Microwave assisted synthesis of pH-responsive swellable adducts of chitosan–polyuronic acids

A facile method for synthesizing super-swellable, pH-responsive and insoluble adducts (e.g. CH–PMA and CH–PGA) of acid-soluble chitosan (CH) with alkali-soluble poly-mannuronic (PMA) and poly-guluronic (PGA) acids using microwave (MW) heating is described. The reactions were also carried out using conventional oil bath heating method. Microwave heating to 100 °C for 5 min produced greatest yields (95–97%) and swelling ratios (2700–3000%) with these two acids. The conventional heating method, however, required 60 min to produce greatest yields (74–80%) and swelling ratios (1450–1900%), which plateaued even on heating up to 120 min. Adducts were characterized by FT-IR and CP-MAS 13C NMR techniques.