Process for isomerization of lower polymers of butadiene

A process for obtaining an isomer having conjugated double bonds of (A) a lower polymer of butadiene or (B) a lower copolymer of butadiene, which comprises performing a lower polymerization of butadiene or a lower copolymerization of butadiene with a monomer selected from the group consisting of a conjugated diolefin other than butadiene and a vinyl-substituted aromatic compound with a catalyst selected from the group consisting of an organic alkali metal compound and an alkali metal dispersion the alkali metal thereof forming said organic alkali metal compound, the alkali metal of the catalyst being lithium, sodium or potassium, to form reaction mixture (i) containing (A) or (B), each of (A) and (B) having non-conjugated bonds therein, adding to said reaction mixture (i) a diamine compound having the formula ##STR17## wherein n is an integer of 2 or 3, and each of R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5 and R.sub.6 represents a hydrogen atom or an organic compound residual group having from 1 to 20 carbon atoms, and any two of R.sub.1, R.sub.2, R.sub.3 and R.sub.4 may be bonded together to form a cyclic structure, in the presence or absence of butadiene and any other monomer, and reacting the resulting reaction mixture (ii) at a temperature of from 0.degree. to 200.degree. C., thereby forming a reaction mixture (iii) containing said isomer, and recovering from said reaction mixture (iii) a product consisting essentially of said isomer.