Synthesis of low‐polydispersity poly(N‐ethylmethylacrylamide) by controlled radical polymerizations and their thermal phase transition behavior

Controlled radical polymerizations of N‐ethylmethylacrylamide (EMA) by atom transfer radical polymerization and reversible addition‐fragmentation chain transfer processes were investigated in detail for the first time, employing complementary characterization techniques including gel permeation chromatography, ¹H NMR spectroscopy, and matrix‐assisted laser desorption ionization time‐of‐flight mass spectrometry. In both cases, relatively good control of the polymerization of EMA was achieved, as revealed by the linear evolution of molecular weights with monomer conversions and the low polydispersity of poly(N‐ethylmethylacrylamide) (PEMA). The thermal phase transitions of well‐defined PEMA homopolymers with polydispersities less than 1.2 and degrees of polymerization up to 320 in aqueous solution were determined by temperature‐dependent turbidity measurements. The obtained cloud points (CPs) vary in the range of 58–68 °C, exhibiting inverse molecular weight and polymer concentration dependences. Moreover, the presence of a carboxyl group instead of an alkyl one at the PEMA chain end can elevate its CP by ～3–4 °C. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 60–69, 2008