PURPOSE: To obtain the subject polymer in high yield and in high polymerization degree, useful as a highly heat-resistant and high-rigidity polymer from a low- purity cyclohexadiene, by anionic polymerization of a raw material mixture comprising cyclohexane, benzene, specific amount of a cycloehexadiene, etc.

CONSTITUTION: This polymer is obtained at low cost by anionic polymerization of a raw material mixture comprising cyclohexane, 10-80 (pref. 30-70)wt.% of 1,3-cyclohexadiene, benzene, methylcyclopentene and pref. 1-40wt.% of cyclohexane, pref. using an organoalkali metal amine complex, esp. an alkyllithium tetramethylethylenediamine complex as catalyst.