Polymerization of n-butyl acrylate by atom transfer radical polymerization. Remarkable effect of ethylene carbonate and other solvents

Atom transfer radical polymerization (ATRP) of n-butyl acrylate with the homogeneous catalyst, (CuBr)-Br-I/4,4'-di(5-nonyl)-2,2'-bipyridine (dNbpy), in benzene, afforded well-defined poly(n-butyl acrylate) with predetermined molecular weights and low polydispersities, M-w/M-n = 1.1. The number-average molecular weight, Mn (measured by GPC and MALDI-TOFMS), was close to the theoretical molecular weight, predetermined by DPn = Delta[M]/[I](o). A similar polymerization in benzene using 2,2'-dipyridine (bpy) as ligand instead of dNbpy displayed poor control, yielding a polymer whose molecular weight was higher than the theoretical value and demonstrating high polydispersity (M-w/M-n = 2.4). Several solvents were subsequently employed for the polymerizations with the (CuBr)-Br-I/bpy catalyst system. Good control of molecular weight and polydispersity were achieved using ethylene carbonate, and in this system the observed rate of polymerization was even faster than in bulk. The rate of polymerization with the (CuBr)-Br-I/bp catalyst in ethylene carbonate was first order with respect to the catalyst concentration; a reduction in the concentation of the catalyst led to an increase in the polydispersity of the resulting polymer. Polydispersity decreased on addition of (CuBr2)-Br-II or by reducing the amount of ethylene carbonate used. The polymerization in ethylene carbonate with CuPF6/bpy catalyst gave results similar to those observed for the (CuBr)-Br-I/bpy catalyst system. The rapid rate of polymerization in the ethylene carbonate was attributed to a monomeric structure of the (CuBr)-Br-I/bpy catalyst, as found for (CuPF6)-P-I.