In this paper, we report atom transfer radical polymerization of N-isopropylacrylamide (NIPAAm) by an enzyme mimetic catalyst, that is, hematin of a ferriprotoporphyrin complex. The hematin-catalyzed polymerization of NIPAAm was carried out in the presence of an alkyl halide as an initiator and a reducing agent in DMF/H2O solvent. The reaction proceeded at room temperature and the M(n)s increased with increasing monomer conversions. The M-n values were relatively close to the theoretical ones. The reaction did not take place in the absence of any one of the initiator, catalyst, and reducing agent. The H-1 NMR spectrum of the low molecular weight polyNIPAAm indicated the presence of the moieties from the initiator at the polymer ends. These results suggested that the reaction was initiated from radical species, which were produced by bromide abstraction from the initiator by the reduced catalyst. (C) 2013 Elsevier Ltd. All rights reserved.