Silica reinforced rubber composition and use in tires

A method of preparing a rubber composition comprises the sequential steps of, based upon parts by weight per 100 parts by weight rubber (phr):

• (A) thermomechanically mixing in at least one non-productive mixing step, in the absence of sulfur and sulfur cure accelerator, in an internal rubber mixer to a temperature within a range of about 140° C. to about 190° C. for such mixing step(s):
• (1) 100 parts by weight of at least one sulfur vulcanizable diene-based elastomer selected from conjugated diene homopolymers and copolymers and copolymers of styrene [vinyl aromatic compound (e.g. styrene)] and at least one conjugated diene;
• (2) about 10 to about 120 phr of particulate reinforcing filler comprised of precipitated silica and rubber reinforcing carbon black, wherein said reinforcing filler contains from 10 to about 110 weight percent precipitated silica;
• (3) an oligomeric organomercaptosilane based coupling agent,
• wherein said organomercaptosilane oligomer is the product of reacting a 2-methyl-1,3-propane diol with S-[3-(triethoxvsilyl)propyl] thiooctanaote, and
• (4) combination of zinc oxide and long chain fatty acid comprised of about 3 phr of zinc oxide and about 4 phr of long chain fatty acid comprised of at least 90 percent by weight of stearic acid and less than 10 percent of long chain fatty acids;
• wherein said zinc oxide and said long chain fatty acid are mixed in at least one non-productive mixing step with said diene-based elastomer(s)in an internal rubber mixer and wherein said zinc oxide and said long chain fatty acid are added coincidentally with or prior to the addition of said organomercaptosilane oligomer, and
• wherein said zinc oxide is mixed with said diene-based elastomer(s) in said non-productive mixing step(s) exclusive of mixing zinc oxide with said diene-based elastomer(s) in a subsequent productive mixing step;
• (B) subsequently blending with the resultant rubber composition of said non-productive mixing step(s), in a final thermomechanical productive mixing step at a temperature in a range of about 100° C. to about 120° C., elemental sulfur and at least one sulfur vulcanization accelerator;
• wherein said oligomeric organomercaptosilane is comprised of a plurality of mercapto and silane moieties and wherein from 50 to about 100 percent of said mercapto groups are not chemically blocked.