Microphase Structure of Solvent-Cast Diblock Copolymers and Copolymer-Homopolymer Blends Containing Spherical Microdomains

Investigated in this work were the effects of solvent-casting conditions, the presence of homopolymer in the continuous phase, and the magnitude of block molecular weights on the structural features of styrene-butadiene diblock copolymers and diblock copolymer-homopolystyrene blends containing spherical domains of polybutadiene. Domain boundary thickness, domain size, and domain packing order were determined from small-angle neutron scattering (SANS) measurements. Domain boundary thickness was essentially identical for all samples and in agreement with theory. Contrary to theory, sphere radius was found to be proportional to the 0.37 power of polybutadiene molecular weight; this is shown to be an artifact of the solvent-casting process. Under equilibrium conditions, the domains form a body-centered-cubic paracrystalline macrolattice which is disrupted by the addition of homopolystyrene.