Polyimide copolymer oligomer, polyimide copolymer, and method for producing each of same

A polyimide copolymer obtained by copolymerizing (A) 3,3′,4,4′-biphenyltetracarboxylic dianhydride with (B) at least one diamine and/or diisocyanate represented by the following Formulae (1) or (2):

• (wherein, X represents an amino group or an isocyanate group;
• R1 to R4 each independently represent a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkenyl group having 2 to 4 carbon atoms or an alkoxy group having 1 to 4 carbon atoms;
• and at least one of said R1 to R4 is not a hydrogen atom), and in which (C) a second acid dianhydride and/or (D) a second diamine and/or diisocyanate is/are further copolymerized, wherein (D) the second diamine and/or diisocyanate is different from the diamine and/or diisocyanate (B) and is selected from the following formulae (5) to (14)
• wherein, X represents an amino group or an isocyanate group;
• R11 to R14 each independently represent a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkenyl group having 2 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, a hydroxyl group, a carboxy group or a trifluoromethyl group;
• R21 to R24 each independently represent an alkyl group having 1 to 4 carbon atoms or a phenyl group;
• Y represents in formula (8) and Y and Z each represent in formulae (9),
• wherein R31 and R32 each independently represent a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkenyl group having 2 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, a hydroxyl group, a carboxy group or a trifluoromethyl group);
• and Y represents, in formula (7)
• wherein R31 and R32 each independently represent an alkyl group having 1 to 4 carbon atoms, an alkenyl group having 2 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, a hydroxyl group, a carboxy group or a trifluoromethyl group), and
• wherein (C), the second acid dianhydride is pyromellitic dianhydride, 4,4′-oxydiphthalic dianhydride, 2,2′-bis[(dicarboxyphenoxy)phenyl]propane dianhydride or ethylene glycol-bis-trimellitic anhydride ester,
• wherein the polyimide copolymer is not obtained by copolymerizing with 3,3′,4,4′-benzophenonetetracarboxylic dianhydride, and
• wherein two of said R1 to R4 are ethyl groups and the other two are a methyl group and a hydrogen atom.