Synthesis of poly(benzyl methacrylate) (PBzMA) by nitroxide-mediated polymerization with a small fraction of fluorescent, controlling comonomer, 9-(4-vinylbenzyl)-9H-carbazole (VBK, 2-11 mol % in the feed), was studied along with the resulting copolymers' LCST phase behavior in the ionic liquid (IL) 1-ethyl-3-methylimidazolium bis(trifluoromethane sulfone)imide. The effectiveness of VBK as a controlling comonomer was demonstrated by a dramatic decrease in the product of average propagation rate constant and average equilibrium constant, , compared to BzMA polymerizations with styrene as comonomer. Linear molecular weight increase with conversion (up to approximate to 40% conversion), with polydispersities of about 1.34-1.42, and successful chain extensions indicated the copolymerizations were relatively well controlled. The incorporation of fluorescent and solvatophobic VBK units in the BzMA/VBK copolymers not only affected transition temperature and reversibility of the LCST-type phase separation in the IL, but also led to about a fivefold phase separation-triggered fluorescent enhancements, likely due to enhanced fluorescence resonance energy transfer from BzMA to VBK being in close proximity during aggregation. (c) 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4702-4715