Patent ID: 7687107

Claim:
In the process of producing a chemically modified siliceous filler by contacting an acidic aqueous suspension of amorphous precipitated silica with a coupling agent to form an acidic aqueous suspension of chemically modified precipitated silica, optionally in the presence of a surfactant and/or a water miscible solvent, and recovering said chemically modified filler, the improvement comprising: (A) providing an acidic aqueous suspension of amorphous precipitated silica having a pH of 2.5 or less; (B) contacting the precipitated silica with a coupling agent comprising a combination of: (a) bis(alkoxysilylalkyl)polysulfide and (b) non-sulfur organometallic compound(s), the weight ratio of (a) to (b) being at least 0.05:1, under conditions that result in essentially complete hydrolysis of any alkoxy groups associated with the coupling agent, thereby to produce chemically modified precipitated silica; (C) raising the pH of the acidic aqueous suspension of chemically modified precipitated silica to from 3.0 to 10 with acid neutralizing agent that does not adversely affect the chemically modified precipitated silica; and (D) separating chemically modified precipitated silica from the aqueous phase while retaining in the aqueous phase substantially all of any alcohol by-product produced by hydrolysis of alkoxy groups associated with the coupling agent, said chemically modified precipitated silica having (i) a carbon content of greater than 1 weight percent, (ii) a sulfur content of greater than 0.1 weight percent, (iii) a Silane Conversion Index of at least 0.3, and (iv) a Standard Tensile Stress at 300 percent elongation of at least 7.0 when incorporated into a vulcanized rubber composition.