Hydrodynamic behaviors of amphiphilic dendritic polymers with different degrees of amidation†
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 (Rh) of the polymers were investigated via dynamic light scattering (DLS). It was found that Rh 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 (Rg). The ratio of Rg and Rh was around 0.77, which indicated that the ADPs were compact. The solvent effects on Rh were investigated which showed that the Rh in chloroform was bigger than that in a poor solvent for HPEI. However, Rh 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 Rh and Mn 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 Rh values remained constant for the synthesized DA within the measured temperature range in chloroform and glycol dimethyl ether.