Structure–Property Relationships in Model Network Elastomers with Controlled Structural Defects

Abstract

Structural defects such as dangling chains, loops, and trapped entanglements can degrade elastomer performance and obscure structure–property relationships. Here, we examine how structural defects influence the mechanical response of elastomer networks using a controllable model network (MN) platform based on end-linking of low-dispersity star prepolymers. We controlled the defect population by varying either the reaction probability of the end-linking reaction (p) or the initial prepolymer volume fraction at preparation (φ0). Decreasing p or φ0 led to a reduction in the elastic modulus, suggesting a decrease in the density of elastically effective chains. An analysis of the uniaxial stress–strain curves based on a scaling theory suggested that the conformation of the network chains was largely unaffected by the defects in the range of p and φ0 investigated. As a result, the stress–strain curves of all the samples normalized by the modulus overlapped with each other over a wide deformation range. In contrast, the defects shifted the onset of strain-induced crystallization and hence the onset of strain stiffening to higher strain, as revealed by in situ X-ray scattering analyses. Despite being created through different pathways, structural defects in p-tuned and φ0-tuned elastomers produced similar trends in the macroscopic response. These findings underscore how structural defects influence the mechanical behavior of elastomers, offering insights into predicting and designing the mechanical performance of elastomers.