Synthesis of six-arm star polymer by nitroxide-mediated "living" radical polymerization

A dendritic multifunctional initiator with 6 TEMPO-based alkoxyamine moieties was prepared from 4-bromophenylethylbenzene in 7 steps and 6-arm star polymers were prepared by the radical polymerization of styrene (St) using the dendritic alkoxyamine as an initiator. The St polymerizations were carried out at 120degreesC using the dendritic alkoxyamine concentrations of 5.0, 12.8, and 18.8 mmol L-1. When the alkoxyamine concentration was 5.0 mmol L-1, the polydispersity indexes of the resulting star polymers increased with conversion and that of the star polymer at 72% conversion was 1.59. On the other hand, when the alkoxyamine concentrations were 12.8 and 18.8 mmol L-1, the polymerization was well controlled to give star polymers with a low polydispersity index even at high conversion. The side reactions disturbing the "living" fashion were discussed on the basis of the SEC elution curves of the star polymers obtained.