Role of N-substituents of maleimides on penultimate unit effect for sequence control during radical copolymerization

Radical copolymerization of N-substituted maleimides (RMIs) and olefins provides AAB sequence-controlled copolymers by penultimate unit (PU) control. In this study, we investigated the steric, resonance, and polar effects of N-substituents on sequence control during copolymerization of RMIs as the M-2 monomer with diisobutene (DIB) and d-limonene (Lim) as the M-1 monomer in chloroform at 60 degrees C. The monomer reactivity ratios (i.e., r(2) (= k(22)/k(21)), r(12) (= k(122)/ k(121)), and r(22) (= k(222)/k(221))) were determined based on the terminal and PU models using a nonlinear least-squares method. For the copolymerization of RMIs with DIB, the introduction of a bulky N-alkyl group suppressed the PU effect and led to the formation of alternating copolymers. The copolymerization of N-phenylmaleimides with o- and p-substituents was also investigated to reveal the steric, resonance, and polar effects of the substituents. In conclusion, less bulky and more electrondonating substituents effectively induced the PU effect during the radical copolymerization of RMIs and olefins.