ABSTRACT:Osmotic pressures for branched polymers in a good solvent were measured over a wide range of concentrations. Two types of branched polymers, star-shaped poly(oc-methylstyrene) s having three branches and comb-shaped polystyrenes having 15-16 branches, were studied. The data were analyzed using the scaling law. The difference in the reduced osmotic pressure between star-shaped polymers having three branches and the corresponding linear polymers results from the difference in radii of gyration. In branched polymers having many branches, there is a region from which the segments of other molecules are excluded as a result of high segment density.

Osmotic pressures of concentrated solutions of polystyrenes with different molecular weights in good solvents were determined by a vapor pressure method. The data obtained as well as the osmotic pressure data in the literature were analyzed based on the scaling theory and the theory of Flory and Huggins. It was shown that the crossover between semidilute and concentrated solutions takes place at a critical concentration C** (0.15-0.2 g/cm3), irrespective of molecular weight.

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