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We rationally designed a monomer that when polymerized formed a well-defined nonionic polymer [poly(2-(methacryloyloxy) ethylureido glycinamide), PMEGA] by reversible addition fragmentation chain transfer with a flat and tunable upper critical solution temperature (UCST) in water. The monomer was made in one pot from commercially available compounds and with ease of purification. Strong hydrogen-bonding side groups on the polymer produced sharp coil-to-globule transitions upon cooling below its UCST. Ideal random copolymers produced with butyl methacrylate also showed flat UCST profiles, in which the UCST increased with a greater butyl methacrylate copolymer composition from 7 to 65 °C. In the presence of NaCl, the UCST decreased linearly with NaCl concentration due to the “salting-in” effect, and it was found that the slopes from the linear decrease of UCST were nearly identical for all …