Novel synthesis of high-molecular-weight prepolymer of poly(p-phenylene benzoxazole) in ionic liquids

Using ionic liquids (ILs) as the reaction solvent for the synthesis of prepolymer polyamide of poly(p-phenylene benzoxazole) (PBO) was investigated. The optimum condition of prepolymer preparation was determined in ILs. A series of 1,3-dialkylimidazolium ILs were used to be the reaction media of the polycondensation. The relationship between the molecular weight of prepolymer and the structure of ILs was analysed by changing the structure of the cation and species of anion of ILs. In order to prove the feasibility of the transformation, the prepolymer was used to prepare PBO in polyphosphoric acid media, and the conversion process was analyzed. The spinnability of the PBO solution was explored by the preparation of PBO fibers. The basic mechanical properties of PBO single fiber were tested. In a word, using 1,3-dialkylimidazolium ILs as the reaction solvents was feasible for the synthesis of high-molecular-weight PBO prepolymer, which could be a promising PBO preparation method.