The present invention provides compositions of phosphorus acid group and methacrylic anhydride group containing telomeric copolymers of methacrylic acid having an as yet never achieved amount of more than 70 wt. %, or, preferably, 72 wt. % or more, and up to 99 wt. %, of methacrylic anhydride groups based on the total weight of polymerized methacrylic acid and/or salt units. The compositions enjoy higher thermal stability than was previously achieved and enable easer processing that does not require the removal of liquids or solvents.