Dynamic Properties of Polyampholyte Hydrogel Elucidated by Proton NMR Spin-spin Relaxation Time

¹H spin-spin relaxation time(T₂) measurement of polyampholyte hydrogel poly(methylacrylic acid-acryloyloxyethyl trimethylammonium chloride)P(MA-DAC)] in different pH, ionic strength and temperature was carried out to reveal the molecular mobility. Spontaneous volume transition of the polyampholyte hydrogel was also investigated by spin-spin relaxation time measurement. Meanwhile T₂ and the proton component fraction were acquired to study the swelling behaviour of the hydrogel. Moreover the changes of T₂ characterized the molecular mobility of polyampholyte hydrogel in various swelling states. And the results suggest that the mobility of the main chains and a few free side chains(the long T₂) of P(MA-DAC) was dominated by the mesh size in the hydrogel network, depending on the swelling ratio(Q) and the mobility of the side chains(the short T₂) was influenced by electrostatic interaction between different charges in polymer side chains. Finally the T₂ measurements of P(MA-DAC) hydrogel in the spontaneous swelling-deswelling process demonstrated the electrostatic interaction of the charged side chains caused deswelling behavior. At the same time, the mobility state transition temperature of the charged side chains was also studied by the ¹H spin-spin relaxation time measurements, and the transition activation energy of the side chains is 2.72 kJ.