Novel graft polymers have been synthesized via an anionic grafting reaction of beta-butyrolactone (beta-BL) on poly(methyl methacrylate) (PMMA). It was found that partially saponified PMMA bearing carboxylate anions complexed by 18-crown-6 potassium counterion acts as a macroinitiator of beta-butyrolactone polymerization. As a result, graft polymers of PMMA with grafted poly(butyrolactone) side chains are produced in high yield over a wide graft composition range.