinity -- lactides -- ring‐opening polymerization -- transesterification; Polymers -- Periodicals; Polymerization -- Periodicals; Synthetic products -- Periodicals; Macromolecules -- Periodicals; 547.7
• DOI: 10.1002/macp.202100019
• Languages: English
• ISSNs: 1022-1352

Abstract

Abstract: One series of BiSub‐catalyzed ring‐opening polymerizations (ROPs) is performed at 160 °C for 3 days with addition of difunctional cocatalysts to find out, if poly(l ‐lactide) crystallizes directly from the reaction mixture. An analogous series is performed with monofunctional cocatalysts. High Tm crystallites (Tm > 190 °C) are obtained from all bifunctional cocatalysts, but not from all monofunctional ones. It is shown by means of SAXS measurements that the high Tm values are mainly a consequence of a transesterification–homogenization process across the lamellar surfaces resulting in thickness and smoothing of the surfaces. An unusual enthalpy‐driven modification of the molecular weight distribution is found for samples that have crystallized during the polymerization. A third series of ROPs is performed at 170 °C for 2 h followed by annealing at 120 °C (2 h) to induce crystallization. Complete transformation of the resulting low Tm crystallites (Tm < 180 °C) into the high Tm crystallites by annealing at 170 °C for 1 d is not achieved, despite variation of the cocatalyst. Abstract : Ring‐opening polymerization of l ‐lactide catalyzed by Bi‐subsalicylate and certain difunctional cocatalysts may yield poly(l ‐lactide)s having melting temperatures (Tm ) above 190 °C. Smoothing of the crystallite surface via transesterification is the key for success.