Thermosensitive properties of a novel poly(methyl 2-acetamidoacrylate-co-methyl acrylate)

Copolymerizations of methyl 2-acetamidoacrylate (MAA) with methyl acrylate (MA) were carried out at 60 °C in chloroform. MAA-rich copolymers are soluble in water and MAA-poor copolymers insoluble. Among water-soluble copolymers obtained, only one (HP-77) which contains 77% of MAA units was thermosensitive. Thermal properties of HP-77 were investigated in the presence or absence of inorganic salts. The cloud point of aqueous HP-77 solution depended on polymer concentration: The cloud point decreased exponentially with an increasing concentration of the polymer. The cloud point of HP-77 was also affected significantly by the type and concentration of salts. The effectiveness of salts to reduce the cloud point is NaBr≈KBr<NaCl≈KCl<Na₂SO₄. The salting-out coefficients were evaluated as 2.45 l/mol for sodium chloride and 14.56 l/mol for sodium sulfate, respectively, from the relationship (Setschenow's equation) between logarithm of the solubility of HP-77 and salt concentration. The salting-out coefficient of sodium sulfate is larger than that of sodium chloride.