Résumé
The activation of associative transamidation via neighboring fluorine atom activation has been unveiled, quantified and applied for the construction of catalyst-free polyamide vitrimers. The inherent thermal and chemical stability of the amide functionality usually renders this linkage not suited 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 polyamides networks. A range of fluorinated transamidation vitrimers were easily and rapidly synthesized by 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 going from 88.5 to 126 kJ.mol-1 were obtained, allowing to easily modulate the vitrimer 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 modulus and glass transition temperature have become accessible, paving the way to further applications of these materials.