About the transformation of low Tm into high Tm poly(l-lactide)s by annealing under the influence of transesterification catalysts. Issue 5 (12th January 2021)

• Record Type: Journal Article
• Authors: Weidner, Steffen M.; Meyer, Andreas; Chatti, Saber; Kricheldorf, Hans R.
• Is Part Of: RSC advances. Volume 11:Issue 5(2021)
• Page Start: 2872
• Page End: 2883
• Publication Date: 2021-01-12
• Subjects: Chemistry -- Periodicals; 540.5
• DOI: 10.1039/d0ra10012a
• Languages: English
• ISSNs: 2046-2069

Abstract

Abstract : Cyclic polylactides were prepared in bulk at 170 °C, crystallized at 120 °C and then annealed at temperatures between 130 and 170 °C with variation of catalyst, catalyst concentration and annealing time. Abstract : Cyclic polylactides were prepared in bulk at 170 °C, crystallized at 120 °C and then annealed at temperatures between 130 and 170 °C with variation of catalyst, catalyst concentration and annealing time. The transformation of the initially formed low melting (L T m ) crystallites, having melting temperatures ( T m ) < 180 °C into high melting (H T m ) crystallites having T m values > 189 °C was monitored by means of DSC measurements and characterized in selected cases by SAXS measurements. It was confirmed that the formation of H T m crystallites involves a significant growth of the thickness of the lamellar crystallites along with smoothing of their surface. Annealing at 170 °C for 1 d or longer causes thermal degradation with lowering of the molecular weights, a gradual transition of cyclic into linear chains and a moderate decrease of lamellar thickness. An unexpected result revealed by MALDI TOF mass spectrometry is a partial reorganization of the molecular weight distribution driven by a gain of crystallization enthalpy.