A novel cross-linkable, polyaspartamide derivative-containing cinnamoyl groups with temperature and pH dual stimuli-responsiveness

A novel cross-linkable polyaspartamide derivative-containing cinnamoyl pendant groups, P(HPA-Az)-CA, was designed and synthesized in this study. Chemical structures of the obtained polymers were confirmed by FTIR, UV, and 1 H NMR techniques. The transmittance measurement results showed that the prepared polymer P(HPA-Az)-CA displayed temperature and pH dual stimuli-responsive behaviors. The cloud point of P(HPA-Az)-CA could be tuned just by adjusting the introduced percentage of hydrophobic moieties or the pH of polymer aqueous solution. The effect of pH on the cloud point of P(HPA-Az)-CA was investigated by zeta potential, and the results showed that it may be related to the weakened electrostatic repulsion caused by decreased zeta potential with pH decreasing. Diamines (ethylenediamine or cystamine) were adopted to prepare cross-linked micelles using the mixture of P(HPA-Az)-CA aqueous solution and diamines just by one-step heating method. The cross-linked micelles were stable, even when the environmental temperature was below the cloud point of P(HPA-Az)-CA. The cross-linking mechanism between the diamines and α,β-unsaturated carbonyl moieties of P(HPA-Az)-CA was confirmed by 1 H NMR. In addition, the micelles cross-linked with cystamine could be disrupted in the presence of 10 mM glutathione. According to the results, the obtained polyaspartamide derivative P(HPA-Az)-CA may be a potential for facilitating drug loading.