Stannous octoate

N-Isopropylacrylamide (NIPAAm), recrystallized twice with toluene/cyclohexane (v/v, 40/60) solvents, was purchased from TCI (Tokyo). N,N′-Azobisisobutyronitrile (AIBN), recrystallized twice with ethanol, was provided by Shanghai Chemical Reagent Co., Ltd. 2-Mercaptoethanol (98%) and stannous octoate (96%) were purchased from Alfa Aesar. l-Lactide was purified by recrystallization from toluene three times and dried in a vacuum at room temperature. Poly(l-lactide) (PLLA) with an average molecular weight of 180 000 and dried in vacuum at 60 °C for 12 h was obtained from Shanghai TJL Co., Ltd. (China). Other reagents and solvents were purchased from Shanghai Chemical Reagent Co., Ltd. (China) and used without further processing.

ε-Caprolactone (ε-CL, 99%; Alfa Asear, Thermo Fisher Scientific, USA) and 2,2′-dithiodiethanol (98%; Alfa Aesar) were dried over CaH₂ and vacuum distilled before use. L-Lysine diisocyanate (LDI, 99+%; Acros, Acros Organics, Belgium) and stannous octoate (96%; Alfa Aesar) were used as received. Poly(ethylene glycol) (mPEG-OH, 5 ​kDa; Alfa Aesar) was dried by azeotropic distillation from toluene. p-Nitrophenyl chloroformate (p-NPC, 97%; Alfa Aesar) and cystamine dihydrochloride (>98%; Alfa Aesar) were used as received. Toluene and N,N-dimethylformamide (DMF), purchased from Chinasun Specialty Products Co. Ltd, Changshu, China, were dried over CaH₂ and vacuum distilled before use.