In this study, a novel semi-interpenetrating polymer network (semi-IPN) hydrogel of poly(diallyldimethylammonium chloride)/poly(N,N-diethylacrylamide) (PDADMAC/PDEA) was prepared using ammonium persulfate as an initiator and N,N,N',N-tetramethylethylenediamide as an accelerator at room temperature. The influence of this additive on the property of resulting PDEA hydrogels was investigated and characterized. The interior morphology by scanning electron microscopy (SEM) revealed that PDADMAC introduced PDEA hydrogels have large and interconnected porous network structures. Differential scanning calorimetry (DSC) studies showed the difference in the state of the water between PDEA and semi-IPN hydrogels. The incorporating of PDADMAC significantly improved the equilibrium swelling ratio of modified hydrogels when comparing with a normal PDEA hydrogel. The semi-IPN hydrogels exhibited improved thermosensitive characteristics, such as faster deswelling and swelling rates and great oscillating deswelling-swelling behavior, and the level of improvement depended on the PDADMAC content. The swelling dynamic transport of the hydrogels was analyzed based on the Fickian equation. (C) 2010 Elsevier B.V. All rights reserved.