A Pentablock Polymer Forming Core-shell Structures

Abstract

In order to elucidate the interplay between hydrophobic and hydrophilic forces as well as electrostatic interactions for a polymer in an aqueous environment, we recently designed a new pentablock polymer, with the configuration ABCBA. This is a linear chain, where two hydrophobic blocks (B) have been attached to each side of a hydrophilic segment (C), and with negatively charged groups (A) at the ends of the chain. In this system there will be a competition between the attractive forces of the hydrophobic blocks, the repulsion between the charged groups, and the tendency for the hydrophilic group to maximize the interaction with the surrounding water. The polymer was made in two versions, with different lengths of the hydrophilic block, having 34 and 77 segments, respectively. We observed that the physical properties of the system are highly dependent on the length of this C block. A sharp and highly reproducible temperature-induced transition, related to changes in chain conformation, is seen at a temperature around 37 °C. The reason for this behavior, as well as the robustness of the transitions discussed.