Preparation,Design And Property Of Benzoxazole Fibers Based On Novel Third Comonomer

With the highest level in fiber strength,elastic modulus,heat resistance,flame retardancy of organic fiber,poly-p-phenylene benzobisoxazole(PBO)fiber has been widely applied in the aerospace,military,fire and other fields.However,even for those commercials PBO fibers,there is still a big gap between the practical mechanical properties and theoretical value in fibers' strength and elasticity modulus,which need to be further improved.In this thesis,the synthesis routes and processes of four monomer hydrochloride,2-(4-aminophenyl)-1H-benzimidazol-5-amine dihydrochloride(APBIA·2HCl),4,6-diaminoresorcinol dihydrochloride(DAR·2HCl),2,3,5,6-pyridinetetramine trihydrochloride hydrate(TAP·3HCl·H2O)and 3,3'-diaminobenzidine tetrahydrochloride(DAB·4HCl)were optimized and the final products with high purity were obtained.Benzoxazole heterocycle molecular was introduced into PBO fiber by adding the third monomer into copolymerization and a new PBO complex fiber was designed and synthesized successfully,to improve the mechanical prop erty of PBO fiber.This thesis designed a new synthetic route of APBIA·2HCl,which used p-nitrobenzaldehyde and 4-nitro-o-phenylenediamine as raw materials to prepare high purity APBIA·2HCl via cyclization,hydrogenation reduction and acidify reaction.The conversion rate and products purity of nitration reaction in the preparation of DAR·2HCl and TAP·3HCl·H2O were improved by using molecular sieve as the catalyst.The structures of five compounds above were characterized b y infrared spectroscopy(IR),H NMR Spectroscopy(1H NMR)and C NMR Spectroscopy(13C NMR).The high performance liquid chromatography(HPLC)results showed that the purity of the compounds was higher than 99.0%,with the highest purity of 99.8%.The mechanism of PBO polymerization was studied by using the theory of quantum chemistry,and the model compound experiment was designed to verify the PBO polymerization process.During the process of PBO polymerization,the initial reaction temperature has a great influence on the structure and molecular weight of PBO polymer after adding two monomers.The results of quantum chemical simulation show that the lower initial reaction temperature is favorable for the reaction,that is,o-amino polyarylester could finally convert to polyparaphenylene benzobisoxazole with a large molecular weight.While the higher initial reaction temperature could lead to form a mixture of o-amino polyarylester and o-hydroxy polyamide,causing a significant reduction in molecular weight.Therefore,the initial reaction temperature of polymerization process should be strictly controlled.In this thesis,four kinds of benzoxazole composite fibers were prepared with APBIA and DAB as the third monomer.PBO-APBIA polymer was synthesized by ternary polymerization of DAR,paraphthaloyl chloride and the new third monomer APBIA.PBO-APBIA-CNTs fibers and PBO-APBIA-GO fibers were synthesized by the quaternary copolymerization of DAR,paraphthaloyl chloride,CNTs(or GO)and the new third monomer APBIA,respectively.PIPD-DAB fibers were synthesized by ternary polymerization of TAP,DHTA and novel third monomer DAB.The measurement results carried by IR,13 C NMR,X-ray diffraction(XRD),scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),Raman spectroscopy,X-ray photoelectron spectroscopy(XPS),atomic force microscopy(AFM),and thermogravimetric analysis(TG)showed that the introduction of new third monomers APBIA and DAB into the molecular structure of benzoxazole polymers,such as PBO and PIPD,could improve the tensile strength and tensile modulus of the complex fibers,but has little affection on the fibers' thermal resistance.Compared with the pristine fiber,the tensile strength and modulus of fabricated fibers were improved by 30.4% and 34.9%,respectively.This research on the preparation of PBO fiber with better comprehensive performance has been explored.