Functional galactomannan platform from convenient esterification in imidazolium-based ionic liquids

Abstract

Various imidazolium-based ionic liquids (ILs), considered as “green” solvents, were used as efficient solvents for galactomannan and more specifically for guar gums of high molecular weight. FT-IR as well as the high activation energies reflect hydrogen bonds between the guar backbone and anions of ILs which act as chaotropic agents. Importantly, the dissolution was conducted under mild conditions which allowed the preservation of the chain integrity, as proved by SEC, FT-IR and ATG analyses collected for guar regenerated from IL solutions. For the first time, ILs were exploited as reactional media in which tailor-made guar derivatives were synthesized through a direct and homogeneous esterification with a variety of acid chlorides. We demonstrated that the degree of substitution of guar can be varied by experimental conditions and that it is necessary to adjust these conditions as a function of the esterifying reagent structure. The use of hexanoyl chloride imparted emulsifying properties to guar and esterification with acryloyl chloride and 2-chloropropionyl chloride allowed generation of reactive precursors such as macromonomer and macroinitiator, respectively. The reactivity of the guar macromonomer was assessed through a thermal cross-linking radical copolymerisation, which led to guar gel with solid-like behaviour.