Microwave-assisted solid-phase synthesis of pH-responsive polyaspartamide derivatives

Biodegradable stimulus-responsive polymers have attracted more attention in biomedical fields. Here, a series of pH-responsive polyaspartamide derivatives are successfully synthesized from poly(N-substituted α/β-asparagines) by a facile, solvent-free and catalyst-free microwave-assisted method. The polymer structure is confirmed by (1)H NMR, IR and UV-Vis spectra. With much shorter reaction time (13-18 min), the degree of substitution (DS) of the anhydride-modified polyaspartamide derivatives obtained by microwave heating is two to three times higher as that obtained by conventional heating in DMF (24h). In addition, pH-induced phase transition behavior of polyaspartamide derivatives is investigated by dynamic light scattering (DLS). The critical pH transition (pHtr) of the resulted polymers increases with increasing DS of the polymers. The hydrophile-lipophile balance (HLB) of the obtained polymers is evaluated to study the relationship between pHtr and polymer structure.