VOLUME PHASE-TRANSITION OF COPOLYMERIZED SULFONIC-ACID GELS IN MIXED ORGANIC-SOLVENTS

Radical copolymerization of 2-acrylamido-2-methylpropane sulfonic acid (AMPS) with 2-hydropropyl methacrylate (HPM) was conducted in ethylene glycol/water (1:1 in weight) at 70 degrees C. The azeotropic composit ion was found at the monomer molar ratio of AMPS/HPM as 8/2, Three sul fonic gels were prepared at this composition with the crosslinker N,N' -methylene-bis(acrylamide) of 2%, 3% and 5% (molar percentage), and re ferred to as G02, G03 and G05, respectively, As expected from their po lyelectrolyte nature, these gels swell in dimethyl sulfoxide(DMSO) but shrink in tetrahydrofuran(THF) at 25 degrees C, The volume phase tran sition takes place in the G02 and G03 swollen in DMSO/THF mixtures whe n THF content is increased beyond 55%similar to 60% (volume ratio), In ethanol/THF mixture, however, no volume phase transition was found th ough the gel still shrunk with increasing THF. The dipole-dipole inter action model in less-polar medium was adopted to interpret these resul ts with the concept of preferential solvation.