Using full‐factorial design analysis and response surface methodology to better understand the production of cationized chitosan from epoxides

The production of cationized chitosan derivatives via reaction between chitosan and quaternary epoxides has the advantage of producing substances with a better regioselectivity and with structures that do not change as a function of pH, unlike N,N,N‐trimethylchitosan. Moreover, this reaction allows the production of cationized derivatives having different hydrophobic/hydrophilic balances because quaternary epoxides with different alkyl chains can be used in this reaction. The effects of reaction parameters, namely time, temperature and glycidyltrimethylammonium chloride (GTMAC)/chitosan (Ch) molar ratio, on the structural and hydrodynamic characteristics of N‐(2‐hydroxy)propyl‐3‐trimethylammoniumchitosan chloride (ChCat) and on reaction yield were evaluated using chemometrics and response surface methodology (RSM). Structural characterization and determination of intrinsic viscosity were realized using spectroscopic techniques (Fourier transform infrared and ¹H NMR) and capillary viscometry, respectively. The polynomial functions and RSM developed from 2³ full‐factorial analysis show the influence of the reaction parameters on the characteristics and properties of the ChCat produced, permitting the choice of appropriate reaction conditions to suit its desired application. Results show, as an example, that when the N‐substitution is carried out for 6 h at 50 °C employing excess of GTMAC (GTMAC/Ch = 4:1), water‐soluble moderately substituted ( = 33.0%) ChCat (η] = 293.4 mL g^?1) can be produced with moderate reaction yield (30.9%). Furthermore, as GTMAC is the simplest quaternary epoxide, the study of its reaction with chitosan serves as a template for more complex quaternary epoxides as they may be used for the production of new cationized chitosan derivatives possessing alkyl chains with various chain lengths. © 2016 Society of Chemical Industry