RAFT Polymerization of “Splitters” and “Cryptos”: Exploiting Azole‑<i>N</i>‑carboxamides As Blocked Isocyanates for Ambient Temperature Postpolymerization Modification

A postpolymerization modification strategy based on ambient temperature nucleophilic chemical deblocking of polymer scaffolds bearing <i>N</i>-heterocycle-blocked isocyanate moieties is reported. Room temperature RAFT polymerization of three azole-<i>N</i>-carboxamide methacrylates, including 3,5-dimethylpyrazole, imidazole, and 1,2,4-triazole derivatives, afforded reactive polymer scaffolds with well-defined molecular weights and narrow dispersities (<i><i>Đ</i></i> < 1.2). Model analogues possessing the same <i>N</i>-heterocycle blocking agents with varied leaving group abilities were synthesized to determine optimal deblocking conditions. The reactivity of the azole-<i>N</i>-carboxamide moieties toward nucleophiles can be tuned simply by varying the structure of the azole blocking agents (reactivity order: pyrazole < imidazole < triazole). DBU-catalyzed reactions of thiols with imidazole- and 1,2,4-triazole-blocked isocyanate scaffolds were shown to occur rapidly and quantitatively under ambient conditions. Differences in reactivity of 1,2,4-triazole- and 3,5-dimethylpyrazole-blocked isocyanate copolymers with various nucleophiles at room temperature facilitated sequential and postpolymerization modification. This strategy advances the utility of blocked isocyanates and promotes the chemistry as a powerful postmodification tool to access multifunctional polymeric materials