Benzobisthiazoles

PBO andPBZT. PBZ, a family of/ -phenylene-heterocycHc rigid-rod and extended chain polymers includes poly(/)-phenylene-2,6-benzobisthiazole) [69794-31-6] trans-V 27V) and poly(/)-phenylene-2,6-benzobisoxazole) [60871-72-9] (ot-PBO). PBZT and PBO were initially prepared at the Air Force Materials Laboratory at Wright-Patterson Air Force Base, Dayton, Ohio. PBZT was prepared by the reaction of... 

As the laser beam can be focused to a small diameter, the Raman technique can be used to analyze materials as small as one micron in diameter. This technique has been often used with high performance fibers for composite applications in recent years. This technique is proven to be a powerful tool to probe the deformation behavior of high molecular polymer fibers (e.g. aramid and polyphenylene benzobisthiazole (PBT) fibers) at the molecular level (Robinson et al., 1986 Day et al., 1987). This work stems from the principle established earlier by Tuinstra and Koenig (1970) that the peak frequencies of the Raman-active bands of certain fibers are sensitive to the level of applied stress or strain. The rate of frequency shift is found to be proportional to the fiber modulus, which is a direct reflection of the high degree of stress experienced by the longitudinally oriented polymer chains in the stiff fibers. 

Scherf, J., Cohen, Y. and Wagner, H.D. (1992). Interfacial strength measurements in poly (p-phenylene benzobisthiazole)/epoxy composites. Intern. J. Adhesion Adhesive, 12, 251-256. 

Solutions of poly(l,4-phenylene-2,6-benzobisthiazole), PBT, exhibit an isotropic to nematic phase transition in a variety of solvents including methane sulfonic acid, MSA, chlorosulfonic acid, CSA, and poly phosphoric acid, PPA (1-4). In the latter case the transition occurs over a range of water -P2O5 compositions. In these acids the polymer, with repeating unit... 

Fibers and films obtained from lyotropic solutions of rigid polymers exhibit high tensile modulus and strength and are therefore of interest for structural applications. Poly(p-phenylene benzobisthiazole) (PBT) is a rigid polymer from which high... 

Few neutron or electron diffraction studies have been reported, although the neutron structure analysis of substituted poly(benzobisthiazole) and poly(benzobisoxazole) derivatives of 19 and 5 has been reported and the torsion angle between the benzobisthiazole and phenyl rings was shown to be 7.2° larger than that determined from X-ray methods <1999MM4010, 2001MM2012>. 

Electron spin resonance (ESR) methods have been used to observe the formation of the radical cations and dications of benzoll,2- 4,5- ]bis[l,2,3]trithiole 13 and benzo[l,2-4 4,5- ]bis[l,2,3]dithiazole 17, and the experimental results confirm the ab initio calculations performed <2003EJ04902, 1997JA12136>. ESR has also been used to confirm the formation of superoxides upon photolysis of aryl benzobisthiazoles and aryl benzobisoxazoles in the presence of molecular oxygen <2003MM4699>. 

In the great majority of examples, mass spectral data have been used only to establish the molecular ions or for elemental analysis. Extended cyclopentadithiophene, benzobisoxazole, and benzobisthiazole systems have been shown to exhibit doubly charged parent ions <2002OL4535, 2003MM2705, 2003MM4699>. 

Gas chromatography-mass spectrometry (GC-MS) has been used to identify the fragments formed upon photolysis of aryl benzobisthiazoles and aryl benzobisoxazoles. It was shown that both compounds undergo different chemical reactions when photolyzed in the solid state with the aryl benzobisthiazole having greater photostability <2003MM4699>. 

The wide structural diversity in the tricyclic compounds considered in this chapter ensures that they have found an equally diverse range of applications. The applications previously outlined <1996CHEC-II(7)841> have continued to be important and have been further developed. Carbocyclic anhydrides and imides continue to find application for the synthesis of polymeric materials which are used extensively in microelectronics due to their excellent thermal and electrical properties <2001PP03>. Similarly, polymers containing benzobisthiazoles, benzobisoxazoles, and... 

Benzobisthiazole random copolymers (X) [38] were also prepared using 2-methyl terephthalic acid and terephthalic acid with l,4-dimercapto-2,5-diamino-1,4-benzene dihydrochloride. Various copolymers provided materials with a wide range of crosslink densities. High quality fibers with spin draw ratios as high as 50 to 1 were obtained by dry-jet wet spinning of anisotropic polymerization mixtures. Heat treatment of the fibers was carried out in a tube oven... 

Lyotropic polymers consisting solely of ring structures are also known, and are exemplified by poly(p-phenylene benzobisthiazole) (IV), which forms a nematic phase in several strongly protonating acids including polyphosphoric acid. Its synthesis and application, like those of the aromatic amide polymers, are discussed later. 

The structures of polymers containing benzobisthiazole and benzobisoxazole have been determined. These form rigid rod-like polymers with high specific strength <81MM935>. For some bis-selenadiazolo analogues of tetracyanoquinodimethane x-ray methods established the presence of extensive intermolecular interactions <87CL2285>. 

Although aramid fiber is by far the most successful fiber made via the liquid crystal route, there are some other important fibers that have been made by this process. For example, poly(p-phenylene benzobisthiazole) (PBT) (Wolfe et al, 1981a, 1981b) is synthesized from terephthalic acid and 2,5-diamino-l,4-ben-zenedithiol dihydrochloride (DBD). The DBD is first dissolved in poly-phosphoric acid (PPA), followed by dehydrochlorination. Terephthalic acid and more PPA are then added and the mixture is heated to 160°C to make a solution. The solution is heated to 180 C and reacted for 18 hours to obtain the... 

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