Creation of Hierarchical Nanophase-Separated Structures via Supramacromolecular Self-Assembly from Two Asymmetric Block Copolymers with Short Interacting Sequences Giving Hydrogen Bonding Interaction

Polystyrene (S) having short poly(4-hydroxystyrene) (H) on one end (SH, M-w = 71.4K, phi(H) = 0.04) and polyisoprenc (1) having short poly(2-vinylpyridine) (P) on one end (IP, M-w = 57:6K, phi(p) = 0.04) were mixed at various molar ratios, where H and P form a complex by hydrogen bonding interaction. The variation of phase-separated structures of solvent cast Films depending on casting solvent and also on pH with heating time at elevated constant temperature were investigated by transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS). Asymmetric morphology for the H/P stoichiometric blend film obtained by casting from polar solvent can be easily transformed into symmetric nanophase-separated structure by the addition of nonpolar solvent. All samples cast from THF/toluene solutions reveal ordered nanophase-separated structures even though the contents of interacting H and P sequences are both merely 4%. the hierarchical three-phase lamellar structure from equimolar SH/IP blend is maintained even after 3 weeks of annealing at constant temperature because of the formation of a very strong one-to-one hydrogen bonded complex. It has been also found that the ordered cylindrical structures for nonstoichiometric blends have periodic three-phase morphologies and that their regular structures gradually disappear and finally reach macrophase separation as annealing time increases. Additionally, pH increase in equimolar blends causes macrophase separation in otherwise stable blends upon isothermal heating.