Synthesis, Structure And Properties Of Modified Poly (P-phenylene Benzoxazole) (PSPBO)

Poly(p-phenylenebenzobisoxzole) ( PBO ) is a kind of aromatic heterocyclic rigid-rod polymer. PBO fiber produced via dry-jet wet-spinning technique has superior tensile strength, modulus, excellent thermal resistance and flame retardant properties. So PBO fiber provides great potential applications as reinforcement fiber for advanced composites. However, the chemically inactive surface and the lower compressive strength will limit the applications of PBO fiber in composite. In this thesis ionic group was introduced to PBO molecular chain to improve its surface property, and a carbon nanotubes (CNTs)/PBO composite was also studied.Firstly,2-sulfoterephthalic acid kalium salt (STPA) was synthesized sulfonation and oxidation of 1, 4-dimethylbenzene. Thecomposition of the intermediates was characterized by means of FTIR, ¹H-NMR and element analysis.Modified PBO (PSPBO) containing ionic groups (-KSO₃) in polymer chains was obtained by copolymerization from 1, 3-diamino-4, 6-dihydroxybenzene dihydrochloride (DAR) and terephthalic acid (TPA), with addition of certain amounts of STPA in replace of TPA, in polyphosphoric acid. The FT-IR and element analysis results showed that STPA was incorporated into polymer chains. The intrinsic viscosity of PSPBO-1.5 (with 1.5 mol% ionic group content) was 21.70dL/g, while which of PSPBO-5 was 18.69dL/g.PSPBO fiber was spun via dry-jet and wet-spinning technique for the first time, and the mechanical property, thermal property and aggregating structure of which were investigated. The tensile strength of PSPBO-1.5 fiber was 2.98GPa. While for PSPBO fiber with 5mol% ionic group content, PSPBO-5, the tensile strength was still as high as 2.49GPa. The aggregating structure of PSPBO was affected by the introduction of ionic group. Although the crystallinity and orientation of PSPBO fiber changed little, the crystal size decreased obviously. Thermal stability of PSPBO fiber was excellent and decomposition temperature was about 700℃in N₂ atmosphere.The surface property of the fibers were analyzed and quantified by contact angle measurement. It was found the contact angle of PSPBO to water, alcohol and acetone got smaller compared to PBO fiber. For PSPBO-1.5 and PSPBO-5 fiber the contact angle to water was 66.2°and 61.2°respectively, while the value for PBO fiber was 71.4°. The surface free energy of PSPBO-1.5 and PSPBO-3 was increased up to 39.4mJ/m² and 40.1mJ/m² , while the value for PBO fiber was 35.5 mJ/m² . The interfacial shear strength (IFSS) was studied by microbond fiber pull-out test. The results showed that the IFSS of PSPBO fiber/ epoxy composite was improved obviously compared to PBO fiber/epoxy system. The IFSS of PSPBO-1.5, PSPBO-3, and PSPBO-5/epoxy were 12.97 MPa, 13.88MPa, and 17.40 MPa respectively, which were increased by 33.7%, 43.1%, and 79.4% compared to PBO fiber/epoxy system (IFSS=9.69MPa).CNTs/Polybenzoxazole(PBO) composites with different CNTs content were synthesized by in situ polymerization from DAR and TPA, with addition of treated CNTs. The factors influenced the polymerization were discussed, and the thermal stability and mechanical property CNTs/PBO composites were studied. It was found the activation, lower content, adding earlier, and pre-dispersion of CNTs in PPA were the main factors to achieved high molecular weight CNTs/PBO composites. The spinnability of CNTs/PBO got worse with the increasing of CNTs content. CNTs/PBO showed excellent thermal stability with a starting decomposition temperature of 689℃in nitrogen atmosphere. CNTs/PBO fiber was obtained by dry-jet wet-spinning technique. The tensile strength of CNTs/PBO (5/95 weight ratio) was 1.97GPa.