The Reactivities of α -Substituted Acrylonitriles and Acrylic Esters in Radical Copolymerizations

In order to clarify the effect of the substituents in a-substituted acrylonitriles and acrylic esters on their relative reactivities toward a polystyryl radical, the radical copolymerizations of diethyl methylenemalonate, ethyl a-chloroacrylate, ethyl a-bromoacrylate, a-chloroacrylonitrile, methyl a-methoxyacrylate, and a-methoxyacrylonitrile with styrene (M2) were investigated at 60°C. From the copolymerization parameters obtained in this study and those reported in the literature, it was confirmed that the a substituents additively contributed to the values of log Q and e of the monomers. Hence, the reactivities of a-substituted acrylonitriles and acrylic esters relative to unsubstituted acrylonitrile and methyl acrylate toward polystyryl radical, respectively, were expressed by the following equation: log (rel. react.) = δlog QX + 0.83 σp where δ log Qx and σp are the resonance and polar substituent constants of α substituents, respectively. The values of δ log Qx were determined for CH30, CH3, C6H5, Cl, Br, OCOCH3, COOCH3, and CN substituents, and these values were closely related to the other resonance substituent constants such as ER and R of corresponding substituents, except for OCH3 substituent. This relationship could also be applied to monosubstituted ethylenic monomers by using the same parameters. However, the reactivities of a-substituted styrenes deviated from this relationship because of the low ceiling temperatures of these monomers.