Copper(I) Bromide/N-(n-Octyl)-2-pyridylmethanimine−Mediated Living-Radical Polymerization of Methyl Methacrylate Using Carbosilane Dendritic Initiators

The zeroth (Si{(CH 2 ) 3 SiMe 2 (C 6 H 4 CH 2 OC(O)CMe 2 Br)} 4 ), 2, and first (Si{(CH 2 ) 3 Si((CH 2 ) 3 SiMe 2 (C 6 H 4 CH 2 OC(O)CMe 2 Br)) 3 } 4 ), 3, generation of 2-bromoisobutyryl functionalized carbosilane dendrimers have been successfully applied as initiators for the copper(I) bromide/ N -( n -octyl)-2-pyridylmethanimine-mediated living-radical polymerization of methyl methacrylate. The overall rate of polymerization are comparable for the two dendritic initiators studied, 2 (3.4 × 10 -5 mol L -1 s -1 ) and 3 (4.8 × 10 -5 mol L -1 s -1 ) with the benzylic model compound C 6 H 5 CH 2 OC(O)CMe 2 Br ( 1 ) showing a lower rate of polymerization for both dendritic initiators, (7.3 × 10 -5 mol L -1 s -1 ) where [initiator sites] = 1.87 × 10 -2 mol L -1 . We postulate that this is caused by initial intramolecular termination. The molecular weight distribution is less than 1.3 after 3 h reaction time. Initiator 3, however, produces star−star coupling throughout the polymerization. When the dendritic periphery is partialy functionalized (statistically two and six arms of the first generation dendrimer, respectively, 4 and 5 ) the control of the molecular weight distribution was lost (PDI > 3) for 4 as a result of too low of a value for [initiator site], i.e., 3.12 × 10 -3 mol L -1 .