Preparation of poly(ethylene oxide)-block-poly(isoprene) by nitroxide-mediated free radical polymerization from PEO macroinitiators

Amphiphilic poly(ethylene oxide)-block-poly(isoprene) (PEO-b-PI) diblock copolymers were prepared by nitroxide-mediated polymerization of isoprene from alkoxyamine-terminal poly(ethylene oxide) (PEO). PEO monomethyl ether (M _n ≈ 5200 g/mol) was functionalized by esterification with 2-bromopropionyl bromide with subsequent copper-mediated replacement of the terminal bromine with 2,2,5-trimethyl-4-phenyl-3-azahexane-3-nitroxide. The resulting PEO-alkoxyamine macroinitiator was used to initiate polymerization of isoprene in bulk and in solution at 125 °C to yield PEO-b-PI block copolymers with narrow molecular weight distributions (M _w/M _n ≤ 1.1). Polymerizations were first order in isoprene through 35% conversion. Micellar aggregates of PEO-b-PI in aqueous solution were crosslinked by treatment with a water-soluble redox initiating system, and persistent micellar structures were observed in the dry state by AFM.