Catalyzed Chain Transfer in Vinyl Acetate Polymerization Mediated by 9-Oxyphenalenone Cobalt(II) Complexes.

The vinyl acetate (VAc) radical polymerization initiated by V-70 at 30 °C in the presence of [Co II (OPN) 2 ] (OPN = deprotonated 9-oxyphenalenone), 1 , leads to PVAc of lower molecular weight (MW) than expected for organometallic-mediated radical polymerization (OMRP), whether reversible termination or degenerate transfer conditions are used. This represents the first clear evidence of catalyzed chain transfer (CCT) in VAc polymerization. The bis-pyridine adduct [Co II (OPN) 2 (py) 2 ], 2 , shows a marginally lower polymerization rate and an increased CCT activity relative to 1 , whereas the activity decreases with marginal effect on the polymerization rate upon addition of excess py. However, raising the temperature to 80 °C (with AIBN as initiator) led to a low MW polymer even in the presence of a large py excess. The CCT was confirmed by 1 H NMR characterization of the chain ends and by a MALDI-TOF MS analysis of the recovered polymer. The collective trends are consistent with greater CCT activity for the 5-coordinate complex [Co II (OPN) 2 (py)] relative to 1 and 2 . The presence of py association/dissociation equilibria relating these three complexes was confirmed by a 1 H NMR investigation.