A method of preparing a vulcanizable composition containing high 1,4-cis-linkage content block copolymers of polybutadiene and polyisoprene, the method comprising: (i) forming a polymerization mixture that includes a pseudo-living polymer by combining a first monomer and a lanthanide-based catalyst, where the lanthanide-based catalyst comprises (a) a lanthanide-containing compound, wherein the lanthanide-containing compound is a neodymium compound, (b) an aluminoxane, (c) an organoaluminum compound defined by the formula AlR n X 3-n, where each R is individually a hydrocarbon group or a substituted hydrocarbon group, each X is individually a hydrogen atom, a carboxylate group, an alkoxide group, or an aryloxide group, and where n is an integer of 1 to 3, and (d) a halogen-containing compound; (ii) adding a second monomer to the polymerization mixture that includes the pseudo-living polymer to obtain the high 1,4-cis-linkage content block copolymer of polybutadiene and polyisoprene, where the first monomer is either 1,3-butadiene or isoprene and the second monomer is not the same as the first monomer and is either 1,3-butadiene or isoprene, and (iii) mixing the high 1,4-cis-linkage content block copolymer of polybutadiene and polyisoprene with a filler and a curing agent to form a vulcanizable composition, wherein the high 1,4-cis-linkage content block copolymer of polybutadiene and polyisoprene is between 50% and 100% by weight of a total rubber component of the vulcanizable composition. (i) forming a polymerization mixture that includes a pseudo-living polymer by combining a first monomer and a lanthanide-based catalyst, where the lanthanide-based catalyst comprises (a) a lanthanide-containing compound, wherein the lanthanide-containing compound is a neodymium compound, (b) an aluminoxane, (c) an organoaluminum compound defined by the formula AlR n X 3-n, where each R is individually a hydrocarbon group or a substituted hydrocarbon group, each X is individually a hydrogen atom, a carboxylate group, an alkoxide group, or an aryloxide group, and where n is an integer of 1 to 3, and (d) a halogen-containing compound; (a) a lanthanide-containing compound, wherein the lanthanide-containing compound is a neodymium compound, (b) an aluminoxane, (c) an organoaluminum compound defined by the formula AlR n X 3-n, where each R is individually a hydrocarbon group or a substituted hydrocarbon group, each X is individually a hydrogen atom, a carboxylate group, an alkoxide group, or an aryloxide group, and where n is an integer of 1 to 3, and (d) a halogen-containing compound; (ii) adding a second monomer to the polymerization mixture that includes the pseudo-living polymer to obtain the high 1,4-cis-linkage content block copolymer of polybutadiene and polyisoprene, where the first monomer is either 1,3-butadiene or isoprene and the second monomer is not the same as the first monomer and is either 1,3-butadiene or isoprene, and (iii) mixing the high 1,4-cis-linkage content block copolymer of polybutadiene and polyisoprene with a filler and a curing agent to form a vulcanizable composition, wherein the high 1,4-cis-linkage content block copolymer of polybutadiene and polyisoprene is between 50% and 100% by weight of a total rubber component of the vulcanizable composition.