Preparation and Properties of Colorless and Transparent Polyimides with Bulky Pendant Groups
In recent years,transparent polyimides(PI)have demonstrated significant potential applications,particularly in areas such as flexible displays.However,balancing the optical and thermal properties of transparent PI remains an important research topic.Herein,a diamine monomer,4,4'-((4-(trifluoromethyl)phenyl)methylene)bis(2-(tert-butyl)aniline)(TPTA),incorporating a bulk group tert-butyl group and a bulky pendant 4-(trifluoromethyl)phenyl group is synthesized.A series of novel high molecular weight PIs are synthesized through polycondensation reaction of the TPTA diamine monomer with several common dianhydride monomers.The results show that the introduction of bulk tert-butyl and 4-(trifluoromethyl)phenyl pendant structures can significantly improve the properties of the PI films.These films exhibit transmittance ranging from 71.6％to 88.3％at 450 nm,with cut-off wavelengths between 312 nm and 360 nm.Additionally,their thermal decomposition temperatures and glass transition temperatures respectively exceed 498 ℃ and 265 ℃.The tensile strength ranges from 64.0 MPa to 132.9 MPa,and elongation at break ranges from 4.5％to 25.5％.Specifically,PI-6FDA,synthesized from TPTA and 4,4'-(hexafluoroisopropylidene)diphthalic anhydride(6FDA),exhibits the most balanced comprehensive performance.It features a transmittance of 88.3％at 450 nm and 89.4％in the visible range,a yellowness index of 2.09,a haze value of 0.6％,and a glass transition temperature of 318 ℃,making it a promising candidate for flexible displays and other related applications.
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