[en] The internal plasticization of chitosan with covalently linked long aliphatic branches, typically 12C, was accomplished through the condensation of the amino groups of chitosan with acidic derivatives of lauric acid, as lauroyl anhydride or lauroyl chloride, that are more reactive than the fatty acid itself. The chemical pathway led to selective N-acylation. The degree of substitution was quantitatively determined by FTIR and ¹H NMR and varied between 3 and 35%. The FTIR quantitative analysis was based in a calibration method with good accuracy. The modified chitosan products were soluble in neutral water and/or DMF according to the degree of substitution. The modified chitosan films were more flexible than the pristine, non-modified ones. (author)