Tunable Blocking Agents for Temperature-Controlled Triazolinedione-Based Cross-Linking Reactions

The remarkable reactivity of triazolinediones (TADs) toward olefin-type substrates marks them as highly attractive click reagents, in particular for polymer modification and cross-linking. Critically, their ultrafast reaction rates result in handling issues and a rather limited shelf life whereas a particular concern for polymer material applications is homogeneous network formation. Herein, we introduce 2-phenylindoles as highly promising blocking agents for TADs, giving bench-stable reagents at ambient temperature from which the initial TADs can be released upon heating. A set of 11 indoles with varying substitution patterns was synthesized, leading to a precise control for the temperature of deblocking within a broad range of 35–100 °C. The established indole–TAD platform was next applied to bivalent TAD reagents to enable on-demand TAD-based cross-linking reactions of a diene-containing polyurethane (Mn = 12.5 kDa). Fine-tuning of the curing temperatures, down to 50 °C, was evidenced via rheological measurements.