Stannous octanoate sn oct 2

Hydroxymethyl-3,4-ethylenedioxythiophene (EDOTMeOH; 95% Sigma-Aldrich, Darmstadt, Germany), ε-caprolactone (ε-CL Aldrich, Darmstadt, Germany), and stannous octanoate (Sn(Oct)₂) (Sigma, Darmstadt, Germany) were used as received. All the solvents were purified and dried using the usual methods.

Polyethylene glycol (PEG; Mn = 6,000) was purchased from Sigma-Aldrich (St. Louis, MO, USA) and dried in a vacuum oven at 70°C before use. L-Lactide (99.5%, Jinan Daigang Biomaterials Co. Ltd., Jinan, China), stannous octanoate [Sn(Oct)₂, 95%, Sigma-Aldrich, St. Louis, MO, USA], 4-carboxybenzaldehyde (98%, Shanghai Darui, Shanghai, China), N,N′-dicyclohexylcarbodiimide (DCC, 98% Shanghai Darui, Shanghai, China), 4-dimethylaminopyridine (DMAP, 98% Shanghai Darui, Shanghai, China), methyl 4-hydroxybenzoate (98%, Shanghai Darui, Shanghai, China), and hydrazine hydrate aqueous solution (80%,Tianjin Kemiou, Tianjin, China) were used as received. Doxorubicin hydrochloride (Dalan Meilun Biotech., Dalian, China) was stirred with TEA (3 equiv.) in DMSO overnight before the solvent was evaporated using a rotary evaporator to get doxorubicin, i.e., DOX. All organic solvents were analytical reagents and used as received, except that toluene was dried by the sodium method to get anhydrous toluene.