Vitrimers constitute a fascinating class of polymer materials which make the link between the historically opposed 3D networks (thermosets) and linear polymers (thermoplastics). Their chemical resistance, reshaping ability and unique rheological behavior upon heating make them promising for future applications in industry. However many vitrimers require the use of high catalyst loadings, which raises concerns for their durability, and limits their potential applications. To cope with this issue, internal catalysis and neighboring group participation (NGP) can be used to enhance the reshaping ability of such materials. A few studies report the effect of activating groups on the exchange reactions in vitrimers. Nevertheless, knowledge on this topic remains scarce, although research on vitrimers would greatly benefit from NGP already known in organic chemistry. The present perspective article presents the different types of exchangeable bonds implemented in vitrimers and discusses chemical groups known to have or potentially capable of an enhancing effect on exchange reactions. This analysis is underpinned by a thorough mechanistic discussion of the various exchangeable bonds presented.

Vitrimers are polymer networks in which associative exchange reactions can take place under specific conditions, thus conferring reprocessability to the insoluble materials. Recently, catalyst-free vitrimers have emerged as a new generation of vitrimers able to overcome potential leaching, ageing and sintering issues of catalysts and to ensure the preservation of the vitrimer properties after numerous reshaping processes. Here, a catalyst-free epoxy vitrimer featuring α-CF3-substituted ester functions is reported. First, a new tetra-acid precursor was synthesized via a catalyst-free thia-Michael addition. A catalyst-free ring-opening polymerization was then performed on two different di-epoxy monomers (DGEBA and BDGE) to obtain polymer networks composed of ester linkages. Curing was evaluated by rheology, DSC and FTIR monitoring of the polymerization kinetics. A gel content of over 70 % was measured after 24 h in THF. Finally, the accelerating effect of the α-CF3 group on the transesterification reactions was highlighted by stress relaxation experiments and analyzed computationally on a molecular model system. Reprocessability tests were carried out at 150 °C for 2 h. The mechanical and thermal properties of the reshaped materials were similar to those of the initial ones. This study demonstrates the potential of fluorinated groups as powerful internal activators for transesterification vitrimers.