The development of bimodal molecular weight distribution in polyisoprene was studied by GPC analysis of samples taken during the polymerizations initiated by the dilithium initiators reported in paper 1 of this series. Isolation of the individual peaks using selective precipitation techniques was applied on several samples to identify the nature of the peaks in GPC chromatograms. The dilithium initiators were found to react quickly with isoprene monomer to form an adduct. Further polymerization from the adduct was very slow and caused the main peak of the distribution to be slightly broader and lower in molecular weight. The higher molecular weight peak of the bimodal distribution was from the inadvertently present monofunctional initiation. The major source of the monofunctional initiating species was identified to be the dilithium initiator partially terminated by the residual impurities in the polymerization feed.