Towards Precise Tunability of Coefficient of Thermal Expansion in Epoxies

Epoxy thermosets are polymeric materials used in structural composites to create robust yet lightweight materials. Their excellent mechanical, chemical, and thermal performance also make epoxies useful as protective potting materials/coatings to mitigate mechanical, thermal, and electrical insult. However, these materials suffer from relatively large coefficients of thermal expansion (CTE). CTE mismatch of epoxies with ceramics, metals, and fiber mats leads to issues such as warpage, delamination, cracking, and ultimately, failure. To combat this issue, fillers are added, but to the detriment of processing, equipment longevity (wear), electrical property performance, and more. Furthermore, fillers impart only moderate CTE reduction. Here, we present a way to tailor epoxy CTE without the use of fillers. Instead, we create CTE tunability within the epoxy backbone chemistry itself using a novel, thermally contracting molecule and demonstrate an epoxy with a glassy CTE less than a third of traditional, unfilled epoxy systems as well as the first negative CTE epoxy.<br/><i>Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. </i>SAND2021-13475 A