Synthesis, Structure And Properties Of Disulfonated Poly(P-Phenylene Benzoxazole) (DSPBO)

Poly (p-phenylene benzobisoxzole) (PBO) fiber can be widely used in advanced composites due to its excellent tensile strength modulus, thermal resistance and flame retardant properties. However, the surface of PBO fiber is relatively inert, and the interfacial adhesion between PBO fiber and resin matrix is not sufficient for practical uses. The poor adhesion is generally the reason. Thereby it is of great significance to increase the surface free energy of PBO fiber. In this paper, disulfonic acid groups were introduced to PBO molecular chain to improve its surface property.A novel monomer, 2, 2’-sodium sulfonate-4, 4’-oxydibenzoic acid (SODBA), was firstly synthesized from 2, 2’-sodium sulfonate-4, 4’-oxydibenzoic acid (ODBA). DSPBO containing sulfonic acid groups in macromolecular chains was obtained by co-polymerization from 4,6 -diamino resorcinol dihydrochloride (DAR) and terephthalic acid (TPA), with addition of certain amounts of SODBA in polyphosphoric acid(PPA). The FTIR and element analysis results showed that SODBA was incorporated into polymer chains. DSPBO fiber was spun via dry-jet wet-spinning technique, and the mechanical property, crystalline morphology and intrinsic viscosity of the fiber were investigated. The tensile strength of DSPBO-1% fiber was 23.2cN/dtex. The intrinsic viscosity decreased slightly after disulfonic acid group was introduced. Morphological survey on DSPBO fiber with different content of SODBA was conducted by X-ray, Raman spectrum and Density measurement. It was found that the crystallinity, orientation of crystal and density decreased with the increase of SODBA content.The surfaces of the fibers were analyzed and quantified. The contact angles between fiber and water, ethyl, alcohol were measured by an OCA40 Microdynamic contact angle analysis system. It was found the contact angle of DSPBO to water and alcohol got smaller than that of PBO to either of them. For DSPBO-1% and DSPBO-3% fiber the contact angle to water was 52.1°and 46.7°respectively, while the value for PBO fiber was 71.4°. The surface free energies of DSPBO-1% and DSPBO-3% were increased up to 48.67mJ/m~2 and 53.46mJ/m~2. While the free energy of PBO fiber was only 35.5mJ/m~2. The interfacial shear strength (IFSS) was determined by a micro-bond fiber pull-out test. The results showed that the interfacial shear strength was improved by 31.7%, when SODBA content was 1.5% mol ratio.The anti UV properties of PBO and DSPBO fibers were investigated under UV accelerated aging condition. After exposing to UV for 310 hours, the strength retention of DSPBO-3% fiber was 63.75%, while for PBO fiber the retention was only 44.17%. The intrinsic viscosity of the DSPBO-3% fiber only decrease about 15%, while that of PBO is 26.34%. The SEM and FTIR analysis both showed that the UV stability of PBO fiber was improved after disulfonic acid groups were introduced.