Atom Transfer Radical Polymerization of Methyl Methacrylate Mediated by Grubbs 1st and 2nd Generation Catalysts: Insight into the Active Species

Abstract

Ruthenium benzylidene complexes were evaluated as catalysts in atom-transfer radical polymerization (ATRP) of methyl methacrylate (MMA) under different reaction conditions. The mechanism by which Grubbs 1st and 2nd generation catalysts mediate olefin metathesis has been studied, little is known regarding the mechanism of ATRP reaction promoted by these complexes. Conversion and semilogarithmic kinetic plots as a function of time were correlated to the different catalysts and reaction conditions; especially in the presence of Al(OiPr)(3) as additive. Molecular weight (M-n) and polydispersity index (PDI) values changed with different catalysts in the presence or absence of Al(OiPr)(3). Kinetic studies by H-1 NMR revealed that two complexes in the presence of Al(OiPr)(3) are converted into ATRP-active with the dissociation of PCy3, but with the benzylidene group preserved. More controlled polymerizations were achieved using Grubbs 1st and, the presence of Al(OiPr)(3) improved the control levels for both catalysts.