Patent ID: 7728097

Claim:
A method for making a macromer of mixture of macromers of the formula wherein f is two or more; “a” is zero or one; and when “a” is one to five, R 1 is where the ethylene oxide portion of R 1 is linear or branched, and c is from 1 to 100; R 2 is —R 3 —R 4 —R 3 — (R2) where R 3 is a linear or branched residue of a water soluble polymer that is capable of forming ester linkages to R 4 , and (i) ester linkages together with the carbonyl group of the benzoyl isocyanate moiety when “a” is zero, or (ii) urethane linkages to R 1 when “a” is one or more; and R 4 is a linear or branched organic residue capable of having two or more carboxylate end-groups, comprising the steps of: (a) condensing a linear polyalkylene glycol with a polycarboxylic acid so that the polycarboxylic acid is terminated with hydroxyl groups from the polyalkylene glycol, to form a polyethylene glycol ester polyol; (b) synthesizing an aromatic dinitro intermediate; (c) hydrogenating the aromatic dinitro intermediate to form a diamine intermediate, (d) purifying the diamine intermediate; (e) phosgenating the diamine intermediate to form a diisocyanate intermediate; and (f) reacting the diisocyanate intermediate with the polyethylene glycol ester polyol to form an isocyanate terminated polyethylene glycol ester urethane, wherein the linear polyalkylene glycol that condensed with a polycarboxylic acid in the presence of a tin catalyst in step (a) to produce the polyethylene glycol ester polyol and the polyethylene glycol ester polyol is purified by removing the tin catalyst with citric acid/silica mixture precipitated in a hydrophobic solvent prior to step (b).