Organosoluble polyimides with low dielectric constant prepared from an asymmetric diamine containing bulky m-trifluoromethyl phenyl group

A series of polyimides (PIs) containing a bulky side group of m -trifluoromethyl phenyl was synthesized via a high-temperature one-step polycondensation of 4-[3′,5′-bis(trifluoromethyl)phenyl]-1,3-phenylenediamine ( 2 ) and various aromatic dianhydrides. The weight-averaged molecular weights ( M w ) of the resulting PIs are between 3.92 and 8.36 × 10 4  g mol −1 with the M w / M n of 1.77–2.09. They are soluble in common organic solvents and easily processed into flexible films by the blade coating of PI solution. At room temperature , the dielectric constants ( k ) of these PI films are lower than 3.04 at 1 MHz and 2.87 at 10 GHz, especially the k of 2 -6FDA film is low to 2.66 at 1 MHz and 2.38 at 10 GHz. The breakdown strength of the resulting PI films (thickness: 10 ± 1 μm) is in the range from 461 to 523 kV mm −1 . Meanwhile, these PI films also show good thermal stability (5 wt% weight-loss temperature in the range of 521–571 °C under N 2 ; glass transition temperatures of 266–307 °C) and mechanical properties (tensile strength of 70.8–103.3 MPa, tensile modulus of 1.3–2.2 GPa, elongation at break of 9.1–10.8%). The average transmittance of these PI films (around 20 μm) is above 80% in the visible light region (400–760 nm). Such attractive comprehensive properties make these PIs as potential candidates for application in microelectronics industry.