Atom transfer radical polymerization of styrene using a novel octafunctional initiator: Synthesis of well-defined polystyrene stars

A novel octafunctional calixarene derivative, namely, 5,11,17,23,29,35,41,47-octa-tert-butyl- 49,50,51,52,53,54,55,56-octakis(2-bromopropionyloxy)calix[8]arene (1) which was readily synthesized in one step, was used to initiate the bulk atom transfer radical polymerization (ATRP) of styrene, at 100 degrees C, in the presence of CuBr/2,2'-bipyridyl. Polystyrene (PS) stars of narrow polydispersity with precisely eight arms could be synthesized by restricting the polymerization to low conversion, typically below 15-20%. At higher conversions, irreversible coupling occurred between stars as evidenced by a size exclusion chromatography line equipped with a multiangle laser light scattering detector (MALLS/SEC). Octafunctional stars of molar masses up to 340 000 g mol(-1) could be prepared by using high ratios of the monomer to the initiator ([M]/[I] = 12 000). The precise octafunctional structure of the stars was confirmed, on one hand, by studying the kinetics of ATRP of styrene initiated by an equimolar mixture of 1 and its monofunctional equivalent, namely 4-tert-butylphenyl(2-bromopropionate) (2) and, on the other hand, by the characterization of the individual arms obtained upon hydrolysis of the ester link between the core and the branches of the stars.