New catalytic systems for the manufacture of poly(aspartic acid)

Aspartic acid (I), when heated to a temperature in excess of 180 °C, undergoes a solid‐state condensation polymerization to afford the useful polymeric intermediate known as poly(succinimide) (II). Treatment of poly(succinimide) with aqueous base, such as sodium hydroxide, affords sodium poly(α,β‐DL‐aspartate) (III) also known as thermal poly(aspartate) (TPA). Acid catalysts, such as phosphoric acid have been added to the aspartic acid to afford higher‐molecular‐weight poly(succinimide) than is obtained in the non‐catalyzed polymerization. Recently, new sulfur‐based catalysts have been disclosed for the polymerization of aspartic acid. The sulfur‐containing catalysts provide a route to highly biodegradable, low‐color poly(aspartate)s in the molecular weight range of 2 000 to 20 000. A comparison of biodegradability, molecular weight, and spectral characteristics of the poly(succinimide)s and poly(aspartate)s derived from the catalyzed and non‐catalyzed polymerizations is presented.