The ionic liquids due to their remarkable properties like nonflammable, high thermal, negligible vapor pressure, Low toxicity and their simple reusability have been widely used as solvent or catalyst in polymerization reactions or industrial technologies. So in this project, four ionic liquids were prepared and characterized by 1 H-NMR and FT-IR spectra. They were used for synthesizing of conjugated polymers and biodegradable polymers. In the first part of the project, the Poly(3,4-ethylenedioxythiophene methine)s were prepared by the acid–catalyzed polymerization of the 3,4-ethylenedioxy thiophene and aldehydes in the presence of the acidic ionic liquids, N -methyl-2-pyrrolidonum hydrogensulfate ([NMP-H]HSO 4 ) and Morpholinium hydrogensulfate ([Mor-H]HSO 4 ). The resulting polymers were obtained in good yields with inherent viscosities ranging between 0.04 and 0.1 dl/g. These polymers were readily soluble in common organic solvents, such as DMF, NMP, CH 2 Cl 2 , p -dioxane, chloroform and etc. The molecular weights (M w , M n ) for PEDOT-MB and PEDOT-NB were (5367, 4626) and (8486, 7411) respectively corresponded to molecular weight distributions (M w /M n ) were rather narrow 1.16 and 1.14 respectively. The polymer structures were confirmed and studied by FT-IR, 1 H-NMR spectra and also elemental and thermo gravimetric analysis techniques. The polymers obtained were highly colored because of dehydrogenation. The degree of dehydrogenation was estimated by the 1 H-NMR results. The thermal gravimetric analysis showed that the polymers had a fairly good thermal stability. The optical and electrochemical band gap of the conjugated polymers was measured by cyclic voltammetry and UV/Vis spectra. The polymer conductivity was tested by EIS studies using K 3 Fe[CN] 6 / K 4 Fe[CN] 6 as a redox probe to evaluate the electron-transfer kinetics of the electrodes. The charge transfer resistances of the reactions at electrodes were compared to the doped and undoped electrodes. Regarding to the obtained results from Nyquist diagram, it was found that electrodes charge transfer resistance was decreased in doping state, and it was closed to the bare carbon paste electrode. In the second part, the biodegradable polycaprolactone was prepared by ring opening polymerization in the presence of the ionic liquids. The resulting polymer exhibited good yield and inherent viscosity was 0.12 dl/g. The obtained polymer chemical structure was verified by the 1 H-NMR and FT-IR spectra. In the following, this polymer was used to improve quality level, mechanical properties and hydrophilic property reduction of the starch, so the ring opening polymerization of the ?-caprolactone in the presence of the starch hydroxyl groups as an initiator and ionic liquid as a catalyst was done. The obtained starch–grafted-polycaprolactone verified by 1 H-NMR and FT-IR spectra. The resulting polymer exhibited inherent viscosity was 0.24 dl/g. The Scanning Electron Microscopy images of the starch and St-g-PCL copolymer to the very good interfacial adhesion between the starch and the PCL chains. The surfaces of the starch granules looked smooth, whereas the surfaces of St-g-PCL exhibited roughness and polygonal appearance, and some connections between granules could be also seen clearly. Therefore, it obviously showed that the PCL was located on the surfaces of the starch granules, which will be helpful to the improvement of the mechanical properties of the modified composites.