Synthesis and Characterization of Novel Conjugated Polyelectrolytes and Electro-Active Starburst Block Copolymers
Date Issued
2008
Date
2008
Author(s)
Yeh, Chih-Fu
Abstract
Since the discovery of electrically conductive polyacetylene in 1977, conducting polymers have attracted considerable attention in academic fields and industrial secters due to their novel optoelectronic properties and apparent potential use in organic electronic devices. An important characteristics of conducting polymers is the conjugated π-system along their backbone, making them typically both fragile and rigid, which severely limits their practical uses. Here, we developed three stratgies to solve this problem. First, we synthesized various types of soluble poly(3,4-propylenedioxythiophene) (PProDOT) derivatives with a long alkyl side chain. The strong dependence of the change in their thermochromic property upon the insertion of long alkyl chain (C12) indicates that side-chain disordering increases their steric hindrance to adopt a nonplanar conformation at high temperatures. On the other hand, their corresponding water soluble conducting polyelectrolytes was hydrolyzed by NaOH(aq.) on the ester polymer precusors. When pH is decreased from 12.5 to 7, the λmax of PProDOT derivatives was blue shift in UV-vis absorption. The blue shift should be related to a transition from rigid-rod to a random-coil conformation of the PProDOT derivatives, as any twisting of the conjugated backbone leads to a decrease of the effective conjugation length. In the second part, we present a new approach for preparing stable conductive core-shell nanoparticles without any surfactants. This method includes synthesis of a starburst polymer via atom transfer radical polymerization (ATRP) of n-butylacrylate as a core using a multi-arm molecule, followed by the growth of conjugated segments from each chain-end of the star polymer to yield a dendritic block copolymer. Atomic force microscopic (AFM) images clearly indicate that these polymers form unimolecular spherical nanoparticles with a well-defined core-shell structure. In the third part, a novel conductive polymer composite with core-shell-like nanostructure was successfully synthesized using 12-armed terthiophene-terminated starburst poly(n-butylacrylate) as precursor. Solid-state coupling among terthienyl groups on the chain-ends of the star polymer can be effectively performed by simple oxidative polymerization using FeCl3 as an oxidant to yield a three-dimensional network of oligoterthiophene. The unique core-shell-like structure enables the composite film to possess good conductivity at very low conjugated moiety content. Furthermore, the use of elastomeric poly(n-butylacrylate) (PBA) as core in the star growth core-shell polymer allows the preparation of a uniform and large-area conductive thin film with notable flexibility and excellent adhesion to a wide variety of substrates.
Subjects
conjugated polyelectrolytes
starburst block copolymer
Type
thesis
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