New High-Pressure Synthesis of Aliphatic Poly(benzoxazoles) from a Bis(o-aminophenol) and Aliphatic Dinitriles

Abstract

The high-pressure synthesis of benzoxazole compounds as well as aliphatic poly(benzoxazoles) was carried out in a sealed Teflon capsule by using a piston-cylinder type hot-pressing apparatus. As the model compound study, 2-phenylbenzoxazole was obtained readily from o-aminophenol and benzonitrile with the elimination of ammonia under 150-400 MPa at 180-190 o C. This reaction was accelerated under high pressure. The high-pressure polycondensation of 4,4'-diamino-3,3'-dihydroxybiphenyl (AHB) with aliphatic dinitriles proceeded under 150-500 MPa at 230-300 o C, affording highly crystalline aliphatic poly(benzoxazoles) having inherent viscosities about 0.2 dL-g -1 . These poly(benzoxazoles) were obtained also by the high-pressure polycondensation of AHB-dihydrochloride with the dinitriles along with the elimination of ammonium chloride under 200-350 MPa at 270-320 o C. Although the latter polymerization required higher reaction temperature, the polymers with higher inherent viscosities up to 0.6 dL-g -1 were readily produced