Thermoreversible hydrogels. VIII. Effect of a zwitterionic monomer on swelling behaviors of thermosensitive hydrogels copolymerized by N-isopropylacrylamide with N,N '-dimethyl (acrylamidopropyl) ammonium propane sulfonate

A series of thermosensitive hydrogels were prepared from the various molar ratios of N-isopropylacrylamide, zwitterionic monomer, N,N'-dimethyl (acryl amidopropyl) ammonium propane sulfonate (DMAAPS), and N,N'-methylene-bis-ac rylamide. The influence of the amount of DMAAPS in the copolymeric gels on the swelling behaviors in water, various saline solutions, and various temp eratures was investigated. Results indicated that the higher the DMAAPS con tent in the hydrogel system, the higher the swelling ratio and the gel tran sition temperature. In the saline solution results showed that, when the sa lt concentration was greater than the minimum salt concentration (MSC) of p oly(DMAAPS), the deswelling behavior of the N-isopropylacrylamide gel was s uppressed more effectively when more DMAAPS was added into the copolymeric gels; but the swelling ratios of the present copolymeric gels did not signi ficantly change while the salt concentration was lower than the MSC of poly (DMAAPS). In addition, only the sample containing 12 mol % DMAAPS (D4) exhi bited an antipolyelectrolyte's swelling behavior when the salt concentratio n was greater than the MSC of poly(DMAAPS). In other words, only when the a mount of DMAAPS added into the gel is over some proportion, can the hydroge l show an antipolyelectrolyte's swelling behavior in concentrated salt solu tion. In saline solutions, the anion effects were greater than the cation e ffects in the presence of common anion (Cl-) with different cations and com mon cation (K+) with different cations for these gels. Finally, the more DM AAPS content in the hydrogel, the higher the diffusion coefficient in dynam ic swelling. (C) 1999 John Wiley & Sons, Inc.