Macroporous, asymmetric, semipermeable membrane

PURPOSE: To simply and economically obtain a chemically and thermally stable porous asymmetric semipermeable membrane by incorporating a carboxylic acid deriv. with a specified structure in repeating units and two kinds of diamine components with specified structures at specified proportions. CONSTITUTION: A macroporous, asymmetric semipermeable membrane is obtained by incorporating a polyamide having repeating structural units of the formula I and also containing structural units of formulae II and III. Wherein, based on 100 mole % of the total of the formulae II and III, 15-100 mole % of the structural units expressed by the formula II and 0-85 mole % of the structural units expressed by the formula III are contained. The ratio by weight of the total formulae II and III to the formula I is 0.9-1.1. Further, -Ar- is a bivalent arom. group or a heteroarom. group, wherein two carboxyl groups bonded to the Ar group are bonded to non-adjacent ring carbon atoms. The Ar group may be unsubstd. or substd. with one or two branched or linear 1-3C alkyl group (s) or alkoxy group (s). -X- is -C(CH3 )2 -, -C(CF3 )2 -, etc., -Y- is -SO2 , -CH2 -, etc.