Studies in polymerization XIX. Initiation by metal chelates in the presence of electron donors

Abstract

Donor additives greatly enhance the rates of initiation of free-radical polymerization by transition metal acetylacetonates. Increases by factors exceeding 10 3 have been observed, and some systems containing these components are effective initiators at room temperatures. A kinetic study has been made of the polymerization of several monomers initiated by Mn(acac) 3 + Me 2 SO and Mn(acac) 3 + H 2 NCHMeCH 2 NH 2 . In the presence of the additives initiation by Mn(acac) 3 becomes monomer-selective, occurring most rapidly with monomers carrying electron-attracting groups. Radiochemical investigations show that each propagating chain carries one acetylacetonate residue, but that fragments derived from the additives are incorporated in the polymer only to a minor extent. Kinetic and spectral observations are consistent with initial complex-formation between the chelate and the additive, followed by reaction of the complex by two possible routes: (i) a non-selective decomposition into an Mn II -derivative and an acetylacetonyl radical, and (ii) a selective anionic monomer addition (or monomer insertion) with subsequent (or simultaneous) internal electron-transfer. Equilibrium and rate constants at 25 °C have been evaluated.