Synthesis of branched polystyrene and poly(styrene-b-4-methoxystyrene) by nitroxyl stable radical controlled polymerization

Branched polystyrene was synthesized through controlled radical polymerizat ion of styrene in the presence of 4-(4'-vinylphenylmethoxy)-2,2,6,6- tetram ethyl-1-piperidinyloxy (STEMPO) which possesses a nitroxyl stable radical a nd a polymerizable vinyl group. During the polymerization, STEMPO played th e role of branching agent since it can polymerize as well as trap the propa gating radical. The resulting polymer contained a labile covalent C-ON bond at each branch point and had broad molecular weight distribution. After be ing heated with phenylhydrazine, the GPC profile of the product became narr ower due to cleavage of the branch points. The molecular weight of the clea ved product was proportional to monomer conversion, demonstrating a control led growth of primary chains. H-1 NMR showed that, in the polymerization of deuterated styrene, the signal intensity of vinyl groups in STEMPO decreas ed at a constant rate with increasing monomer conversion. ESR measurement i llustrated that the labile C-ON bonds at branch points were subject to ther mal homolysis. The branchcd product was used as a macroinitiator for radica l polymerization of 4-methoxystyrene. The resulting copolymer possessed a b ranched architecture of diblock primary chains with controlled length and n arrow distribution.