Block copolymers composed of PCL and PEG were synthesized. First, CL was polymerized by ring-opening polymerization (ROP) using mPEG as the initiator and Sn(Oct)2 as the catalyst. In a typical synthesis, mPEG (0.75 mmol) and Sn(Oct)2 (0.62 mmol) were dissolved in dried toluene under an argon atmosphere, followed by CL (32 mmol) addition. The reaction mixture was then stirred at 110 °C for 24 h. The reaction was stopped by the addition of cold diethyl ether to precipitate the polymer. The solid product was recovered via filtration and dried under reduced pressure at room temperature. In 1H-NMR (400 MHz, CDCl3, δ, ppm), the distinctive signals of PCL were as follows: 4.08 (t, J = 6.6), 2.33 (t, J = 6.6 Hz, 73H), 1.72–1.62 (m, 146H), 1.40 (m, 73H), and mPEG:3.66 (s, 494H).
The copolymers were characterized by 1H-NMR and GPC. The spectrum of copolymers was recorded on a 400 Ultrashield spectrometer operated at 400 MHz (Bruker, Mannheim, Germany) using CDCl3 as the solvent. The molecular weight distribution and polydispersity index (PDI) were determined by GPC using a high-performance liquid chromatography (HPLC) system (Thermoscitific, Ultimate 3000) equipped with a differential refractive index detector. Analyses were performed in THF at 0.8 mL/min flow rate in an HR 4E column. The calibration curve was constructed using polystyrene standards (2.5–50 kDa).
The copolymers were characterized by 1H-NMR and GPC. The spectrum of copolymers was recorded on a 400 Ultrashield spectrometer operated at 400 MHz (Bruker, Mannheim, Germany) using CDCl3 as the solvent. The molecular weight distribution and polydispersity index (PDI) were determined by GPC using a high-performance liquid chromatography (HPLC) system (Thermoscitific, Ultimate 3000) equipped with a differential refractive index detector. Analyses were performed in THF at 0.8 mL/min flow rate in an HR 4E column. The calibration curve was constructed using polystyrene standards (2.5–50 kDa).