Transesterification in Alcohol-Initiated ROPs of l - and meso -Lactide Catalyzed by Sn(II) and Sn(IV) Compounds at Low Temperatures

Syntheses of polylactides by means of tin catalysts

Reaction mechanisms and synthetic methods used for the preparation of homo- and copolylactides based on tin(ii) and tin(iv) catalysts are reviewed.

About the transformation of low T m into high T m poly(l-lactide)s by annealing under the influence of transesterification catalysts

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 (LT m) crystallites, having melting temperatures (T m) < 180 °C into high melting (HT 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 HT 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.

Reversible polycondensations outside the Jacobson–Stockmayer theory and a new concept of reversible polycondensations

Reversible polycondensations exist involving intermolecular transesterification in the absence of back-biting, which may be understood as part of a so-called ‘polycondensation triangle’ based on the definition of three polycondensation classes.

High molar mass cyclic poly(l-lactide) obtained by means of neat tin(ii) 2-ethylhexanoate

l-Lactide was polymerized in bulk at 120, 140, 160 and 180 °C with neat tin(ii) 2-ethylhexanoate (SnOct₂) as the catalyst and a cyclic topology was detected.

Stereocomplexation of cyclic polylactides with each other and with linear poly(l-lactide)s

This study describes for the first time syntheses and properties of stereocomplexes based on cyclic polylactides.