Synthesis of PEG-b-DB Block Copolymers

Butyl methacrylate (BMA), poly(ethylene glycol) 4-cyano-4-(phenylcarbonothioylthio)pentanoate, M_n=2,000 Da and M_n=10,000 Da (PEG-CPADB), 4-cyano-4-(phenylcarbonothioylthio)pentanoate (CPADB), N,N’-Dicyclohexylcarbodiimide (DCC), 4-(Dimethylamino)pyridine (DMAP), DL-Dithiothreitol (DTT), 4,4’-azobis(4-Cyanovaleric acid) (V501), dichloromethane, 1,4-dioxane, and poly(ethylene glycol) methyl ether (M_n = 5,000 Da) were purchased from Sigma-Aldrich. 2-(Diethylamino)ethyl methacrlate (DEAEMA) was procured from TCI Chemicals, and 2,2’-Azobis(4-methoxy-2,4-dimethylvaleronitrile) (V70) was purchased from Wako Chemicals. Pyridyl disulfide ethyl methacrylate (PDSMA) was synthesized according to a previously reported procedure.⁵⁴ BHT inhibitor was removed from methacrylate monomers before further use by gravity chromatography using basic alumina (Sigma).
For synthesis of PEG-b-DB polymers, the appropriate PEG-CPADB macroRAFT chain transfer agent (mCTA) was dissolved in anhydrous dioxane with purified BMA, DEAEMA, and V501 at a 60:40 molar ratio of BMA:DEAEMA, sealed with septa, purged with N₂ for 20 minutes, and polymerized at 70˚C for 18 h. An initiator to mCTA (I:mCTA) ratio of 0.2:1 was used with a combined monomer and mCTA to dioxane weight ratio of 0.4. Polymers were precipitated 2x in cold pentane and vacuum dried. Polymer composition were characterized via ¹H-NMR in CDCl₃ on a Bruker AV400 spectrometer (Supplementary Figure S10). Molecular weight and polydispersity index (PDI) were quantified using gel permeation chromatography (Agilent) with DMF containing 0.1M LiBr as the mobile phase and in line light scattering (Wyatt) and refractive index (Agilent) detectors. PEG_5kDa-CPADB or PEG_10kDa-CPADB mCTAs were synthesized as previously described.⁵⁵ PEG_2kDa-DBP_4.5kDa was synthesized with similar conditions, substituting V70 for V501 and a reaction temperature of 30°C for 24h.