Patent ID: 7291713

Claim:
A branched polyalkylene glycol represented by formula (I): (R 1 -M n -X 1 ) m L(X 2 —X 3 —R 2 ) q (I) wherein L represents M represents OCH 2 CH 2 , OCH 2 CH 2 CH 2 , OCH(CH 3 )CH 2 , (OCH 2 CH 2 ) r —(OCH 2 CH 2 CH 2 ) s (in which r and s, independently represent a positive integer) or (OCH 2 CH 2 ) ra —[OCH(CH 3 )CH 2 ] sa (in which ra and sa independently represent a positive integer); n represents a positive integer; m represents 3; q represents 1; R 1 represents a hydrogen atom, lower alkyl or lower alkanoyl; R 2 represents a group having reactivity with an amino acid side chain, the N-terminal amino group or the C-terminal carboxyl group in a polypeptide, or a group convertible into the group having reactivity; X 1 represents —CH 2 —NH(C═O)—; X 2 represents a bond, O or (CH 2 ) te O (in which te represents an integer of 1 to 8); X 3 represents a bond or alkylene; and three or more R 1 -M n -X 1 's may be the same or different, and when q is 2 or 3, X 2 —X 3 —R 2 's may be the same or different.