Phase Equilibria and Transition in Mixtures of a Homopolymer and a Block Copolymer. I. Small-Angle X-Ray Scattering Study

摘要

The small-angle X-ray scattering technique is utilized to study the phase separation and phase transition occurring in the mixtures of a styrene butadiene diblock copolymer with a low molecular weight polystyrene. At low temperatures the scattering curve shows a main peak and a secondary peak indicating the presence of well-developed microdomains. As the temperature is raised the peaks gradually lose intensity. The binodal and spinodal temperatures for the transition between the ordered structure at low temperature and the disordered, homogeneous structure at high temperature are determined and found to increase with increasing amount of the added polystyrene. With increasing amount of polystyrene the main peak at first shifts toward lower angles, indicating an increased distance between microdomains. However, at concentrations beyond about 50% polystyrene, which evidently corresponds to the solubility limit of the latter in the microdomains, the peak position remains constant. The observed shift in the relative position of the secondary peak suggests that the morphology of the microdomains changes gradually from spherical to lamellar as the proportion of polystyrene is increased. With all the mixtures no evidence is found for an increase in the microdomain boundary thickness with increasing temperature.