Triple copolymers of methylacrylate, methylmethacrylate and acrylic acid were synthesized by copolymerization of monomers in isopropyl alcohol solution at 343 K in the presence of benzoyl peroxide initiator and 1 % dodecylmercaptane regulator. It was shown that the mixing of copolymer with caprylic acid proceeds with top critical temperature of solution which rises at polymer molecular weight growth. Homogeneous mixing of copolymer with monocarboxylic acids having great hydrocarbon radical was not observed over 238-443 K range.