Methyl methacrylate/styrene (MMA/S), ethyl methacrylate/styrene (EMA/S) and butyl methacrylate/styrene (BMA/S) feeds (>90 mol % methacrylate) were copolymerized in 50 wt % p-xylene at 90 degrees C with 10 mol % of additional SG1-free nitroxide mediator relative to unimolecular initiator (BlocBuilder (R)) to yield methacrylate rich copolymers with polydispersities (M) over bar (w)/(M) over bar (n)= 1.23-1.46. k(p)K values (k(p) = propagation rate constant, K = equilibrium constant) for MMA/S copolymerizations were comparable with previous literature, whereas EMA/S and BMA/S copolymerizations were characterized by slightly higher k(p)K's. Chain extensions with styrene at 11.0 degrees C initiated by the methacrylate-rich macroinitiators (number average molecular weight (M) over bar (n) = 12.9-33.5 kg mol(-1)) resulted in slightly broader molecular weight distributions with (M) over bar (w)/(M) over bar (n) = 1.24-1.86 and were often bimodal. Chain extensions with glycidyl methacrylate/styrene/methacrylate (GMA/S/XMA where XMA = MMA, EMA or BMA) mixtures at 90 degrees C using the same macroinitiators resulted frequently in bimodal molecular weight distributions with many inactive macroinitiators and higher (M) over bar (w)/(M) over bar (n) = 2.01-2.48. P(XMA/S) macroinitiators ((M) over bar (n) = 4.9-8.9 kg mol(-1)), polymerized to low conversion and purified to remove "dead" chains, initiated chain extensions with GMA/MMA/S and GMA/EMA/S giving products with (M) over bar (w)/(M) over bar (n) similar to 1.5 and much fewer unreacted macroinitiators (<5%), whereas the GMA/BMA/S chain extension was characterized by slightly more unreacted macroinitiators (similar to 20%). (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2574-2588, 2009