Preparing Studies And Industrialization Techniques Of New AB-Type PBO Monomers

Poly（p-phenylene-2,6-benzobisoxazole） （PBO） fiber span by the polymer is considered as the organic fiber with the best mechanic and thermostable properties. New AB-type monoers were proposed in order to increase the performance of PBO resin and novel methods for preparing these monoers: 2-（4-methoxycarbonylphenyl）-5-amino-6- hydroxy benzoxazole （MAB）, 4-（5-amino-6-hydroxybenzoxazol-2-yl）benzoic acid salt （ABAS） and their analysis here developed in industrialization.The critical monomer precursor methyl 4-(5-nitro-6-hydroxy -benzoxazole-2-yl benzoate （MNB） was stepwise or one-pot synthesized from methyl terephthalate （MTA） and 4-amino-6-nitroresorcin·HCl. In stepwise synthesis, 4-methoxycarbonyl benzoyl chloride （MBC） was firstly obtained from MTA and SOCl₂ which as acylating agent by acylation, and then undergoing condensation and cyclization to form MNB with a yield of 87% and purity of 97.30% in 4-methyl-2-pentanone solvent.The process of preparing high-purity new AB-PBO monomer: 4-（5-Amino-6-hydroxybenzoxazole-2-yl）benzoic acid （ABA） was studied systematically. The results showed that ABA was conveniently synthesized from MAB with purity of 99.5% and yield of 85% via alkali hydrolysis of K₂CO₃ at 60- 100℃and pH 6.0 crystal in water with Na₂S₂O₄ or NaHSO₃; ABAS was one-pot synthesized from MNB with a yield of 86.84% and purity of 99% via alkali hydrolysis of Na₂CO₃ and reduction, which had the advantages of simple procedure, low pollution and cost saving, polym. Retarder DMF-free, excellent thermo- and antioxydative-stability, safe operation in polym and etc..Trial production and technical development were completed for the industrialization of ABAS 50T/a. The results showed that commercial ABAS product reached total yield of 66. 7% （based on ANR·HCl） and polymer-grade quality. This process had the properities of cost-saving and environmentally-friendly, the quality of the product was also ranked on the top of polym. monomer in domestic market.The 4-（5-Amino-6-hydroxybenzoxazole-2-yl）benzoic acid salt （ABAS） was identified with ¹H-NMR, ¹³C-NMR, FT-IR. Its initial decomposition temperature was measured to be 290℃, and it had excellent thermostability,oxidation resistance and outstanding storage stability.