Synthesis of conducting polymers and investigation of their electrical properties


Thesis Type: Doctorate

Institution Of The Thesis: Istanbul Technical University, Fen Bilimleri Enstitüsü, Polymer Science and Technology, Turkey

Approval Date: 2015

Thesis Language: English

Student: ESMA AHLATCIOĞLU

Principal Consultant (For Co-Consultant Theses): Bahire Filiz Şenkal

Co-Consultant: Mustafa Okutan

Abstract:

This thesis is consisting of two parts. First part concerning with synthesis of new conducting polymers. For this purpose, chemical polymerization of aniline in the presence of propiolic acid as dopant and synthesis and polymerization of chalcone substituted aniline, and the other one is preparation of the poly (N-vinyl carbazole)- co-poly (2-(dimethylamino) ethyl methacrylate) based hydrogen bonded side-chain liquid crystal copolymer. Among the conducting polymers, polyaniline is one of the important electronic materials because of its easy synthesis, environmental stability, reversible proton dopability, redox recyclability, cost-effectiveness, and reasonable electrical conductivity. Polyaniline is one of the most promising conducting materials for applications in optoelectronics and microelectronics devices. In the present work, polyaniline (PANI) was synthesized in the presence of propiolic acid. The effects of the dopant on the course of oxidation and properties of final products have been studied by Fourier Transform Infrared Spectroscopy (FTIR) spectroscopy, and conductivity measurements. The dielectric properties of PANI and doped PANI were investigated using the impedance spectroscopy (IS) dependency of the frequency and the temperatures. New chalcone substituted aniline derivative, was synthesized by starting from 3-aminoacetophenone and 4-pyrridinecarboxyaldehyde in the presence of NaOH. The obtained chalcone containing aniline was polymerized oxidatively in water in the presence of dopant such as methanesulfonic acid, formic acid, HBr and acetic acid using ammonium persulfate as oxidant at room temperature for 24h. Chalcone containing polyaniline (Cs-PANI) was characterized by using FTIR and physical methods. Side-chain liquid crystalline polymers (SLCPs), which represent a combination of liquid crystalline behavior and polymeric properties, have been the subject of intensive research during the last decade since these polymers are regarded as materials with promising optical and electro-optical properties for potential applications in optical switching and image storage. The liquid crystallinity and physical properties of LCPs depend on the molecular structures chosen for polymer design. In this study, new side chain liquid crystalline copolymers were prepared from N-vinyl carbazole (NVC) and 2-(dimethylamino) ethyl methacrylate) (DMAEM) as a hydrogen bond acceptor copolymer and 8-(4-cyanobiphenyl-4'-oxy) octan-1-ol (LC8) by molecular self-assembly processes via hydrogen bond formation between nitrogen of (DMAEM) and hydroxyl group of the LC8.The formation of H bond was confirmed by using FTIR spectroscopy. The liquid crystalline behavior of the copolymers and homopolymer of the (DMAEM) was investigated using a differential scanning calorimeter (DSC) and polarized optical microscopy. The dielectric relaxation properties of H-bonded Side Chain LC Copolymers (HB-LCP) doped 8-(4-cyanobiphenyl-4'-oxy) octan-1-ol(LC8) and pure LC8 liquid crystals have been investigated by the dielectric spectroscopy (DS) method. The second part of the thesis, conducting polymer composites was prepared physical and chemical characterizations were performed. PANI was interacted with nanoclay, magnetite and graphite to obtain its composites. The thermal stability, mechanical strength, gas barrier, fire retardant properties, processability, etc. can be enhanced by the synthesis of the composites. The formation of polyaniline composites with inorganic materials provides new synergistic properties that cannot be attained from individual materials. The combination of clays and functional polymers interacting at atomic level constitutes the basis for the preparation of an important class of inorganic–organic nanostructured materials. In this study, aniline was polymerized oxidatively in the presence of boric acid as dopant and nanoclay with different weight percentage. The electrical properties of polyaniline nanoclay composite were studied using impedance spectroscopy. The magnetic nanoparticles were synthesized by mixing a water solution of FeCl2.4H2O (1.0 M) and FeCl3.6H2O (1.5 M). Composites of poly (aniline) and magnetite were prepared by using oxidative polymerization of aniline in the presence of different weight percentage of magnetite (2%, 5% and 10%). Field Emittion Scanning electron microscopy (FESEM) and FTIR analyses were performed to understand the structure of PANI-magnetite composites. The magnetic and electric properties of PANI, magnetite, magnetite doped PANI were investigated by electron paramagnetic resonance and impedance spectroscopy techniques, respectively. Also, dielectric properties were investigated by impedance spectroscopy for undoped PANI, magnetite and different weight percentage of magnetite doped Polyaniline–magnetite composites. In this work, synthesis and characterization of composite materials based on graphite (GH) and boric acid doped PANI were studied. PANI + GH composites were prepared via a simple in situ polymerization of aniline in graphite dispersion. The resulting composites of the PANI + GH were characterized by using spectroscopic, morphologic and physical methods. Polythiophene-boron nitride composites were prepared and characterized accordingly. Polythiophene/different weight percentage of Boron nitride (BN) (1% and 2%) (BN) composites were prepared via in situ oxidative polymerization of thiophene by using FeCl3 as oxidant at room temperature for 48 h. FESEM and FTIR spectroscopy were used to characterize the morphology and structure of the samples. Also, electrical characterizations of the composites have been investigated by impedance spectroscopy.