Synthesis and Characterization of New Polyimides Containing Nitrile Groups

Abstract

Two new nitrile-containing diamine monomers, 4-[bis(4-aminophenyl)amino]benzonitrile and 4-[4-(1-cyanopropoxy)phenyl]2,6-bis(4-aminophenyl)pyridine were synthesized. The diamine monomers were reacted with various tetracarboxylic dianhydrides, followed by cyclodehydration (imidization) without isolation to produce a series of novel polyimides with pendant nitrile groups on the side chain. The polymers were obtained in quantitative yields with high molecular weight. Among them, polymers derived from ODPA and 6FDA showed good solubility, they could dissolve in polar solvents such as DMF, NMP, DMSO and even pyridine and m-cresol. These tough, transparent and flexible polyimide films had a tensile strength of 80–120 MPa, an elongation at break of 4–12% and a tensile modulus of 1.2–2.3 GPa. The polymers obtained exhibited high glass transition temperatures between 305 and 360 C. Moreover, they were fairly stable up to a temperature around or above 400 C and lost 10% weight in the range of 500–590 C and 470–580 C in nitrogen and air, respectively. Together the dielectric constants of the polyimides were measured to be 3.10–3.73 at 10 GHz. On the other hand, blank polyimides with no – CN groups were also prepared for comparison and the results revealed that the nitrile group affected the thermal property of polyimides as well as the electrical properties. Introduction of the –CN groups would increase the glass transition temperature and also the dielectric constant.