The copolymerization of allyl chloroacetate (ACAc) and N-propyl maleimide (PMI), catalyzed by Cu(I)Br or ferric(III) acetylacetonate (Fe(acac)(3)) at 110 degreesC, respectively, was studied through electron-impact mass spectrometry. Both Cu(I)Br and Fe(acac)(3) catalyzed the copolymerization by an atom transfer process. However, the copolymerization of ACAc and PMI was not in an alternative way, because propyl maleimide has high tendency to form homogeneous polymeric segments under the conditions of this work.