Fluorescent, Thermoresponsive Oligo(ethylene glycol) Methacrylate/9-(4-Vinylbenzyl)-9H-carbazole Copolymers Designed with Multiple LCSTs via Nitroxide Mediated Controlled Radical Polymerization

Abstract

9-(4-Vinylbenzyl)-9H-carbazole (VBK) was used as the “controlling” comonomer for nitroxide mediated polymerization with 10 mol % SG1 free nitroxide relative to BlocBuilder initiator at 80 °C of oligo(ethylene glycol) methyl ether methacrylate (8–9 ethylene glycol (EG) units) (OEGMA8–9), 2-(2-methoxyethoxy)ethyl methacrylate (MEO2MA) and for an OEGMA8–9/MEO2MA-mixed feed. The synthesis of MEO2MA/VBK and OEGMA8–9/VBK copolymers and MEO2MA/OEGMA8–9/VBK terpolymers exhibited linear increases in number-average molecular weight (M̅n) versus conversion X, up until X = 0.6, with final copolymers characterized by relatively narrow, monomodal molecular weight distributions (M̅w/M̅n < 1.4, in most cases). A series of MEO2MA/OEGMA8–9/VBK terpolymers were synthesized and by varying the OEGMA8–9:MEO2MA feed ratios, the terpolymers exhibited tunable lower critical solution temperatures in water (28 °C < LCSTs < 81 °C). MEO2MA/OEGMA8–9/VBK terpolymers were deemed sufficiently pseudo-“living” to reinitiate a second batch of MEO2MA/OEGMA8–9/VBK, with few apparent dead chains, as indicated by the monomodal shift in the GPC chromatograms. The resulting MEO2MA/OEGMA8–9/VBK block copolymers were designed so that each block exhibited a distinct LCST, which was confirmed by UV–vis and dynamic light scattering. In addition to controlling the terpolymerization, the VBK units imparted thermo-responsive fluorescence into the final copolymers.