Thermally expandable microspheres with high expansion ratios: Design of core and shell for largest size change

Abstract Thermally expandable microspheres (TEMs) are liquid‐core, polymer‐shelled particles that are useful in both current industry and future manufacturing and basic research applications. Here, we systematically optimize TEMs for highest expansion ratio using a broad‐spectrum infrared head source. Microspheres are synthesized from a copolymer of 2‐hydroxyethyl methacrylate (HEMA), methyl methacrylate, and acrylonitrile as the shell, which is optimized for greatest expansion ratio. This represents the first time that HEMA is used in TEMs. The liquid blowing agent core is next optimized, followed by the prepolymerization emulsion time. It is found that particle morphology is greatly variable and influenced by kinetic and thermodynamic factors, with various phase‐separated and aniosotropic morphologies accessed.