Amphiphilic derivatives of chitosan using microwave irradiation. Toward an eco-friendly process to chitosan derivatives

• To compare conventional heating and microwave irradiation for reductive amination of chitosan.
• The amphiphilic derivatives of chitosan are obtained within very short time with quantitative yields.
• Neither degradation nor modification was observed but the alkylation.
• Same physic-chemical properties were observed whatever the reaction process.
• It is possible to use microwave irradiation to go toward “green chemistry” of chitosan derivatives.

Conventional heating and microwave irradiation have been compared for the synthesis of chitosans grafted with alkyl chains. Reaction time (1–60 min), temperature (25 and 40 °C) and chitosan molar mass have been studied onto the yield of alkylation. The irradiation mode has been scrupulously controlled to highlight the effect of the use of microwaves. The chemical structure of modified polymers (degree of alkylation) is determined from NMR. In relation to the rheological behavior and surface tension measurements, the evolution of hydrophobic interactions is studied as a function of the yield of alkylation. A maximum of intrinsic viscosity and hydrodynamic diameter was observed for a degree of alkylation of around 10%. All the results tend to prove that microwave assisted synthesis is a powerful method to obtain modified chitosan under extremely low reaction time without any degradation and/or property modifications.