This work deals with design of maleimide monomer toward more precise control of alternating sequence for radical copolymerization with styrene. Crucial in this study is sequence analysis by MALDI-TOF-MS for resultant copolymers that was obtained via ruthenium-catalyzed living radical copolymerization with a malonate-based alkyl halide initiator showing selective initiation ability. The copolymers of a simple N-alkyl maleimide [e.g., N-ethyl maleimide (EMI)] with styrene gave complicated peak patterns for the MALDI-TOF-MS spectra indicating low degree of alternating sequence, in contrary to expectation from the reactivity ratios (almost zero). A simple substitution of methyl group (CH3) of EMI with trifluoromethyl (CF3: CF3-MI) made the peak patterns much simpler giving the copolymer with higher alternating sequence. More interestingly, the peak interval of the copolymer at earlier polymerization stage was equal to sum of the molecular weights of CF3-MI and styrene, suggesting possibility of the pair propagation of the monomers. Indeed, H-1 NMR analyses of the mixture of maleimide with styrene suggested stronger interaction of CF3-MI than EMI. Based on the results, maleimide derivatives carrying a substituent-designable electron-withdrawing group [ROC((sic)O)N-: R = substituent] were newly designed toward incorporation of functional side chains. They also gave higher alternating sequence for the copolymerization with styrene. (c) 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 367-375