Reactivities of acrylic monomers and their radicals in radical polymerization

The reactivities of acrylic derivatives in radical polymerization were largely dependent on polar, resonance and steric effects of their substituents. Although the change in ester alkyl substituents resulted in only polar effects, the introduction of the substituent into α‐position increased both resonance and steric effects, and that into β‐position increased steric effect greatly. The steric effects of o− and N–alkyl substituents in phenyl methacrylates and methacrylamides, respectively, were also important, i.e. 2,6‐di‐t‐butylphenyl methacrylate and N,N‐dialkylmeth‐acrylamides did not homopolymerize, although the respective acrylates and acrylamides could easily polymerize. It was noted that the steric effect by three alkyl groups bonded at α‐and o− or N‐positions played an important role. However, fumaric esters, β‐alkoxycarbonyl–acrylic esters, having bulky ester substituents were found to be readily polymerized to give high‐molecular‐weight and less‐ or non‐flexible polymers. In these polymerizations, the bimolecular termination is hindered, i.e. the life‐time of the propagating radical becomes longer. The propagating radicals were easily detectable from the polymerization mixtures by direct ESR measurement. Some features of these radical polymerizations are also discussed.