Synthesis and characterization of unsymmetrical benzonitrile‐containing polyimides: Viscosity‐lowering effect and dielectric properties

Abstract

A new unsymmetrical diamine, 2-(3-aminophenoxy)-6-(4-aminophenoxy)benzonitrile (3,4-APBN), is synthesized via two consecutive S N Ar reactions and the temperature-dependent reactivity of the fluorides in 2,6-difluorobenzonitrile, whose first S N Ar reaction occurs at 70 C and second, at 100 C, allowing timing control of reaction sequence and circumventing the transetherification side reaction. Thus, a series of polyimides (PIs) is prepared from the polymerization of 3,4-APBN with five common dianhydrides (6FDA, DSDA, OPDA, BTDA, and PMDA). For comparison, a second series is also prepared from two symmetrical diamines ([2,6-bis(3-aminophenoxy)benzonitrile (3,3-APBN) and 2,6-bis(4-aminophenoxy)benzonitrile (4,4-APBN)] and 6FDA or PMDA. The processability of the poly(amic acids) (PAAs), for the first series is greatly improved since their solution viscosities are much lower than PAAs based on symmetrical diamines. Besides having high glass-transition temperatures (249-332 C), and thermal stability [5% weight loss in the range of 505-542 C (air) and 512-546 C (nitrogen)], these PIs form tough, transparent and flexible films that have a tensile-strength range of 82.1-121.3 MPa, elongations-at-break of 5.33-9.81%, and tensile moduli of 2.11-2.97 GPa. Their film dielectric constants are 3.08-3.62 at 10 kHz, moderately higher than that (2.92) of analogous PI (CP2) without nitrile groups. Overall, we found that the reduction of structural symmetry in repeat units can improve the polymer processibility as well as increasing their dielectric constants.

Enhancing electrical energy storage using polar polyimides with nitrile groups directly attached to the main chain

“…[35][36][37] An example of PI synthesis is described in Section I of the ESI. [35][36][37] An example of PI synthesis is described in Section I of the ESI.…”

Synthesis and characterization of high nitrile content polyimides as dielectric films for electrical energy storage

“…In our previous work, an asymmetric and two symmetric diamino monomers as well as the resulting PIs containing a single nitrile group per repeat unit were synthesized. We found that the enhanced entropy resulted from the presence of asymmetric structure in each repeat unit improved the processing of poly(amic acids) into PI films with increased dielectric constants and relatively low dielectric loss . As a continuing effort to probe additional structural factors, for example, dipole moment density to balance the need for high dielectric constant, low dielectric loss, and thermal stability as well as processability in developing high temperature capacitors, we report here the synthesis of new PIs containing three nitrile groups in each repeat‐unit structure, their thermochemical stability and film fabrication as well as thermal, mechanical, and dielectric properties.…”

Activated‐Carbon‐Supported Calcium Oxide: A Selective and Efficient Catalyst for Nitrile‐Containing Diaryl Ether Synthesis

“…Generally, the reactivity of benzonitriles was far lower than that of phthalonitriles, and azeotropic operations (temperatures around 140–180 °C) were essential for the complete substitution . Furthermore, obvious trans‐etherification (up to 10 −2 –10 −1 scale) would occur during the substitution of the second fluorine, especially when the second phenol has similar or higher reactivity ,. By using CaO@AC as the catalyst, reaction temperature can be significantly lowered; and asymmetric products could be obtained in excellent purity and yields.…”