Polyfunctional vinyl aromatic copolymer and method for manufacturing same, copolymer rubber obtained therefrom, rubber composition, rubber crosslinked material, and tire member

A polyfunctional vinyl aromatic copolymer, comprising

• 0.5 mol % or more and 75 mol % or less of a structural unit (a) derived from a divinyl aromatic compound, 5.0 mol % or more and 75 mol % or less of a structural unit (b) derived from a monovinyl aromatic compound having no substituent at the α position, and 5.0 mol % or more and 75 mol % or less of a structural unit (c) derived from an α,α-disubstituted olefin compound, in which at least some of the structural units (a) are a crosslinked structural unit (a2) represented by the following Formula (2) and a vinyl-group-containing structural unit (a1) represented by the following Formula (1):
• in the formulas, R1's independently represent an aromatic hydrocarbon group having 6 to 30 carbon atoms,
• wherein the molar fraction of the crosslinked structural unit (a2) with respect to the structural unit (a) is within a range of 0.05 to 0.60, and the molar fraction of the vinyl-group-containing structural unit (a1) with respect to the total amount of the structural units (a), (b) and (c) is within a range of 0.001 to 0.60, and
• the number average molecular weight Mn of the polyfunctional vinyl aromatic copolymer is 300 to 50,000, and the molecular weight distribution (Mw/Mn) represented by the ratio of the weight average molecular weight Mw to the number average molecular weight Mn is 10.0 or less,
• and wherein the α,α-disubstituted olefin compound is at least one monomer selected from the group consisting of isobutylene, diisobutylene, 2-methyl-1-butene, 2-methyl-1-pentene, 1-methyl-1-cyclopentene, 2-methyl-1-hexene, 1-methyl-1-cyclohexene, 2-methyl-1-heptene, 2-methyl-1-octene, 2-methyl-1-nonene, 2-methyl-1-decene, 2-methyl-1-dodecene, 2-methyl-1-tetradecene, 2-methyl-1-hexadecene, 2-methyl-1-octadecene, 2-methyl-1-eicosene, 2-methyl-1-docosene, 2-methyl-1-tetracosene, and α-methylstyrene.