Phenolic Ester-Based Initiators for Transition Metal Mediated Living Polymerization
journal contributionposted on 03.12.1999, 00:00 by David M. Haddleton, Carl Waterson
A range of phenolic esters derived form the esterification of substituted phenols with 2-bromoisobutyryl bromide and 2-chloroisobutyryl chloride have been demonstrated to be effective atom transfer polymerization initiators in conjunction with N-(n-octyl)-2-pyridylmethanimine and copper(I) chloride and bromide. All initiators have been fully characterized. Methoxy, phenyl ether, primary aryl amino, aldehyde, nitro, and benzyl ether functional initiators lead to efficacious atom transfer polymerization without imparting any detrimental effects on the polymerization. Polymerizations have been shown to proceed with excellent first-order kinetics with small amount of termination, as seen by narrow polydispersity indices, often below 1.10. Rates of polymerization are of the of the order of 1 × 10-4 s-1, which gives PMMA of approximately 10 000 g mol-1 after 4 h under typical polymerization conditions. Mn increases linearly with conversion. Polymerization of a range of alkyl methacrylates is demonstrated including ethyl methacrylate, butyl methacrylate (iso- and n-) while tert-butyl methacrylate terminates early in the reaction, with the production of a broad molar mass distribution polymer. Polymerization of styrene proceeds effectively, but at a much slower rate than for MMA. Polymerization of MMA with a chloro functional initiator and CuCl proceeds at approximately half the rate of the bromo analogues with a broadening of PDI. Difunctional and trifunctional initiators are derived from the appropriate polyphenols. The multifunctional initiators are shown to be effective atom transfer initiators to give narrow PDI polymer with controlled Mn. The role of deactivating copper(II) species is further seen by the effect of the polymerization rate in a range of kinetic experiments. Esterified phenols are an extremely versatile and simple route into α-functional polymers via atom transfer polymerization.