Effect of aliphatic spacer substitution on the reactivity of phenyl carbamate acrylate monomers

Novel monoacrylate monomers with a carbamate secondary functionality and a terminal aryl group were synthesized to study the mechanisms that allow for increased reactivity of these monomers compared to typical monoacrylate monomers. To test for the possibility of hydrogen abstraction from the two-carbon aliphatic spacer group, varying methyl substituents were added to one or both of the spacer carbons. Single methylation at the alpha and beta carbons showed no drastic effect on the polymerization rate. However, dual methylation of the alpha carbon reduced the overall polymerization rate by approximately 5-fold. Conversely, dual methylation at the beta carbon reduced the polymerization rate by only 2-fold. Unsteady state analysis of the alpha,alpha-methylated monomer showed that the apparent kinetic constants approach that of traditional monoacrylate monomers. Thus, hydrogen abstraction appears to be a likely explanation for these unique substitution effects on monoacrylate reactivity where the substitution number and location have a profound impact on the polymerization rate of these novel monomers. Disubstitution at the alpha-position has the most profound influence on the rate.