Synthesis And Properties Of Asymmetric Triphenylamine Type Fluorinated PI Materials

Flexible display device is a hot research and development topic in the frontier field of intelligent technology era because of its features such as thin and light,foldable,low power consumption and various display modes.The substrate material is an essential part of the overall application of flexible display devices,and it is also an important and difficult point in the field of material preparation.Polyimide(PI)film has excellent comprehensive properties such as optical properties,thermal properties,and mechanical properties,and is one of the candidate materials for flexible substrates.This dissertation focuses on the design and preparation of a new type of asymmetric triphenylamine-type fluorinated diamine monomer,from which a series of PI films are prepared,and comprehensive performance testing and regular exploration are carried out.It mainly includes the following research contents:Two novel asymmetric triphenylamine containing fluorotriamine monomers 4,4’-diamino-2 "-methyl-4"-fluorotriphenylamine(Diamine 1)and 4,4’-diamino-3 "-methyl-4"-fluorotriphenylamine(Diamine 2)have been designed and synthesized.The structure and properties of the monomers were characterized by FT-IR,NMR,MS,elemental analysis and DSC.We are based on diamine 1 and different commercial dianhydrides,such as pyromellitic dianhydride(PMDA),4,4’-oxydiphthalic anhydride(ODPA),3,3’,4,4’-diphenyl ketone tetracarboxylic dianhydride(BTDA),hexafluoro dianhydride(6FDA),3,3,4,4-diphenyl sulfone tetracarboxylic dianhydride(DSDA),prepared homopolymer PI film,and the above-mentioned PI film was subjected to structural analysis and performance evaluation.The highly distorted triphenylamine(TPA)structure of diamine 1 makes the polymer exhibit superior solubility and mechanical properties,as well as superior optical and thermal properties,compared with traditional aromatic PI.At the same time,the TPA structure showed a redox peak in the electrochemical test.From the analysis of the test results,PI-6FDA also showed excellent solubility in ethyl acetate and acetone.The transmittance of PI-6FDA obtained by one step method at 500 nm reached 77.5%,and the cutoff wavelength was379 nm.The tensile strength of PI-BTDA prepared by two-step chemical imine method is 164.3 MPa,and the elastic modulus of PI-BTDA prepared by one-step chemical imine method is 4.2 GPa,and the mechanical properties are excellent.This series of PI in nitrogen atmosphere,5%,10% thermal weight loss temperature range is 345～511 ℃,495～538 ℃.We also studied the properties of a series of PI films prepared by diamine 1 or diamine 2,with the third monomer 2,2’-bis(trifluoromethyl)diaminobiphenyl(TFMB)and dianhydride 6FDA at different feed ratios.The optical properties of copolymerized PI increased with the increase of TFMB content,while the thermal properties decreased with the increase of TFMB content.When the ratio of diamine 1 to TFMB is 1:1,the elastic modulus of PI film with the best mechanical properties is as high as 4.3 GPa,the tensile strength is as high as 188.4 MPa,and the elongation at break is 8.1%.