Stimuli-responsive nanoparticles from ionic cellulose derivatives†
Stimuli-responsive nanoparticles (NPs) based on sustainable polymeric feedstock still need more exploration in comparison with NPs based on synthetic polymers. In this report, stimuli-responsive NPs from novel ionic cellulose derivatives were prepared via a facile nanoprecipitation. Cellulose 10-undecenoyl ester (CUE) with a degree of substitution (DS) of 3 was synthesized by esterification of cellulose with 10-undecenoyl chloride. Then, CUE was modified by photo-induced thiol–ene reactions, in order to obtain organo-soluble ionic cellulose derivatives with DSs of ∼3, namely cellulose 11-((3-carboxyl)ethylthio)undecanoate (CUE–MPA), cellulose 11-((2-aminoethyl)thio)undecanoate (CUE–CA), cellulose 11-(2-(2-(diethylamino)ethyl)thio)undecanoate (CUE–DEAET) and cellulose 11-(2-(2-(dimethylamino)ethyl)thio)undecanoate (CUE–DMAET). CUE–MPA could be transformed into NPs with average diameters in the range of 80–330 nm, but these NPs did not show particular stimuli-responsive properties. Moreover, the dropping technique resulted in smaller NPs than a dialysis technique. Stable NPs with average diameters in the range of 90–180 nm showing pH-responsive and switchable sizes were obtained from CUE–DEAET and CUE–DMAET possessing tertiary amines using nanoprecipitation. Thus, altering the terminal functional groups will be a new approach to prepare stimuli-responsive cellulose-derived polymeric NPs.