Extremely High Thermal Resistive Poly(p-phenylene benzobisoxazole) with Desired Shape and Form from a Newly Synthesized Soluble Precursor

The poly­(p-phenylene benzobisoxazole) (PPBO) fiber, known as Zylon, has a very high thermal stability as well as mechanical strength when compared to any other polymers due to its ladder-like rigid structure. However, one of the critical drawbacks of its stiff structure is its insolubility in organic solvents, and only strong acids can be used use for fiber spinning of this polymer. To overcome the poor processability caused by this insolubility in organic solvents, a soluble PPBO precursor was designed and synthesized by the reaction of tert-butyldimethylsilyl (TBS) group-functionalized 4,6-diaminoresoisinol with terephthaloyl chloride for polycondensation. The obtained TBS-functionalized PPBO precursor (TBS-prePBO) shows an excellent solubility in common organic solvents, such as N-methylpyrrolidone (NMP), N,N-dimethylacetamide (DMAc), and dimethyl sulfoxide (DMSO). Transparent TBS-prePBO films made by the solution-cast method provided PPBO films after thermal treatment at 500 °C for 1 h. The structure of the obtained PPBO films was characterized by IR and XRD techniques and found that the films exhibited extremely high thermal stabilities, namely, the synthesized PPBO polymer decomposition temperature reached 670 °C in flowing N₂, which is the highest temperature among the organic polymers reported so far.