Thermally stable alkaline chitin solutions via cryogenic processing enable homogeneous functionalization

Alkali/urea solvents enable rapid dissolution of chitin and chitosan, advancing homogeneous chemical modification and functional materials construction. Nevertheless, the pronounced tendency of these solutions to gel at elevated temperatures critically limits their utility in thermally driven reactions. We demonstrate that initially dissolved chitin chains retain residual inter-chain associations, facilitating hydrogen-bond-driven crosslinking and aggregation during heating. To circumvent this limitation, we introduced a post-dissolution low-temperature conditioning strategy (-20 °C for ≥24 h). This treatment profoundly enhances molecular dispersion, yielding solutions with exceptional thermal stability that retain fluidity for >24 h at 55 °C. Leveraging this stabilized system, we achieved efficient homogeneous alkylation, carboxylation, and quaternization of chitin at 55 °C. The reactions proceeded with high efficiency, affording derivatives with degrees of substitution (DS) exceeding 90%. Critically, quaternized chitin exhibited excellent water solubility. This work resolves a fundamental limitation in chitin processing and versatile and efficient route for thermally demanding homogeneous chemistry using alkali/urea solvents, broadening their applicability in biopolymer functionalization.