Understanding Organometallic-Mediated Radical Polymerization with an Iron(II) Amine–Bis(phenolate)

The organometallic-mediated radical polymerization (OMRP) of methyl methacrylate (MMA), styrene, and vinyl acetate, mediated by a novel tert-butyl-substituted amine–bis­(phenolate) iron­(II) complex in the absence of a halide source, accesses an organometallic-only route to controlled radical polymerization. Detailed kinetic and end-group studies were used to further understand the mechanism of control and the relative rates of propagation and termination reactions by using V-70, a low-temperature radical initiator. For the polymerization of MMA, propagation is favored at low conversions, with good control and reasonable dispersities achieved. Mechanistic studies suggest propagation proceeds through a RT-OMRP mechanism, while termination reactions become dominant at higher conversions. The polymerization temperature greatly affects the nature of termination, tuning whether bimolecular termination or catalytic chain transfer (CCT) dominates. With careful control of reaction conditions, the polymerization of styrene also shows good control, with dispersities as low as 1.27, and while not comparable to ATRP conditions, this research represents the most effective iron-mediated OMRP of styrene to date.