Poly [(benzo[l,2-d:4,5-d ~bisthiazole-2,6-diyl)-1,4-phenylene] (PBT) was prepared by the polycondensation of 2,5-diamino-l,4-benzenedithiol dihydrochloride with terephthalic acid in poly(phosphoric acid) (PPA). Polymerization mixtures with polymer concentrations between 5 and 10 wt % were liquid crystalline at early stages of conversion and were suitable for dry-jet wet spinning into high-modulus/high-strength fibers either directly from PPA or after isolation and redissolution in strong acids. Polymerization in the liquid crystalline state by using concentrations >5% gave lower viscosity solutions than polymerizations that remained isotropic, owing to the use of polymer concentrations of <3%. The lower bulk viscosity for a given molecular weight facilitated the attainment of higher molecular weight samples. Intrinsic viscosities of isolated PBT measured in methanesulfonic acid were a high as 30.3 dL/g. PBT showed excellent thermal and oxidative stability as determined by vacuum thermogravimetric-mas spectral analysis and isothermal aging at 316 and 371 "C. Rigid-rod poly(benzobisthiazo1es) with various degrees of phenyl substitution were prepared but were soluble only at low concentrations in certain mixed solvents.The attainment of a new ultrahigh-modulus, ultrahighstrength, thermally stable organic fiber has been realized with the synthesis and spinning of nematic solutions of poly [ (benzo[ 1,2-d:4,5-d ' I bisthiazole-2,6-diyl)-1,4phenylene], referred to as PBT. This paper describes the synthesis and thermal properties of PBT and related poly(benzobisthiazo1es) with phenyl substituents on the rigid-rod chain. Another paper in this series2 describes the preparation of PBT fiben that have tensile moduli greater than 2000 g/denier and tenacities greater than 20 g/denier.

Raman microscopy was used to investigate microstructural properties of amorphous MoO3 thin films that had been subjected to a photochromic (PC) or electrochromic (EC) process. The Raman spectra changed reversibly when the films went through PC or EC coloration and decoloration cycles. Different molybdenum bronzes were produced with PC and EC treatments, as indicated by the shifts in the Raman bands. The same observation was made in the surface photovoltage spectral experiments. Hence, it was concluded that the microstructure of molybdenum bronze was affected by the coloration means (PC or EC process); the injected cations in an EC process were bonded to the triply coordinated O atoms, whereas the injected H+ ions in a PC process were bonded to both the triply coordinated and doubly coordinated O atoms. The size of the injected cations via EC processes had little effect on the microstructure of the colored films.

Conductive boron-doped diamond thin-film electrodes were used for the electrochemical detection of selected N-methylcarbamate pesticides (carbaryl, carbofuran, methyl 2-benzimidazolecarbamate, bendiocarb) after liquid chromatographic separation. Two kinds of detection methods were adopted in this study. In the first method, a direct detection of underivatized pesticides was carried out at an operating potential of 1.45 V versus Ag/AgCl, which resulted in the detection limits of 5-20 ng/mL (or 5-20 ppb) with S/N = 2 due to the low background current and wide potential window of the diamond electrode. In the second method, the detection limits were improved by subjecting the pesticide samples to alkaline hydrolysis in a separate step prior to injection. The phenolic derivatives obtained by alkaline hydrolysis oxidize at a relatively lower potential (0.9 V vs Ag/AgCl), which increases the sensitivity drastically. The advantage of the diamond electrode for the detection of phenolic derivatives is that it offers excellent stability in comparison to other electrodes. This method gives the detection limits of 0.6-1 ng/mL (or 0.6-1 ppb), which are well below the maximum residue levels allowed for carbaryl, carbofuran, and bendiocarb. While the lowest detection limits (LOD) obtained by the direct detection of pesticides are comparable to the those reported by the well-established HPLC-fluorescence, the LODs of the alkaline hydrolysis method are found to be even lower than the reported limits. On-line reactivation of the diamond electrode surface was shown to be possible by an anodic treatment of the electrode at approximately 3 V for 30 min in case of electrode fouling, which may occur after a prolonged use. Such a treatment damages the glassy carbon (GC) and metal electrodes, while the diamond electrode remains stable. These results suggest that the diamond electrode is superior to the other previously used electrodes such as GC and Kelgraf type for highly sensitive and stable detection of carbamate pesticides.