Figure 1.

Synthesis procedure of PSI, PASP, and poly(aspartamide). PSI can either be obtained through poly-condensation (usually at elevated temperature >160°C using an acid as the catalyst) of ASP or malic acid (synthesized by maleic anhydride and a nitrogen source such as urea or ammonia). PSI can be hydrolysed under alkali media to yield PASP or reacted with primary amines (without catalyst at room temperature) to yield poly(aspartamide) derivatives. The ring opening of succinimde groups occurs both at α and β sites in amidation and hydrolysis reaction.