Preparation And Thermal Properties Of High Heat Resistant Polyimide Plastics

Engineering plastics which can be used over 150? can be called high temperature plastics or high performance engineering plastics.The main structures of these materials are aromatic rings and heterocyclic rings,which not only have superior mechanical properties,but also endow materials with high thermal resistance.Such superior performance makes it more and more attention and application in some special fields such as aviation,aerospace,electronics,nuclear power,machinery and so on that the general plastic can not meet the demand of performance.Since the 1970 s,more and more national research institutions and enterprises have developed many varieties of aromatic and heterocyclic as the main chain structure of the polymer.Commercially,there are mainly PI,PEEK,PES,PPS,LCP.These materials have the characteristics of high temperature resistance,corrosion resistance,high strength,wear resistance,self lubrication,high modulus,light weight,insulation and so on.Polyimide has excellent heat resistance due to its large number of aromatic heterocyclic structures in its main chain.It is the highest grade of heat-resistant in special engineering plastics.Polyether ether ketone,polyphenylene sulfide and other materials compared with polyimide,glass transition temperature is relatively low,generally not more than 150 ?,which limits its application at higher temperatures.In the environment of 200? degrees or higher,a more obvious softening deformation will occur,and the strength and modulus of the material will be seriously attenuated.Polyimide material can be used at 200 ? for a long time,some special structure of high heat resistant varieties can be used at 300 ? for a long time.Higher heat-resistant grades require a higher glass transition temperature.High glass transition temperature melt viscosity is relatively high,resulting in difficult molding process.Plastic molding methods are mainly Compression molding,extrusion molding,injection molding.Therefore,the main research direction of polyimide plastic: First,the development of ultra-high temperature(300? above)and easy compression molding,the second is to develop high temperature(200? above)and can be extruded,injection molding.Polyimide(PI)and thermoplastic polyimide(TPI)these two types of polyimide plastic in China is still relatively low degree of industrialization,the country's application is also more dependent on similar imported products.It is very important to study the technology of synthesis,modification and processing of these materials in order to promote the industrialization of polyimide materials in China.In this paper,through the different structure of the dianhydride and diamine monomer reaction,the preparation of polyimide resin and processed into plastic.By adjusting the combination of dianhydride and diamine,the copolymerized third monomer is introduced at the same time.Polyimide(PI)and thermoplastic polyimide(TPI)with high glass transition temperature were prepared.The higher the glass transition temperature,the more difficult the molding process.A polyimide resin having a high glass transition temperature and good processability was prepared by introducing a third monomer or adjusting the plugging ratio,reducing the rigidity of the polyimide macromolecule and the melt viscosity.The parameters such as glass transition temperature,thermal expansion coefficient,thermal stability,melting temperature and melt rheology were characterized by DMA,TMA,TGA,DSC and rotary rheometer.The results of dynamic thermal mechanical analysis(DMA)show that the glass transition temperature of polyimide(PI)is between 300? and 380?,and the glass transition temperature of thermoplastic polyimide(TPI)is between 240? and 260?.