Smart graft copolymer based on gellan and poly(N-isopropylacrylamide): Synthesis and studies on structure and thermal...

A smart graft copolymer based on a thermoresponsive synthetic polymer poly(N-isopropylacrylamide) (PNIPAM) and gellan gum (GLL) was prepared using a two-step process. The first step involves the synthesis of PNIPAM via reversible addition-fragmentation chain transfer polymerization (RAFT) and the second step consists in grafting of PNIPAM onto gellan via a direct "grafting to" approach. Elemental analysis, attenuated total-reflection Fourier transform infrared (ATR-FTIR) and nuclear magnetic resonance (¹H NMR) spectroscopies confirm the chemical stucture of the graft copolymers. The degree of substitution (DS = 1.59) of the graft copolymer was determined using ¹H NMR spectroscopy and according to the calculations based on this value it was found that the grafting density is about one PNIPAM chain for every 24 gellan monomeric units. The thermoresponsive behavior of both PNIPAM and graft copolymer was highlighted by UV-Vis spectroscopy by determining the cloud point temperature (T_{CP, PNIPAM} = 32.9 °C, T_{CP, graft copolymer} = 35 °C). Self-assembly capacity and zeta potential of the graft copolymer in aqueous media were investigated in the different pH values by dynamic and electrophoretic light scattering. Also, the rheological properties of graft copolymer were studied. Thermogravimetry-Infrared spectroscopy-Mass spectrometry (TG-FTIR-MS) coupled analysis was used to study the thermal decomposition of gellan, PNIPAM and graft copolymer.