Abstract
Abstract This dissertation investigates the special phase transition behavior of block copolymers, including the unusual lower critical ordering transition (LCOT) and the order-order transition of the macrolattice of the spherical microdomains. Temperaure-dependent small angle X-ray scattering (SAXS) was employed to reveal the LCOT behavior of a new block copolymer system composed of poly(ethylene oxide) (PEO) and poly(vinyl pyridine) (P2VP and P4VP) blocks. We have studied the effects of copolymer composoiton and molecular weight on the phase transition temperature; moreover, a thermodynamic theory considering the compressibility of the constituents was adopted to calauclate the phase diagrams of PEO/P2VP and PEO/P4VP blends. Through comparing the phase diagrams and experimentally measured disorder-to-order transition (DOT) temperatures of the two system, the drastic effect of the structure of the pyridine moiety in PVP has been revealed. We further studied the hierarchical structure and phase behavior of the supramolecular comb-coil block copolymer formed by the complexation of the P2VP block in PEO-b-P2VP with an amphiphilic surfactant dodecylbenzene sulfonic acid (DBSA). It was found that the crystallization kinetics of PEO blocks in the system exhibited a distinct correlation with the hierarchical structure of the comb-coil copolymer. The phase transition behavior of PEO-b-P2VP was also modified by the complexation with DBSA, where the original LCOT behavior transformed to UCOT type when the binding frcaton was sufficiently high. Finally, we investigated the packing lattice of the PEO spherical microdomains formed in the blend of poly(ethylene oxide)-block-poly(1,4-butadiene) (PEO-b-PB) and PB homopolymer (h-PB). The sphere-forming blend was first heated to the disordered micelle state followed by cooling below TODT. It was found that PEO spherical microdomains packed in the closely-packed lattice. In contrast to the previously observed face-centered cubic (FCC) packing, the spherical domains packed into the hexagonal closely-packed (hcp) lattice. The result implies that the free energy of hcp phase is lower than that of FCC phase and may henve represent the stable CPS structure for block copolymer blends.