A New Class of Organosoluble Rigid-Rod Fully Aromatic Poly(1,3,4-oxadiazole)s and Their Solid-State Properties, 1. Synthesis

Since it is known, that poly(p-phenylene-1,3,4-oxadiazole) exhibits reversible reduction behaviour in cyclovoltammetric measurements, it may be used as an electron transport material in electronic devices such as light emitting diodes (LEDs). However, the polymers are difficult to process, for example as thin films. By introducing linear or branched alkoxy side groups into the backbone it is possible to obtain rigid rod, fully aromatic poly(1,3,4-oxadiazole)s which are soluble in organic solvents. Various polycondensation routes were investigated to prepare symmetrical and unsymmetrical dialkoxy-substituted aromatic poly(1,3,4-oxadiazole)s. Initially the interfacial polycondensation and the low-temperature solution polycondensation between aromatic dihydrazides and diacid chlorides in N-methylpyrrolidone were used. These methods were not successful for the synthesis of the polyoxadiazole with branched side chains. Thus, a new synthetic method for the preparation of such polymers was developed. The polycondensations are carried out in hot 1,2-dichlorobenzene in the presence of a basic acceptor like pyridine. These conditions are unusual for such types of reaction.