Novel method of alkylation for promoting high molecular weight chitosan by microwaves

The invention discloses a novel method for alkalifying high molecular weight chitosan under the condition of microwave irradiation to prepare N-alkyl chitosan with high molecular weight and high substitution. The novel method is characterized by comprising the following steps: dispersing chitosan with the molecular weight of 900-1500 thousand and deacetylated degree of above 70% in a mixed solution of alkali and isopropanol, alkalifying under the condition of microwave irradiation, shifting out of a microwave reactor, heating to a certain temperature, dropwise adding halohydrocarbon (C2-C16) slowly, and processing to obtain the N-alkyl chitosan with the substitution of 40-70%.