Synthesis And Characterization Of Poly(Thieno[3,4-b]-1,4-oxathiane)

Bearing the characteristics of mechanical flexibility in traditional polymers and the regulated optoelectronic property in semiconductors, conducting polymers have found a wide variety of applications, e.g., antistatic coating, organic light emitting diode, organic field-effect transistors, organic solar cells, electrochromic devices, supercapacitors, and bio/chemical sensors owing to the features of the source material abundance, the structure tunability, and the ease of processing. The polythiophene derivative, poly(3,4-ethylenedioxythiophene) (PEDOT), stand out to become a "star molecule" for its excellent environmental stability, high electrical conductivity and high transmittance in the doped state, good redox-active capability and long cycle life in the field of conducting polymers in approaching 40 years of research and development. The research about PEDOT derivatives and analogs is currently a hot spot in the field of functional polymers and has potential practical value and broad application prospects, which even arouse great interest in the entire scientific community. Given that these analogs have great theoretical significance and research value but far from sufficient focus, therefore to promote the research work is imperative. This thesis focuses on the asymmetric PEDOT thio-analog, poly(thieno[3,4-b]-1,4-oxathiane) (PEOTT), and systematically explores the optoelectronic properties, electrical conductivity, thermal stability, processability, electrochromic and capacitance performance of PEOTT prepared under different polymerization methods.1. By the acid catalyzed etherification route, the successful synthesis of thieno[3,4-b]-1,4-oxathiane (EOTT) was realized using 3,4-dimethoxy-thiophene and mercaptoethanol as the raw materials with an total yield of 75%, consistent with the already reported yield.2. By the bromination on EOTT using N-bromosuccinimide (NBS), a new brominated product of EOTT,2,5-dibromo-thieno[3,4-b]-1,4-oxathiane (DBEOTT), was obtained in 68% yield; another new iodinated derivative of EOTT, 2,5-diiodo-thieno[3,4-b]-1,4-oxathiane (DIEOTT) was also available in a yield of 47% using N-iodosuccinimide (NIS) as the halogenating reagent.3. EOTT was synthesized and its electropolymerization was comparatively investigated by employing different solvent-electrolyte systems (room temperature ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (BmimPF6, CH2Cl2-BmimPF6 and CH2Cl2-Bu4NPF6). Further, the effect of solvents and supporting electrolytes on the structure, morphology, electrochemical, electronic, and optical properties and electrochromic performance of the obtained PEOTT films were minutely studied. PEOTT film with a band gap (Eg) of about 1.6 eV could be facilely electrodeposited in all the solvent-electrolytes and displayed excellent electroactivity, outstanding redox stability in a wide potential window, and improved thermal stability. Cyclic voltammetry showed that EOTT could be electropolymerized at a lower oxidation potential in BmimPF6 (?1.0 V vs Ag/AgCl) due to several advantanges of RTIL BmimPF6 itself, such as high intrinsic conductivity and mild chemical conditions, etc., and the resulting PEOTT film exhibited compact morphology with better electroactivity and stability and higher electrical conductivity. On the other hand, PEOTT films from all the sovent-electrolytes also showed the electrochromic nature by color changing from gray blue to green, and further kinetic studies revealed that PEOTT had decent contrast ratios (36%), higher coloration efficiencies (212 cm2/C in BmimPF6), low switching voltages, moderate response time (1.2 s), excellent stability, and color persistence.4. For the ameliorating the processing performance of PEOTT, EOTT was chemically polymerized firstly in aqueous poly(styrene sulfonic sodium) (PSS) solution and then EOTT together with EDOT was also polymerized in the aforementioned polyelectrolyte solution to yield PEOTT/PSS and poly(EOTT-co-EDOT)/PSS. As-formed free-standing PEOTT/PSS film exhibited electrical conductivity of?10-4 S/cm while the copolymer had electrical conductivity of 10-1 S/cm. After DMSO treatment, the electrical conductivity of the copolymer was enhanced to 100 S/cm; however, the conductivity of PEOTT/PSS was reduced (?10-5 S/cm). Kinetic studies revealed that the copolymer had high coloration efficiencies (375 cm2/C) superior to PEDOT (137 cm2/C), low switching voltages (-0.8 to+0.6 V), decent contrast ratios (45%), moderate response time (1.0 s), excellent stability and color persistence (90% retention of the optical density after 100 cycles).5. The chemical oxidative polymerization of EOTT was carried out in different solvents (CH2C12, H2O, and ACN) and the conducting powers of PEOTT were prepared (named as PEOTT-1, PEOTT-2, and PEOTT-3, respectively). The structure, crystalline characteristics, optoelectronic properties, electrical conductivity, and thermal stability of as-obtained PEOTT were comparatively evaluated. PEOTT-2 exhibited more robust thermal stability and higher electrical conductivity (0.99 S/cm), two orders of magnitude higher than that of PEOTT-3. Further, the electrochemical capacitance performance of PEOTT-2 electrode in different solvent-electrolyte systems (H2O-H2SO4, H2O-HClO4, H2O-LiClO4, and ACN-LiC104) was investigated comparatively by cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscope techniques. The electrochemical results revealed that the specific capacitance of PEOTT-2 electrode in H2O-HClO4 was enhanced to 208 from 133 F/g at 1 A/g and the energy density was also improved to 28.9 Wh/kg from 18.5 Wh/kg compared to those of PEOTT-2 electrode in ACN-LiC104.6. The solid state polymerization of the raw materials DBEOTT and DIEOTT proceeded spontaneously at ambient temperature and pressure state without adding any reagent solvent, oxidant, and catalyst. As-synthesized conducting polymer SSP-DBEOTT had distinct crystalline characteristic and an electrical conductivity of 0.0079 S/cm, one order of magnitude higher than that of SSP-DIEOTT. However, both the thermal stability and electrical conductivity of which were slightly inferior to those of chemically prepared PEOTT. In addition, the electrochemical capacitance performance test of SSP-DBEOTT in H2O-HC1O4 system revealed that the specific capacitance of the electrode was 83.0 F/g at the applied current density of 1 A/g, with the energy density of 11.5 Wh/kg when the power density was set as 0.5 kW/kg.