Preparation and properties of light-colored and transparent semi-alicyclic polyimide films with enhanced flame retardancy from alicyclic dianhydrides and aromatic diamine containing phenolphthalein unit

• Published in: Journal of polymer research 2021-08, Vol.28 (8), Article 310
• Main Authors: Wu, Lin, Wang, Han-li, An, Yuan-cheng, Jia, Yan-jiang, Tan, Yao-yao, Wei, Xin-ying, Zhi, Xin-xin, Zhang, Yan, Liu, Jin-gang
• Format: Article
• Language: English
• Subjects: Baking; Characterization and Evaluation of Materials; Chemistry; Chemistry and Materials Science; Diamines; Dianhydrides; Dimensional stability; Dimethyl acetamide; Glass substrates; Glass transition temperature; Haze; High temperature; Industrial Chemistry/Chemical Engineering; Nitrogen; Original Paper; Phenolphthalein; Polyimide resins; Polymer Sciences; Temperature; Thermal expansion; Thermal stability; Weight loss
• ISSN: 1022-9760; 1572-8935
• DOI: 10.1007/s10965-021-02676-x

Two semi-alicyclic polyimide (PI) films with light colors, good thermal stability, and enhanced flame retardancy were successfully developed from an aromatic diamine containing phenolphthalein unit, 3,3-bis[4-(4-aminophenoxy)phenyl]phthalide (BAPPT) and alicyclic dianhydrides, including 1,2,4,5-cyclohexanetetracarboxylic acid dianhydride (HPMDA) and 3,3',4,4'-bicyclohexanetetracarboxylic acid dianhydride (HBPDA). For this target, two organo-soluble PI resins, including PI-1 (HPMDA-BAPPT) and PI-2 (HBPDA-BAPPT) were first synthesized by a high-temperature polymerization route. The derived preimidized PI resins were soluble in N -methyl-2-pyrrolidinone (NMP), N,N -dimethylacetamide (DMAc), and other polar aprotic solvents. Corresponding PI films with pale-yellow appearances at the thickness of 25 μm were prepared by casting the PI solutions on glass substrates, followed by thermally baking at elevated temperatures up to 280 °C in nitrogen. The obtained PI films exhibited the cutoff wavelengths ( λ cut ) lower than 300 nm, the optical transmittances as high as 84.5% at the wavelength of 450 nm, the yellow indices ( b * ) as low as 3.10, and the haze values as low as 3.71%. Both of the PI films exhibited good thermal stability with the 5% weight loss temperatures ( T 5% ) higher than 480 °C in nitrogen, char yields higher than 40% at 700 °C, and glass transition temperatures ( T g ) as high as 318.1 °C. In addition, the semi-alicyclic PI films showed acceptable high-temperature dimensional stability with the linear coefficients of thermal expansion (CTE) values of 52.3 × 10 –6 /K for PI-1 and 60.4 × 10 –6 /K for PI-2 in the temperature range of 50–200 °C, respectively. At last, the PI-1 film showed good flame retardancy with the limited oxygen index (LOI) of 32.8%, the flame retardancy class of UL94 VTM-0, and good smoke suppression properties.