Comparative studies of thermal and mechanical properties of macrocyclic versus linear polylactide

Poly(l-lactide): optimization of melting temperature and melting enthalpy and a comparison of linear and cyclic species

“…Model compounds are in fact not suited as models of high molar mass homo-PLLAs. A comparison of cyclic and linear PLLAs was also reported by Louisy et al 41 with higher T m and DH m values for the linear chains. However, those authors did prove that their cyclic PLLA mainly consists of cycles because a MALDI TOF mass spectrum up to a mass of m/z 2500 was presented as the only evidence for a cyclic topology.…”

Accelerating the crystallization kinetics of linear polylactides by adding cyclic poly ( -lactide): Nucleation, plasticization and topological effects

“…Polylactide (PLA) is considered a sustainable alternative to conventional polymers (i.e., petroleum-based polymers) in different fields because, in addition to being biodegradable, it is biobased (i.e., it is obtained from natural renewable sources, like sugar in corn starch and beets) and biocompatible [1]. PLA is commercially available in a wide range of grades [2], including grades for biomedical uses [3].…”

“…From the crystallization point of view, the comparisons of cyclic and linear polymers in the literature show different and sometimes even opposite trends [1,[25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44], hence, their crystallization is still a debated topic [22]. As an alternative for such debate, simulations studies have been performed, but even for them, contradicting results have also been found in their predictions of the relative melting and equilibrium melting temperatures of cyclic and linear polymers [45][46][47].…”

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

“…linear chains can adopt the same high melting morphology with T m values in the range of 193-196 C in contrast to reports of other research groups. 17,18,21 Yet another consequence of this nding concerns the calculation of the equilibrium T m0 of perfect crystals (215 C) as described by Kalb and Pennings. 19 The present and previous 20 experimental T m values suggest that the extrapolated 215 C are close to reality, whereas T m0 values below 205 C are certainly too low.…”

“… 20 Hence, it is probable, that the Pennings group observed cyclic poly( l -lactide) by microscope, and that their results were influenced by the presence of the catalyst. Finally, a recent study (2020) of Louisy et al should be mentioned, 21 which describes a comparison of cyclic and linear poly(L-lactides) having identical molar masses ( M w < 50 000 g mol −1 , respectively <30 000 g mol −1 with a correction for THF as SEC solvent). Lanthanum borohydride was used as catalyst, but despite its basicity no information about optical purity was given.…”