pH/temperature-responsive poly(dimethylaminoethyl methacrylate) grafted κ-carrageenan copolymer: Synthesis and physicochemical properties

κ-Carrageenan-graft-poly(dimethylaminoethyl methacrylate) (CRG-g-PDMA) was synthesized via free-radical copolymerization under microwave irradiation. ¹³C-Nuclear magnetic resonance spectroscopy (¹³C-NMR), fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and X-ray diffraction (XRD) methods were used for characterization of the CRG-g-PDMA structure. The effect of reaction variables including the concentrations of the initiator and dimethylaminoethyl methacrylate (DMA) as well as the microwave irradiation time and power on graft ratio and conversion was investigated, and their highest values were obtained to be 179 and 76%, respectively. The lower critical solution temperatures (LCSTs) of the CRG-g-PDMA copolymers were determined at various pH conditions, and their value in distilled water was found as 47°C. Besides, the swelling capacity of the copolymers under different pH levels was investigated and it was seen that the swelling capacity of the copolymer increased with the decrease in the pH value of the medium. The CRG-g-PDMA copolymer exhibited excellent swelling performance in acidic pH conditions and possessed responsiveness to pH and temperature stimuli.