Synthesis, characterization and swelling performance of a temperature/pH-sensitive κ-carrageenan graft copolymer

A binary graft copolymerization of dimethylaminoethyl methacrylate (DMAEMA) and acrylic acid (AA) onto κ-carrageenan (CG) was performed by using microwave irradiation in the presence of 4,4'-Azobis(4-cyanovaleric acid) (ACVA). The structure of the CG-g-P(DMAEMA/AA) copolymers was confirmed using ¹³C NMR, FTIR, DSC/TGA and XRD. The effects of the DMAEMA/AA ratio, the microwave power and irradiation duration, and the concentrations of CG and ACVA on grafting yield and grafting efficiency were all investigated, and the best values of them were found to be 150% and 85%, respectively. The lower critical solution temperatures (LCST) for CG-g-P(DMAEMA/AA) copolymers at various pH conditions were determined, and when the pH value of the medium was increased from 1.2 to 10, the LCST of the copolymer decreased from 53 °C to 39 °C. Moreover, swelling performance of the copolymers under various pH conditions was examined, and it was observed that the swelling ratio of the copolymer increased with a decrease in the pH value of the medium.