Method for making an aqueous hydrogel composition

A method for making an aqueous hydrogel composition, comprising:

• mixing an aqueous solution of a vinylphosphonic acid having chemical formula I:
• and an aqueous solution of bis[2-(methyacryloyloxy)ethyl] phosphate (BMEP) to form an aqueous mixture;
• and
• initiating a polymerization reaction in the aqueous mixture by adding an azo compound initiator to form a polymerization reaction mixture,
• adjusting the pH of the polymerization reaction mixture to about 9,
• heating the polymerization reaction mixture to form the aqueous hydrogel composition, wherein the aqueous hydrogel composition comprises a cross linked polyvinyl polymer;
• wherein Formula I R1 is phosphonate;
• and R2, R3, and R4 are independently hydrogen, sulfonate, carboxylate, phosphonate, optionally substituted methyl, ethyl, propyl, optionally substituted cycloalkyl, or optionally substituted aryl or heteroaryl;
• wherein the BMEP is present in the cross linked polyvinyl polymer in an amount of about 40 mol % based on the total molar amount of the vinylphosphonic acid of formula I and the BMEP;
• and
• wherein the cross linked polyvinyl polymer consists essentially of polymerized units of the vinylphosphonic acid having chemical formula I and the BMEP.