RAFT Polymerization of "Splitters" and Cryptos": Exploiting Azole-N-Carboxamides As Blocked Isocyanates for Ambient Temperature Postpolymerization Modification
Polymers and High Performance Materials
A postpolymerization modification strategy based on ambient temperature nucleophilic chemical deblocking of polymer scaffolds bearing N-heterocycle-blocked isocyanate moieties is reported. Room temperature RAFT polymerization of three azole-N-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 (Đ < 1.2). Model analogues possessing the same N-heterocycle blocking agents with varied leaving group abilities were synthesized to determine optimal deblocking conditions. The reactivity of the azole-N-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.
Hoff, E. A.,
Abel, B. A.,
McCormick, C. L.,
Patton, D. L.
(2016). RAFT Polymerization of "Splitters" and Cryptos": Exploiting Azole-N-Carboxamides As Blocked Isocyanates for Ambient Temperature Postpolymerization Modification. Macromolecules, 49(2), 554-563.
Available at: https://aquila.usm.edu/fac_pubs/15186