Synthesis and characterization of omega-unsaturated poly(styrene-b-n-butylmethacrylate) block copolymers using TEMPO-mediated controlled radical polymerization

n-Butyl methacrylate has been polymerized in bulk at 130 degrees C in the p resence of given amounts of a nitroxide stable free radical (TEMPO = 2,2,6, 6-tetramethylpiperidine-N-oxyl) using either a low molar mass alkoxyamine i nitiator (2,2,6,6-tetramethyl-1-(1-phenethyloxy)piperidine) or a TEMPO-capp ed polystyrene macroinitiator. Complete consumption of both initiators was always observed. In contrast, very low final monomer conversions were found . Proton NMR spectroscopy and MALDI-TOF mass spectrometry were used for inv estigation of the polymer structure. They showed that the formed poly(n-but yl methacrylate) had the attached initiator at one end and that a block cop olymer was synthesized when the polystyrene macroinitiator was used. The ot her terminal functionality of the polymer was not a TEMPO-based alkoxyamine but a methylene unsaturation exclusively. Particularly, no saturated polym er which would also be formed by conventional disproportionation reaction b etween two propagating radicals could be detected. From this result, it was concluded that the main chain-breaking event is the beta-hydrogen transfer from a propagating radical to TEMPO (also called disproportionation reacti on). The initial concentration of added TEMPO was shown to directly influen ce the poly(n-butyl methacrylate) block length independently of the initial concentration of alkoxyamine: the larger the concentration of TEMPO, the s horter the block length. The rate constant of disproportionation was calcul ated to be k(dis) = 1.4 x 10(6) L mol(-1) s(-1) at 130 degrees C.