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Copolymerisation radicalaire du macromere polydimethylsiloxane avec le methacrylate de methyle

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.

Twenty low-conversion statistical copolymers of styrene and 2-methoxyethyl methacrylate with various composition were prepared. The dependence of the copolymer composition, molecular weight, initiation efficiency and other parameters on the composition of the monomer mixture is discussed. Kinetic data are correlated by means of various models of the copolymerization kinetics. The best fit with experimental data is provided by a diffusion-controlled termination model, especially its dyad variant suggested in this study.

In aqueous KSCN solutions the salt is preferentially desorbed from the domain of gelatin molecules, similarly to synthetic polyelectrolytes. Light-scattering measurements in gelatin solutions in 0,5 M KSCN and in a single solvent (formamide) show that both solvents are suited for the molecular characterization of gelatin at room temperature. Neglecting the effect of selective sorption in salt solutions does not cause any considerable error in the molar mass determination of gelatin.

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.

When methyl methacrylate is polymerized in aqueous medium in the presence of gelatin, graft copolymer macromolecules with gelatine backbones and poly(methyl methacrylate) (PMMA) grafts are formed. Due to the presence of graft copolymer, polymolecular micelles consisting of about 100 macromolecules are created. These micelles prevent macroscopic precipitation of PMMA. Fractionation in demixing solvents has been used to separate the components of the polymerization mixture, and the light-scattering method has been employed to determine their molecular weights. Each grafted macromolecule carries about one graft. The hypothesis of random grafting from gelatin backbones seems to explain most of the experimental observations.

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.

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.

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.