Horseradish Peroxidase as a Catalyst for Atom Transfer Radical Polymerization

The hemoprotein horseradish peroxidase (HRP) catalyzes the polymn. of N-isopropylacrylamide with an alkyl bromide initiator under conditions of activators regenerated by electron transfer atom transfer radical polymn. (ARGET ATRP) in the absence of any peroxide. This is a novel activity of HRP, which we propose to name ATRPase activity. Bromine-terminated polymers with polydispersity indexes (PDIs) as low as 1.44 are obtained. The polymn. follows first order kinetics, but the evolution of mol. wt. and the PDI upon increasing conversion deviate from the results expected for an ATRP mechanism. Conversion, ?Mn and PDI depend on the pH and on the concn. of the reducing agent, sodium ascorbate. HRP is stable during the polymn. and does not unfold or form conjugates.