Method for making hydrophilic random interpolymer compositions

A process for preparing a random interpolymer derived from the polymerization of a mixture of monomers, said interpolymer having a water adsorbing capacity of at least about 10 times its own weight after having been dried at a temperature of about 100.degree. C. for about 3 hours;

• this process comprising the steps of (1) selecting said mixture of monomers so that it comprises:
• (A) from about 10 to about 90% by weight of said mixture of a first monomer which is an ester of an .alpha.,.beta.-olefinically unsaturated carboxylic acid and a monohydric or polyhydric alcohol having a terminal quaternary ammonium group and (B), correspondingly, from about 90 to about 10% by weight of said mixture of at least one .alpha.,.beta.-olefinically unsaturated comonomer capable of being dispersed in aqueous media, said comonomer (B) comprising (1) at least 10% by weight of said mixture of monomers of an acid comonomer, or (2) at least 20% by weight of said mixture of monomers of an amide comonomer, or (3) at least 10% by weight of said mixture of monomers of a combination of acid and amide comonomers, said combination containing at least 5% by weight of said mixture of an acid monomer;
• (II) distributing said mixture of monomers in from about 9 to about 20 parts by weight of an aqueous medium per part of total monomers, said aqueous medium comprising at least 40% by weight of water and up to about 60% by weight of a water miscible organic solvent, and then (III) initiating said polymerization by means of a free radical initiator selected from the group consisting of high energy radiation, photochemical free radical initiators and chemical free radical initiators that are dispersible or soluble in said aqueous medium in the presence of (IV) at least 0.02% by weight, based on the weight of said mixture, of a cross-linking agent comprising a difunctional monomer which is capable of being dispersed or dissolved in said aqueous medium and is an ester or amide of an .alpha.,.beta.-olefinically unsaturated carboxylic acid.