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

Abstract

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 (Mw) of the resulting PIs are between 3.92 and 8.36 × 104 g mol−1 with the Mw/Mn 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 N2; 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.