There is growing interest in developing sustainable alternatives to traditional thermoset and thermoplastic materials. While the former are utilized for their chemical resistance and other properties, these properties also make them inherently difficult to recycle. In contrast, the latter are often easier to recycle but not chemically resistant. Vitrimers, a type of covalent adaptable network, have recently garnered significant attention in literature due to being both solvent resistant and recyclable, combining some of the most desirable properties of traditional thermoset and thermoplastic polymers. Dynamic covalent bonds in vitrimers undergo dynamic exchange reactions to enable reprocessing. In the last decade, a variety of exchange chemistries have been reported. Diketoenamine (DKE) vitrimer systems have arisen as one of the few exchange chemistries that do not require an externally added catalyst. However, there is limited knowledge regarding how the structures adjacent to dynamic moieties impact material properties. We recently demonstrated the preparation of DKE vitrimers through thiol-ene photopolymerization with varied network structures, and unlike the earliest reports of DKE vitrimers, the systems do not require a multi-functional amine monomer to facilitate cross-linking. With the widespread commercial availability of a variety of diamine monomers, the adjacent structure to dynamic moieties can be uniformly modified to study the impact on vitrimer properties. DKE monomers were synthesized by reacting commercially available diamines with an alkene-functionalized, β-triketone precursor at a 15% molar excess of amine functional groups. The DKE monomers were subsequently incorporated into polymer networks by cross-linking with a tetra-functional thiol monomer. The resulting networks were characterized by thermogravimetric analysis, differential scanning calorimetry, and dynamic mechanical analysis.

Diketoenamine vtrimers by thiol-ene photopolymerization: Impact of diamine structure

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