Soluble and Colorless Polyimides from Bicyclo[2.2.2]octane-2,3,5,6-tetracarboxylic 2,3:5,6-Dianhydrides

Abstract

Two tetracarboxylic dianhydrides with a polyalicyclic structure, bicyclo[2.2.2]octane-2-endo,3-endo,5-exo,6-exo-tetracarboxylic 2,3:5,6-dianhydride (5a) and bicyclo[2.2.2]octane-2-exo,3-exo,5-exo,6-exo-tetracarboxylic 2,3:5,6-dianhydride (5b), were synthesized, and polycondensations of the dianhydrides with aromatic diamines were carried out in well-purified N,N-dimethylacetamide (DMAc) at 85−105 °C under N2. The resulting poly(amic acid)s as precipitated possessed inherent viscosities in the range 0.5−0.1 dL/g. Some of the poly(amic acid)s formed flexible and tough films after curing. Polyimides were also obtained by a thermal solution imidization method where the DMAc solutions of poly(amic acid)s were heated at reflux temperature for 6 h. All of the examined polyimides were soluble at room temperature in aprotic and protic polar solvents such as DMAc and m-cresol. All of the polyimides showed excellent thermal stability with no significant weight loss up to approximately 400 °C, and the 5% weight loss temperatures in N2 were over 450 °C. The polyimides had glass transition temperatures over 380 °C except for the polyimides using 1,3-bis(4-aminophenoxy)benzene as an aromatic diamine. The flexible polyimide films possessed a tensile modulus range of 1.5−2.6 GPa, a tensile strength range of 52−96 MPa, an elongation at break of 3−11%, and a dielectric constant range of 3.2−3.7. These films exhibited cutoffs at wavelengths shorter than 320 nm and were entirely colorless. Normalized transparencies in the visible region (400−780 nm) were over 86% and, notably, the film prepared from 5a and 4,4‘-diaminodiphenyl ether had an excellent transparency of 94%. Colorlessness and transparency of the film at room temperature were maintained up to 200 °C when the film was heated in air and to 400 °C in N2. The polyimide of which the end group (the aromatic amino group) was capped using acetic anhydride was almost colorless even when heated at 300 °C in air.

Design and synthesis of organosoluble and transparent polyimides containing bulky substituents and noncoplanar structures

“…37 Moreover, compared with a Kapton film ( Figure 8) with a similar thickness of about 50 mm, the PI films presented a lighter color. Usually, most PIs have a strong absorption in the UV and visible regions, and this is due to the highly conjugated aromatic structures and intermolecular charge-transfer complex (CTC) formation of PIs.…”

Structural effects of pendant groups on thermal and electrical properties of polyimides

“…These disadvantages make conventional polyimides extremely difficult to process and severely limit their commercial uses. Various attempts have been made to overcome these deficiencies, including the use of noncoplanar or alicyclic monomers [7][8][9][10] and the introduction of flexible segments into the polymer backbone. [11][12][13] Methods for overcoming these deficiencies include reducing chain crystallinity, intermolecular charge-transfer, and electronic polarization interactions.…”

Soluble Polyimides with Polyalicyclic Structure. Part 9. A Polyalicyclic Polyimide Bearing Spiro Structure.

“…In recent years, we have reported the preparation and characterization of soluble and colorless polyimide films without TPP/Py from cycloaliphatic monomers. [28][29][30][31] In the present article, a novel colorless polyimide with a polyalicyclic and spiro structure will be reported. give the corresponding dimethyl esters, 2a and 2b.…”