Patent ID: 7550556

Claim:
A production method for a highly stable polymer comprising the steps of: (1) reacting a polymer having a principal chain including at least a component unit having a pendant acidic group and a component unit having a pendant hydroxyl group with an isocyanate compound until an isocyanate group, as measured by an IR absorption spectrum at a peak of 2,200 cm −1 , is no longer present to form an intermediate product, said intermediate product featuring: pendant groups having amido linkages and/or pendant groups having urethane linkages, and pendant acid anhydride groups formed by dehydration of un-reacted acidic groups; (2) preparing a solution by dissolving or dispersing the intermediate product in a solvent; and (3) adding an alcohol to the solution, before viscosity rise of the solution or before completion of viscosity rise of the solution, and thereby reacting the alcohol with said pendant acid anhydride groups of the intermediate product; wherein said alcohol has about 1 to 20 carbon atoms and is selected from the group consisting of linear alkanols, cellosolve-based alcohols, carbitol-based alcohols, ether-based alcohols, and ethylenically unsaturated alcohols.