Synthesis and properties of thermo- and pH-sensitive poly[(sodium humate)-(N-isopropylacrylamide)-(acrylic acid)] intelligent hydrogel

A novel intelligent hydrogel of poly(Humic acid - Nisopropylacrylamide - Acrylic acid) (P(NIPAAm-HA-AA)) was prepared at 70 degrees C by inverse suspension polymerization. The reactions include uses N,N-methylene-bis-acrylamide (MBA) as a cross-linking agent, ammonium persulfate (KPS) as an initiator, cyclohexane As a continuous-phase and span-65 as dispersant. The influence such as concentration of monomers and cross-linking agent, mole fraction of span-65 in mixed monomers, and temperature of polymerization on the property of resulting P(NIPAAm-HA-AA) hydrogels was investigated in detail. Fourier transform infrared (FTIR) demonstrated that NIPAAm, HA and AA was synthetized successfully. The results showed that the swelling ratio (SR) of modified hydrogel was improved significantly with the dosage of NIPAAm. It was also observed that the thermosensitive and pH sensitive characteristics was strongly affected by concentrations of NIPAAm. At last, we choose NIPAAm: HA=0.3.