Polymerization of γ‐benzyl‐ L ‐glutamate N‐carboxy‐ anhydride: Effects of conditions of polymer precipitation on the molecular weight distribution

Poly‐γ‐berizyl‐L‐glutamate prepared by polymerization of γ‐benzyl‐L‐glutamate NCA in dimethylformamide (DMF) with the use of diisopropylamine as the initiator was precipitated from the polymerization mixture under different conditions. A portion of the almost completely polymerized solution was treated with an excess of isopropylamine and then precipitated into diethyl ether (sample A). The remaining portion of the polymerization mixture was concentrated in a rotating evaporator, stored at room temperature for a few days, and then diluted with DMF and precipitated into diethyl ether (sample B). The molecular weight distributions of the two polymer samples were determined by the chromatographic procedure of Baker and Williams. The molecular weight of sample B is roughly three times that of sample A. However both samples have the “most probable” distribution of molecular weight. The results are interpreted according to Bamford's polymerization mechanism.