Surface ionic charge dependence on the molecular mobility and self-assembly behavior of ionomers produced from carboxylic acid-terminated dendrimers

Dendrimers are unique molecular structures terminated by a multitude of peripheral functional groups that are accessible for targeted chemistry. Carboxyl-terminated dendrimers are attractive because their surface charge can be tuned, thus providing a highly versatile template for producing a range of ionomers with tailored properties. Here, a carboxylic acid-terminated dendrimer was synthesized from Boltorn, an aliphatic polyether polyol dendrimer, via a Steglich esterification with a succinic anhydride. A series of ionic dendrimers were subsequently produced by progressively neutralizing between 4 and 16 of the terminal carboxylic acid groups with sodium hydroxide, yielding their corresponding carboxylate sodium salts. With progressive neutralization, anion-cation electrostatic interactions in the ionic clusters dramatically affected the polymer chains' mobility, resulting in large increases in the order-disorder transition temperature. This result was substantiated with small angle X-ray scattering data, suggesting that the size of the ionic clusters increased from 2.2 to 3.8 nm as a result of long-range electrostatic interactions and core stretching. Self-assembly behavior in aqueous media into a large, 2D, tree-like morphology was demonstrated, highlighting potential applications as a multifunctional semiconductor in the drug delivery, colloidal science, sensing and catalysis fields.