Hexafluoro dianhydride preparation method

Abstract

The invention discloses a hexafluoro dianhydride preparation method comprising the following steps: (1) hexafluoro tetraacid is added into anhydrous acetic anhydride; the mixture is stirred and heated to reflux, such that a first ring-closure dehydration reaction is carried out; when the reaction is finished, a treatment is carried out, such that a hexafluoro dianhydride crude product with a ring-closure rate no higher than 98.0% is obtained; (2) the hexafluoro dianhydride crude product obtained in the step (1) is added into anhydrous trifluoroacetic anhydride; the mixture is stirred and heated to reflux, such that a second ring-closure dehydration reaction is carried out; when the reaction is finished, a treatment is carried out, such that a hexafluoro dianhydride finished product with a ring-closure rate no lower than 99.5% is obtained. Polyimide synthesized with the high-ring-closure-rate hexafluoro dianhydride prepared with the method provided by the invention has relatively high molecular weight, good mechanical performance, and good thermal properties. The polyimide can be widely applied in high-tech fields such as optical communication, colorless transparent flexible circuit board, solar cell substrate, organic flexible transparent conductive film substrate, and the like.

Description

technical field [0001] The invention relates to a preparation method of a fluorine-containing dianhydride monomer, in particular to a preparation method of hexafluorodianhydride. Background technique [0002] At present, the application of fluorine-containing polyimide is mainly developed in the optical field, and the research and development in optical communication, colorless transparent flexible circuit board, solar cell substrate, organic flexible transparent conductive film substrate and other applications are in full swing. When polyimide is applied to optical materials, it must meet the following basic properties: cut-off wavelength ≤ 300nm, light transmittance ≥ 85% in the range above 400nm visible light wavelength, glass transition temperature Tg ≥ 260 ℃, yellow index Y.I ≤ 4.0, Linear expansion coefficient CTE≤20ppm, can be dissolved in solvents such as DMAc. [0003] Hexafluorodianhydride (also known as 4,4'-(hexafluoroisopropylidene) diphthalic anhydride, 6FDA) ...

AI Technical Summary

Problems solved by technology

[0007] Hexafluorodianhydride is used to prepare colorless and transparent polyimide. If the anhydride is formed by physical method, since the melting point of hexafluorotetraacid is greater than 250°C, the color of hexafluorodianhydride will increase, which will lead to the production of polyimide. The obtained colorless and transparent polyimide is light yellow, or the yellowness index is high, and the light transmittance in the full wavelength range will drop significantly, which cannot meet the requirements as a high-temperature-resistant flexible colorless and transparent material.

[0008] However, the ring closure rate of intramolecular dehydration of hexafluorotetraacid in acetic anhydride to form anhydride is usually only about 96%, and the highest is only 98%.

When polyimide is synthesized with hexafluorodianhydride with such a low ring-closing rate, it will lead to differences in the molar ratio of raw materials and incomplete reaction, which will eventually make the molecular weight of the polyimide product too low, and the mechanical and thermal properties cannot reach Requirements