Synthesis of a₃B₃-type polystyrene-poly (methyl methacrylate) miktoarm star polymers via combination of stable free radical and atom transfer radical polymerization routes

An A₃B₃-type miktoarm star polymer was prepared utilizing a "core-out" method via combination of stable free radical polymerization (SFRP) and atom transfer radical polymerization (ATRP). First, SFRP of styrene was carried out by using a miktofunctional initiator, benzene-1,3,5-tricarboxylic acid tris{3-(2-bromo-2-methyl-propionyloxy)-2- methyl-2-[2-phenyl-2-(2,2,6,6-tetramethylpiperidin-1-yloxy)ethoxy-carbonyl] propyl} ester, at 125°C. Second, previously obtained polystyrene (A ₃-type PSt) precursor with three bromine functionalities in the core was used as a macroinitiator for ATRP of methyl methacrylate (MMA) in the presence of Cu(I)Cl and pentamethyldiethylenetriamine at 90°C in order to give an A₃B₃-type miktoarm star polymer, (PSt) ₃(-PMMA)₃, with controlled molecular weight and moderate polydispersity (M_w/M_n < 1.41). The obtained polymers were characterized by gel-permeation chromatography and ¹H-NMR.