New developments of polymer cross-linking: Slide-ring polymeric materials

Abstract

Since the discovery of cross-linking in natural rubber with sulfur in 1839 by Goodyear, the cross-linking of polymeric materials has become one of the most important topics in polymer science and technology. We have recently developed a novel type of gel called the slide-ring gel or topological gel that is different from physical and chemical gels by using a supramolecular architecture with topological characteristics. In this gel, polymer chains with bulky end groups exhibit neither covalent cross-links as in chemical gels nor attractive interactions as in physical gels but are topologically interlocked by figure-of-eight cross-links. Hence, these cross-links can pass along the polymer chains freely to equalize the tension of the threading polymer chains similarly to pulleys; this is called the pulley effect. The slide-ring material is a new cross-linking concept for the polymer network as well as a real example of a slip-link model or sliding gel, which was previously considered only theoretically. In this report, we review recent research on progress in the cross-linking of polymeric materials together with the synthesis, structure, and mechanical properties of the slide-ring gels. This concept of the slide-ring material can be applied to not only gels but also to a wide variety of polymeric materials without solvents. © 2008, The Society of Polymer Science, Japan.