Free radical polymerizations have been widely used for a variety of applications, including coating, packaging, adhesives, inks and dental materials. However, shrinkage stress in network systems due to volumetric shrinkage during polymerization often results in poor mechanical performance of final materials, often limiting end use. Delaying gelation during polymerization while incorporating functional structure or functionalized groups into the polymer networks may lead to significantly reduced shrinkage stress and, consequently, enhanced thermomechanical properties. In this review, we summarize several practical methods, including thiol–ene radical polymerization, addition–fragmentation chain transfer, controlled radical polymerization, covalent adaptable networks, ring‐opening polymerization and cyclopolymerization, that have shown promise in reducing volumetric shrinkage and associated stress in network‐forming systems. The resulting enhanced (thermo)mechanical material properties of these modified polymers are also introduced. These methods have proven to be powerful tools for fabricating polymers with novel functionality and properties and thereby show potential to expand application of free radical thermoset materials. © 2021 Society of Industrial Chemistry.

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