US Patent 7906611 Polyamic acid and polyimide

Disclosed are a polyamic acid containing not less than 10 mol % of a repeating unit represented by the formula [1] below, and a polyimide represented by the formula [2] below which is obtained from such a polyamic acid. The polyamic acid and polyimide have high heat resistance as shown by a thermal decomposition temperature of not less than 300° C. In addition, the polyamic acid and polyimide have good workability because of their high solubility in solvents, while exhibiting good light transmission. (In the formula, R1 and R2 independently represent a hydrogen atom or an alkyl group having 1 to 10 carbon atoms; R3 and R4 independently represent a hydrogen atom, a halogen atom, an alkyl group having 1 to 10 carbon atoms or a phenyl group, or alternatively R3 and R4 on adjacent carbon atoms may combine together to form a cycloalkyl group having 3 to 8 carbon atoms or a phenyl group; R5 represents a divalent organic group; and n represents an integer of not less than 2.)