Preparation and characterization of CO₂-responsive poly(amino acid) derivatives with guanidine group

Polyaspartamides, which are termed to a variety of amide derivatives of poly(aspartic acid), one of the poly(amino acid)s or polypeptides, have been intensively investigated as biodegradable and biocompatible polymers with a broad range of potential biomedical applications as well as eco-friendly industrial uses. By discovering that polymers containing amidine or guanidine functionality have been shown to be reversibly responsive to carbon dioxide (CO₂), we have developed two polyaspartamide systems: novel CO₂-responsive hydrogel and amphiphilic polyaspartamide derivative containing l-arginine. In this work, poly(2-hydroxyethyl aspartamide) derivative was modified with l-arginine unit (PHEA-Larg), before cross-linked by hexamethylene diisocyanate in the presence of dibutyltin dilaurate catalyst to provide a hydrogel having not only good gel strength, but reversible CO₂ absorption characteristics. On the other hand, amphiphilic polyaspartamide derivative containing hydrophobic long alkyl moiety (octyl) and l-arginine unit was synthesized, and the CO₂-responsive solubility and molecular self-assembly behaviors of the systems were investigated. These new polyaspartamide systems have potential in several applications including CO₂ capture, CO₂-responsive and switchable surface, sensor, smart hydrogel for controlled drug delivery system, etc.