STUDY OF SWELLING BEHAVIOR FOR IONICALLY CROSSLINKED POLYAMPHOLYTE HYDROGELS IN SOLUTIONS WITH VARIOUS pH AND ELECTROLYTES

A series of polyampholyte hydrogels were prepared by free radical aqueous copolymerization of ionic complex of acrylic acid and(N,N-diethylamino)ethyl methacrylate and acrylamide(PADA gels).Owing to the hydrogen bonding interaction among acrylic acid molecules,PADA hydrogels in water had the maximum deswelling when the molar ratio of anionc and cationic monomers(A/C) was 1.55,but not 1.0 as ordinary.By comparison with covalently crosslinked polyampholyte hydrogels,PADA gels were more pH sensitive in swelling behavior.The swelling experiments indicated that PADA gels deswelled in buffer solutions of pH 3～4,but swelled when the pH deviated from this pH range.Furthermore,the swelling degree of PADA gels decreased with an increase of A/C in buffer solutions of pH value below 3 and increased in the buffer solutions of pH value higher than 4.The ion strength greatly influenced the equilibrium swelling ratio of PADA gels in the solutions of salts with varied valences.PADA gels exhibited typical antipolyelectrolyte effect in univalent NaCl solutions.In multivalent CaCl_2 and trisodium citrate(TSC) solutions,however,PADA gels also exhibited antipolyelectrolyte effect only in lower concentrations of salt.In salt solutions with higher concentration,the swelling ratios of PADA gels decreased with the increment of concentration.This might be attributed to the ionic crosslinkage formed by multivalent ions.Similar to the influence of pH on the swelling degree of PADA gels,the swelling ratios of PADA gels decreased in CaCl_2 solutions with the increment of A/C,whereas,increased in TSC solutions with the increment of A/C.The unique behavior seems to be related to the charge characteristics of multivalent ions.