Abstract
Abstract Polyaniline and other conducting polymers have been demonstrated to be particularly useful in many applications, such as light-emitting diodes, molecular devices, optical switches, smart windows, transistors and rechargeable batteries. Like other unsubstituted conjugated polymers, due to the poor solubility the application of polyaniline is limited in the electronic industry. Improved solution processability can be achieved by attaching various alkyl and alkoxy-substituents to the polymer backbone. However, such substituted polyaniline have always been found to exhibit much lower conductivity (10-1–10-7 S/cm) than unsubstituted polyaniline (1–5 S/cm). In general, the conductivity reduces dramatically as the size of the substituent group becomes larger. This diminishing of conductivity has long been ascribed to the possible steric hindrance effect of the substituent groups. New highly solution-processable aniline/butylthioaniline copolymers were prepared via oxidative copolymerization (OCP) and by concurrent reduction and substitution (CRS) route. Butylthio-substituted polyaniline Pan-SBu obtained via the CRS route, displayed a lowered redox potential (E0) and a red-shifted maximum wavelength (λmax; ultraviolet–visible) in comparison with its parent unsubstituted polyaniline. The results were in line with the expected property changes after the addition of an electron donating substituent to the polymer backbone. On the contrary, copolymers obtained via the OCP method displayed higher E0 values and blue-shift in λmax than the unsubstituted Pan. The results suggested that copolymers obtained via the OCP method might have shorter conjugation length than the unsubstituted Pan, possibly attributed to their main chain conjugation defects (e.g., 1,3-linkage structures), as evidenced by IR studies. The results of 1H NMR studies indicated that Pan-SBu showed much higher structural homogeneity than copolymer CP4. Since the CRS synthetic route involved no backbone alteration, the resultant copolymer (Pan-SBu) should have maintained the same backbone structure and hence the high conductivity as same as that of the parent unsubstituted Pan. We synthesized polyaniline derivative Pan-MPS in large scale, in which the substituent contains self-doping ability via CRS route. By detailed analyses, the reproducible and reliable experimental results were successfully obtained for Pan-MPS. Surprisingly, the conductivity of self-doped Pan-MPS exhibited a 4 order increase than the SPan reported on literature. Based on the in-situ dedoping concept, self-doping Pan-MPS was found to be highly soluble in NMP, DMF and DMSO together with a catalytic amount of base (NR3). By comparing the different self-doping degree of Pan-MPS and different TsOH doping degree of polyaniline, it could be concluded that the homogeneous distribution of self-doping substituent on the Pan-MPS backbone might be the reason for such a high conductivity than the unsubstituted polyaniline and SPan at the same doping degree. Moreover, we have developed an efficient route to synthesize Pan-MPS with a high substitution degree, by the reaction of a nucleophilic substituent to a stable high oxidation state polyaniline prepared from electrochemical method via CRS route. In the last chapter, we synthesized various types of conductive and processable functionalized polyanilines via the novel concurrent reduction and substitution (CRS) method and we explored their potentials as dye materials for the dye-sensitized solar cell devices.