Design,Synthesis And Properities Of Azo Electroactive Polymers

As the fundament of human society, material has been playing a crucial role in the activities of reforming the nature. However, the demanding for multifunctional polymer materials is increasingly exigent nowadays, so as to meet the requirements of human being. How to design and prepare multifunctional polymer materials with low cost, high performance and excellent functions is becoming a tremendous challenge in polymer science.Photoactive polymers using azobenzene chromophore have attracted much attention in recent years because of their potential utilities in optic, photonic device, optical switching and digital optical storage applications. The reversible photoisomerization of azobenzene between the less stable cis isomer and the more stable trans isomer is the property exploited in all works. What makes azobenzene particular interesting as compared with other chromophores includes the high isomerization efficiency, the drastic change in the shape of the molecule (switched between the stretched trans and the contracted cis conformations), and the photoinduced orientation.Conducting polymers are a unique class of materials which though they structurally resemble organic insulating polymers are actually semiconductors or conductors, properties normally expected of inorganic materials. Polyaniline has been of significant interest due to its low cost, stability and easy synthesis, relative to other conducting polymers. The electronic and optical properties of polyaniline, which can be prepared from aniline monomers via oxidation or electrochemical polymerization, have been well studied over the past 30 years. As is the case with most conducting polymers, polyaniline possesses an array of interesting properties, including a range of electrical conductivity that span up to ten orders of magnitude, depending on oxidation state, doping level, solvent used, and exact method of preparation, leading to its use in a host of applications including chemical sensing, corrosion inhibition coatings, light emitting diodes, a template for metal sorption and et al.Similar to other conjugated polymers, polyaniline cannot be processed in the melt because PANI decomposes before softening or melting. Solution processing also suffered from the insolubility of the polymer in common organic solvents, especially in their electrically conductive forms. In the pursuit of processible conjugated polymers, various strategies have been explored, and only a little progress has been made. Therefore, the major drawback of PANI containing the issue of defect sites, ill-defined structure, poor solubility and processability, has greatly impeded its practical applications, and hindered a better understanding of the structure-property correlations and the conducting mechanism of PANI. Monodispersed oligoanilines, for their remarkably similar electronic properties to those of PANI and the potential for a variety of applications, have been considered as ideal candidates of PANI. However, it is a pity that oligoanilines lack good stability and mechanical properties compared with that of polymers.Therefore, the attempts to synthesize multifunctional polymers with positive mechanical and physical properties based on azobenzene chromophores and oligoanilines might be a wise choice with a series of advantages:First, the unique functions of azobenzene chromophore and oligoanilines can be maintained in these polymers. Second, positive mechanical and physical properties bearing from these polymers can eliminate the limit of oligoanilines on applications. Third, the properties of these polymers might be adjusted utilizing the method of varying the oxidations states and doping levels of oligoaniline segments or changing the conformations of azobenzene chromophores between the stretched trans isomer and the contracted cis isomer.Bearing all this in mind, in this dissertation, we tried to introduce azobenzene chromophores and oligoaniline segments into the polymers with positive mechanical and physical properties, and achieved successfully a series of multifunctional polymers not only with photoactivity but also with electroactivity, which were all characterized in detail by Fourier-transform infrared (FTIR) spectra,'H NMR spectroscopy, gel permeation chromatography (GPC), cyclic voltammetry (CV), thermogravimetric analysis (TGA) and UV-Vis spectrum.First, two novel electroactive alternating polyamides with oligoanilines and azo chromophores in the backbone, were prepared by oxidative coupling polymerization of oligoaniline macromonomer and p-phenylenediamine. Both of them exhibited obvious photoactive and electroactive, and the cyclic voltammogrames of polyamides showed three pairs of redox peaks, different from PANI which has two pairs of redox peaks, and the difference might be applied in some fields. Ratifying results were obtained in the investigation on dielectric properties of the as-synthesized polymers. The dielectric constants were greatly increased by treating the conjugated oligoaniline segments with hydrochloric acid.Second, by an oxidative coupling polymerization approach, we have synthesized a novel electroactive poly(aryl ether) (PAE) with good solubility containing alternating phenyl-capped aniline tetramer in the main chain and azo chromophores in the side chain. Dielectric properties of the as-synthesized polymer were investigated in detail and gratifying results have been made. A large enhancement in the dielectric constant was achieved utilizing the method of doping the conjugated oligoaniline segments with hydrochloric acid. The adjustment of dielectric constant was implemented primarily by means of exposing the samples to UV and Vis irradiation, mainly owing to the photoisomerization derived from azo chromophores in the side chain. A novel azo electroactive copolymers of poly(ether sulphone) (PES) bearing pendant aniline tetramer groups was prepared from conventional aromatic nucleophilic reaction between novel electroactive monomer containing aniline tetramer group, bis(4-chlorophenyl) sulphone and 4,4'-dihydroxyazobenzene in the presence of K2CO3, with DMSO as the solvent, at 176℃, after removing the water from the reaction system by the azeotropic distillation of toluene. The structures of the copolymer are confirmed by FTIR and 'H NMR measurements. The obtained PES exhibited excellent thermal stability, outstanding mechanical properties and wonderful solubility. We also investigated the photoinduced birefringences and three-dimensional SRGs (surface relief gratings) structure on the films of PES, indicating that the polymer has potential in digital optical storage application.Third, two novel hyperbranched electroactive azo polyamides containing oligoaniline were synthesized by an oxidative coupling polymerization approach. The polymers in HCl-doped form possessed much higher dielectric constants compared with that of the similar linear polymer reported before, mainly owing to both the highly branched three-dimensional molecular architecture and the high content of the oligoaniline segments. The detailed characteristics of the obtained polyamides were systematically studied by FTIR,'H NMR and GPC. The TGA curves revealed a good thermal resistance of the polymers. And the photoisomerization process and doping process of the polymers were monitored with UV-vis spectra. Moreover, the electrochemical behaviors of the polymers were explored by CV, and the mechanism of electrochemical oxidation process was well studied.Finally, a novel hyperbranched azo fluorescent polyamide was prepared via direct polycondensation within an A2+B3 strategy. Then the as-synthesized polyamide was treated by end functionalization with oligoanilines to achieve multifunctional polymers. By monitoring the changes of fluorescence spectra of the polymer solution, we found that the different oxidation states of the oligoaniline segments could affect the fluorescence intensity obviously. In order to obtain the same type polymer with high molecular weight, we synthesized an anisomerous B3 monomer and prepared a novel hyperbranched azo poly(ether amide) successfully via direct polycondensation within an A2+BB'2 strategy. After the end functionalization with oligoanilines, the as-synthesized poly(ether amide) also exhibited photoactivity and electroactivity. The studies of optical information storages properties of the two polymers mentioned above have been made, suggesting that the polymers possess huge potential in digital optical storage application.