Deviant polymerization behavior of 4-acetoxystyrene found through a detailed study on the ATRP of para-substituted styrenes

The atom transfer radical polymerization (ATRPs) of para-substituted styrenes bearing nitro, cyano, acetoxy, acetoxymethyl, and methoxy groups were performed to elucidate the effects of these substituents in terms of the Hammett equation. 4-Cyanostyrene (4CS) polymerized rapidly in acrylonitrile at 80？°C and afforded polymers with a narrow molecular weight distribution, while the ATRP of 4-acetoxystyrene (4AS) proceeded very slowly and gave the corresponding polymer in a low yield. The apparent polymerization rate constants (kpapp) of 4CS and 4-acetoxymethyl styrene were consistent with the Hammett equation with ρ？=？1.52; however, the rate constant for the polymerization of 4AS did not follow the Hammett relation. The polymerization rate of 4AS was increased by the addition of 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP); however, the NMR and MALDI-TOF-MS spectra of the resulting polymer revealed that a chain transfer radical polymerization took place to give a polymer with relatively low molecular weight. On the other hand, 4-methoxystyrene was immediately polymerized in 2,2,2-trifluoroethanol (TFE) and pentafluorophenol (PFP) by a cationic mechanism because of the electron-donating methoxy group, whereas 4AS did not polymerize in TFE and PFP. The deviant and irregular polymerization behavior of 4AS has been discussed in comparison with the reactivities of various para-substituted styrenes bearing electron-withdrawing and electron-donating groups