Cyclodextrin-Complexed RAFT Agents for the Ambient Temperature Aqueous Living/Controlled Radical Polymerization of Acrylamido Monomers

Abstract

The first aqueous reversible addition–fragmentation transfer (RAFT) polymerization of N,N-dimethylacrylamide (DMAAm), N,N-diethylacrylamide (DEAAm), and N-isopropylacrylamide (NIPAAm) utilizing host/guest complexes of cyclodextrin and hydrophobic chain transfer agents (CTAs) at 25 °C is described. Three novel guest-functionalized CTAs, namely 4-(tert-butyl)phenyl 2-(((ethylthio)carbonothioyl)thio)-2-methylpropanoate, bis(4-tert-butyl)benzyl carbonotrithioate, and benzyl (3-((4-(tert-butyl)phenyl)amino)-3-oxopropyl)carbonotrithioate, were synthesized and employed in aqueous RAFT polymerizations. The presented technique allows for the facile preparation of hydrophilic polymers with hydrophobic end groups in aqueous environments. The living/controlled radical polymerization afforded high molecular masses (7500 ≤ Mn ≤ 116 000 g mol–1 for poly(DMAAm), 2500 ≤ Mn ≤ 150 000 g mol–1 for poly(DEAAm), and 4000 ≤ Mn ≤ 50 000 g mol–1 for poly(NIPAAm)) with low PDIs (1.06 ≤ PDI ≤ 1.54 for poly(DMAAm), 1.05 ≤ PDI ≤ 1.39 for poly(DEAAm), and 1.15 ≤ PDI ≤ 1.46 for poly(NIPAAm)). To confirm the living character of the polymerizations, kinetic measurements were undertaken that evidence a linear evolution of molecular weight with conversion. Furthermore, chain extensions were carried out that indicate a very high reinitiation efficiency (poly(DMAAm): from 10 500 to 97 500 g mol–1, PDI = 1.08; poly(DEAAm): from 8500 to 83 000 g mol–1, PDI = 1.13; poly(NIPAAm): from 9000 to 90 000 g mol–1, PDI = 1.11). The resulting polymers were thoroughly characterized via N,N-dimethylacetamide (DMAc) size exclusion chromatography, 1H NMR, and electrospray ionization-mass spectrometry (ESI-MS).