Nitroxide-mediated polymerization (NMP) of styrene using N-tert-butyl-N-[1-diethylphosphono-(2,2-dimethylpropyl)]nitroxide (SG1) in the presence of poly(styrene) macromonomers containing two different 2-carboalkoxy-2-propenyl (CH2=C(CO2R)CH2-: R = Et, tBu) omega-end groups proceeded in a controlled/living manner, as indicated by a continuous increase in the number average molecular weight with conversion giving values close to approximated theoretical values and efficient chain extension of the resultant branched polymers obtained. The polymerization rate decreased with increasing macromonomer content, but was independent of macromonomer omega-end group. Replacing styrene by alpha,beta,beta-trideuterio-styrene (St-d3) in copolymerizations with macromonomers allowed estimation of the reactivity ratio rSt-d3 to be 0.42 using ¹H NMR analysis. This was used to obtain an estimate of the theoretical number average molecular weight as a function of conversion and to calculate the microstructure of the gradient branched copolymers obtained. (c) 2007 Elsevier Ltd. All rights reserved.