Preparation and properties of high-pretilt-angle polyimides based on an alicyclic dianhydride and long alkyloxy side-group-containing diamines

A series of polyimides were prepared by a solution polycondensation reaction between 3-carboxylmethylcyclopentane-1,2,4-tricarboxylic dianhydride and 4-alkyloxybenzene-1,3-diamines in N-methyl-2-pyrrolidone and chemical imidization with triethylamine and acetic anhydride. These polyimides possess great organo-solubility, high optical transparency, and high pretilt angles. They are soluble not only in strong polar aprotic organic solvents such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide, m-cresol, and 1,4-butyrolactone but also in common low-boiling-point solvents such as chloroform and tetrahydrofuran, and some are even soluble in acetone. They exhibit high transparency at wavelengths greater than 320 nm. They can generate pretilt angles greater than 5°, and some can even achieve pretilt angles greater than 10°. The pretilt angle of a polyimide increases with the increasing length of the alkyloxy side group. The polyimides possess glass-transition temperatures between 180 and 230 °C and thermal decomposition temperatures (onset temperatures) of about 435 °C.