Synthesis Of Polyaniline Derivatives And Their Chiroptical And Adsorption Properties

The synthesis of structures that have controlled helicity continues to be achallenging area in the field of polymer and supramolecular chemistry. Polyanilinebeing conducting polymers has potential applications in electrical, optical andchemical active materials and devices. These device-oriented applications are basedon the materials to be in solid state making the study of helical inversion ofnanostructures of great importance. This thesis mainly deals with the synthesis ofchiral nanofibers of polyaniline and its derivatives and tuning of their helicalconformation by controlling steric hindrance.The first chapter of this thesis presentsliterature reviews about methods of synthesis, properties and application of chiralpolyaniline. The synthesis of polyaniline and its derivatives by chemical andelectrochemical has been explained and the effect of different reaction conditions onthe chiroptical properties of polyaniline has been reviewed. The various applicationsof polyaniline have also been supplemented. Rapid developments in the field ofnanoscience and nanotechnology have made synthesis of nanostructures of polyanilinevery important because nanostructured polyaniline can offer better performance ornew properties compared with its bulk counterpart. The mechanism ofpolyamerization and formation of different morphological structures such asnanofibers, nanotubes nanowires and micro/nanospheres has been elucidatedconsidering the two important models i.e.“the phenazine model” and “the electricaldouble layers model”. Polyaniline can adsorb variety of compounds such as dyes anddrug due to its unique structural composition of amine and imine group. This sectionalso throughs light on how polyaniline backbone interacts with dyes and helps toremove contaminants from waste water. The second chapter deals with the synthesisof optically active nanofibers of polyaniline derivatives, such as polyorthoanisidine,polyorthotoluidine, polyorthoethylaniline and polyorthochloroaniline and thechiroptical properties of these ortho substituted polymers were studied by circulardichroism 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 tothat of parent PANI, which reveals that the presence of substituent at ortho positioncan cause helical inversion of conformation from right handed to left-handed. Thisinversion of conformation has been explained by proposing a mechanism wherein thepresence of a substituent at ortho position affects the formation pattern of helicalchain to grow in the opposite direction during polymerization. To study the effect ofsteric hindrance of the substituent copolymers of aniline with its derivatives weresythsized and it was found that larger substituent induces causes inversion of chiralityto greater extent. A clarified relationship between the steric hindrance and thechirality of the polymer has been established which can enable us to tailor thechiroptical properties of functional polymer materials for future application. Effects ofdifferent reaction condition such as concentration of dopant acid, monomer, oligomer,oxidant and temperature on chirality have been dicussed. The SEM images ofpolyaniline, its derivative and copolymer showed the the fiberous morphology provingthat chirality was the result of one directional helical growth of polymer chain. TheUV-visible spectra of polyaniline derivatives showed the blue shift which suggestedthat introduction of substituent at ortho position not only causes inversion of chiralitybut also changes the conformation from ‘extended coil’ to ‘compact coil’conformation.The third chapter focuses on the fabrication of hollow microspheres ofpoly(o-chloroaniline) simple oxidative polymerization of o-chloroaniline withcamphorsulfonic acid as dopant acid and ammonium persulfate as oxidant in whichformation of micelles of camphorsulfonic acid in aqueous solution is a key factor inframing hollow spherical morphology. A mechanism has been proposed to explain theformation of POC hollow spheres which is supported by UV-visible spectroscopy andSEM data. Adsorption characteristics of POC spheres were also studied by usingmethyl orange as adsorbate. The pseudo-first-order, pseudo-second-order andintra-particle diffusion model were applied to the experimental data. It was found thatadsorption 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 experimentaldata and adsorption capacity of POC microspheres was found to be35.21mg g-1indicating that porous microspheres can be used as a novel and inexpensive adsorbentsfor removal of dye from aqueous solution. Finally, chapter4presents total summaryof the work and suggestions for the future study.