Microstructure determination of methyl methacrylate and n-butyl acrylate copolymers synthesized by atom transfer radical polymerization with two-dimensional NMR spectroscopy

Copolymers of methyl methacrylate (MMA) and n-butyl acrylate (n-BA) were synthesized under atom transfer radical polymerization (ATRP) conditions. The molar infeed ratio was varied to obtain copolymers with different compositions. Methyl 2-bromo propionate was used as the initiator with CuBr/Cu(0)/N,N,N',N",N"-pentamethyldiethylenetriamine as the catalyst at 60 degreesC. Molecular weight distribution was determined by gel permeation chromatography (GPC). Copolymer compositions (F,,) were calculated from H-1 NMR spectra. Reactivity ratios calculated with the Mao-Huglin terminal model at a high conversion were found to be r(M) = 2.17 and r(B) 0.47. The polymerization mechanism was studied with the alpha-methyl region of MMA. The backbone methylene and carbonyl carbons of both MMA and n-BA units were found to be compositionally as well as configurationally sensitive. Complete spectral assignments were performed with the help of heteronuclear single quantum coherence (HSQC) spectroscopy along with total correlated spectroscopy (TOCSY). Further, the assignments of the carbonyl region were made with the help of heteronuclear multiple quantum coherence (HMBC) spectroscopy. (C) 2005 Wiley Periodicals, Inc.