Transamidation vitrimers enabled by neighbouring fluorine atom activation

Abstract

The activation of associative transamidation via neighbouring fluorine atom activation has been unveiled, quantified and applied to the construction of catalyst-free polyamide vitrimers. The inherent thermal and chemical stability of the amide functionality usually renders this linkage unsuitable for chemical exchange. The present study demonstrated that the positioning of a CF₂ group α to the amide group strongly activates this functionality, effectively turning on the dynamic transamidation. This effect was initially studied through combined DFT and kinetic investigations on the transamidation of small model molecules, prior to its application to polyamide networks. A range of fluorinated transamidation vitrimers were easily and rapidly synthesized by the reaction of α,α-difluoroesters with amines. Different amide/free amine ratios were employed, leading to materials that feature a range of relaxation and mechanical properties. Hence, flow activation energies ranging from 88.5 to 126 kJ mol⁻¹ were obtained, allowing the facile modulation of the vitrimers’ dynamic properties. Recycling tests of these additive-free transamidation vitrimers were performed at temperatures ranging from 150 to 200 °C and the mechanical and thermal properties of the reshaped materials were compared to those of the initial ones. Thanks to this approach, transamidation vitrimers with tuneable reshaping temperature, Young's modulus and glass transition temperature have become accessible, paving the way for further applications of these materials.