Synthesis of well-defined macromonomers and comb copolymers from polymers made by atom transfer radical polymerization

Poly(n-butyl acrylate) macromonomers with predetermined molecular weights (1300 < number-average molecular weight < 23,000) and low polydispersity indices (<1.2) were synthesized from bromine-terminated atom transfer radical polymerization polymers via end-group substitution with acrylic acid and methacrylic acid. These macromonomers, having a high degree of end-group functionalization (>90%), were radically homopolymerized to obtain comb polymers. A high macromonomer concentration, combined with a low radical flux, was needed to obtain a high conversion of the macromonomers and a reasonable degree of polymerization. By the traditional radical copolymerization of the hydrophobic macromonomers with the hydrophilic monomer N,N-dimethylaminoethyl methacrylate (DMAEMA), amphiphilic comb copolymers were obtained. The conversions of the macromonomers and comonomer were almost quantitative under optimized reaction conditions. The molecular weights were high (number-average molecular weight approximate to 70,000), and the molecular weight distribution was broad (polydispersity index approximate to 3.5). Kinetic measurements showed simultaneous decreases in the macromonomer and DMAEMA concentrations, indicating a relatively homogeneous composition of the comb copolymers over the whole molecular weight range. This was supported by preparative size exclusion chromatography. The copolymerization of poly(n-butyl acrylate) macromonomers with other hydrophilic monomers such as acrylic acid or N,N-dimethylacrylamide gave comb copolymers with multimodal molecular weight distributions in size exclusion chromatography and extremely high apparent molecular weights. Dynamic light scattering showed a heterogeneous composition consisting of small (6-9 nm) and large (23-143 nm) particles, probably micelles or other type of aggregates. (C) 2003 Wiley Periodicals, Inc.