Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Factorial design analysis was applied to optimize the synthesis, via a new route, of N, N, N-trimethylchitosan, based on dimethylsulfate as a methylating agent. The responses analyzed were weight yield, solubility and average degree of quaternization. Temperature was verified as the most important variable, as it caused the most variation in the response. X(T) = -54.52,-9.50 and -7.25, respectively, for weight yield, solubility and degree of quaternization. A sharp decrease in the viscosimetric and gel permeation chromatography parameters proved that severe depolymerization took place at high reaction temperatures. Contact angle measurements showed a decrease in the hydrophilic character of over-methylated samples. (C) 2011 Society of Chemical Industry606SI910915EMBRAPAFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)