Two reaction routes for the preparation of aromatic polyoxadiazoles and polytriazoles: Syntheses and properties

Abstract

SYNOPSISTwo reaction routes for the preparation of aromatic poly-1,3,4-oxadiazoles and poly-1,2,4-triazoles are studied and their influence on the physical properties, i.e., inherent viscosity, glass transition, degradation temperature, and film integrity of the final products are discussed. Aromatic poly-1,3,4-oxadiazoles are prepared by means of a polycondensation reaction of terephthaloyl chloride and isophthalic dihydrazide yielding a precursor polymer, poly (p,m-phenylene ) hydrazide, which is converted into the corresponding poly-1,3,4-0~-adiazole by means of a cyclodehydration reaction. Poly-1,3,4-oxadiazoles are also prepared by means of a polycondensation reaction between terephthalic and isophthalic acid and hydrazine yielding poly-1,3,4-oxadiazoles with higher inherent viscosities. Flexible poly-1,3,4-oxadiazole films are obtained only if the inherent viscosities of the polymers used are higher than 2.7 dL/g. The thermal stability is found to i n c r e a s with increasing content of p-phenylene groups in the polymer backbone. Aromatic poly-1,2,4-triazoles are prepared using polyhydrazides with alternating para-and meta-phenylene groups and poly-1,3,4-oxadiazoles with a random incorporation of para-and rneta-phenylene groups in the main chain as precursor polymers. The glass transition temperatures are found to increase with increasing content of p -phenylene groups in the main chain of these polymers. Cold crystallization is observed only for the alternating polymer. 0 1994 John Wiley & Sons, Inc. Keywords: poly-1,3,4-oxadiazoles polyhydrazide poly-l,2,4-triazoles cold crystallization I NTRO DU CTI ON Aromatic poly-1,3,4-oxadiazoles and poly-1,2,4-triazoles are chemically resistant and thermally stable polymers soluble only in strong acids and stable up to 45OOC.l We have studied these polymers as new membrane material^,^'^ with the aim to develop membranes that can be applied under severe operating conditions, such as elevated temperatures and acidic or basic environments. Such membranes also should be highly resistant towards organic solvents. A number of reaction routes are known for the preparation of these poly-l,3,4-oxadiazoles and poly-1,2,4-triazoles.~ We decided to study the preparation of aromatic poly-1,3,4-oxadiazoles by means of a solid state cy- To whom correspondence should be addressed.clodehydration reaction of an aromatic polyhydra~i d e ,~'~ the latter being used as a tractable precursor polymer. Since poly-1,3,4-oxadiazoles with inferior mechanical properties were obtained,' a second reaction route was also studied. This route directly yields aromatic poly-1,3,4-oxadiazoles from hydrazine sulphate, and terephthalic and isophthalic acid as m o n o m e r~.~ Aromatic poly-1,2,4-triazoles were prepared by a reaction of an aromatic polyhydrazide' and poly-1,3,4-oxadiazoles9 with aniline in polyphosphoric acid.The synthesis routes are represented in Figure 1. Polyhydrazides with alternating para-and metaphenylene groups in the main chain were prepared using terephthaloyl chloride and iso...

Synthesis and fabrication of nanostructured hydrophobic polyazole membranes for low-energy water recovery

“…They are known for their high temperature stability and their synthesis has been optimized to supply high molecular weight polymers with the best film-forming characteristics for membranes. While poly (phenylene oxadiazole) [22] is hardly soluble, enabling film casting only from strongly acid solution, the substitution of the phenylene group by diphenyl ether or diphenyl hexafluoroisopropylidene increases the solubility in dimethylformamide and dimethylacetamide, facilitating membrane casting by phase inversion and electrospinning. Particularly when fluorinated groups, like diphenyl hexafluoroisopropylidene, are chosen for polyoxadiazole or polytriazole synthesis, highly hydrophobic products are expected.…”

Poly(oxadiazole)s

“…23 Random copolymers can be obtained by allowing a reaction of a mixture of terephthalic and isophthalic acid and hydrazine. 24 The molecular weight of the polymers obtained from this route is higher than the molecular weight of polymers obtained from the respective acid chlorides.…”

“…The thermal stability increases with increasing content of p-phenylene moieties in the polymer backbone. 24 Further, they exhibit other desirable properties, e.g., good hydrolytic stability, high glass transition temperatures, low dielectric constants, and good mechanical properties. Flexible PODA films can be obtained only if the inherent viscosities of the polymers are higher than 2.7 dl g −1 .…”

Noncoplanar rigid‐rod aromatic polyhydrazides containing Tröger's base

“…3 In particular, they are soluble polymers with potential to convert to other highly thermally stable polymers like polyoxadizoles and polytriazoles. 4,5 Aromatic polyhydrazides (that are classified under a category of heat resistance materials) are usually made by reacting diacyl chloride with dihydrazide at low temperature or Yamazaki's phosphorylation method using dihydrazide and dicarboxylic acid. 3,6 The rigid V-shaped Trö ger's base unit suppresses coplanar structures, lower regularity, and molecular ordering.…”