| Chitosan-derived brush polymers with well-defined chemical structure were synthesized by combining ATRP with sodium dodecyl sulphate-chitosan complex (SCC)-based regioselective modification strategy. Macromolecular ATRP initiator, O-brominated CS (CS-Br), was conveniently prepared by conjugating bromoisobutyrate onto the hydroxyl groups of SCC and subsequently removing SDS from the O-brominated SCC. ATRP polymerization of oligo(ethylene glyol) methacrylate (OEGMA) in an aqueous medium (pH 5.1) was initiated by CS-Br and catalyzed by Cu(â… )Br/1,1,4,7,10,10-hexamethyltriethylenetetramine (HMTETA). It was found that the polymerization of OEGMA displayed living characteristics. In addition, the grafting level of POEGMA could be adjusted by varying the degree of substitution (DS) of bromobutyrate. By changing molar feeding ratio of OEGMA to CS-Br, the degree of polymerization (DP) of POEGMA could be modulated.The structure of CS-POEGMA was modified in the following aspects. Firstly, click reaction conducted between thiol ligands and terminal bromine atoms of POEGMA, by this way, tag molecules were coupled to POEGMA. Secondly, through the reaction between CS-POEGMA and succinic anhydride, succinylated chitosan-POEGMA (SC-POEGMA) was prepared. The results showed that terminal bromine atoms of CS-POEGMA can be quantitatively displaced by ligand by bromo-thio reaction, when DMSO was used as solvent and triethylamine as catalyst. The degree of succinylation of SC-POEGMA can be adjusted by changing the molar ratio between CS-POEGMA and succinic anhydride, and a series of copolymers with different isoelectric points were obtained, whose backbone was zwitterionic chitosan and sides group were PEG bushes. And then, we studied advanced assembly behavior of SC-POEGMA and quaternary ammonium chitosan-O-polycaprolactone (TMC-PCL). The experimental data showed that core-shell-crown three-tier structure micelles can be formed by the electrostatic interactions between SC-POEGMA and TMC-PCL in pH 7.4 medium. However, the formed core-shell-crown micelles can be disassembled as the reduction of medium pH and re-transformed into TMC-PCL micelles. Besides, the critical pH where the disassembly of three-tier structure micelles occurred can be adjusted by changing the succinyl degree of SC-POEGMA. |
