Hyperbranched poly(ether nitrile)s were prepared from a novel AB(2) type monomer, 2-ebloro-4-(3,5-dihydroxyphenoxy)benzonitrile, via nucleophilic aromatic substitution. Soluble and low-viscous hyperbranched polymers with molecular weights upto 233,600 (M-w) were isolated. According to the H-1 NMR and GPC data, the unique polymerization behavior was observed, which implies that the weight average molecular weight increased after the number average molecular weight reached plateau region. Model compounds were prepared to characterize the branching structure. Spectroscopic measurements of the model compounds and the resulting polymers, such as H-1, DEPT C-13 NMR, and MS, strongly suggest that the ether exchange reaction and cyclization are involved in the propagation reaction. The side reactions would affect the unique polymerization behavior. The resulting polymers showed a good solubility in organic solvents similar to other hyperbranched aromatic polymers. The hydroxy-terminated polymer was even soluble in basic water. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5835-5844, 2009