Swelling experiments were carried out with three cationic polyelectrolyte gels of N-n-butyl-4-vinylpyridinium bromide (BPyBr), N-n-butyl-N,N-dimethyl-4-vinylanilinium bromide (BAnBr) and N-n-butyl-N,N-dimethyl-(N'-acryloyl-3-aminopropyl)ammonium bromide (BAPABr). The swelling equilibria of the gels were measured in aqueous solutions of inorganic electrolytes: HBr, NaBr, KBr, NaCl and NaI. The swelling ratios of the gels did not depend on the cationic species of the electrolytes examined but depended strongly on the anionic species. Volume phase transitions were not observed with the BPyBr and BAnBr gels in aqueous solutions of NaCl and NaBr whereas a phase transition was observed in an aqueous solution of NaI. The NaI concentration at which the phase transition occurred was raised with an increase in temperature. On the other hand, no discontinuous change was observed in the swelling equilibria of the BAPABr gel, even in the NaI aqueous solution. Comparison of the present results for the BAPABr gel with previous results for a polyelectrolyte gel verified the importance of hydrophobic interactions, which enhance the occurrence of volume phase transitions.
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