Effects of salts and copolymer composition on the lower critical solution temperature of poly(methyl 2-acetamidoacrylate-co-methyl methacrylate) solutions

Copolymerizations of methyl 2-acetamidoacrylate (MAA) with methyl methacrylate (MMA) were carried out at 60 °C in chloroform. Copolymers containing MAA units in the range of 83-90 mol % exhibited a lower critical solution temperature (LCST), although homopolymers of MAA and MMA did not. The LCST of polymer solutions decreased with (1) an increase in the concentration of the copolymer, (2) a decrease in the MAA content in the copolymer, and (3) an increase in the concentration of salts added. The effectiveness of anionic species for reducing the LCST is NO₃^- < Cl^- < SO₄^2- < SO₃^2-. Divalent anion is more effective for lowering the LCST than monovalent anion. However, there is no difference between cationic species in the salting-out effect. Sodium carbonate and sodium phosphate had a salting-in effect. Salting-out coefficients were evaluated from the relationship between the logarithm of solubility of the copolymers and the salt concentration. Salting-out coefficients of the copolymer depended not on the composition of the copolymers but on the salt added.