New grafted polysaccharides based on O-carboxymethyl-O-hydroxypropyl guar gum and N-isopropylacrylamide: Synthesis and phase transition behavior in aqueous media

Poly(N-isopropylacrylamide) (PNIPAAm) was grafted onto O-carboxymethyl-O-hydroxypropyl guar gum (CMHPG) in aqueous solutions by using potassium persulfate (KPS) and N,N,N,N′-tetramethylethylene diamine (TMEDA) as the initiation system, resulting in new stimuli-responsive grafted polysaccharides. The effects of various factors such as the concentrations of KPS and TMEDA, the feed weight ratio of NIPAAm to CMHPG, and polymerization temperature on the graft copolymerization were studied with respect to the grafting percentage (%G), grafting efficiency of the reaction (%E) and grafting conversion of the monomer (%C). It was found that the %G, %E, and %C increased and then decreased with increasing the concentrations of TMEDA and KPS, as well as polymerization temperature. With the increase of NIPAAm amount, the %G increased whereas the %E and %C both decreased. The resulting grafted polysaccharides could exhibit lower critical solution temperatures in aqueous media due to the thermosensitivity of their PNIAAm graft chains, and their temperature-induced phase transitions were influenced by the grafting percentage, the solution concentration of grafted polysaccharide, as well as the kind and concentration of added salts, as confirmed by determining the optical transmittance of the solutions under various conditions.