Thermal hysteresis of aggregation states of thermoresponsive block copolymers forming intermolecular hydrogen bonds

The aggregation behaviors of a diblock copolymer and a triblock copolymer of poly(2-ethyl-2-oxazoline) (PEOX) and polyethylene oxide (PEO) in aqueous solutions were investigated mainly by static and dynamic light scattering and infrared spectroscopy. PEOX is a thermoresponsive polymer that is soluble in water at room temperature, but insoluble above 60 °C, and it forms aggregates with poly(methacrylic acid) (PMAA) by using intermolecular hydrogen bonds. The structures of the aggregates of PEOX, which were formed due to the thermoresponsive interactions and intermolecular hydrogen bonds were estimated by measuring the aqueous solutions and precipitates formed by mixing solution of the block copolymers of PEOX and PEO and solution of PMAA at various mixing ratios and temperatures. The differences between the structure formed by mixing aqueous solution of the block copolymers of PEOX and PEO and that of PMAA mixed at 25 °C and measured at 65 °C and that formed in aqueous solutions mixed and measured at 65 °C were investigated to elucidate the influences of thermoresponsive interactions and intermolecular hydrogen bonds. There were no significant differences between the aggregates formed by the diblock copolymer and PMAA mixed at different temperatures, and the aggregates formed by the triblock copolymer and PMAA mixed at 65 °C had higher molar mass than that mixed at 25 °C. The aggregation behaviors of a diblock copolymer and a triblock copolymer of poly(2-ethyl-2-oxazoline) (PEOX) and polyethylene oxide (PEO) in aqueous solutions were investigated mainly by static and dynamic light scattering and infrared spectroscopy. PEOX is a thermoresponsive polymer that is soluble in water at room temperature, but insoluble above 60 °C, and it forms aggregates with poly(methacrylic acid) (PMAA) by using intermolecular hydrogen bonds.