Activators Regenerated by Electron Transfer for Atom Transfer Radical Polymerization of Styrene

Abstract

The amount of Cu-based catalysts in atom transfer radical polymerization (ATRP) of styrene has been reduced to a few ppm in the presence of the appropriate reducing agents such as FDA approved tin(II) 2-ethylhexanoate (Sn(EH)2) or glucose. The reducing agents constantly regenerate ATRP activator, the Cu(I) species, from the Cu(II) species, formed during termination process, without directly or indirectly producing initiating species that generate new chains. Moreover, the reducing agents allow starting an ATRP with the oxidatively stable Cu(II) species. The reducing/reactivating cycle may also eliminate air or some other radical traps in the system. This new catalytic system is based on regeneration of the activators for an ATRP by electron transfer and therefore was named activators regenerated by electron transfer (ARGET) ATRP. The optimum amount of reducing agent and minimal amount of ATRP Cu catalyst depend on the particular system. For example, styrene was polymerized with 10 ppm of CuCl2/Me6TREN and 100 ppm of Sn(EH)2 resulting in a polystyrene with Mn = 63 000 (Mn,th = 64 000) and Mw/Mn = 1.17.