Styrene/tert-butyl rnethacrylate (S/TBMA) mixtures, with initial TBMA rnolar feed compositions integral(TBMA,0) = 0.1-0.92, were copolymerized by nitroxide-mediated polymerization (NMP) in bulk at 90 degrees C using 10 mol % {tert-butyl{1-(diethoxyphosphoryl)-2,2-dimethylpropyl]amino) nitroxide (SG1) relative to 2-({tert-butyl[1-(diethoxyphosphoryl)-2,2-dimethylpropyl]amino}oxy)-2-me thylpropionic acid unimolecular initiator (BlocBuilder) to form SG1-terminated macroinitiators. k(p)K values (k(p) = propagation rate constant, K = equilibrium constant) for S/TBMA increased significantly as integral(TBMA,0) increased, with k(P)K = (7.4 +/- 0.03) x 10(-7) to (5.4 +/- 0.9) x 10(-5) s(-1). Copolymer reactivity ratios were P-TBMA= 0.13-0.27 and r(S) = 0.43-0.59 using Fineman-Ross, Kelen-Tudos, and nonlinear least-squares fitting to the Mayo-Lewis terminal model. All S/TBMA copolymers (number-average molecular weight (M) over bar (n) = 4.5- 15.6 kg mol(-1)) exhibited low polydispersities ((M) over bar (w)/(M) over bar (n) <= 1.30), and (M) over bar (n) exhibited linear behavior with conversion up to 25-40% and monomodal molecular weight distributions. TBMA-rich copolymer ((M) over bar (n) = 14.21 kg mol(-1) and (M) over bar (w)/(M) over bar (n) = 1.30) was shown to have a high degree of "livingness" based upon P-31 NMR measurements for the SG1 end group (approximate to 75%), and successful reinitiations of fresh batches or styrene, tert-butylstyrene, N-isopropylacrylamide, and a ternary mixture of glycidyl methacrylate/methyl methacrylate/styrene (all products were monomodal with (M) over bar (n) = 17.8-81.0 kg mol(-1) and (M) over bar (w)/(M) over bar (n) = 1.33-1.59).