Synthesis Of Fluorine-containing Polyimide With High Transparency And Large Side Groups, Construction Of Porous Polyimide And Research On Their Respective Properties

In nearly half a century of hybrid polymer development,polyimide(PI)has become one of the most widely developed because of its high use temperature.Its structure can be accurately designed,a variety of synthetic means,can be processed in a variety of ways,has a good combination property,so that it is diffusely used in electrical engineering,environmental conservation,chemical engineering and other fields.On account of the structural performance of polyimide,this paper is split into two parts,respectively,the research of polyimide film and porous polyimide materials.Part ?:Polyimide films(PI)are widely used in optical fields as a result of their excellent solubility,mechanical properties,electrical properties,thermal stability and optical properties.PI has a high optical absorption rate in the UV-Vis spectrum.In addition,excessive absorption of light in the UV-Vis region prevents light from reaching photosensitive groups deeply embedded in the film,thus reducing the function of this material.At the same time,if PI is to be used in optoelectronic devices,PI needs to have good optical transmission in the near-infrared communication window(1310and 1550 nm).However,traditional PI has a relatively long cut-off wavelength and is brown,which affects its light transmittance.In addition,the processability of traditional PI is limited by its poor solubility and limited compatibility with other materials.It can be seen that the traditional PI is not suitable for optical equipment.Therefore,the study of soluble light-colored polyimides has attracted great attention.In our group,we synthesized a series of novel fluorinated hyperbranched polyimides by a two-step chemical imination method through the polycondensation reaction of TFAPOB with four kinds of dianhydride monomers containing large volume side group substituents.Properties of synthetic FHPIs(FHPI I-IV,respectively).In addition,the permittivity,chromaticity,refractive index and bicycle values of these materials are also determined.The obtained FHPIs showed good solubility and film formation.FHPIs exhibit excellent optical properties,including very light color,excellent optical transparency(80-85%at 450nm,86-88%at 550 nm,86-88%at 550nm,and 88-89%at 800 nm),double reflection values ranging from 0.0011 to 0.0020,Adjustable refractive index(1.4721?1.5644 at 650 nm),wavelength within 353 nm,low absorption range in the near infrared region.These materials are candidates for optical devices.In the wake of the growth of global industrialization and rapid economic development,carbon dioxide discharged into the air by coal,oil and natural gas combustion is also gradually increasing,thus aggravating the earth's greenhouse effect.Therefore,the research on the recovery and reuse of carbon dioxide in the environment has attracted a lot of attention.COFs are a class of ordered porous materials with covalent bond structure which can be generated by thermodynamically controlled reversible polymerization reactions.Due to its high specific surface area,regular network structure,excellent thermal stability,accurate structure design and other advantages,it has great application potential in gas adsorption and separation and other fields.At the same time,because the quadrupole-dipole interaction betwixt N atom and CO₂ molecule can increase the adsorption of CO₂ by the polymer,so the introduction of a large number of nitrogen element can increase the adsorption capacity of COFs for CO₂.In the past studies,COFs with special functions and specific pore sizes were usually prepared by adjusting structural units,changing the length of organic monomers,and introducing special functional groups into coordination nodes of structural units.However,reactive raw materials are expensive and difficult to obtain.Based on the above characteristics,our group used a two-step method to react melamine with high nitrogen content and cheap melamine with triphenylitic anhydride to produce a new nitrogen-rich triacid TTDOA,and then the triacid TTDOA was polycondensation reaction with diamine monomer,and a polyimide with porous structure was obtained.The obtained polymer was characterized,which proved that the structure of the polymer was consistent with the molecular design.In addition,the pore size,distribution and specific surface area of the polymer were measured by BET.The results show that the pore sizes of the prepared porous polyimides are in the range of10?30 nm.