Synthetic and mechanistic aspects of metal-free polymerizations of acrylates

Metal-free initiators are easily prepared from neutral CH- and NH-acidic compounds such as malonic acid esters, nitriles, sulfones, nitro-alkanes, cyclopentadiene, fluorene derivatives, carbazoles and succinimide. These anions have tetrabutylammonium ions as cationic counterions, but they are not completely free “naked” anions as traditionally assumed. Rather, anion and cation are intimately connected to each other via H-bonds. These salts initiate the polymerization of acrylates, methacrylates and acrylonitrile, forming polymers in the MW range of 1500 to 20000 with narrow molecular weight distributions (D = 1.1–1.4) in optimized cases. A completely different approach involves initiators of the type α-iodo malonic acid esters CH₃C(I)(CO₂R)₂ and α- iodo isobutyric acid esters (CH₃)₂C(I)CO₂R in combination with (nBu)₄N⁺I⁻ at 60°C. This novel initiator system is specific for metharcylates, i. e., acrylates are not polymerized.