Dry dimethylformamide

Three different types of PEGdA macromers with varying susceptibility to hydrolytic degradation were synthesized by a two-step process as previously reported [35 (link)]. Briefly, PEG (4000 MW, Fluka, Buchs, Switzerland) was reacted with either chloroacetyl chloride, 2-chloropropionyl chloride, or 4-chlorobutuyrl chloride (Sigma-Aldrich, St. Louis, MO) in the presence of triethylamine (TEA, Sigma) at a 1:4:1.8 molar ratio in dry dichloromethane (Sigma). After 24 hours reaction at room temperature, the reactants were filtered, washed with sodium bicarbonate and water, dried with anhydrous sodium sulfate, and then precipitated in ethyl ether. After recovery, each resulting intermediate product was reacted with sodium acrylate (5X molar ratio) in dry dimethylformamide (Acros, Morris Plains, NJ) for 30 hours at 50, 85, and 100 °C to yield PEG-bis-(acryloyloxy acetate) [PEG-bis-AA], PEG-bis-(acryloyloxy propanoate) [PEG-bis-AP], and PEG-bis-(acryloyloxy butyrate) [PEG-bis-AB], respectively. The products were purified by filtration, rotary evaporation, and precipitation in ethyl ether and dried under vacuum. The structures of each PEGdA and the degree of acrylation were determined from the ¹H-NMR (Brucker 300 MHz, CDCl₃) spectra. All samples achieved acrylation efficiencies greater than 90%.