The present invention provides polymer compositions of one or more phosphorus acid group containing, polymers of six-membered cyclic methacrylic acid imide comprising a backbone polymer having one or more one methacrylic acid in polymerized form or its salt, quaternary ammonium group, ester side chain group or amide side chain group, wherein the backbone polymers comprise from 60 to 100 wt.%, based on the total weight of monomers used to make the backbone polymer, of total methacrylic acid polymerized units, regardless of their form, and wherein a total of from 7.5 to 95 wt.%, or, preferably, less than 70 wt.% of the methacrylic acid polymerized units comprise methacrylic anhydride groups or six-membered cyclic methacrylic imide groups. The polymer can be readily tailored to boost modulus and modify surface energies when added to polymers like polyolefins, and to make them compatible with other polymers, like polyamide.