Abstract: There is provided a compatibilizer for polyester resin which can produce better compatibility than conventional counterparts, and a polyester resin composition using the compatibilizer. The compatibilizer comprises a polycarbodiimide compound represented by the formula (1) describe below wherein the carbodiimide equivalent of the polycarbodiimide compound is 280 or higher; and in the formula (1), R1 and R2 are residues formed by eliminating a functional group from an organic compound having the one functional group reactive with an isocyanate group; R3 is a divalent residue formed by eliminating two isocyanate groups from a diisocyanate compound; R4 is a divalent residue formed by eliminating two hydroxyl groups from a diol compound; X1 and X2 are bonds formed by reaction of the functional group of the organic compound with one of the two isocyanate groups of the diisocyanate compound; and m and n=1 to 20, m+n?25, and p=0 to 39, provided that the number of carbodiimide groups in one molecule is 2 to 40.

Abstract: A modified polycarbodiimide compound which is obtained by modifying at least some of carbodiimide groups in a polycarbodiimide derived from a diisocyanate compound, said polycarbodiimide having a terminal blocked with a hydrophilic compound, with an aromatic heterocyclic compound such as 3,5-dimethylpyrazole having endocyclic secondary amine nitrogen has a potential for a cuing agent, and exhibits the activity of the carbodiimide groups by being unblocked at relatively low temperatures.