Anionic synthesis, Self-Assembly, and Supramolecular Hybrids of Rod-Coil Block Copolymers

Rcently, π-conjugated rigid-rod polymers with semiconducting properties have gained great interests since they possess unique optoelectronic properties with potential for use as an active component in large-area, flexible, and low-cost optoelectric devices. Over the last decade, diblock copolymers with one block consisting of the π-conjugated polymer chain and the other block of a flexible random coil-like chain have received a great deal of attention since they offer a new strategy to create nanometer-scale morphology for the organization of many conjugated polymers, thus providing synergistic improvements in their mechanical and optoelectronic properties. Compared with coil-coil diblock copolymer systems, the self-assembly behavior of a rod-coil system is further complicated due to the presence of the anisotropic interaction between the rod blocks.
First, in Chapter 2, a series of PPV-P2VP rod-coil block copolymers with different block ratios was synthesized by using an end-coupling reaction between an aldehyde-terminated PPV of a fixed contour length with different molecular weigh P2VP living anions. The microphase-separated morphology of these block copolymers varies from lamellar, to broken lamellar, to strip-like, and to puck-like phase as the coil volume fraction, f, increases. Through the evolution of SAXS and WAXS patterns as a function of temperature, the detailed phase diagram of the system was then established.
In Chapter 3, I studied the supramolecular rod-comb block copolymers formed by complexation of an amphiiphlic surfactant, dodecylbenzesulfonic acid (DBSA), with the P2VP blocks in PPV-P2VP rod-coil block copolymers. Hierarchical structure was exhibited in rod-comb complexes, where PPV blocks are microphase-separated from the P2VP(DBSA)X blocks and the small-scale mesophase organized by the P2VP(DBSA)X comb blocks
In Chapter 4, a series of novel π-conjugated rod-coil-coil triblock copolymers of PPV-PVP-PSs was synthesized and their self-assembly behavior was explored. Three different triblock copolymers of PPV-PVP-PS1, PPV-PVP-PS2, and PPV-PVP-PS3, each with PPV, PS, and PVP, respectively in the copolymers as the major species, were used to study the effects of copolymer composition and the rod-rod interaction between PPV blocks on their morphology. Simultaneous SAXS and WAXS measurements show that all three triblock copolymers undergo the ordered lamella-to-disorder transition and the smectic/isotropic transition at the same temperature, indicating that the rod-rod interaction between PPV rods plays a critical role in forming and stabilizing these lamellar structures. The observation of the phase transformations is in good agreement with a recent mean-field prediction of a rod-coil-coil triblock copolymer system.
In Chapter 5, I study the self-assembly of a hybrid system by the stoichiometric complexation of hydrogen tetrachloroaurate trihydrate (HAuCl4) with a compositinally coil-coil PS-P2VP block copolymer. A series of morphological transformations were observed from an originally body-centered cubic spherical structure of neat PS-P2VP to hexagonally packed cylinders, to the lamella, to inverted honeycomb-like cylinders, and eventually to disordered phase with increasing amount of HAuCl4 incorporated with P2VP chains. The intrachain-to-interchain intercalation of HAuCl4 to the P2VP domain was observed below and above the saturation Au/N loading ratio of 0.83/1, as evidenced by SAXS, WAXS, and the analysis of 1-D correlation function. In addition, the increasing amount of HAuCl4 would cause a rod-like chain conformation for P2VP chains. Consequently, the conformational asymmetry between PS and HAuCl4-incorporated P2VP chain leaded the order-order transitions (OOTs) to move towards a lower total P2VP/HAuCl4 volume fraction, elucidating the interesting phase behavior in this hybrid system that all phase transformations occurred when only a small amount of HAuCl4 was needed for phase transformation compared with the volume fraction.