Unity plus 400 m nuclear magnetic resonance spectrometer

¹H-NMR spectra were obtained on a UNITY-plus 400 M nuclear magnetic resonance spectrometer (Varian, Palo Alto, CA, USA) using chloroform-d (CDCl₃), heavy water (D₂O), and deuterated sodium hydroxide (NaOD) as solvents. Gel permeation chromatography (GPC) measurements of block copolymers were conducted at 35 °C by using a Waters 1515 chromatography system (Waters, Milford, MA, USA) equipped with a Waters 2414 refractive index detector. Tetrahydrofuran (THF) and DMF containing 500 mM lithium bromide (LiBr) were separately used as eluent at a flow rate of 1 mL min⁻¹. Polystyrene standards were employed in calibration.

As shown in Figure 2, firstly, PAM-PBLG₃₈₄-NH₂ was synthesized according to our previous work (Liu et al., 2017a (link)). Then PAM-PBLG-NH₂ (1 g) was reacted with excess TPGS-COOH and EDC at 4°C for 2 h to obtain the dendritic block copolymer PAM-PBLG-b-TPGS. The degree of polymerization of TPGS in PAM-PBLG-NH₂ was verified by ¹H-NMR spectroscopy (Varian UNITY-plus 400 M nuclear magnetic resonance spectrometer, solvent: CDCl₃). After that, 20 mL trifluoroacetic acid dissolving PAM-PBLG-b-TPGS was added in 2 mL hydrogen bromide (HBr) (33% in acetic acid) and stirred for 1 h at room temperature. Then the solution was neutralized by sodium hydroxide (NaOH) and dialyzed against distilled water (DI water) using a dialysis membrane with molecular weight cutoff (MWCO) of 5 kDa. The aqueous solution of purified product was lyophilized to obtain PAM-PGlu-b-TPGS.