Influence of Interfacial Bonding on the Mechanical and Impact Properties Ring-Opening Metathesis Polymer (ROMP) Silica Composites

Polymers formed by ring-opening metathesis polymerization (ROMP) such as poly(dicyclopentadiene) (pDCPD) exhibit a technologically desirable combination of high toughness, high glass transition temperature, and outstanding low-temperature performance. However, because of their nonpolar molecular structure, they tend to suffer from relatively low elastic moduli and poor adhesion to common fillers, fibers, and substrates, limiting their utility as adhesives and composite binders without specialized bonding agents. Here, we investigate the mechanical properties of a pDCPD-based copolymer filled with well-defined spherical microparticles having four distinct surface chemistries capable of strong, moderate, or weak bonding to the matrix with surfaces ranging from polar to nonpolar. Measurements in uniaxial tension, quasi-static fracture, and high-velocity impact are complemented by digital image correlation (DIC), scanning electron microscopy (SEM) fractography, and X-ray computed tomography (X-mu CT) of subcritically loaded crack tips, yielding insight into the complex roles played by interfacial bonding in strength, stiffness, and toughening mechanisms of an already tough polymer. Analysis using quantitative fracture and impact mechanism models provided valuable guidelines for designing heterogeneous systems that combine structural and tough performance.