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Parameters characterizing the interaction of nonidentical polymer molecules in dilute solutions of mixtures of two polymers have been defined on the basis of Stockmayer's theory of light scattering in multicomponent systems. Various procedures for evaluation of the interaction parameters from experimental data have been compared. Specific features of the investigation of such interactions are demonstrated with the scattering behavior of the system polystyrene-poly-(methyl methacrylate)-dioxane.

Sometimes, it is desirable in light scattering measurements on copolymers (or polymer mixtures) that the solvent has definite refractive and thermodynamic properties. Such solvents can, e.g., mask optically one copolymer component and be theta solvents for the polymer system studied. This enables the other copolymer component to be measured directly by light scattering. These solvent systems have to be generally ternary mixtures. Some optical and thermodynamic properties of mixed solvents are discussed. The application of ternary solvent systems is illustrated by measurements of butadiene/styrene block copolymers ((poly)butadiene-b-styrenes)) in acetophenone/cyclohexane/ethanol mixtures. The experimental limitations of this approach are demonstrated on the example of poly(styrene-co-methyl methacrylate). Bei Streulichtmessungen an Copolymerisaten (oder Polymergemischen) ist es manchmal erwunscht, das das Losungsmittel einen bestimmten Brechungsindex und vorgegebene thermodynamische Eigenschaften aufweist. Solche Losungsmittel konnen z. B. eine Copolymerisatkomponente optisch maskieren und fur das untersuchte Polymersystem ein Theta-Losungsmittel darstellen. Dies ermoglicht, die andere Copolymerisationskomponente mittels der Lichtstreuung direkt zu messen. Solche Losungsmittelsysteme mussen im allgemeinen ternare Gemische sein. Einige optische und thermodynamische Eigenschaften der Losungsmittelgemische werden diskutiert. Die Anwendung der ternaren Losungsmittelsysteme wird durch Messungen an Losungen von Butadien/Styrol-Block-copolymeren (Poly(butadien-b-styrol) in Acetophenon/Cyclohexan/Athanol-Gemischen illustriert. Die experimentellen Einschrankungen dieser Methode werden am Beispiel des Poly(styrol-co-methylmethacrylats) demonstriert.

Conditions have been established suitable for the determination of the molecular characteristics and the parameters of composition heterogeneity for copolymers by the light scattering method in dilute solutions. These conditions are easiest to realize by using mixed solvents. A relationship has been derived describing the intensity of light scattered from the solution of a chemically heterogeneous copolymer in a mixed solvent. The method can also be applied to copolymers of components having equal refractive indices; it has been checked on mixtures of polyethyleneglycol methacrylate, polymethyl methacrylate and their copolymers in the system methylcellosolve-α-bromonaphthalene. Experimental results were in good agreement with the calculated values.

The refractive index increments of polybutadiene in cyclohexane have been found to be a linearly decreasing function of the content of 1.2-units in the polymer. The extrapolated values at 25°C for a pure 1.4- and pure 1.2-polymer respectively are (in ml/g) : 0.121 and 0.092 (4360 A); 0.113 and 0.087 (5461 A). Die Brechungsinkremente des Polybutadiens in Cyclohexan sind eine linear abnehmende Funktion des Gehalts an 1,2-Einheiten im Polymeren. Die extrapolierten Werte bei 25°C fur das reine 1,4- bzw. 1,2-Polymere betragen (in ml/g): 0,121 bzw. 0,092 (4360 A) oder 0,113 bzw. 0,087 (5461 A).

Tetrahydrofuran (THF) with 8–9 vol.-% of water (depending on the polymer tacticity) is at 25°C a Θ-solvent for poly(vinyl chloride). The refractive index increment (dn/dc)μ (i.e. measured after dialysis) for this system is 0.1085 and 0.112 ml/g for λ0 = 546 and 436 nm, respectively. The light scattering measurements yield correct molecular weights of the polymer. The measurements, however, require special care. Evaporation of THF and polymer aggregation in solvents with even slightly negative second virial coefficients are the major source of error.