The puzzling role of symmetry: a tool for macromolecular engineering

Abstract

Abstract Modern polymer chemistry enables the syntheses of many functional macromolecules with essentially unlimited range of tunable parameters to control the macroscopic material properties. One overlooked approach in macromolecular engineering is the use of symmetry in polymer design. Symmetry is a powerful force of nature, and it has a profound effect on polymers’ glass transition temperature, barrier and other properties. In this contribution, we review the unique properties of symmetric polymers, such as polyisobutylene—the cornerstone polymer in Dr. Kennedy s exemplary career. Although the mechanistic aspect of the role of symmetry in the macroscopic properties of polymers remains a puzzle, we suggest that removing isomerism of macromolecules can be a key to unlocking some of their unusual behavior. With the help of Raman spectroscopy, we demonstrate that symmetric polymers have strongly suppressed fast dynamic fluctuations, which indicates tight packing of structural units. This tight packing is one of the major reasons for the exceptional barrier properties of symmetric polymers. Now that “living” and controlled polymerization technologies have become staples of polymer synthesis, symmetry can become an additional valuable tool in the macromolecular engineering toolbox.