Synthesis And Properties Of Cross-linkable High Temperature Resistant And High Transparent PI Materials

Flexible wearable display devices have become one of the most high-profile frontiers in today's increasingly intelligent and technological world due to their thinness and flexibility.The polyimide(PI)optical film has excellent comprehensive properties and has become the most promising polymer flexible substrate material.Based on the application requirements of flexible optical substrates,a new type of fluorine-containing diamine monomer was designed and synthesized,and a series of thermally cross-linked polyimide films were prepared in this paper.The main contents are as followed:The comprehensive properties of the PI films before and after thermal cross-linking based on diamine DFPTM and different commercial dianhydrides4,4'-oxydiphthalic dianhydride(ODPA),benzophenone dicarboxylic dianhydride(BTDA)and hexafluorodianhydride(6FDA)were tested and characterized.The highly twisted triphenylmethane backbone and the bulky tetrafluorostyrene pendant group in DFPTM gave our polymer films enhanced solubility and optical properties relative to traditional aromatic PI.And it can be proved that the cross-linking reaction could effectively improve its thermal and mechanical properties.Among them,6FDA/DF exhibited the highest transparency,heat resistance and mechanical strength due to the presence of its strong electronegativity-CF₃group with a high bond energy.After cross-linking at 260?for 2 h under vacuum,the light transmittance at 450 nm of the thermally cross-linked film C-6FDA/DF was slightly reduced from 90.5%to88.6%,and the glass transition temperature increased from 257.0?to 312.7?,the thermal weight loss temperature T_5%increased from 472.2?to 500?,the tensile strength increased from 33.8 MPa to 39.7 MPa,and the elongation at break decreased from 8.1%to 3.9%.The comprehensive properties of a series of PI films before and after thermal cross-linking prepared by copolymerization of diamine DFPTM with the third monomer 4,4'-diaminodiphenylmethane(DDM)and dianhydride 6FDA at different feed ratios were tested and characterized.The experiment demonstrated that the optical properties of the copolymerized PIs improved with the increase of the content of DFPTM,rather the thermal properties decreased with the increase of the content of DFPTM.However,the thermodynamic properties of the thermally cross-linked film could be greatly improved,even exceeding the maximum value of the best PI before cross-linking.