PROBLEM TO BE SOLVED: To provide a copolyester which has high hygroscopicity and can be easily formed into chips. SOLUTION: This composition comprises a polyester prepared by copolymerizing a polyoxyalkylene glycol and 0.01-30mol% crosslinking agent represented by the formula: (R2 O)m R1 (COOR3 )n (wherein R1 is a tetra- to hexa-valent organic residue; R2 is hydrogen or acetyl; R3 is hydrogen or an alkyl; and 3 .