Polymer association. I. Osmotic pressure of solutions of mixed acidic and basic polymers

Methyl methacrylate was copolymerized with small amounts of methacrylic acid or dimethylaminoethyl methacrylate. The molecular weight of the basic copolymer calculated from osmotic pressure data in butanone and benzene gave consistent results. The molecular weight of the acidic copolymer was obtained from osmotic pressures of pyridine solutions, but in butanone and particularly in benzene strong molecular association was observed. Osmotic pressures of mixtures of the two copolymers in butanone at 30.2 and 50.1 and in benzene at 49.7°C. were determined. The reduced osmotic pressure plots were linear but indicated the persistence of molecular associations to the highest dilutions at which osmotic pressures could be measured. A thermodynamic analysis of the data showed that under certain conditions the activity of one or the other polymer component decreases with increasing concentration of the mixture.