Functional nanogels through thermoreversible self-assembling and thiol-ene crosslinking of polysaccharide derivatives with LCST

A series of cellulose carbamates (CC) and xylan carbamates (XC) with hydroxyalkyl or tertiary amino side groups were prepared by a modular synthesis. Their solubility in organic and aqueous media was investigated. Several compounds showed either an upper critical solution temperature (UCST) or lower critical solution temperature (LCST) in water in the temperature range between 5 °C and 85 °C. The thermoresponsive properties could be tuned by tailoring their molecular structure. Mixed derivatives were synthesized that combined reactive allyl groups and thermoresponsive tertiary amino groups. Turbidity and dynamic light scattering (DLS) measurements showed that these polymers self-assemble upon heating (≥ 25 °C) yielding particles sizes in the range of several hundred nanometers depending on the temperature and preparation conditions and that the phase transition is fully reversible (≤ 5 °C). Nanogels were prepared by selective crosslinking of the self-assemblies through thiol-ene click chemistry induced by UV irradiation. Depending on the preparation conditions, stable dispersions were obtained with particle sizes in the range of 100 to 500 nm. It was also possible to post-functionalize the nanogels with molecules that contain thiol moieties without affecting the particles sizes. Functionalization with amphoteric compounds like cysteine (Cys) yielded pH-sensitive nanomaterials with tailored surface charges.