Styrene-butadiene block copolymer

A process for the synthesis of a styrene-butadiene block copolymer having syndiotactic polystyrene blocks which comprises copolymerizing 1,3-butadiene and styrene at a temperature which is within the range of about 0 C. to about 100 C. and a 1,3-butadiene partial pressure which is within the range of about 10 mm of mercury to about 50 mm of mercury, wherein said copolymerization is conducted in the presence of a catalyst system which is comprised of a catalyst component and a co-catalyst component;

• wherein the catalyst component is of a structural formula selected from the group consisting of CpMX3, CpMX2, MX4 and MX3 wherein Cp represents an aromatic anion of the formula C5RnH5−n wherein R represents a member select from the group consisting of alkyl, aryl, alkaryl, arlyalkyl, haloalkyl, haloaryl, haloalkaryl, haloarylalkyl, silyalkyl, silylaryl, silylalkaryl, silylarylalkyl, halosilylalkyl, halosilylaryl, halosilylalryl, halosilylarylalkyl, silylhaloalkyl, silylhaloaryl, silylhaloalkaryl, halosilylarylalkyl, alkoxy, siloxy, NR′2, PR′2, SR′, and BR′2 groups, wherein the NR′2, PR′2, SR′, and BR′2 groups are connected though one or more carbon and/or silicon atoms, with the proviso that if there are more than one carbon atoms, they may be saturated or unsaturated, where each R′ is the same or different and is hydride, or is hydorcarbyl or silyl, optionally substituted with one or more halogen atoms or alkoxy groups and having up to 20 carbon and/or silicon atoms, wherein the R groups can be the same or different, wherein the R can be bound to Cp in one or more places, wherein n represents an integer from 0 to 5, wherein M represents a metal selected from the group consisting of titanium, zirconium and hafnium and wherein X represents a member selected from the group consisting of hydrogen, halogen, alkyl, aryl, alkaryl, arlyalkyl, haloalkyl, haloaryl, haloalkaryl, haloarylalkyl, silylalkyl, silylaryl, silylalkaryl, silylarylalkyl, halosilylalkyl, halosilylaryl, halosilylalkaryl, halosilylarylalkyl, silylhaloalkyl, silylhaloaryl, silylhaloalkaryl, halosilylarylalkyl, alkoxy, siloxy, NR′2, PR′2, SR′, and BR′2;
• with the proviso that for MX3, X is an organic acid containing from 1 to 20 carbon atoms, wherein X groups may be bound to M in one or more places;
• wherein the co-catalyst component is of a formula selected from the group consisting of
• wherein R″ represents an alkyl group contain from 1 to about 10 carbon atoms, wherein R′″ represents a 2,3,4,5,6-pentafluorophenyl group or a 3,5-trifloromethylphenyl group, wherein R″″ represents a 2,3,4,5,6-pentafluorophenyl group, a 3,5-trifluoromethylphenyl group, or a phenyl group and wherein Z represents an ammonium salt, a silver atom, or a triphenylmethyl group;
• with the proviso that, if the catalyst component is MX4, then the co-catalyst component is of the formula
• with the proviso that, if the metallocene component is MX3, then the co-catalyst component is of the formula
• with the proviso that, if the co-catalyst component is of the formula BR′″3, then at least one X represents an alkyl group, an aryl group, or an alkarly group;
• and with the proviso that, if the co-catalyst component is of the formula Z+B−R″4, then at least one X represents an alkyl group, an aryl group, or an alkaryl group.