Preparation,Characterization And Properties Of Soluble Polyimide And Its Composite Films

Aromatic polyimides are representative of high performance materials,which are well-known for their excellent thermal stability,electrical and mechanical properties.They are widely used in many high technology fields,such as aerospace,automobile and microelectronics etc.However,the applications of conventional aromatic polyimides are often limited because of their poor solubility and high processing temperatures.In order to overcome these problems and meet the need of development in some special areas,more and more researches have been focused on the preparation of functional polyimides,such as good solubility,high transparence,low dielectric constant,high refractive index and so on.In this paper,the development of polyimide was summarized,discussed the molecular structural characteristics of polyimides and the function of various structure on the properties of functional polyimides.Based on the knowledge of soluble polyimides,three kind of diamine monomers 1,3-bis(4-aminophenoxy)benzene(TPER),1,4-bis(3-aminophenoxy)benzene(FPER)and 9,9-(4-(4-aminophenoxy)phenyl)fluorene(BAOFL)were synthesized successfully,introducing ether bond on polyimide main chain.Based on the three kind of monomers,a series of polyimide films,thermoplastic polyimide powder and polyimide/TiO2 composite films were prepared.Their solubility?mechanical properties?dielectric properties and transmissibility were characterized and analyzed in detail by NMR,DSC,TGA,SEM,FT-IR and XRD.The details and key conclusions are described as follows:1.1,3-bis(4-aminophenoxy)benzene(TPER)and 1,4-bis(3-aminophenoxy)benzene(FPER)were synthesized successfully.Based on the two diamines and 4,4'-(4,4'-isopropylidenediphenoxy)bis(phthalic anhydride)(BPADA),4,4'-oxydiphthalic anhydride(ODPA),3,3',4,4'-biphenyltetracarboxylic dianhydride(BPDA),pyromellitic dianhydride(PMDA)and 3,3',4,4'-benzophenonetetmcarboxylic dianhydride(BTDA),two series of polyimide films(PI1 and PI2)were prepared by thermal imidization respectively.The polyimide containing BPADA has excellent solubility,which can be easily dissolved in NMP,DMAc,DMF,DMSO and other high boiling point polar solvents at room temperature,as well as in CHCl3,THF and even acetone.Polyimides containing ODPA can be dissolved in some kind of solvents when heated,while polyimides prepared with other dianhydrides are insoluble.At 1 MHz,the dielectric constants of(PI1)and(PI2)were between 3.15~3.80 and 3.46~3.96,respectively,and the dielectric losses were between 0.0018~0.0092 and 0.0028-0.025,respectively.Two series of polyimide has good thermal stability,and thermal decomposition temperature are between 502~534?and 509~539?,the glass transition temperature is between185.2~254.7?and between 218~258?,respectively.The two series of polyimides prepared by thermal imidization method have excellent flexibility,tensile strength between 69~105 MPa and 64~93 MPa,and elongation at break between 10~19%and11~16%,respectively.2.With different molar ratio(4:1~1:1)of TPER(or FPER)and BAOFL as diamine,BDAPA as dianhydride,Two series of polyimide film(PI1 and PI2)were prepared by thermal imidization method.At 1 MHz,the dielectric constants of polyimide films are between 3.17~3.53 and 2.87~3.15,respectively,and it is worth noting that the dielectric constants of the two series polyimide films gradually decrease with the increase of BAOFL content,and the dielectric losses are between 0.0005~0.0074 and0.0007~0.0079,respectively.At the same time,two series of polyimide with excellent thermal stability,thermal decomposition temperature is between 481~528?and480~530?,the glass transition temperature is between 192~208?and 186~218?,respectively.The two series of polyimides have excellent flexibility,the tensile strength is between 58.5~69.7 MPa and 62.8~71.4 MPa,and the elongation at break is between11.2~16.8%and 10.1~17.3%,respectively.PI1 and PI2 series thin film samples are of light color and similar in light transmittance.UV-vis indicates that their cutoff wavelength is 363 nm and the transmittance exceeds 70%at 450 nm.The two series of polyimides have excellent solubility and can be dissolved in NMP,DMAc,DMF,CHCl3,THF and other solvents at room temperature rapidly.3.Nano TiO2 was prepared from tetrabutyl titanate and modified by KH-550.PI/TiO2 composite films were prepared,using TiO2 with different volume contents(10~40%)as filling materials,and PI1 and PI2 as matrix.At 1 MHz,the dielectric constants of PI1 and PI2 series composite films were between 6.1~11.9 and 5.1~7.6,respectively,and the dielectric losses were between 0.02~0.14 and 0.02~0.12,respectively.The breakdown field strength decreases gradually with the decrease of TiO2 doping content.When the doped TiO2 is 40%Vol,the breakdown field strength is109.94 kV/mm and 100.69 kV/mm respectively,which is 47.8%and 55.5%lower than the pure PI.The energy storage density was 0.691 and 0.481 J/cm~3,respectively,which was 47.8%and 55.5%lower than the pure PI.With the change of TiO2 volume fraction,the crystallization degree and particle distribution in the composite film changed.The thermal decomposition temperature of PI1 and PI2 composite films was between514~537?and 517~541?,respectively.