Ultraviolet resistance modification of poly(1,3,4-oxadiazole) fibers by dihydroxyterephthalic acid

Dihydroxyl poly(1,3,4-oxadiazole) (DHPOD) polymers are synthesized by copolymerization of 2,5-dihydroxyterephthalic acid (2,5-DHTA) and terephthalic acid with hydrazine sulfate in oleum, and then DHPOD fibers are prepared by wet-spinning. The effects of UV irradiation on POD fibers' mechanical properties and surface morphology with and without hydroxyl groups were investigated. As proved by tensile testing and scanning electron microscope measurement, the UV resistance of DHPOD fibers is improved compared to that of p-POD fibers. Besides, the heat resistance of POD fibers is not damaged by the introduction of phenolic hydroxyl groups. The UV and fluorescence spectra are used to analyze the UV resistance mechanism of the POD containing phenolic hydroxyl groups. Results show that the UV resistance mechanism of DHPOD is related to the proton transfer reaction between the 1,3,4-oxadiazole ring and ortho phenolic hydroxyl group.