H-1 and C-13 NMR spectra of copolymers of methyl methacrylate (M) and butyl acrylate (B) were analyzed in terms of sequence distribution and stereoregularity of monomer units. The copolymers were prepared by atom transfer radical polymerization (ATRP) in bulk and 25% (v/v) benzonitrile solution. The different experimental conditions resulted in different levels of polymerization control. Under our experimental conditions, the experimental data agreed well with data calculated from the Mayo-Lewis terminal model and Bernoullian statistics with monomer reactivity ratios of r(M) = 1.44 +/- 0.11 and r(B) = 0.56 +/- 0.06 and an isotacticity parameter of sigma (M) = 0.23 and coisotacticity parameter of sigma = 0.30. Therefore, the copolymer compositions and microstructures are independent of the controllability of the ATRP process.