PURPOSE: To obtain the titled solvent-soluble copolymer moldable in a molten state, having heat resistance and high strength, by reacting separately an aromatic diamine with isophthalic acid dichloride and an aromatic tetracarboxylic acid dianhydride, blending the reaction products, and reacting the blend with a polyfunctional carboxylic acid component.

CONSTITUTION: An aromatic diamine shown by the formula I[X is C(CH3)2, SO2, CO or CH2] is reacted with isophthalic acid chloride in the presence of a solvent, to give an amino group end-containing aromatic polyamide oligomer. On the other hand, the aromatic diamine shown by the formula I is reacted with a tetracarboxylic acid dianhyride shown by the formula II(Ar is group shown by the formula III, formula IV, etc.,) in the presence of a solvent, to give an amino end group-containing aromatic polyamic acid oligomer. Then, these oligomers are blended and reacted with isophthalic acid dichloride or the aromatic tetracarboxylic acid dianhydride, to give the aimed block copolymer containing a group shown by the formula V(n is natural number) and a group shown by the formula VI(m is natural number).