The copolymer of m-PEG macromer grafted onto Cs was prepared by a modified method to that reported by Yoksan et al.32 and Yoksan and Chirachanchai.33 (link) The synthesis sequence was as follows.
Firstly, the free NH2 groups of Cs were protected via N-phthaloylation. In brief, 10 g Cs was reacted with phthalic anhydride (44.8 g, 5 mol equivalent to pyranose rings) in DMF (200 mL) at 130°C under nitrogen atmosphere for 8 h. The product of N-phthaloyl Cs (NPHCs) was then collected by filtration after precipitation in cold water, washed with methanol, and then dried under vacuum.
m-PEG was converted into m-PEG-COOH by reacting with succinic anhydride. Briefly, m-PEG (100 g, 20 mmol), succinic anhydride (2.4 g, 24 mmol), DMAP (2.44 g, 20 mmol), and triethylamine (2.02 g, 20 mmol) were dissolved in dry dioxane (350 mL). The reaction mixture was stirred at room temperature for 48 h under nitrogen atmosphere. Dioxane was evaporated under vacuum and the residue was taken up in CCl4, filtered, and precipitated by diethyl ether.
Grafting of m-PEG-COOH onto NPHCs was then performed by stirring m-PEG-COOH (37.9 g) with NPHCs (5.0 g, 0.4 mol equivalent to m-PEG-COOH) in 75 mL of DMF. HOBt (3.4 g, 3 mol equivalent to m-PEG-COOH) was then added and the stirring was continued at room temperature until obtaining a clear solution. Then, EDC·HCl (4.25 g, 3 mol equivalent to m-PEG-COOH) was added and the reaction was stirred overnight at room temperature. The reaction mixture was then dialyzed against distilled water and washed with ethanol to remove unreacted macromer.
Finally, the PEG-g-Cs copolymer was synthesized by deprotection of the NH2 groups of the PEG-g-NPHCs produced in the previous step using hydrazine monohydrate. Typically, PEG-g-NPHCs (4.0 g) was heated to 100°C with stirring under nitrogen in 15 mL of DMF. Then hydrazine monohydrate (20 mL) was added and the reaction was continued for 2 h. The mixture was then dialyzed against distilled water and ethanol and then dried under vacuum.
Firstly, the free NH2 groups of Cs were protected via N-phthaloylation. In brief, 10 g Cs was reacted with phthalic anhydride (44.8 g, 5 mol equivalent to pyranose rings) in DMF (200 mL) at 130°C under nitrogen atmosphere for 8 h. The product of N-phthaloyl Cs (NPHCs) was then collected by filtration after precipitation in cold water, washed with methanol, and then dried under vacuum.
m-PEG was converted into m-PEG-COOH by reacting with succinic anhydride. Briefly, m-PEG (100 g, 20 mmol), succinic anhydride (2.4 g, 24 mmol), DMAP (2.44 g, 20 mmol), and triethylamine (2.02 g, 20 mmol) were dissolved in dry dioxane (350 mL). The reaction mixture was stirred at room temperature for 48 h under nitrogen atmosphere. Dioxane was evaporated under vacuum and the residue was taken up in CCl4, filtered, and precipitated by diethyl ether.
Grafting of m-PEG-COOH onto NPHCs was then performed by stirring m-PEG-COOH (37.9 g) with NPHCs (5.0 g, 0.4 mol equivalent to m-PEG-COOH) in 75 mL of DMF. HOBt (3.4 g, 3 mol equivalent to m-PEG-COOH) was then added and the stirring was continued at room temperature until obtaining a clear solution. Then, EDC·HCl (4.25 g, 3 mol equivalent to m-PEG-COOH) was added and the reaction was stirred overnight at room temperature. The reaction mixture was then dialyzed against distilled water and washed with ethanol to remove unreacted macromer.
Finally, the PEG-g-Cs copolymer was synthesized by deprotection of the NH2 groups of the PEG-g-NPHCs produced in the previous step using hydrazine monohydrate. Typically, PEG-g-NPHCs (4.0 g) was heated to 100°C with stirring under nitrogen in 15 mL of DMF. Then hydrazine monohydrate (20 mL) was added and the reaction was continued for 2 h. The mixture was then dialyzed against distilled water and ethanol and then dried under vacuum.
