Polymerization-induced phase separation in epoxy-amine networks with broadly and systematically tunable length scales

Polymer thermosets are frequently modified by the addition of a secondary polymer that phase separates during the thermoset polymerization. Generally speaking, it is challenging to control domain sizes in such materials beyond a limited range. We introduce an approach to polymerization-induced phase separation in epoxy-amine networks that enables domain sizes to be tuned over a broad range, from nanoscale to macroscale. The key element of this approach is a balance of multiple reactive species (e.g., amine curing agents) that simultaneously favor and disfavor phase separation. We demonstrate how ensuing, systematic variation of the length scale of phase separation leads to exquisite control over the curing behavior and glass transition of the resultant materials. In particular, we discuss application to rubber-toughened epoxies, where mechanical properties are critically impacted by rubber particle size. These results and insights may help guide the future design of polymer thermosets with precisely targeted microstructures and consequent thermomechanical properties.