Determination of the structure parameters of styrene/butadiene block copolymer in heptane by means of small‐angle X‐ray scattering

Small‐angle X‐ray scattering was used to investigate dilute solutions of the styrene/butadiene block copolymer in heptane as a selective solvent for polybutadiene. The solutions contained two types of particles of different size. The weight fraction and sizes of both types of particles were determined at four temperatures ranging from 18 to 50°C. Absolute intensity measurements were used to determine the weight of the micelles (large particles) and the degree of swelling of the individual copolymer components. By using a simple structure model as a basis, the data determined by absolute intensity measurements at the four temperatures were employed to calculate the diameter of the polystyrene nucleus (222–181 Å), the total diameter (558–532 Å), and the radius of gyration (191–180 Å) of the micelles. The values obtained were in good agreement with those determined directly from the small‐angle scattering curves in a relative scale. The number of macromolecules in a micelle varies from 100 (at 50°C) to 190 (at 18°C).