ORDERED STRUCTURES OF BLOCK POLYMER HOMOPOLYMER MIXTURES .3. TEMPERATURE-DEPENDENCE

The ordered structures in the binary mixtures of poly(styrene-block-isoprene) (SI) and polystyrene (HS) were investigated as a function of temperature T using small-angle X-ray scattering. The mixtures were studied in a regime in which HS is solubilized in polystyrene microdomains of SI, as a function of the volume fraction, phi-HS, and the molecular weight, M(HS), of HS as well as the total polymer volume fraction phi-p (0.66 less-than-or-equal-to phi-p less-than-or-equal-to 1) when dioctyl phthalate (DOP) was added to the mixtures as a neutral solvent. The exponent n characterizing the temperature dependence of the interdomain distance (D approximately T(-n)) was found to depend strongly on phi-HS and M(HS), n increasing with increasing phi-HS and decreasing M(HS). Such a scaling behavior as (D - D(S))/D(S) approximately epsilon-T = (chi-eff - chi-ODT)/chi-ODT was found under the condition that chi-eff = A + B-phi-p2/3/T. Here D(S) is the wavelength of the dominant mode of the composition fluctuations in the disordered state, chi-eff is the effective Flory interaction parameter between polystyrene and polyisoprene per segment base in presence of DOP when DOP is added to the mixture, and chi-ODT is chi-eff at the order-disorder transition temperature.