Synthesis of star polymers by a combination of ATRP and the "click" coupling method

Three-arm and four-arm star polystyrene (PS) polymers were synthesized by a combination of atom transfer radical polymerization (ATRP) and click coupling chemistry. The click reaction between an azido-terminated PS (PS-N-3) and an alkyne- containing multifunctional compound proved to be fast and efficient. All coupling reactions were finished within 3 h, proven by the disappearance of signals from the azido groups in NMR spectra and the high yields of the coupled products by GPC analysis. For the model coupling reaction between a PS-N-3 polymer and a dialkyne-containing compound, the final yield of the coupled PS-PS polymer was ca. 95%. When a PS-N-3 polymer was reacted with a trialkyne-containing or tetraalkyne-containing compound, the yields of 3-arm star and 4-arm star polymers were around 90% and 83%, respectively. The influence of several parameters on the efficiency of the click coupling reaction was studied, including the molecular weight of the PS-N-3 polymer, the presence of an added reducing agent, Cu(0), and the stoichiometry between the azido and alkynyl groups. The results indicated that the yield of the coupled product was higher when a lower molecular weight PS-N-3 was employed in conjunction with a small amount of reducing agent, and the molar ratio of azido and alkynyl groups was close to 1.