To a mixture of SCMHBMA (180 mg), DMAEMA (1 g), and MBA (20 mg) in 4 mL 2 M HCl
aqueous1 solution, 0.2 mL Na2S2O8 solution (40 mg/mL) was added and then the mixture was
heated up to 70 o
C in a sealed tube for 20h, leading to a hydrogel. Resulting hydrogel was
immersed in saturated NaHCO3 aqueous solution (100 mL) for 48 h before further measurement.