Synthesis And Characterization Of Poly(3,4-ethylenedithiathiophene)and Its Derivatives

As it owns the electrical properties of both metals and semiconductors, and good mechanical properties, flexible structural design, great variety of sources, and easy process of polymers, conducting polymer has been a hotspot of current research in the field of functional polymers. Up to now, poly(3,4-ethylenedioxythiophene)(PEDOT), as one of the polythiophene derivatives, has been one of the most successful conducting polymers no matter in academic or in industrial research. However, relevant research is still far from fully. So in view of the important academic significance and application value of its derivatives and analogues, in this thesis, poly(3,4-ethylenedithiathiophene)(PEDTT), as the most important all-sulfur analogue of PEDOT, was studied in-depth. Generally, the electrical, optical, thermal and processing properties of PEDTT prepared from different polymerization methods were systematically investigated.1. Following an acid-catalyzed etherification route,3,4-ethylenedithiathiophene (EDTT) has been successfully synthesized from3,4-dibromothiophene and1,2-ethanedithiol with an total yield of86%, which is higher than now. Followed this route, EDOT has been achieved from3,4-dibromothiophene and ethylene glycol with an overall yield of81%.2. By using EDTT as the starting material and N-iodosuccinimide as the halogenated agent, a novel compound2,5-diiodo-3,4-ethylenedithiathiophene (DIEDTT) was synthesized in41%yield, while2,5-dibromo-3,4-ethylenedithia-thiophene (DBEDTT) was prepared by straightforward bromination of EDTT with N-bromosuccinimide with a slightly higher yield of58%.3. The effects of different oxidants (FeCl3,(NH4)2S2O8, H2O2/Fe2+, Ce(SO4)2,(NH4)2Ce(NO3)6) and solvents (H2O, CH3CN, CH3CN/H2O) on chemical oxidative polymerization of EDTT and properties of resulting PEDTT powders were systematically investigated for the first time. For synthesis of PEDTT with high yields and electrical conductivities, the best results were obtained in CH3CN using as the oxidant which led to polymers with yield of61%and conductivity of0.19Scm-1. These polymers could be partly soluble in N-methyl-2-pyrrolidone and dimethyl sulfoxide.4. To improve the processing performance of PEDTT, a mechanical method was first introduced to prepare processable PEDTT dispersions by dispersing PEDTT powders in aqueous surfactant solutions through a high speed shear treatment. Several common sulfonate surfactants, including sodium dodecylsulfate, sodium dodecyl benzene sulphonate, polystyrene sulfonic acid and polystyrene sulfonate sodium salt were used. It had been found that the dispersing PEDTT in aqueous PSSH or PSSNa solutions led to relatively stable dispersions which owned good film-forming properties. Subsequently, chemical oxidative polymerization of EDTT in aqueous PSSH solutions, which combined the polymerization of EDTT with the dispersion of PEDTT, finally led to more stable PEDTT/PSS complex dispersions. Coating these dispersions onto polypropylene substrate formed free-standing polymer films and their conductivities ranged from10-5S cm-1to10-3Scm-1.5. Chemical oxidative co-polymerization of EDTT with EDOT or2’-hydroxymethyl-3,4-ethylenedioxythiophene (EDOT-MeOH) in aqueous PSSH solution was successfully carried out to form stable dark-blue colloidal dispersions in water. Coating these dispersions onto PP substrates, free-standing polymer films were formed and their mechanical, electrical and thermoelectric properties were superior to PEDTT/PSS. Comparably, EDTT and EDOT copolymer films achieved much better values of electrical conductivity (8.2×10-2Scm-1) and Seebeck coefficient (10μV K-1) at room temperature. The electrical conductivities of copolymer films can be improved by adding DMSO into polymer dispersions, but the Seebeck coefficients were basically unchanged.6. Solid-state polymerization of DBEDTT and DIEDTT under conditions without any external components (solvents, oxidants, etc.) was systematically investigated for the first time. The effects of polymerization conditions (temperature, time, pressure, etc.) on the polymerization reactions were discussed. The electrically conductive, thermoelectric, thermal and other properties of corresponding polymers were comparatively studied. It had been found that SSP-DIEDTT exhibited the higher electrical conductivities which can be up to0.2S cm-1, while SSP-DBEDTT showed the better Seebeck coefficient which can be up to122μV K-1and a power factor of6.7×10-9Wm-1K-2.