Copper(I) bromide/N-(n-octyl)-2-pyridylmethanimine-mediated living-radical polymerization of methyl methacrylate using carbosilane dendritic initiators

The zeroth (Si{(CH2)(3)SiMe2(C6H4CH2OC(O)CMe2Br)}(4)), 2, and first (Si{(CH2)(3)Si((CH2)(3)SiMe2(C6H4CH2OC(O)CMe2Br))(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 x 10(-5) mol L-1 s(-1)) and 3 (4.8 x 10(-5) mol L-1 s(-1)) with the benzylic model compound C6H5CH2OC(O)CMe2Br (1) showing a lower rate of polymerization for both dendritic initiators, (7.3 x 10(-5) mol L-1 s(-1)) where [initiator sites] = 1.87 x 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 x 10(-3) mol L-1.