Hydroquinone

Poly(ethyleneglycol) monomethyl ether (MeO-PEG-OH, Sigma-Aldrich) with a molecular (M_n) weight of 5 kDa was dried at 35 °C in vacuum overnight before using. 2-(Diethylamino) ethyl methacrylate (DEA, Sigma-Aldrich) was passed through a basic alumina column to remove the inhibitor. Dichloromethane, triethylamine (TEA), N-methyl pyrrolidone (NMP) and dimethyl sulfoxide (DMSO) (Sinopharm Chemical Reagent Co. Ltd.) were purified according to standard procedures. Doxorubicin hydrochloride (DOX·HCl, J&K Scientific) was deprotonated by excess triethylamine. CuBr, 2,2-bipyridine (bpy), d-gluconolactone, hydroquinone, 2-bromoisobutyryl bromide, 2-aminoethyl methacrylate hydrochloride were purchased from J&K Scientific without further purification before use. The macro-initiator PEG-Br^{24,25 (link)} and the monomer 2-gluconamidoethylmethacrylate (GAMA) were prepared according to reported procedures.^{26–28 (link)}