Mechanical properties of model network elastomers: Impacts of network geometry and chemistry

Abstract

Elastomers exhibit excellent elasticity and deformability because of their three-dimensional cross-linked polymer networks. Conventional elastomers contain various defects in network geometry, stemming from random cross-linking between precursor polymer chains. These defects can be decreased or controlled in model networks, which are constructed by end-linking well-defined precursor polymers. The model network strategy enables the systematic study of the effects of network geometry as well as those of the chemical details of network chains on the mechanical properties. In this Focus Review, I first discuss the progress made in understanding the relationship between network geometry (network chain lengths, low-order loops, and trapped entanglements) and the macroscopic mechanical properties of model network elastomers. Second, recent studies on the effects of the chemical structure of network chains are reviewed. The mechanical performance of model network elastomers can be significantly altered by incorporating transient cross-links, by using a bottlebrush polymer, and by incorporating polymers capable of strain-induced crystallization. These findings not only help elucidate the structure‒property relationships of elastomers in general but also provide insights into the development of high-performance materials. Conventional elastomers contain various geometric defects in their network structure. The model network strategy, in which well-defined precursor polymers are joined specifically at their ends, enables the reduction or control of these defects. This Focus Review highlights recent advances in understanding the structure-property relationships of model network elastomers from two viewpoints: the geometry of the polymer network and the chemical structure of the network chains. Control of these two factors opens diverse possibilities for unique and advanced properties in elastomers.