Synthesis of Poly(Lactic Acid-co-Arginine) and Construction of Its Ternary Phase Diagram for Nonsolvent Induced Phase Separation

L-arginine, a basic amino acid, exhibits high biocompatibility, reactivity, and absorbability. It was selected as the co-polymer modification monomer for L-lactic acid with the objective of enhancing the hydrophilicity of poly(lactic acid) (PLA), neutralizing the acidity of PLA degradation products, and regulating the degradation cycle. The copolymer poly(lactic acid-<i>co</i>-arginine) (PLAA) was synthesized by direct melting polycondensation of L-arginine and L-lactic acid, and the structures and properties of PLAA were characterized. The results indicated the presence of -NH₂, -NH-, and NH= in the molecular chain of the copolymer PLAA. Furthermore, the PLAA was identified as an amorphous copolymer. The "PLAA/CHCl₃/C₆H₁₄" ternary phase diagram was constituted by nonsolvent-induced phase separation (NIPS) by selecting chloroform (CHCl₃) as a good solvent and n-hexane (C₆H₁₄) as a nonsolvent. The phase diagram displays three distinguishable regions: the homogeneous zone, the metastable zone, and the phase separation zone. These regions are identified by the binodal and spinodal curves. The ternary phase diagram establishes a theoretical foundation for the preparation and processing of PLAA nanoparticles, composite materials, and porous fibers or membranes.