The effects of various additional non-nitrile-containing monomers on the heat resistance of thermoplastic expandable microspheres containing acrylonitrile and methacrylonitrile were investigated to determine the correlation between the chemical structure and expandable properties. Thermoplastic expandable microspheres were synthesized by suspension polymerization, with acrylonitrile and methacrylonitrile as the main ingredients and seven kinds of methacrylic acid derivatives, methacrylic acid, and acrylic acid as non-nitrile-containing monomers. The expandable properties, that is, the maximum expansion temperature, the expansion start temperature, and the maximum dimension change, were measured with thermomechanical analysis. For the development of heat-resistant microspheres, polymer structures with smaller functional free volumes, higher glass-transition temperatures, and higher cohesive energy densities, such as methyl acrylic acid, were applied as nonnitrile-containing monomers. Molecular structures such as -COOH groups with strong electrostatic interactions and hydrogen-bonding forces were found to be suitable for high heat resistance. (c) 2005 Wiley Periodicals, Inc.