Siloxane-modified cationic polyelectrolytes were synthesized through the quaternization reaction of a poly(ethylene glycol)-based polymer containing tertiary amine groups in the chain with chloroalkyl-functionalized siloxanes. Linear or crosslinked structures were obtained, depending on the functionality of the siloxane: a chloroalkyl-monofunctionalized or -polyfunctionalized siloxane was used. The reaction occurred in solution with n-propanol as a solvent and NaI as a catalyst. All products were characterized with elemental analysis and IR and H-1 NMR spectrometry. Viscometric measurements of the linear polymer in dilute aqueous solutions revealed typical polyelectrolyte behavior. The swelling capacities in various solvents of the crosslinked structures were determined. The thermal stability of the crosslinked cationic structures obtained with a polyfunctional siloxane as a quaternization agent was much higher than that of the parent polymer. (C) 2004 Wiley Periodicals, Inc.