Microwave‐Assisted Synthesis of PLLA‐PEG‐PLLA Triblock Copolymers

Poly(L‐lactide)‐block‐poly(ethylene glycol)‐block‐poly(L‐lactide) (PLLA‐PEG‐PLLA) triblock copolymers were synthesized effectively by poly(ethylene glycol) initiated ring‐opening polymerization (ROP) of L‐lactide under microwave irradiation. The products were characterized by 1H NMR, GPC, and DSC. The experimental results have demonstrated that PLLA‐PEG‐PLLA triblock copolymer with a number‐average molar mass of 28 230 g · mol−1 and an L‐lactide conversion of 92.4% could be synthesized after the L‐lactide/PEG2000 reaction mixture was irradiated for 3 min at 100 °C. The L‐lactide/PEG feed ratio had a strong influence on the microwave‐assisted ring‐opening polymerization, in which higher L‐lactide/PEG feed ratios led to copolymers with higher molar masses and lower L‐lactide conversions. Prolonged microwave irradiation at 100 °C did not change the molar mass of the copolymers significantly. The DSC study indicated that higher glass transition and melting temperatures were obtained for PLLA‐PEG‐PLLA triblock copolymers with longer PLLA segment length. The synthesis of the triblock copolymers via microwave heating was much faster than via conventional heating. magnified image