Thermally foamable microsphere, method of producing the same, and use thereof

A thermally foamable microsphere, comprising:

• a foaming agent;
• and
• an outer shell encapsulating the foaming agent, the outer shell formed of a copolymer having a polymethacrylimide structure, wherein the copolymer is obtained by polymerizing a mixture of polymerizable monomers, the polymerizable monomers comprise methacrylonitrile and methacrylic acid in a total weight of 90 to 100% by weight, in which a molar ratio of methacrylonitrile to methacrylic acid is 1:9 to 9:1, and wherein the polymerizable monomers further comprise 10% by weight or less of an additional polymerizable monomer or monomers, the additional monomer or monomers comprise acrylonitrile, and the weight-% ratio of acrylonitrile to methacrylonitrile is 0:55 to 10:49.5,
• wherein the thermally foamable microsphere exhibits a b* value, and the b* value after heating at 240° C. for 2 minutes is 35.4 or lower.