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-ieri-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 °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.