Reactivities of ω‐Unsaturated Methacrylate Oligomers toward tert‐Butoxy Radicals: Investigation of the Effect of Degree of Polymerization and Ester Alkyl Group

Abstract

AbstractThe reactivities of ω‐unsaturated methacrylate oligomers (RMA‐n; n = 2–5) toward tert‐butoxy radicals (t‐BuO·) as a model of the addition step in addition‐fragmentation chain transfer (AFCT) have been investigated by the nitroxide trapping technique in combination with HPLC and electrospray ionization mass spectrometry. The ratio of the rate coefficients for the addition of ω‐unsaturated methyl methacrylate oligomers (MMA‐n) to t‐BuO· to the β‐fragmentation of t‐BuO· (kadd/kβ), where kβ can be treated as a constant, has been shown to decrease with increasing n due to increased steric hindrance of the α‐substituents. However, the value of kadd/kβ reaches a constant value at n = 3–4, and the greatest extent of suppression of the addition rate compared with MMA is less than a factor of four. Comparison of the values of kadd/kβ for ω‐unsaturated cyclohexyl methacrylate oligomers (CHMA‐n; n = 2 and 3) with MMA‐n revealed that the extent of suppression increased with increasing n without regard to the ester alkyl group. Hydrogen abstraction by t‐BuO· from RMA‐n appears to occur mainly at the ester alkyl groups, and the extent is much greater from CHMA‐n than from MMA‐n. magnified image