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.