Abstract:
A colorless and transparent polyimide (PI) film with excellent comprehensive properties was synthesized via chemical imidization process by using 4,4'-diaminodiphenyl ether (ODA) and 9,9-bis(3-fluoro-4-aminophenyl)fluorene (FFDA) as diamine monomers, 4,4'-oxydiphthalic anhydride (ODPA) as a dianhydride monomer in dimethylformamide (DMF). The relationship between the content of FFDA and the performance of PI was studied. The optical properties, heat resistance, mechanical properties and solubilities of PI were characterized by ultraviolet-visible spectrophotometer (UV-Vis), differential scanning calorimeter (DSC), thermogravimetric analyzer (TGA), universal material testing machine, etc. The addition of diamine monomer with asymmetric large side group can increase the degree of distortion of the molecular chain to a certain extent, increase the free volume between molecules, reduce the stacking of molecular chains, and reduce the interaction among molecular chains, which weakening the charge transfer complexing effect and improving the optical transparency of the PI film. The addition of ether bonds can increase the flexibility of PI molecular chains and improve the solubility. The fluorine-containing group of the diamine part has a strong electron withdrawing effect, which significantly reduces the electron donating effect of the diamine monomer, thereby inhibiting the charge transfer complexing (CTC) effect and improving the optical performance of PI film. The results show that the PI sample with
n(FFDA):
n(ODPA) of 50% exhibits excellent solubility and the film presents good optical property. At ambient temperature, PI is soluble in many strong polar solvents such as
N-methyl pyrrolidone (NMP), dimethyl formamide (DMF), dimethyl acetamide (DMAc) and dimethyl sulfoxide (DMSO), which also has good solubility in weak polar solvents such as tetrahydrofuran (THF). The transmittance of PI film at 500 nm attains 85%, and its UV cutoff wavelength is as low as 365 nm. Meanwhile, the PI film has excellent thermal stability and mechanical properties.