Highly transparent and soluble polyimides with synergistic effects of pyridine and cyclohexane

Abstract

In order to prepare novel polyimides (PI) with high transparency and solubility in common solvents, three diamine monomers containing pyridine or methyl-substituted pyridine and cyclohexane, 1,1′-bis[4-(5-amino-2-pyridinoxy)phenyl]cyclohexane (IIIa), 1,1′-bis[4-(5-amino-3-methyl-2-pyridinoxy)phenyl]cyclohexane (IIIb), and 1,1′-bis[4-(5-amino-2-methyl-6-pyridinoxy)phenyl]cyclohexane (IIIc), were synthesized and characterized. The diamine monomer (IIIa) was subsequently polymerized with 3,3′,4,4′-oxydiphthalic anhydride, 4,4′-(hexafluoroisopropylidene)-diphthalic anhydride (6FDA) to obtain PIs, PI-1 and PI-2. Furthermore, PI-3 (IIIb/6FDA) and PI-4 (IIIc/6FDA) were prepared for structure–property comparison studies. The structures of the resulting PIs were characterized by fourier transform infrared spectroscopy (FT-IR), X-ray diffraction, and elemental analysis. The physical properties of the PI films were investigated by thermogravimetric analysis, differential scanning calorimetric analysis, dynamic mechanical analysis, and ultraviolet–visible spectroscopy. In general, the PIs showed excellent thermal properties and good mechanical properties. Most had good solubility in polar organic solvents such as N, N-dimethylacetamide, N, N-dimethylformamide, N-methylpyrrolidone (NMP), m-cresol, and even soluble in low boiling solvents such as tetrahydrofuran (THF) and CHCl3. The PI films also exhibited high optical transmittance of 94–97% at 500 nm and cut-off wavelength at 345–359 nm. In summary, the introduction of methyl, cyclohexane, and pyridine groups into the backbone was shown to improve the solubility and transparency of PI films.

Synthetic strategies for highly transparent and colorless polyimide film

“…Yao et al 107 polymerized 1,1′‐bis[4‐(5‐amino‐2‐pyridinoxy)phenyl]cyclohexane, 1,1′‐bis[4‐(5‐amino‐3‐methyl‐2pyridinoxy)phenyl]cyclohexane, and 1,1′‐bis[4‐(5‐amino‐2‐methyl‐6‐pyridinoxy)phenyl]cyclohexane (III a ‐III c in Figure 6a), three diamine monomers containing alicyclic structures, with 6FDA and other dianhydrides, respectively, to obtain a series of highly transparent PI films (~30 μm). Due to the introduction of pendant cyclohexane and pyridine with high refractive index, the λ 0 of these PI films are between 345 and 359 nm, and T 500 are as high as 94%–97%.…”

Colorless Polyamide–Imide Films with Enhanced Thermal and Dimensional Stability and Their Application in Flexible OLED Devices

“…The formation of CTCs can be inhibited by introducing strong electronegative groups (such as −CF 3 ), − alicyclic structures, − and inorganic particles , into PI. However, these changes also reduce the linearity and rigidity of the polymer chains, resulting in poor thermal and mechanical properties of PI.…”

Soluble and transparent polyimides with high Tgs from a new semi-aliphatic diamine with cyclohexyl and ortho-methyl groups

“…[28][29][30] Fortunately, it is considered an effective way that incorporating bulky pendant groups into PIs to improve their processability and transparency, and meanwhile maintain their high thermal stability. [31][32][33][34] In previous work, we found that the introduction of cyclohexyl and tert-butyl groups into PIs was able to increase their T g s, solubility and transparency, 34 but the cost was relatively high. In order to decrease the cost and further enhance the T g s of PIs, we intend to use methyl instead of tert-butyl.…”