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The large scale architecture of polymers is recognized to create special properties in functional polymers. One of the more striking examples is the ability of certain diblock copolymers to associate into micelles in a selective solvent for one of the blocks.(1) The insoluble block forms a dense core that is kept in solution by a soluble corona. The diblock micelle has the overall conformation of a star polymer.(2,3) However, the self-association of block copolymers into micelles depends strongly on the chemical nature of the two blocks, on the respective sizes of the blocks and on the selective solvent. In general, it is observed that the molecular weight of the insoluble block must be kept low in order to form micelles. This is especially true when water or a polar solvent is used as the selective good solvent.(1,4) Otherwise, a cloudy unstable two phase system is produced. The association number of diblocks in micelles varies considerably and makes their systematic study difficult. The associa...

DSC data show that anionically prepared monodisperse 1,2-polybutadiene (>99% 1,2; 1,2-PBd) and polyisoprene (93% 1,4; PI) are miscible but the glass transition region is very broad for blends with high 1,2-PBd content. The viscoelastic properties of the blends have been studied over a wide temperature range. Individual relaxations of the components are observed. The blends are thermorheologically complex because the temperature dependence of the 1,2-PBd relaxation is stronger than that of PI. Analysis of the temperature dependence of the relaxation times suggests that each component in the blend experiences its own T g

The measurement of the sedimentation velocity coefficient of narrow distribution linear, four-arm and six-arm star and comb polystyrenes in a theta solvent permits the experimental determination of h, i.e., the ratio of the translational friction coefficients of the branched polymer to that of its linear homolog. A comparison of experimental h/g1/2 values with theoretical predictions can then be made. It was observed that the equivalent hydrodynamic radii derived from sedimentation and intrinsic viscosity measurements are identical within experimental error.

A series of eighteen-arm regular star polybutadienes with molecular weights between 9.9 × 104 and 1.9 × 106 were prepared and characterized. Evidence is presented for the expanded configuration of the large eighteen-arm stars in a θ solvent. The intrinsic viscosities of the eighteen-arm stars gave g′ = [η]/[η]l = 0.284 in dioxane at 27°C (θ solvent) and 0.225 in toluene at 35°C (good solvent). The linear viscoelastic properties of the melts were also determined. The plateau modulus, GN°, is the same as for linear polybutadiene. The zero-shear viscosities (η0) and the longest relaxation times (Tmax) increase exponentially with the arm molecular weight Ma and are identical to those of four-arm polybutadienes with the same Ma. The zero-shear recoverable compliance (Je°) increases linearly with molecular weight. v′ in Je°GN° = v′Na, where Na is the number of entanglements per arm, is 0.95 slightly larger than 0.66 for four-arm polybutadienes. Similarly, g2 is higher than calculated from the Rouse–Ham theory.

The glass transition temperatures of linear and four- and six-branched regular star polystyrenes are measured by penetration, differential scanning calorimetry, and a density gradient technique. The results of the three methods show that the glass transition temperature depends on the concentration of chain ends in the polymer sample. An attempt is made to assess the influence of the presence of the branch point on the glass transition temperature using a series of four-branched polystyrenes containing varying amounts of isoprene near the branch point. However, any effect of the central branch point on the glass transition temperature is obscured by plastification of polystyrene by polyisoprene.

Different series of poly(styrene–isoprene) diblock and poly(styrene–isoprene–styrene) triblock copolymers were prepared. In each series, the low molecular weight polystyrene block was kept constant, and the molecular weight of the polyisoprene block varied. The glass transition behavior of these polymers was studied and their glass transition temperatures compared with those of the random copolymers of styrene and isoprene. It is concluded that some low molecular weight styrene-isoprene block copolymers form a single phase. Krause's thermodynamic treatment of phase separation in block copolymers was applied to the data. One arrives at a polystyrene–polyisoprene interaction parameter χ1,2 ≈ 0.1. The experimental and theoretical limitations of this result are discussed.

The effect of microstructure on the glass temperature T(g) of poly(alpha-methyl styrene) has been investigated. It has been observed that T(g) increases as the syndiotacticity of the molecule increases-thus T(g) = 446K for polymer with 67% syndiotactic placements, while a value of T(g) = 453K is found for a sample with 95% syndiotactic placements. Coefficients of expansion for the liquid and glassy states have been calculated and from these a chain stiffness parameter has been estimated using the Gibbs-DiMarzio theory. The result indicates that the flex energy of the alpha-methyl styrene chain is about 20% larger than for the polystyrene chain. (Author)

The viscosities and densities of several mixtures of dimethyl sulphoxide and water have been measured at 25°, 45°, and 65 °C. Heats of mixing and refractive indices at 25 °C are also reported. The results indicate there is strong association of the two liquids which may be attributed to hydrogen bonding.