Mechanochemical and Aging-Based S_N2 Method to Access CO₂-Responsive, High-Amine-Loading Chitosan.

Area of Science:

• Biomaterials Science
• Polymer Chemistry
• Green Chemistry

Background:

• Tertiary amines in water show reversible property changes in response to carbon dioxide (CO2).
• Chitosan, a biopolymer, can be chemically modified to incorporate desired functionalities.
• Existing methods for chitosan functionalization often require excess reagents and harsh conditions.

Purpose of the Study:

• To develop a novel, efficient, and scalable method for functionalizing chitosan with tertiary amines.
• To achieve a high degree of substitution (DS) on chitosan using mechanochemical techniques.
• To create a CO2-responsive biopolymer material with improved properties.

Main Methods:

• A one-pot S_N2-type aminoalkylation reaction using mechanochemical and aging-based approaches.
• Functionalization of both amine and primary alcohol groups on chitosan.
• Demonstration of scalability across various chitosan molecular weights and O-functionalization on chitin.

Main Results:

• Achieved a high DS of up to 1.67 per sugar unit, doubling previous solvothermal method results.
• Successfully functionalized both amine and alcohol groups, a unique capability of this method.
• Demonstrated a 47% reversible increase in osmotic pressure of aminoalkylated chitosan solutions upon carbonation.
• Showcased O-functionalization on chitin up to a DS of 0.15.

Conclusions:

• Mechanochemistry enables significantly improved DS for functionalizing recalcitrant substrates like chitinous biomass.
• The developed method offers reduced process mass intensity and energy consumption compared to prior techniques.
• This work successfully produces a CO2-responsive material derived from biomass using an efficient mechanochemical approach.