Radical Polymerization Behavior of 4-Monosubstituted and 2,4-Disubstituted Enynes

The radical polymerization of 4-mono- and 2,4-disubstituted enyne monomers (CH2=CH—C≡C—R and CH2=C(CH3)—C≡C—R, respectively; R = Ph, n-Bu, t-Bu, and (CH3)3Si—) was carried out to elucidate the polymerizability of the monomers and the effect of substituents on the structure of the resulting polymers. The polymerization of 4-monosubstituted monomers proceeded in a specific 1,2-fashion to give polymers having acetylene moieties as pendent groups. In contrast, that of 2,4-disubstituted monomers accompanied ca. 10% of the 1,4-polymerization to give allenic main chain structures. The monomer reactivity ratios of monosubstituted monomers were estimated from the copolymerization system with methyl methacrylate, from which the Q and e values were estimated as Q = 1.52–2.11 and e = –0.63 to –0.73, respectively. The Q and e values demonstrated that the resonance stabilizing character of the substituents on the 4-position affects the reactivity of the monomers.