Polymer derivatives having particular atom arrangements

A polymeric reagent of the following structure

• wherein:
• POLY1 is a linear, water-soluble homopolymer selected from the group consisting of a poly(alkylene oxide), poly(vinyl pyrrolidone), poly(vinyl alcohol), polyoxazoline, poly(acryloylmorpholine), and poly(oxyethylated polyols);
• POLY2 is a linear, water-soluble homopolymer selected from the group consisting of a poly(alkylene oxide), poly(vinyl pyrrolidone), poly(vinyl alcohol), polyoxazoline, poly(acryloylmorpholine), and poly(oxyethylated polyols);
• (a) is 0, 1, 2 or 3;
• (b) is 0, 1, 2 or 3;
• (e) is 0, 1, 2 or 3;
• (f) is 0, 1, 2 or 3;
• (g′) is 0, 1, 2 or 3;
• (h) is 0, 1, 2 or 3;
• (j) is 0 to 20;
• each R1 is independently H or an organic radical selected from the group consisting of alkyl, substituted alkyl, alkenyl, substituted alkenyl, alkynyl, substituted alkynyl, aryl and substituted aryl;
• X1, when present, is a first spacer moiety of a linear chain of from one to twenty atoms in length wherein the first spacer moiety is composed of one or more atoms each independently selected from the group consisting of carbon, nitrogen, oxygen, sulfur and hydrogen;
• X2, when present, is a second spacer moiety of a linear chain of from one to twenty atoms in length wherein the second spacer moiety is composed of one or more atoms each independently selected from the group consisting of carbon, nitrogen, oxygen, sulfur and hydrogen;
• X5, when present, is a fifth spacer moiety of a linear chain of from one to twenty atoms in length wherein the fifth spacer moiety is composed of one or more atoms each independently selected from the group consisting of carbon, nitrogen, oxygen, sulfur and hydrogen;
• X6, when present, is a sixth spacer moiety of a linear chain of from one to twenty atoms in length wherein the sixth spacer moiety is composed of one or more atoms each independently selected from the group consisting of carbon, nitrogen, oxygen, sulfur and hydrogen;
• X7, when present, is a seventh spacer moiety of a linear chain of from one to twenty atoms in length wherein the seventh spacer moiety is composed of one or more atoms each independently selected from the group consisting of carbon, nitrogen, oxygen, sulfur and hydrogen;
• X8, when present, is an eighth spacer moiety of a linear chain of from one to twenty atoms in length wherein the eighth spacer moiety is composed of one or more atoms each independently selected from the group consisting of carbon, nitrogen, oxygen, sulfur and hydrogen;
• R5 is a three-way branching moiety selected from the group consisting of
• wherein (p) is 1-8 and (q) is 1-8;
• and
• Z is a reactive group suitable for reaction with an electrophile or a nucleophile of a biologically active agent.