Solvent-Free and Catalyst-Free Synthesis of Cross-Linkable Polyfumaramides via Topochemical Azide-Alkyne Cycloaddition Polymerization

Unsaturated polymers are important materials having a lot of applications. Among polymers, polyamides possess a prime position due to their thermal and chemical stability. Herein, we report a simple, greener, catalyst-free, and solid-state synthesis of two unsaturated polyamides via a topochemical azide-alkyne cycloaddition reaction. Two designed fumaramide monomers M1 and M2, functionalized with complementary azide and alkyne reactive motifs at the termini, reacted upon heating their crystalline powders and resulted in the formation of triazolyl-linked unsaturated polyfumaramides P1 and P2, respectively. We have characterized the reaction using various time-dependent techniques such as NMR, FTIR, PXRD, and DSC measurements. Interestingly, the monomer M1 resulted in 1,5-disubstituted triazole-linked unsaturated polyfumaramide (P1), whereas the monomer M2 polymerized into a polyfumaramide having both 1,4-disubstituted and 1,5-disubstituted triazole linkages (P2). Also, the trans-olefinic bond of both the fumaramide monomers was unaffected in the polymerization process and hence yielded unsaturated polymers having trans-olefin units in the repeating unit. Demonstrating the scope of postsynthetic modification, we have shown that unsaturation can be exploited for cross-linking via a light-induced [2 + 2] cycloaddition reaction. This first report on the solid-state synthesis of unsaturated polyfumaramides will be of great interest.

Automated summary

This study presents a simple, greener, and catalyst-free solid-state synthesis of unsaturated polyamides via a topochemical azide-alkyne cycloaddition reaction. Characterization of the reaction using various time-dependent techniques was conducted, showing the successful formation of unsaturated polyfumaramides. The study demonstrates the potential for post-synthetic modifications, such as cross-linking via light-induced cycloaddition reactions, utilizing the unsaturation present in the polymer structures.