Polar modifier systems based on a blend of DTHFP, ETE, TMEDA, DMTHFMA and/or functionally similar compounds with BDMAEE and SMT are used to make block copolymers having high levels of pendant vinyl double bond repeat units, which is through highly selective 1,2-bond butadiene addition, low vinylcyclopentane formation, unimodal narrow molecular weight distribution, and a low level of randomized co-monomer repeat units. The block copolymers have very high levels of 1,2-vinyl content and high 3,4-vinyl bond addition of the conjugated diene monomer and low vinylcyclopentane content. The polar modifier systems provide a fast polymerization rate, with a unimodal narrow molecular weight distribution. The polar modifier systems allow operation at a higher temperature than in prior art systems, which reduces cooling requirements.