3-(Trimethoxysilyl)-propyldimethyloctadecyl ammonium chloride (AEM 5700) is a trifunctional monomer that can be polymerized under acidic conditions at temperatures greater than 100 degreesC. Under such conditions, coatings based on AEM 5700 formed on PET substrates are relatively hydrophobic and exhibit rewetting times higher than 100 min. Hydrophilic coatings exhibiting a rewetting time of 2.8 min can be also formed when AEM 5700 is initially hydrolyzed under alkaline conditions and then polymerized under acidic conditions. This effect could be related to the accessibility of unreacted hydroxyl groups and quaternary ammonium groups for interaction with water. Excellent antimicrobial action was demonstrated for all coatings based on AEM 5700 on PET substrates. Polyester fabrics having AEM 5700 coating can be dyed with direct dyes. The loss of hydrophilic properties for AEM 5700 coatings is observed after dyeing with direct dyes. (C) 2004 Elsevier Ltd. All rights reserved.