In general formula I the ether groups may be incorporated by copolymerizing an unsaturated carboxylic acid with an unsaturated ether, for example, acrylic acid, maleic acid, crotonic acid and the like with the vinyl ethers of from about 3 to about 10 carbon atoms such as methyl vinyl ether, ethyl vinyl ether, butyl vinyl ether, hexyl vinyl ether and the like, for example by the method described in