Polyethylene glycol derivatives, their modified peptides, methods for producing them and use of the modified peptides

Polyethylene glycol derivatives of the formula wherein Ri, and R2 are the same or different and each represents a lower alkyl, m and n are the same or different and each represents a positive integer and p is 0 or a positive integer, peptides modified by the polyethylene glycol derivatives, methods for producing them and use of the modified peptides. The peptides modified by the polyethylene glycol derivatives (I) of the invention as compared with the corresponding non-modified peptides, show decreased antigenicity, are considerably delayed in biological clearance, and exhibit their physiological activities effectively over the long period, rendering themselves very effective as pharmaceuticals as well as drugs for animals.