Synthesis Of Polyaniline Derivatives And Their Chiroptical And Adsorption Properties

The synthesis of structures that have controlled helicity continues to be a challenging area in the field of polymer and supramolecular chemistry. Polyaniline being conducting polymers has potential applications in electrical, optical and chemical active materials and devices. These device-oriented applications are based on the materials to be in solid state making the study of helical inversion of nanostructures of great importance. This thesis mainly deals with the synthesis of chiral nanofibers of polyaniline and its derivatives and tuning of their helical conformation by controlling steric hindrance.The first chapter of this thesis presents literature reviews about methods of synthesis, properties and application of chiral polyaniline. The synthesis of polyaniline and its derivatives by chemical and electrochemical has been explained and the effect of different reaction conditions on the chiroptical properties of polyaniline has been reviewed. The various applications of polyaniline have also been supplemented. Rapid developments in the field of nanoscience and nanotechnology have made synthesis of nanostructures of polyaniline very important because nanostructured polyaniline can offer better performance or new properties compared with its bulk counterpart. The mechanism of polyamerization and formation of different morphological structures such as nanofibers, nanotubes nanowires and micro/nanospheres has been elucidated considering the two important models i.e. "the phenazine model" and "the electrical double layers model". Polyaniline can adsorb variety of compounds such as dyes and drug due to its unique structural composition of amine and imine group. This section also throughs light on how polyaniline backbone interacts with dyes and helps to remove contaminants from waste water. The second chapter deals with the synthesis of optically active nanofibers of polyaniline derivatives, such as polyorthoanisidine, polyorthotoluidine, polyorthoethylaniline and polyorthochloroaniline and the chiroptical properties of these ortho substituted polymers were studied by circular dichroism spectroscopy in comparison with parent PANI. Generally, PANI prepared with D- and L-CSA forms right-handed (P) helix and left-handed (M) helix, respectively. It was found that the chirality of these substituted PANIs was opposite to that of parent PANI, which reveals that the presence of substituent at ortho position can cause helical inversion of conformation from right handed to left-handed. This inversion of conformation has been explained by proposing a mechanism wherein the presence of a substituent at ortho position affects the formation pattern of helical chain to grow in the opposite direction during polymerization. To study the effect of steric hindrance of the substituent copolymers of aniline with its derivatives were sythsized and it was found that larger substituent induces causes inversion of chirality to greater extent. A clarified relationship between the steric hindrance and the chirality of the polymer has been established which can enable us to tailor the chiroptical properties of functional polymer materials for future application. Effects of different reaction condition such as concentration of dopant acid, monomer, oligomer, oxidant and temperature on chirality have been dicussed. The SEM images of polyaniline, its derivative and copolymer showed the the fiberous morphology proving that chirality was the result of one directional helical growth of polymer chain. The UV-visible spectra of polyaniline derivatives showed the blue shift which suggested that introduction of substituent at ortho position not only causes inversion of chirality but also changes the conformation from 'extended coil' to 'compact coil' conformation.The third chapter focuses on the fabrication of hollow microspheres of poly(o-chloroaniline) simple oxidative polymerization of o-chloroaniline with camphorsulfonic acid as dopant acid and ammonium persulfate as oxidant in which formation of micelles of camphorsulfonic acid in aqueous solution is a key factor in framing hollow spherical morphology. A mechanism has been proposed to explain the formation of POC hollow spheres which is supported by UV-visible spectroscopy and SEM data. Adsorption characteristics of POC spheres were also studied by using methyl orange as adsorbate. The pseudo-first-order, pseudo-second-order and intra-particle diffusion model were applied to the experimental data. It was found that adsorption of MO by POC was better described by pseudo-second-order kinetics than any other kinetic model. Langmuir isotherm model was the best to fit experimental data and adsorption capacity of POC microspheres was found to be 35.21 mg g-1 indicating that porous microspheres can be used as a novel and inexpensive adsorbents for removal of dye from aqueous solution. Finally, chapter 4 presents total summary of the work and suggestions for the future study.