PEG-PLLA was synthesized by ring opening polymerization as described previously.18 (link),19 Briefly, d,l-lactide (Purac, Corbion) and PEG (Fluka, Sigma-Aldrich) were stirred at 160°C for 6 hours after adding stannous octoate as a catalyst under a nitrogen purge. The copolymer was dissolved in dichloromethane and then precipitated in cold ether, followed by filtering and drying steps. The polymer was then acrylated at both ends to obtain PEG-PLLA-DA as follows. Ten grams of PEG-PLLA was dissolved in 100 mL dichloromethane and cooled to 0°C in an ice bath. Triethylamine and acryloyl chloride were added at 4 times the molar ratio. The reaction mixture was stirred for 12 hours at 0°C and then for 12 hours at room temperature. The solution was filtered to remove salt and then filtered in a large excess of diethyl ether. The white macromer obtained from this step was analyzed with nuclear magnetic resonance and gel permeation chromatography.