Synthesis of new amphiphilic star polymers derived from a hyperbranched macroinitiator by the cationic ‘grafting from’ method

New amphiphilic star polymers possessing a hyperbranched core and hydrophilic graft arms have been prepared. The synthetic strategy involved esterification of the 4,4-bis(4′-hydroxyphenyl)valeric acid based hyperbranched polymer with 3-(chloromethyl)benzoyl chloride to obtain the hyperbranched macroinitiator followed by cationic ring-opening polymerization of 2-methyl-2-oxazoline to give amphiphilic polymers. Exchange of the chloride counter ion with trifluoromethanesulfonate (KCF3SO3 or AgCF3SO3) or iodide (KI) anions leads to higher polymerization rates. Phenyl 2-(chloromethyl)benzoate was used as a model initiator to study the effect of different coinitiators on the initiator efficiency. KI as a coinitiator yielded 56–86% initiator conversion whereas only 30–37% initiator conversion was achieved with KCF3SO3 or AgCF3SO3 as coinitiator after quantitative monomer consumption. Photon correlation spectroscopy (PCS) in methanol and chloroform for selected graft copolymers revealed the formation of single star molecules ranging from 22 to 50 nm in diameter.