PURPOSE: To obtain a polymer in particulate foam which is excellent in electrical insulating property, chemical resistance, and oxidation resistance and has a high melting point and a high glass transition temp. by polymerizing a specific monomer to attain given physical properties.

CONSTITUTION: This polymer contains the repeating units represented by the formula and has a solution viscosity of 0.30dl/g or higher as measured at 30°C in a 1:1 (by weight) mixture of m-chlorophenol and 1,2,4-trichlorobenzene at a concentration of 0.4g/dl, a retention of enthalpy through melt crystallization as measured under given conditions (400°C/20min) of 60% or higher, a melting point of 340-360°C, a glass transition temp. of 125°C or higher, and an average particle diameter of 0.1-2mm.