The process and catalyst of this invention can be utilized to synthesize homo and copolymers of
conjugated diene monomers and vinyl aromatic monomers having high trans contents of greater than 60% with low melting points. These homo and copolymers of
conjugated diene monomers and vinyl aromatic monomers can be utilized in tire
tread and sidewall rubbers that exhibit outstanding
wear and tear characteristics in the
tread and excellent flexing properties in the sidewall. The rubber polymers of this invention are made utilizing an improved catalyst
system. This catalyst
system is comprised of (a) organo aluminum compounds, (b) organo
lithium compounds, (c) a
barium compound selected from
barium salts of (i) di(
ethylene glycol) ethyl
ether, (ii) di(
ethylene glycol)
propyl ether, (iii) di(
ethylene glycol) hexyl
ether, (iv) di(N,N-dimethyl amino glycol) ethyl
ether, (v)
menthol and
thymol in the presence of polar modifier consisting of water, alcohols, amines, thiols, phosphates and phosphites. The trans polymers and copolymers of this invention made with the above catalyst
system typically have a
glass transition temperature
ranging from −97° C. to −40° C., a
melt temperature ranging from −30° C. to +30° C., and a number average molecular weight from 20,000 to 250,000. The inclusion of such polar modifiers in the
barium catalyst system results in a high
styrene content in copolymerization, a high trans content, and high molecular weight. Copolymers of conjugated diolefin monomers and vinyl aromatic monomers made with the catalyst system of this invention also have a tapered macrostructure.