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

• Published in: Macromolecules 2016-01, Vol.49 (2), p.554-563
• Main Authors: Hoff, Emily A, Abel, Brooks A, Tretbar, Chase A, McCormick, Charles L, Patton, Derek L
• Format: Article
• Language: English
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/acs.macromol.5b02377

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.