Synthesis of water-soluble grafted chitosan copolymers by atom transfer radical polymerization

Chitosan acylation with 2-bromoisobutyryl bromide in dimethylformamide was studied to obtain a macroinitiator for the subsequent synthesis of graft copolymers of chitosan with trimethyloxyethylmethacryloylammonium methyl sulfate using Atom Transfer Radical Polymerization. The acylation reaction under heterophase conditions is a distinctive feature of the proposed approach. The advantages of this approach are the ease of obtaining a macroinitiator and zero destruction of chitosan samples. This will allow to obtain high molecular weight copolymers of chitosan. In this work, chitosan samples with different molecular weight (ranging from 110 to 260 kDa) and degree of deacetylation (80–92%) were studied. Elemental analysis, IR spectroscopy, and energy-dispersive analysis have shown that the acylation reaction proceeds via the NH2 group, because it is most reactive. Regardless of the molecular weight and degree of deacetylation, the degree of acylation is 76–99% with the optimal synthesis time of 1 day. Due to the extremely high sensitivity to contamination of the reaction and of the subsequent polymerization reaction, special attention is paid to the preparation of initial chitosan samples (i.e., purification from unreacted chitin and various impurities). The presented results on obtaining chitosan macroinitiator are novel and serve as the basis for the synthesis of graft copolymers of chitosan using Atom Transfer Radical Polymerization with a variable hydrophilic–lipophilic balance.