Effects of hydroxyl groups on the properties of polybenzoxazoles (pbos): synthesis of trans-HPBO fibers and trans-2,5DHPBO fibers

The two novel <i>trans</i>-polys(hydroxy-p-phenylenebenzobisoxazole) (<i>trans</i>-HPBO/2,5-DHPBO) were synthesized by 2,5-diaminohydroquinone hydrochloride (DAQH·2HCl) and 2-hydroxyterephthalic acid (HTA), 2,5-dihydroxyterephthalic acid (2,5-DHTA). The <i>trans</i>-HPBO/2,5-DHPBO fibres were characterized by infrared spectra and the thermogravimetric analysis. The experimental results were shown that the purple <i>trans</i>-HPBO primary fibers with a characteristic viscosity of 2.87 dL·g^-1 and the brown <i>trans</i>-2,5DHPBO primary fibers with a characteristic viscosity of 3.24 dL·g^-1. The <i>trans</i>-HPBO primary fibers′ maximum thermal decomposition rate was 602.7 &deg;C, while the sample still had 36.79&percnt; residual weight at 980 &deg;C, which showed that the monohydroxy modified <i>trans</i>-PBO primary fibers had a better thermal stability under the nitrogen environment. The <i>trans</i>-2,5DHPBO primary fibers′ maximum thermal decomposition rate was 581.1 &deg;C, and when the sample temperature reached 980 &deg;C, there was still 35.83&percnt; of residual weight. It can be seen that although the heat resistance of double hydroxyl modified <i>trans</i>-PBO is slightly lower than that of single hydroxyl modified <i>trans</i>-PBO, it is still significantly higher than that of other fibers.