Amphiphilic diblock, triblock, and star block copolymers by living radical polymerization: Synthesis and aggregation behavior

Copper(I)-mediated living radical polymerization was used to synthesize amphiphilic block copolymers of poly(n-butyl methacrylate) [P(n-BMA)] and poly[(2-dimethylamino)ethyl methacrylate] (PDMAEMA). Functionalized bromo P(n-BMA) macroinitiators were prepared from monofunctional, difunctional, and trifunctional initiators: 2'-bromo-2'-methylpropionic acid 4-methoxyphenyl ester, 1,4-(2'-bromo-2'-methyl-propionate)benzene, and 1,3,5-(2'-bromo-2'-methylpropionato)benzene. The living nature of the polymerizations involved was investigated in each case, leading to narrow-polydispersity polymers for which the number-average molecular weight increased fairly linearly with time with good first-order kinetics in the monomer. These macroinitiators were subsequently used for the polymerization of (2-dimethylamino)ethyl methacrylate to obtain well-defined [P(n-BMA)(x)-b-PDMAEMA(y)](z) diblock (15,900; polydispersity index = 1.60), triblock (23,200; polydispersity index = 1.24), and star block copolymers (50,700; polydispersity index = 1.46). Amphiphilic block copolymers contained between 60 and 80 mol % hydrophilic PDMAEMA blocks to solubilize them in water. The polymers were quaternized with methyl iodide to render them even more hydrophilic. The aggregation behavior of these copolymers was investigated with fluorescence spectroscopy and dynamic light scattering. For blocks of similar comonomer compositions, the apparent critical aggregation concentration (cac = 3.22-7.13 X 10(-3) g L-1) and the aggregate size (ca. 65 nm) were both dependent on the copolymer architecture. However, for the same copolymer structure, increasing the hydrophilic PDMAEMA block length had little effect on the cac but resulted in a change in the aggregate size. (C) 2002 John Wiley Sons, Inc.