Random copolymers of 2-(2-methoxyethoxy)ethyl methacrylate (MEO₂MA) and oligo(ethylene glycol) methacrylate (OEGMA) have a temperature-induced phase transition in aqueous solutions, which can be tuned for different temperatures from ca. 20 °C to 90 °C, by changing their monomer ratio. Here, we explore a novel approach combining UV–Vis measurements (light scattering) with standard and modulated-temperature differential scanning calorimetry (DSC), to obtain the phase diagrams of copolymers with different compositions over an unprecedented wide concentration range (0.7–800 mg/mL). We used three copolymers synthesized by RAFT polymerization with very low size dispersity, and containing 6, 8 and 11 mol% of OEGMA. The change in their phase transition temperature with concentration show that they reach different lower critical solution temperature (LCST) in the concentration interval 20–30 mg/mL. Our results offer new insights on the influence of concentration, in particular for high concentrations, on the temperature, the reversibility and the kinetics of the phase transition. This information can be used to assist the design of copolymers with predetermined temperature response.