About the Phase Transitions in Aqueous Solutions of Thermoresponsive Copolymers and Hydrogels Based on 2-(2-methoxyethoxy)ethyl Methacrylate and Oligo(ethylene glycol) Methacrylate

The phase transitions in water of well-defined copolymers of 2-(2-methoxyethoxy)ethyl methacrylate (MEO 2 MA) and oligo(ethylene glycol) methacrylate (OEGMA, M n = 475 g mol -1 ) were studied by means of 1 H NMR, dynamic light scattering (DLS) and turbidimetry. These copolymers were synthesized by atom transfer radical polymerization (ATRP) in order to obtain macromolecules with a homogeneous chain-to-chain comonomer composition and therefore with a narrow phase transition. As previously reported, copolymers containing 10 mol % of OEGMA per chain ( M n = 20 100 g mol -1; M w / M n = 1.35) exhibited a sharp LCST in water around 40 °C, whereas copolymers having 20 mol % of OEGMA per chain ( M n = 19 500 g mol -1; M w / M n = 1.32) precipitated slightly above 50 °C. DLS indicated that these phase transitions are most likely due to a reversible coil-to-globule transition. Moreover covalently cross-linked networks of MEO 2 MA and OEGMA were synthesized by ATRP in the presence of the cross-linker ethylene glycol dimethacrylate. These hydrogels were thermoresponsive and exhibited LCST values comparable to those measured for their single-chains analogues (e.g., hydrogels containing 20 mol % of OEGMA within the network underwent phase transitions at approximately 51−53 °C).