Patent ID: 7547765

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 is 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, which may be the same or different, each represent an arbitrary positive integer) or (OCH 2 CH 2 ) ra —[OCH(CH 3 )CH 2 ] sa (in which ra and sa have the same meanings as the above r and s, respectively); n represents an arbitrary positive integer; m represents an integer of 3 or more; q represents an integer of 1 to 3; 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 R 4 —NH—C(═O)—R 5 [in which R 4 represents a bond, alkylene or O(CH 2 ) tc (in which tc represents an integer of 1 to 8) and R 5 represents a bond; X 2 represents a bond, O or (CH 2 ) te O (in which te has the same meaning as the above tc); 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 two or three X 2 —X 3 —R 2 's are present (when q is 2 or 3), they may be the same or different}.