Polyoxadiazoles

Polysulfanyldibenzamides Polyhydrazides Melting points up to 330°C (626°F) soluble good fiber properties Dehydrate at 200°C (392°F) to over 400° C (752°F) to form polyoxadiazoles good fiber properties. 

Polydithiazoles Polyoxadiazoles Polyamidines Pyrolyzed polyacrylonitrile Polyvinyl isocyanate ladder polymer Polyamide-imide Polysulfone Decompose at 525°C (977°F) soluble in concentrated sulfuric acid. Decompose at 450-500°C (842-932°F) can be made into fiber or film. Stable to oxidation up to 500°C (932°F) can make flexible elastomer. Stable above 900°C (1625°F) fiber resists abrasion with low tenacity. Soluble polymer that decomposes at 385°C (725°F) prepolymer melts above 405° C (76l.°F). Service temperatures up to 288° C (550°F) amenable to fabrication. Thermoplastic use temperature —102°C (—152°F) to greater than 150° C (302°F) acid and base resistant. 

N.C. Yang, Y.H. Park, and D.H. Suh, Synthesis and properties of new ultraviolet-blue-emissive fluorene-based aromatic polyoxadiazoles with confinement moieties, J. Polym. Sci., Part A Polym. Chem., 41 674-683, 2003. 

Yang NC, Chang S, Suh DH (2003) Synthesis and optically acid-sensory properties of novel polyoxadiazole derivatives. Polymer 44 2143-2148... 

I. polyhydrazide [hydrazine-aft-(terephthalic acid)] n. polyoxadiazole [hydrazine-aft-(terephthalic acid)]... 

Polycyclic oxadiazoles linked to phenyl groups have been prepared. Table 8 compares their physical properties with those of the corresponding polyphenyls the solubility of polyoxadiazoles in organic solvents is much higher and their melting point is lower 18 a). 

A review of the chemistry of 1,2,4-oxadiazoles Table 8. Polyoxadiazoles and polyphenyls... 

The application of the classical (Tiemann) method in the preparation of polyoxadiazoles has led to untractable products of low molecular weight 18 a). Such materials have been obtained from diamidoximes and diacid chlorides ... 

More recently, we have seen other new plastics arrive, including such exotic, high performance materials as the polybenzimidazoles, polyoxadiazoles, polyperfluorotriazines, polyphenylenes, and such inorganic materials as the boron polymers, the metalloxanes, and the polysilazanes, to name only a few. These exotic materials are mostly development products today, they are very expensive and will undoubtedly find their first uses, if any, in the aerospace industry which requires the high performance offered by these materials and can afford to pay for them. Some of these new materials will become commercial successes, others will not. 

Synthesis and Properties. Polyoxadiazoles containing aromatic moieties with aliphatic linkages/groups have been widely explored in the literature. The aromatic moieties increase the rigidity of the polymer the presence of aliphatic groups makes the chain more flexible and processible. 

The fibers of aromatic PODs are known to have a combination of good properties, such as strength and stiffness, fatigue resistance, and relatively low density, in the range of 1.2 to 1.4 g/cm3. PODs have been used to improve the heat resistance of many synthetic fibers. This is usually done by dissolving the POD in sulfuric acid and then treating the fibers with this solution. Poly( >-phenylene-l,3,4-oxadiazole) is the most commonly used commercial polyoxadiazole, and the fiber spun from this polymer is called Oksalon. 

Pyrolysis and Graphitization of Polyoxadiazole. Table 1 shows electrical conductiyity at room temperature for yarious condensation polymers heat-treated at 1000 and 2500 C. For a HTT near 1000 C, poly(p-phenylene-1,3,4-oxadiazole) (POD) has the highest conductivity of 340 S/cm, twice as high as that of polyimide (KAP)... 

Figure 1. The interplanar spacing do 02 as a function of HTT for polyamideimide (HI), polyamide-1 (KEY), polyimide (KAP), polyamide-2 (MX), polybenzimidazole (FBI) and polyoxadiazole (POD).

Pyrolysis of polyoxadiazole (POD) yielded a highly conductive pyropolymer at heat treatment temperatures (HTT) near 1000 C and... 

The aromatic polyimides, cited earlier, separate carbon dioxide over methane with a-valves of 150-160. Aromatic polyoxadiazoles have a-valves of 100-2 00.157 The permeability of one aromatic polyimide was improved by two to four orders of magnitude by carbonizing it on porous alumina,158 the final a-valve being 100. In this case, the final actual membrane was probably a porous carbon molecular sieve. Facilitated transport has also been used to increase the separation factor. A porous poly(vinylidene difluoride) membrane with ethanolamine or diethanolamine in the pores gave a separation factor of carbon dioxide over methane of 2000.159 Such a method is less energy-intensive than when an amine is used in the usual solvent method. 

The reaction of polyvinyl alcohol to give polyacetals or polyketals has been already described in Vol. II of this series. In addition the conversion of polyhydrazides to polyoxadiazoles, and polymeric acids to polyimides is also described in Vol. I of this series [14] and in Section 5 of this chapter. 

The polyhydrazide was converted to the polyoxadiazole by heating at the m.p. for approximately 30 min or until the melting temperature of the product corresponded to the polyoxadiazole in Table VII. 

The polyoxadiazoles were soluble at room temperature in w-cresol, 1,2-dichloroethane, and chloroform. 

P. E. Cassidy and N. Fawcett. Thermally stable polymers Polyoxadiazoles, polyoxadiazole-A-oxides, polythiazoles, and polythiadiazoles.. J. Macro-mol. Set, Rev. Macromol. Chem., C17(2) 209-266,1979. 

M. J. Nanjan. Polyhydrazid.es and polyoxadiazoles. In H. F. Mark, N. Bikales, C. G. Overberger, and G. Menges, editors. Encyclopedia of Polymer Science and Engineering, volume 12, pages 332-339. Wiley Interscience, New York, 2nd edition, 1988. 

D. Gomes, S. P. Nunes, J. Carlos Pinto, and C. Borges. Synthesis and characterization of flexible polyoxadiazole films through cyclodehydration of polyhydrazides. Polymer, 44(13) 3633-3639, June 2003. 

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