Preparation Of Polyimide And Composite Film

Polyimide is a polymer material with excellent overall properties,which has excellent heat resistance,mechanical properties and electrical properties.With the rapid advancement of modern technology,traditional polyimide materials have not met the demand for their performance.In order to obtain polyimide with superior performance,domestic and foreign researchers have done a lot of research on the modification of polyimide film.In the research of polyimide?PI?modification,people pay great attention to PI/SiO₂nanocomposite film,which has made in-depth research on improving the mechanical properties,heat resistance and electrical properties of the film.In this paper,firstly,pyromellitic dianhydride?PMDA?and 4,4'-diaminodiphenyl ether?ODA?were used as raw materials,and DMAc was used as a solvent to form a polyamic acid solution by polycondensation.Then a series of PI/SiO₂ composite filmwith different silica contents containing coupling agent vinyl trimethoxysilane?or no coupling agent?was prepared by sol-gel method using tetraethyl orthosilicate as precursor.At the same time,the chemical structure and microstructure of the film were characterized by infrared spectroscopy,XRD and SEM.The thermal properties of the film were tested by thermogravimetric analyzer.The mechanical properties of the composite film were investigated by spring scales and weights.The results show that the SiO₂ nanoparticles in the composite film added with the coupling agent are more uniformly dispersed in the PI matrix than the film to which the coupling agent is not added,and the particle size is about20-30 nm.Moreover,the thermal stability of the obtained composite film is higher than that of pure PI,and the mechanical properties are also significantly improved.Among them,when the content of SiO₂ nanoparticles is 10%,the prepared PI/SiO₂ composite film has the strongest mechanical properties.Secondly,in this thesis,micron-sized tubular mesoporous silica?mSiO₂?with cadmium sulfide quantum dots and double-tube tubular diatomaceous earth particles of the genus Diatoms were prepared by chemical deposition method.On this basis,using citric acid as the carbon source and 3-aminopropyltrimethoxysilane?APS?as the passivating agent,carbon quantum dots?CDs?self-assembly was carried out on the surface of the above materials by one-step hydrothermal method.Thus,a cluster type fluorescent particle is obtained.Then,it was blended and uniformly dispersed in a solution of a polyamic acid,and a polyimide film having a fluorescent property was prepared by a film casting molding technique.The chemical structure and microstructure of the film were characterized by infrared spectroscopy,XRD and SEM.The fluorescence properties of the film were tested by fluorescence spectrophotometer?FL?.The results show that the prepared CdS quantum dots and carbon quantum dots are uniformly dispersed in mSiO₂ and diatomaceous earth.The size of CdS nanoparticles is about 30⁴0 nm,which has excellent fluorescence performance.In contrast,fluorescent particles?diatomite@CdS@CDs?with diatomaceous earth as a carrier have lower fluorescence performance than mSiO₂-supported fluorescent particles?mSiO₂@CdS@CDs?.When they are incorporated into a polyimide film,their fluorescence properties are degraded.For example,the fluorescence performance of PI/mSiO₂@CdS@CDs is inferior to that of mSiO₂@CdS@CDs.Further,the mechanical properties of the obtained composite film deteriorated as the content of the inorganic component increased.Thirdly,polyimide resin was prepared by using biphenyltetracarboxylic dianhydride?s-BPDA?and 4,4'-diaminodiphenyl ether as raw materials,acetic anhydride as dehydrating agent and triethylamine as catalyst for homopolymerization..The chemical structure and microstructure of the resin were observed by infrared spectroscopy,XRD and SEM.The thermal properties of the resin were tested by thermogravimetric analyzer.The results show that the prepared biphenyl type polyimide resin has stronger heat resistance than the film,and the thermal decomposition rate of 5%is as high as 587°C.Fourth,in order to construct a new multifunctional polyimide composite material,we designed and prepared a carbon quantum dot coated magnetic silica hollow sphere.First,magnetic silica hollow spheres?MHSS?having a uniform cavity size and shell thickness were prepared using functionalized polystyrene microspheres as a template.In this material,the magnetic nanoparticles are uniformly deposited on the outer surface of the silica hollow sphere.The obtained MHSS can exhibit superparamagnetism at room temperature.Next,with the aid of APS,carbon dots were coated on the surface of the MHSS by hydrothermal reaction at 180°C to synthesize MHSS?MHSS@CDs?coated with carbon quantum dots.Subsequently,MHSS and MHSS@CDs were characterized by scanning electron microscopy,transmission electron microscopy,X-ray powder diffraction,X-ray energy spectrum analysis,Raman spectroscopy and laser scattering particle analyzer.Finally,the application of the above materials in medical diagnosis was initially investigated.