Conformational influence of fluorinated building blocks on the physical properties of polyesters

© 2019 Elsevier Ltd The interplay of the relative configuration of diastereomeric vicinal difluoride groups on the conformational properties of polyesters has been investigated and compared to their non-fluorinated and per-fluorinated counterparts. The incorporation of syn and meso vicinal difluoride units in the polymer backbone was expected to influence the rigidity and stacking behaviour of the polymers in a significant way, and therefore to result in different thermal properties, such as melting point and melting enthalpy. Both syn and meso-2,3-difluoro butanediol have been reacted with the diester dimethyl succinate, leading to the formation of polyesters that have been characterized with 1 H, 13 C and 19 F NMR. The polyesters showed molar masses up to 20 kg/mol (SEC). Surprisingly, the syn and meso-polymers displayed identical crystallization and melting behaviour. In contrast, differences were observed in the crystallization kinetics and melting points of syn and meso oligomers. Relying on time-resolved synchrotron SAXS and WAXD experiments, the complex multiple melting behaviour of these oligomers was explained in terms of crystal size and surface effects. The slower crystallization kinetics for the meso oligomers was tentatively associated with a stronger tendency to adopt gauche configurations. Apparently, such effects no longer affect the crystallization kinetics when larger polymers crystallize. It was also found that the syn and meso-polymers have identical equilibrium melting points and melting enthalpies notwithstanding molecular and crystallographic differences.

Publication year:2019

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Authors:International

Authors from:Higher Education

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