Zur phasentrennung von polymergemischen in lösung

Usually, mixtures of solutions of two different polymers in the same solvent are incompatible. This incompatibility leads to an intensive turbidity of the mixture and finally, to the formation of two phases. The turbidity disappears on dilution with the same solvent, because the polymers are compatible below a certain polymer concentration c_kr. In principle, the same effects occur also with mixtures of polymers in the solid state (polymer blends), but here the aggregation of the microphases is impossible due to the high viscosity. Up to now, there is little known about the composition of the two phases above c_kr. Therefore, we studied the distribution of two different polymersin solution regarding molecular weight and concentration into both phases. It was varied the polymer ratio, the molecular weight, the overall concentration and the nature of the solvent. Polystyrene and polyvinyl acetate were used as polymers because they can easily be separated from each other which is necessary when analysing the different phases; this analytical separation was carried out for each individual phase. The following results were obtained: Each phase contains both polymers; in addition there occurs a fractionation according to molecular weight during the phase separation for both polymers. The polymer distribution in the two phases regarding molecular weight, amount of polymer, and concentration depends not only upon initial concentration, molecular weight and weight ratio of the two polymers but also upon the different degree of solvation of the macromolecules in different solvents. When mixtures of solvents are used, an additional partially separation of the solvent into both layers takes place.