Polyaniline (PAni) was synthesized by a new miniemulsion polymerization. The monomer to oxidant and polymer to dopant mole ratio were optimized. The PAni formed by this method shows higher solubility and lower particle size compared to that of conventional oxidative polymerization. The conductivity of this polymer was further improved after partial reduction using stannous chloride (SnCl2). Plausible reduction mechanism with SnCl2 is proposed. Polyaniline (PANI), poly (m-nitro aniline) (PMNA), poly (m-amino phenol) (PMAP) and poly (o-ethyl aniline) (POEA) were synthesized by chemical oxidative polymerization under identical conditions. Presence of substituent on the benzene ring of polyaniline affects the conductivity and solubility of the polymers along with other properties. The crystal structure of PANI, PMNA and PMAP were thoroughly studied directly from powder X-ray diffraction data using available softwares. PAni was also prepared by electropolymerization techniques. Effect of different reaction parameters during electropolymerization on the structure and properties of resultant PAni were studied with a view to standardize the reaction condition to produce polymer of desirable conductivity. Regression technique had been adopted to correlate conductivity with different reaction parameters. A comparative study between PAni samples synthesized by chemical and electrochemical methods had been carried out. PAni obtained from electropolymerization method shows lower conductivity and crystallinity but higher solubility and particle size compared to that from chemical polymerization. The partial reduction of PAni during electropolymerization was accomplished by reversing the polarity of the electrodes after a specified time of polymerization. By this process PAni with appropriate oxidation level could be achieved which is reflected in significant improvement in conductivity. A plausible reduction mechanism due to reversal of polarity during electrochemical polymerization is also proposed. Dual functionality of p - toluene sulphonic acid (PTSA) as dopant and electrolyte during electrochemical synthesis of PAni had also been studied. Available literatures report wide variation of glass-rubber transition temperature (Tg) for PAni, which ranges from -120C to +2500C. An effort was made to determine the Tg of PAni using different techniques like DSC, DMA, dilatometry and electrical conductivity. The Tg of PAni found to be within 30-400C. Presence of moisture and dopant affect the Tg, of PAni. The experimental result was corroborated with theoretically determined Tg value of PAni using molecular dynamic (MD) simulation. Prolonged thermal treatment on doped PAni at different temperatures was carried out. Major processes that taking place during heat treatment are oxidation, change in crystallinity and crystal structure, doping, dedoping, chain scission and crosslink formation. The occurrence of different processes depends on the treatment temperature. MD simulation study supports the occurrence of chain scission and cross-linking process during heat treatment. The effect of electron beam irradiation on the structure and properties of PAni had been studied. During irradiation both chain scission and cross-linking processes take place in PAni, this again depends on irradiation dose.