Synthesis and use of chain-coupled polymeric sulfide compounds in rubber formulations

A method of making a polymeric sulfide compound having the formula

• (PS)nM+zP′z−n
• where P is a polymer chain;
• S is sulfur;
• P′ is another polymer chain P or is an “R” group selected from the group consisting of alkyl groups having one to about 30 carbon atoms, aromatic groups having about 6 to about 20 carbon atoms, and cycloalkyl groups having about 5 to about 20 carbon atoms;
• M+z is a metal atom or a nonmetal atom, having an oxidation state “z” of greater than one, wherein the nonmetal atom is selected from the group consisting of atoms of phosphorus, boron, nitrogen and sulfur;
• and n is an integer having a value of from 1 to z,
• comprising the steps of:
• providing a polymer chain prepared by anionic solution polymerization and comprising a living end,
• reacting the living end of the polymer chain, after polymerization but while still in the presence of an inert solvent, with an alkylene sulfide compound;
• subsequently reacting the resulting polymer chain, while still in the presence of the inert solvent, with a coupling agent having the formula
• M+zXz−mRm
• where M+z and R are the same as above, X is a halide;
• (z−m) represents an integer having a value of at least 2, and m is an integer having a value of zero to (z−2).

A vulcanizable elastomeric compound comprising a polymeric sulfide compound having the formula

• (PS)nM+zP′z−n
• where P is a polymer chain;
• S is sulfur;
• P′ is another polymer chain P or is an “R” group selected from the group consisting of alkyl groups having one to about 30 carbon atoms, aromatic groups having about 6 to about 20 carbon atoms, and cycloalkyl groups having about 5 to about 20 carbon atoms;
• M is a metal atom or a nonmetal atom, having an oxidation state “z” of greater than one, wherein the nonmetal atom is selected from the group consisting of atoms of phosphorus, boron, nitrogen and sulfur;
• and n is an integer having a value of from 1 to z;
• a reinforcing filler selected from the group consisting of silica, carbon black, and mixtures thereof;
• and
• a cure agent including sulfur.

A pneumatic tire comprising a component produced from a vulcanized elastomeric compound having the formula

• (PS)nM−zP′z−a
• where P is a polymer chain;
• S is sulfur;
• P′ is another polymer chain P or is an “R” group selected from the group consisting of alkyl groups having one to about 30 carbon atoms, aromatic groups having about 6 to about 20 carbon atoms, and cycloalkyl groups having about 5 to about 20 carbon atoms;
• M is a metal atom or a nonmetal atom, having an oxidation state “z” of greater than one, wherein the nonmetal atom is selected from the group consisting of atoms of phosphorus, boron, nitrogen and sulfur;
• and n is an integer having a value of from 1 to z;
• a reinforcing filler selected from the group consisting of silica, carbon black, and mixtures thereof, and
• a cure agent including sulfur.

A method for improving mixing efficiency during compounding of an elastomer with a reinforcing filler, comprising the steps of:

• providing a polymeric sulfide compound having the formula
• (PS)nM+zP′z−n
• where P is a polymer chain;
• S is sulfur;
• P′ is another polymer chain P or is an “R” group selected from the group consisting of alkyl groups having one to about 30 carbon atoms, aromatic groups having about 6 to about 20 carbon atoms, and cycloalkyl groups having about 5 to about 20 carbon atoms;
• M+z is a metal atom or a nonmetal atom, having an oxidation state “z” of greater than one, wherein the nonmetal atom is selected from the group consisting of atoms of phosphorus, boron, nitrogen and sulfur;
• and n is an integer having a value of from 1 to z,
• mixing the polymeric sulfide compound in a mixer with a reinforcing filler selected from the group consisting of silica, carbon black, and mixtures thereof,
• providing a source of moisture;
• heating the mixture to a temperature of about 60° C. to about 200° C.;
• wherein during the mixing step up to “n” S-M groups are hydrolyzed in the presence of the moisture and heat resulting in uncoupling of up to “n” polymer chains and a decrease in the viscosity of the mixture.