Study of Aromatic Polyimides Containing Cyano Groups

Aromatic polyimides containing cyano groups have been synthesized by solution polycondensation reaction of an aromatic diamine having cyano and ether groups, with various aromatic dianhydrides containing flexible groups such as carbonyl and hexafluoroisopropylidene. The properties of these polyimides were compared with those of related polymers based on rigid aromatic dianhydrides, such as biphenyltetracarboxylic and pyromellitic dianhydride, and the same cyano containing diamine. The polymers were easily soluble in polar organic solvents, such as N-methylpyrrolidinone, N, N-dimethylacetamide and N, N-dimethylformamide and exhibited remarkable film forming ability, except for polyimide derived from pyromellitic dianhydride. They showed high thermal stability, with initial decomposition temperature being above 400 °C and glass transition temperature in the range of 210—260 °C. Conformational rigidity parameters of these polymers have been calculated by Monte Carlo method with allowance for hindered rotation. Several physical properties such as solubility and glass transition temperature are discussed in relation to the structure of the polymers and rigidity of their chains. The calculation of parameters of conformational rigidity showed that the glass transition temperature values (220—230 °C) increase with the increase of the rigidity. The polymers based on pyromellitic dianhydride form a separate group having the glass transition temperature values above 250 °C.