VOC-free coupling agents for rubber compositions

1 . A coupling agent according to Formula I, which is capable of linking at least one of a mineral oxide, carbon black and brass to an unsaturated elastomer,

where FG1 and FG2 each represent a functionalized arylene group, which can be the same or different;

LG1 and LG2 each represent a linking group, which can be the same or different; and

S a represents a sequence of two or more connected sulfur atoms, where a is a number which is at least 2;

wherein at least one of the functionalized arylene groups FG1 and FG2 includes at least one reactive substituent selected from hydroxyl groups (—OH), primary or secondary amino groups (—NH2, —NHR), sulfhydryl groups (—SH), boronic acid groups [—B(OH)2], and mixtures thereof, wherein in the case of —NHR, each R is a hydrocarbyl group; and

wherein at least one of the functionalized arylene groups FG1 and FG2 has the general form shown in Formula II:

wherein each X is independently selected from —OH, —NH2, —NHR, —B(OH)2, and —SH, wherein in the case of —NHR, each R is a hydrocarbyl group; n is 1 or 2; each R 1 is independently a hydrocarbyl group or where two R 1 groups together form a ring; m is 0; and “*” represents a connection to a respective one of the linking groups.

2 . The coupling agent of claim 1 , wherein each X is OH.

3 . The coupling agent of claim 1 , wherein LG1 is of the general form:

—CH═N—(CH(COOH)) q —(CR 2 R 3 ) p —CH 2 —,

where each p is 0, or at least 1, or at least 2, and/or up to 10, or up to 5;

each q is 0, or at least 1;

p+q≥1; and

each of R 2 and R 3 is independently H, a hydrocarbyl group, or an oxygen-containing group.

4 . The coupling agent of claim 1 , wherein:

LG1 is of the general form: —CH═N—CH 2 —CH 2 —, and LG2 is its inverse, or

LG1 is —CH═N—CH(COOH)—(CH 2 )—, and LG2 is its inverse.

5 . The coupling agent of claim 1 , wherein the coupling agent is selected from the group consisting of:

and amino-substituted, boronic acid substituted, and/or sulfhydryl substituted equivalents thereof.

6 . A mixture or reaction product of the coupling agent of claim 1 and silica.

7 . A rubber composition comprising, or being the reaction product of:

an unsaturated elastomer;

the coupling agent of claim 1 ;

at least one filler selected from a mineral oxide filler and carbon black; and

a sulfur-based curing agent.

8 . The rubber composition of claim 7 , wherein the mineral oxide filler comprises silica.

9 . An article formed from the rubber composition of claim 7 .

10 . The article of claim 9 , wherein the article comprises a pneumatic tire or a portion thereof.

11 . A method of forming a tire comprising:

combining a coupling agent with an unsaturated elastomer, at least one filler selected from a mineral oxide filler and carbon black, and a sulfur-based curing agent to form a mixture, the coupling agent formed by the reaction of:

a difunctional organic polysulfide having a first reactive group at a first end and a second reactive group at a second end; and

a polyfunctional arylene compound which has a first functional group that is capable of reaction with the reactive groups of the difunctional organic polysulfide and a second functional group that is capable of interaction with a substrate surface, the polyfunctional arylene compound being in sufficient amount to react with the first and second reactive groups of the difunctional organic polysulfide;

shaping the mixture to form a green component of a tire; and

curing the green component with other green components to form the tire.

12 . The method of claim 11 , wherein the difunctional organic polysulfide is selected from L-cystine, cystamine, and 2-hydroxyethyl disulfide.

13 . The method of claim 11 , wherein the first functional group is selected from an aldehyde group, a carboxylic acid group, an ether group, and an ester group.

14 . The method of claim 11 , wherein the second functional group is selected from the group consisting of a hydroxyl group, an amino group, a thiol group, and combinations thereof.

15 . The method of claim 11 , wherein the polyfunctional arylene compound has the general formula:

where Y represents the first functional group;

X represents the second functional group;

n is at least 1;

each R 1 is independently a hydrocarbyl group or where two R 1 groups together form a ring; and

m is 0, or at least 1.