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Interaction between non-identical polymer molecules in a dilute solution of a mixture of two polymers is quantitatively characterized by the interaction parameter A 24 , which is the second virial coefficient for interaction of unlike species. The value of A 24 may be experimentally obtained by light scattering. The determination of A 24 is very sensitive to experimental error in the input data, particularly for mixtures in which one polymer is greatly in excess, and for mixtures of polymers having molecular weights differing by orders of magnitude. A slight rise in A 24 with temperature has been observed for solutions of mixtures of polystyrene and poly(methyl methacrylate) in diethyl malonate in the range 25–100 C. This change in A 24 reflects the increased mutual miscibility of the polymers in solution at elevated temperatures.

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.

Interaction of nonidentical polymer molecules in a dilute solution of a mixture of two polymers is quantitatively characterized by A24, the second virial coefficient for interaction of unlike species. This parameter is related to the compatibility of the two polymers in solution and is obtainable experimentally, e.g., by light scattering. With chemically markedly different polymers, A24 depends neither on the molecular weight of the polymers nor on the solvent and becomes characteristic of the polymer pair. For a mixture of two copolymers or of a homopolymer and a copolymer with similar compositions, A24 depends both on the solvent and on the molecular weight of polymers. Under such circumstances A24 ceases to be a quantity given only by the chemical structure of the two polymers; however, under suitable conditions it remains a sensitive function of the difference between the chemical nature of polymer components.

The intensity of light scattered from dilute solutions of mixtures of two nonidentical polymers in a single solvent was measured. The parameter A24 characterising the thermo-dynamic interaction of two nonidentical polymer molecules in solution was calculated for several systems polymer 2 - polymer 4 - solvent. For chemically strongly different polymers, A24 is independent of molecular weights of the polymers and probably also of solvent. A24 is related to the compatibility of both polymers and decreases contrary to expectation with increasing chemical difference between polymers 2 and 4.

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.

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.

A kinetic study formation of large size complexes of non-precipitating pig-Dnp anti-Dnp antibody and multivalent dinitrophenylated serum albumin was performed using light scattering and absorption spectroscopy of the Dnp-group. A very rapid phase of the process resulted in the formation of complexes having molecular weight of about 2 × 10 6 . Further increase of the complex size was much slower. Addition of PEG affected positively the rate of complex growth even in concentrations below 1%. The spectroscopic kinetic curves also showed a rapid and a slow phase, sensitive to the presence of PEG. The character of the kinetic data does not support the simple view that polymers enhance precipitate-formation by the steric exclusion of complexes from the polymer domains. It can be assumed that the interaction of the polymer with the antigen-antibody system consists of a subtle temporary attachment of the polymer to the antibody molecule resulting in a change of the shape and/or flexibility of the antibody molecule, favouring its cross-linking capacity.