Synthesis, mechanical and dielectric properties of poly(acrylate-co-isocyanide) vitrimers

The rampant production and persistence of plastics in the environment have underscored the urgent need for a paradigm shift towards developing and adopting new materials with their end-of-life design in mind. Vitrimers are a class of crosslinked polymers that exhibit recyclable characteristics as sustainable alternatives to thermosets due to their dynamic bonds. Here, we develop multifunctional isocyanides as readily accessible cross-linking monomers capable of directly integrating a dynamic covalent network into polyacrylate backbones. These cross-linkers offer a simple, cost-effective approach to producing vitrimers via photo copolymerization. The resulting material exhibits high cross-linking density along with reprocessability. Dynamic mechanical analysis (DMA) and broadband dielectric spectroscopy (BDS) were conducted to investigate the bond exchange kinetics and segmental dynamics of the network. Compared to non-dynamically crosslinked PMA, the introduction of dynamic bonds shows faster segmental dynamics, i.e. dynamic Tg, by BDS analysis, which accelerates further with increasing cross-linking density. Our investigation shows both bond exchange and plasticization contribute to the reduction of Tg. Additionally, the bond exchange relaxation exhibited a dual Arrhenius-like behavior, which was attributed to the rapid incorporation of free amines as the temperature increased. Finally, the high dipole moment of the dynamic bond led to the higher permittivity of the vitrimers compared to non-dynamically cross-linked PMA, demonstrating the potential of these polymers as dielectric materials.