Small Angle Neutron Scattering Studies on Miscible Blends of Poly(styrene-ran-vinyl phenol) with Liquid Crystalline Polyurethane

The production of uniformly dispersed rigid-rod liquid crystalline polymer (LCP) molecules in a flexible amorphous polymer, with an experimentally accessible miscibility window, has become possible by modifying the architecture of the flexible polymer, so as to induce favorable inter-species hydrogen bonding. The conformation of LCP chains that are uniformly dispersed in a flexible coil matrix are examined by studying a system consisting of a liquid crystalline polyurethane (LCPU) and a copolymer containing 12% vinylphenol and deuterated styrene, utilizing small-angle neutron scattering. Intramolecular hydrogen bond interaction within the vinylphenol segments of the copolymer leads to the formation of a dynamically cross-linked structure, characterized by the large amount of scattering seen at low angle. Addition of the LCPU in the blend results in formation of hydrogen bonding interactions between the LCP and the copolymer; demonstrated by an initial reduction in the correlated size of the dynamic network at the lowest LCP dosage, whereas the network size is recovered in blends containing higher amounts of the LCPU. Using FTIR to quantify the amount of intramolecular hydrogen bonding between the polymers, the results demonstrate the conversion from intra-species to inter-species hydrogen bonding; further corroborating the observation that the LCPU molecules integrate themselves into the hydrogen bonded physical network. Investigation of the high-angle portion of the scattering curves reveals that the LCPU molecules exhibit presence of anisotropic structures staggered along its length, resulting in rods that are shorter and thicker than a fully extended LCPU chain. With increasing concentration of the LCPU, interference between individual LCP molecules leads to orientation and structures with greater lengths of the anisotropic portions, leading up to formation of anisotropic aggregates that contain multiple LCPU molecules.