Hydrodynamic behaviors of amphiphilic dendritic polymers with different degrees of amidation

Abstract

A series of amphiphilic dendritic copolymers (ADPs) with different degrees of amidation (DA) were synthesized by the amidation reaction of polyethyleneimine (HPEI) with dendritic palmitate tails. The hydrodynamic radii (R_h) of the polymers were investigated via dynamic light scattering (DLS). It was found that R_h increased with increasing DA, and a sharp increase was noted when DA was near 51 percent. The intrinsic viscosity was measured using an Ubbelohde capillary viscometer to understand the structure evolution of the ADPs. The results showed that the intrinsic viscosity decreased slowly with increasing DA. The Fox–Flory formula was employed to calculate the radius of gyration (R_g). The ratio of R_g and R_h was around 0.77, which indicated that the ADPs were compact. The solvent effects on R_h were investigated which showed that the R_h in chloroform was bigger than that in a poor solvent for HPEI. However, R_h remained unchanged with the increasing volume fraction of poor solvent for HPEI from twenty percent to eighty percent. The solvent quality has no obvious influence on the relationship between R_h and M_n before DA = 51 percent, but a sharper slope is noted after DA = 51 percent. This phenomenon can be explained by the compact structure of the ADPs. The R_h values remained constant for the synthesized DA within the measured temperature range in chloroform and glycol dimethyl ether.