This article deals with the characterization of high trans-1,4-poly(butadiene) (TPBD) prepared by means of an anionic polymerization using an initiator composed of alkyl aluminum, n-butyl lithium, and barium alkoxide. By controlling both initiator composition and polymerization temperature, a set of TPBD was prepared with well-known number of 1,4-trans units, molecular weight distribution, and average molecular weight. Analyses by differential scanning calorimetry and diffraction of wide-angle X-rays showed a direct relationship between the microstructure of the polymer and its thermal properties. By increasing the number of 1,4-trans units (70-90%), the crystallinity of the polymer was increased (10-30%); polymers with less than 65% of 1,4-trans units were amorphous, whereas TPBD with a number of 1,4-trans units greater than 80% were polymorphous and presented two endothermic transitions. Summing up, the results presented in this article indicate that cyclohexane solutions of alkyl aluminum, n-butyl lithium, and barium alkoxide allow produce poly-butadienes with enough amount of 1,4-trans units to display a regular microstructure that makes them susceptible to experience-induced crystallization, likewise at a reaction rate similar to that observed for the commercial production of poly(butadiene) with n-butyl lithium. POLYM. ENG. SCI., 49:1-10, 2009. (C) 2008 Society of Plastics Engineers