Preparation Of Low Dielectric Benzoxazole-based Polymer Resins And Research On Their Electrospinning

With the rapid development of advanced high-frequency mobile communication technology,high temperature resistant and low dielectric properties polymer materials are urgently needed.Common candidate materials,such as polyimide（PI）,have excellent heat resistance,but their relatively high dielectric constant（D_k）and dielectric loss factor（D_f）limit their applications in the field of high-frequency communication.Therefore,in the work of this article,benzoxazole groups with low moisture absorption and good dielectric stability were introduced into the PI molecular structure,and poly（imide-benzoxazole）（PIBO）nanofiber membranes（NFMs）with porous structure were prepared by electrospinning technology because of the low dielectric constant of air.Finally,the influence mechanism of molecular structure and composition structure on the physical and chemical properties of fiber membrane was systematically studied,and the relationship between structure and properties was obtained.The specific research work and achievements are as follows.Firstly,two aromatic diamine monomers containing bis（o-hydroxy substituted benzamide）groups were designed and synthesized respectively,2,2-bis[3-（4-aminobenzamide）-4-hydroxy phenyl]hexafluoropropane（p6FAHP）and 2,2-bis[3-（3-aminobenzamide）-4-hydroxy phenyl]hexafluoropropane（m6FAHP）,and their chemical structures were characterized.Secondly,p6FAHP and m6FAHP,the two monomers prepared above,were reacted with pyromellitic dianhydride（PMDA）monomer respectively,and two kinds of polyamic acid（PAA）solution were obtained by low-temperature solution polycondensation,then PAA NFMS were prepared by electrospinning process.After that,two conventional PIBO NFMs were further prepared by cyclization at high temperatures（300-350℃）.The test results showed that the whiteness of the fiber membranes decreased with high-temperature treatment,and the whiteness index（WI）values ranged from 58.42 to 69.59.The 5%weight loss temperatures(T_5%)of PIBO NFMs were all higher than 560℃,and the residual mass ratios at 700℃(R_w700)were above63.6%,indicating excellent heat resistance.In addition,the dielectric constant of p-PIBO NFMs was 2.11@1MHz,and that of m-PIBO NFMs was 1.99@1MHz.Finally,on the basis of the above research work,to further reduce the dielectric constant of PIBO nanofiber membranes,the preparation and performance of PIBO nanofiber membranes with high fluoride content were further studied.Soluble PI resin was prepared by high-temperature solution polycondensation of p6FAHP and m6FAHP with 2,2’-bis（3,4-dicarboxyphenyl）hexafluoropropane（6FDA）,respectively.After the PI resin solution was made into PI NFMs,high-temperature processing was performed to obtain PIBO NFMs with high fluorine content.The T_5%values of the membranes were higher than 500℃,R_w700 values were higher than 55%,and the glass transition temperature（T_gs）was between 312.6℃and 364.2℃,with good heat resistance.In addition,PIBO fiber membranes showed low dielectric properties,with dielectric constant（D_k）values of 1.64@1MHz（PIBO-1）and 1.82@1MHz（PIBO-2）,which allowed the fiber membranes to become a new generation of materials with high-performance and low-dielectric.