(JP10218853-A)      Preparation of isoimide comprises:    (a) reacting a compound (I) having carboxyl group(s) and amide bond(s) in the same molecule in the presence of a halo-iminium salt and a basic substance;    (b) reacting a compound (II) having COOH group(s) with a compound (III) having amide bond(s) in the presence of a halo-iminium salt and a basic substance.    Also claimed are bis-isoimide derivatives of e.g. formula (XIII):    USE -   Phenyl male-isoimide, N,N-phenylene bis-iso-maleimide, phenyl isophthalimide and other isoimide monomers are useful as raw material monomers and intermediates of agricultural chemicals and medicines. The solution of polyisoimide can be used in the preparation of eg film for a heat resistant insulation tape, heat resistant adhesive tape, heat resistant adhesive tape, high density magnetic recording base, condenser and flexible printed circuit board, structural material reinforced with fluororesin or carbon fibre, moulded material and formed articles such as bobbin of a small coil, sleeve and terminal insulation tube, laminated material used for power transistor insulating spacer, magnetic head spacer, power relay spacer and transformer spacer, enamel coating material used for wire and cable insulating coating, solar cell, low temperature storage tank, space craft heat insulation material, integrated circuit and slot liner, membrane for ultrafiltration, reverse osmosis and gas separation, and heat resistant fibres used for thread, fabric and non-woven fabric.    ADVANTAGE -   The process gives isoimides in high selectivity within short reaction times.    (US5892061-A)      Preparation of isoimide comprises:    (a) reacting a compound (I) having carboxyl group(s) and amide bond(s) in the same molecule in the presence of a halo-iminium salt and a basic substance;    (b) reacting a compound (II) having COOH group(s) with a compound (III) having amide bond(s) in the presence of a halo-iminium salt and a basic substance.    Also claimed are bis-isoimide derivatives of e.g. formula (XIII):    USE -   Phenyl male-isoimide, N,N-phenylene bis-iso-maleimide, phenyl isophthalimide and other isoimide monomers are useful as raw material monomers and intermediates of agricultural chemicals and medicines. The solution of polyisoimide can be used in the preparation of eg film for a heat resistant insulation tape, heat resistant adhesive tape, heat resistant adhesive tape, high density magnetic recording base, condenser and flexible printed circuit board, structural material reinforced with fluororesin or carbon fibre, moulded material and formed articles such as bobbin of a small coil, sleeve and terminal insulation tube, laminated material used for power transistor insulating spacer, magnetic head spacer, power relay spacer and transformer spacer, enamel coating material used for wire and cable insulating coating, solar cell, low temperature storage tank, space craft heat insulation material, integrated circuit and slot liner, membrane for ultrafiltration, reverse osmosis and gas separation, and heat resistant fibres used for thread, fabric and non-woven fabric.    ADVANTAGE -   The process gives isoimides in high selectivity within short reaction times.