Synthesis and swelling behavior of pH- and temperature-sensitive poly[2-(dimethylamino)ethyl methacrylate-co-2-acrylamido-2-methylpropane-1-sulfonic acid] hydrogels

Summary Poly2-(dimethylamino)ethyl methacrylate-co-2-acrylamido-2-methylpropane-1-sulfonic acid], poly(DMAEMA-co-AMPS), hydrogels were prepared by chain polymerization in water at 60 °C in the presence of tetraethyleneglycol diacrylate (TEGDA) as crosslinking agent. Ammonium persulfate (APS) and N,N,N’,N’-tetramethylethylenediamine (TEMED) were used as initiator and accelerator, respectively. Hydrogels with different feed compositions were prepared by keeping the total monomer concentration constant at 1 or 0.5 M. The concentration of TEGDA in the feed was adjusted so that it made for 3 or 2 mol % of the total monomer content while it was 1% for APS. In order to observe the effects of pH and ionic strength of the medium on swelling, the equilibrium swelling behavior of these hydrogels were investigated both in distilled water at various temperatures between 30 and 90 °C and in different buffer solutions with pH of 2.8, 5.3, 7.0, 10.0, and 12.4 at constant ionic strength (I=0.08 mol/l) at room temperature. The effects of temperature and co-monomer AMPS content on the swelling behavior of poly(DMAEMA-co-AMPS) in distilled water were also investigated. The copolymers with equimolar contents of DMAEMA and AMPS displayed minimum swelling both in distilled water and in buffer solutions due to ionic complex formation. Their swelling values in distilled water between 30 and 90 °C were constant. While equilibrium swelling values of copolymers in buffer solutions with pH between 2.8 and 7 were almost constant, they increased with increasing pH. The increase in the AMPS content and decrease in initial monomer concentration increased the equilibrium swelling values of copolymers.