To impart antimicrobial property, a moiety of 2,2,5,5-tetramethyl-imidozatidin-4-one (TMIO) hydantoin was successfully grafted onto microporous polyurethane (PU) membrane surface as an N-halamine precursor through a two-step grafting procedure. A combination of techniques was used to confirm the surface grafting. Thermal and mechanical properties of modified PU membranes were evaluated accordingly. Upon exposure to chlorine bleaching, the hydantoin structures on the grafted PU membranes were transformed into N-halamines. Energy-dispersive X-ray (EDX) microanalysis and iodometric titration were used to analyze the chlorine contents of the PU membranes after chlorination. A total reduction of both Escherichia coli (Gram-negative bacteria) and Staphylococcus aureus (Gram-positive bacteria) was observed after a 2-h contact period. Water vapor transmission rate (WVTR) remained essentially unchanged after surface modification with TMIO. Consequently, a microporous PU membrane that not only possesses good barrier and hygiene protections, but also maintains sufficient WVTR for comfort was developed. (c) 2006 Elsevier B.V. All rights reserved.