Study of the quantitative aminolysis reaction of poly(β-benzyl l-aspartate) (PBLA) as a platform polymer for functionality materials

A facile and quantitative aminolysis of poly(β-benzyl l-aspartate) (PBLA) as well as the solution properties of the prepared cationic polyaspartamide were investigated in this study. The reaction was found to proceed in good yield without undesired side reactions via the formation of a succinimide intermediate in the polymer backbone, which was efficiently converted to polyaspartamide accompanying the α,β isomerization of the main chain. The polarity of solvents and the secondary structure of the polymer strand were closely related to each other in terms of reactivity and stereoselectivity. The aminolysis of PBLA treated with one equivalent amine against benzyl ester groups resulted in the complete conversion at 35 °C in random-coil solvents within 1 h. The racemization that accompanied this reaction was observed in random-coil solvents, but was efficiently suppressed in helicogenic solvents, with 95% of the optical purity maintained in CH₂Cl₂. In addition, the quantitative introduction of N,N-diisopropylethylenediamine (DIP) led to the formation of cationic polyaspartamide, poly[N-(N′,N′-diisopropylaminoethyl)aspartamide] (PAsp(DIP)), which showed pH and thermo-sensitivities in aqueous media. This systematic investigation of the aminolysis of PBLA with DIP demonstrates the feasibility of a PBLA-aminolysis system for designing functionalized polyaspartamides which can be useful as biomaterials.