The present invention is directed to a batch process for synthesizing rubbery polymers, such as styrene-butadiene rubber, having a high trans microstructure. In one embodiment, the batch process involves mixing a catalyst system with styrene and butadiene monomers in a single reactor, with additional butadiene monomer being added after a desired period of time to further drive styrene conversion and, thus, provide a desirable high trans rubbery polymer, e.g., styrene-butadiene rubber. The copolymerization process can be conducted at a temperature in the range of about 20.degree. C. to about 180.degree. and over a period of about 1 to about 4 hours. The catalyst system can include (a) an organolithium compound, (b) a group IIa metal salt, and (c) an organoaluminum compound. The catalyst system may further optionally include an amine compound and/or an organomagnesium compound.