PRODUCTION OF COPOLYAMIC ACID AND COPOLYIMIDE FIBER

PURPOSE:To provide a copolyamic acid which can give a copolyimide fiber excellent in modulus, elongation, etc., by incorporating two specified kinds of aromatic carboxylic acid structural units and two specified kinds of aromatic diamine structural units in specified amount in the copolyamic acid. CONSTITUTION:This copolyamic acid contains structural units of formulas I and II (wherein R and R' are each H or a 1 to 4C alkyl) derived from aromatic carboxylic acid components and structural units of formulas III and IV (wherein X1 is a 1 to 2C alkyl or an alkoxy; and (n) is 0 to 4) or formula V derived from aromatic diamine components and having a composition in such a range that (m1)/(m2) is 100/0 to 30/70, (m3)/(m4) is 100/0 to 30/70, and (m2)+(m4) is 5 to 70, wherein (m1) and (m2) are the molar percentages of groups of formula I and groups of formula II in the structural units derived from the total acid component, and (m3) and (m4) are the molar percentages of groups of formulas II and IV or V in the structural units derived from the total diamine component).