THE USE OF TRIORGANOPHOSPHINES FOR IMPROVING THE EFFECTIVITY OF POLYSULPHIDE ALKOXYSILANE COUPLING AGENTS

Abstract: The coupling action of polysulfide alkoxy silanes in rubbers is enhanced by the utilization of triorganophosphine compositions.

Description: POLYSULFIDE ALKOXY SLANT COUPLING AGENTS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to sulfur vulcanizable elastomer composites which are based upon vulcanizable unsaturated polymers and copolymers such as natural rubbers, polyisoprenes, polybutadienes, poly(butadiene-co-styrene), poly(butadiene-co-acrylontrile), poly(isobutylene-cobutadiene, and the like. More particularly, this invention relates to means for enhancing the coupling action, in such sulfur v.lcanizable elastomers, of polysulfie alkoxy silane coupling agents. 2. Description of the Prior Art Polysulfide alkoxy silane coupling agents are known, and are described e.g. in U.S. Patents Nos. 3,842,111, 3,873,489, 4,003,843, and 4,044,037. Polysulfide-functional organosilanes are, like mercapto-functional organosilanes, useful as coupling agents in silica-filled and silicate-filled sulfur vulcanizable elastomer composites. However, the polysulfide-functional organosilanes are, as compared to themercapto-functional organosilanes, less active. Under comparable conditions, the former produce lesser improvements than do the latter in elastomer vulcanizate properties such as tensile modulus. BRIEF SUMMARY OF THE INVENTION It has now been found that triorganophosphines can be utilized to enhance the coupling action of polysulfide alkoxy silane coupling agents. More specifically, it has been found that compositions which contain triorganophosphine referably in admixture with water1 lower alkanol, and porous inert organic solid carrier) can be utilized to enhance the coupling action of polysulfide alkoxy silane coupling agents in the preparation of vulcanizable rubber from formulations comprising a major proportion of vulcaniz-able unsaturated polymer or copolymer and a small amount of polysulfide alkoxy silane coupling agent. Also, it has been Sound that compositions which contain a polysulfide alkoxy sflane coupling agent and a triorganophosphine, (referably in admixture with water, lower alkanol, and porous inert organic solid) can be utilized in the vulcanization of sulfur-vulcanizable formulations containing a major proportion of vulcanizable unsaturated polymer or copolymer. The utilization of such compositions improves the elastomer vulcanizate properties as compared to the use of similar compositions without the triorganophosphine. DESCRIPTION OF THE PREFERRED EMBODIMENTS The sulfur-vulcanizable elastomer composites in waich improved coupling action according to the present invention can be obtained are those based upon unsaturated polymers and copolymers such as natural rubbers, polyisoprenes, polybutadienes, poly(butadiene-co-styrene), poly(butadieneco-acrylonitrile), poly(isobutylene-co-butadiene), and the like. The preferred sulfur-vulcanizable elastomer composites are those based upon styrene-butadiene copolymers. The polysulfide alkoxy silane coupling agents which can be employed according to the present invention are known as a class and are described, for example in U.S. Patents Nos. 3,842,111, 3,873,489, 4,003,843, and 4,044,037. A preferred variety of these coupling agents is represented by the formula EMI3.1 wherein X represents an alkoxy radical, R' represents an alkyl radical having up to four carbon atoms, y has a value of from 0 to 2 inclusive, R represents a divalent bridging group selected from the group consisting of alkylene and alkyleneoxy radicals having up to seven carbon atoms, n has a value of 0 or 1, p has a value of 0 or 1, Ar represents an aryl radical containing from 6 to 12 carbon atoms, (S)x represents a divalent polysulfide radical each free valence thereof being directly bonded to an aromatic carbon atom of an Ar radical whereby each Ar radical is bonded to another Ar radical through a (S) radical, x has a value of from 2 to 6, a has a value of at least 2, b has a value of at least 1, and the ratio of a to b is a value of not more than 2. Illustrative of this preferred variety of coupling agents are the silanes having the formulae [(CH30)3Si(CH2)3]2[Sx] wherein x has an average value of about 4, [(CH30)3Si(CH2)3)2[S2i, and EMI4.1 where y has an average value of about 3. The latter silane is most preferred. The organophosphines which can be used according to the present invention are those of the formula R1R2R3P, wherein each R represents an organo radical. The preferred organo radicals are alkyl radicals, especially those having up to eight carbon atoms. Exemplary organophosphines include trimethylphosphine, - triethylphosphine, triisopropyl- phosphine, triheptylphosphine, etc. The most preferred organophosphine is tri-n-butylphosphine. The organophosphine additive is conveniently utilized in the form of a dry concentrate. One approach is to stir the organophosphine and water in a lower alkanol,e.g. methanol solvent for a few minutes at room temperature, and then to take up the liquid on a porous inert inorganic solid1 .g. calcium silicate,carrier to form a dry concentrate. The dry concentrate can then be added to sulfur-vulcanizable rubber formulations which contain polysulfide silane coupling agent. Another approach is to stir the polysulfide silane coupling agent as well as the organophosphine and water in a lower alkanol,e.g. methanol,solvent for a few minutes at room temperature, and again to take up the liquid on a porous inert organic solid g. calcium silicate,carrier to for: a dry concentrate. Said dry concentrate can then be added to sulfur-vulcanizable rubber foroula ions. It is believed that the water supplies protons which reduce the polysulfide linkages. The anount of water utilized will be that necessary to obtain the desired rubber curing rate. EXAMPLES The specific examples which follow are illustrative of the principles of the invention. Elastomer Base: A typical elastomer base contains 100 parts by weight of SBE 1502, a styrene-butadiene copolymer (as described in "The Elastomers Manual", International Institute of Synthetic Rubber Producers, 1974 Edition, page 22), 50 parts by weight of precipitated high surface area silica, 8 parts by weight of aromatic hydrocarbon oil, 1.0 parts by weight of tetramethylthiuram monosulfide, 1.5 parts by weight of 2-mercaptobenzothiazole, 2.0 parts by weight of sulfur, 5.0 parts by weight of zinc oxide, 1.0 part by weight of stearic acid, and varying parts by weight of additives according to the present invention. The elastomer base is processed as follows: The SBR 1502 is banded on a two-roll 6" to 12" laboratory 51 C rubber mill at a roll temperature of 1250F and is milled for one minute, dry concentrates according to the present invention are added and dispersed by further milling for about two minutes, half of the silica filler are added followed by the ado ton of the remaining half along with the aromatic hydrocarbon oil, and these components are dispersed by further milling for two to tepee minutes, at which time the remaining (vulcanizing) chemicals is added and dispersed; the mixture so-obtained is from the mill as a sheet and is press-vulcanized at 320 F to form ASTM tensile test sheets Physical tests of the vulcanizate were performed acccrding to standard ASTM test methods. Tensile Modulus: Evidence of action by a coupling agent in a composite is manifested through changes in composite physical property values away from the values displayed by the composite in the absence of the agent. Composite properties which may be favorably altered by coupling agent action are many and varied. For example, in elastomeric composites, the effects of coupling agents are seen in terms of increased tensile modulus and abrasion resistance and in decreased hysteresis losses in flexure. In highly extensible elastomeric composites, the measurement of changes in tensile modulus is a particularly useful way of observing coupling effects and has been used extensively in the experimental work described herein. Tensile modulus is defined here as the tensile stress in pounds per square inch of original cross-sectional area necessary to produce a selected extension in a composite specimen, usually 100%, 2007., or 300% of the unstressed length; these parameters are sually indicated as M100, M200, or M300, resDectively. Example: Silane/Phosphine Additive In this Example, additives compositions as indicated were added to the Elastomer 3ase described above (the values given are in parts per 100 parts 53R '502): EMI7.1 <tb> Additive <SEP> cH3 <SEP> 1 <SEP> 2 <SEP> 3 <tb> r(C2H50)3Si(CH2)2 <SEP> ? <SEP> 0 <SEP> 1.5 <SEP> 1.5 <SEP> 1.5 <tb> Tri-n-butylphosphine <SEP> O <SEP> O <SEP> 0 <SEP> 1.8 <tb> Microporous <SEP> Synthetic <SEP> Calcium <tb> Silicate <SEP> 0 <SEP> 0 <SEP> 3.5 <SEP> 3.5 <tb> Methanol <SEP> O <SEP> 0 <SEP> 3.0 <SEP> 3.0 <tb> Water <SEP> O <SEP> 0 <SEP> 0.2 <SEP> 0.2 <tb> The ASTM test results were ("ppsi" = pounds per square inch): N/cm2 Vulcanizate 1 2 3 4 Hardness (Shore A) 60 60 60 65 86,25 120,75 120,75 155,25 M100 (ppsi) N/cm2 (125) (175) (175) (225) 172,50 345 345 690 M300 (ppsi) N/cm2 (250) (500) (500) (1000) 1518 2139 2070 1518 Tensile (ppsi) N/cm2 (2200) (3100) (3000) (2200) Elongation (7.) 1000 800 800 500 138 207 207 207 C Tear (ppsi) N/cm2 (200) (300) (300) (300) It is evident that the use of an organophosphine according to the present invention results in a significant and unexpected increase in the tensile moduli (e.g., M100 atd M300) of vulcanizates embodying it. Example: Phosphine Additive In this Example, 1.5 parts per 100 parts SBR 1502 of a polysulfide silane coupling agent, EMI8.1 was added to the Elastomer Base described above (except in the Control Run, 1) prior to the addition of the indicated amounts of the other additives (the values given are in parts per 100 parts SBR 1502): Additive 1 2 3 4 5 6 7 Tri-n-butylphos phine 0 0 0.4 0.8 1.2 1.6 2.0 Microporus Syn thetic Calcium 0 0 0.4 0.8 1.2 1.6 2.0 Silicate Methanol O 0 0.38 0.76 1.14 1.52 1.90 Water 0 0 0.01 0.04 0.06 0.08 0.10 The ASTM test results were ("ppsi" = pounds per square inch): N/cm2 Vulcanizate 1 2 3 4 5 6 7 Hardness (Shcre A) 60 65 65 65 65 65 70 86,25 138 155,25 155,25 172,50 189,75 189. M100 (ppsi)N/cm2 (125) (200) (225)(225) (250) (275) (275) 172,50 414 483 552 655,5 621 621 M300 (ppsi)N/cm2 (250) (600) (700) (800) (950) (900) (900) N/cm2 1518 2001 1863 1725 1656 1518 1518 Tensile (ppsi) (2200) (2900) (2700)(2500) (2400) (2200) (2200) Elongation (%) 1000 700 650 600 550 550 550 138 207 207 207 207 207 207 C Tear (ppsi)N/cm2(200) (300) (300 (300) (300) (300) (300) It is again evident that the use of an organo phosphine according to the present invention results in a significant increase in the tensile moduli (e.g., M100 and M300) of vulcanizates embodying it. Various modificaticns and variations of these illustrative Examples will be obvious to those workers skilled in the art. Such modifications and variations are included with the purview of this invention and are encompassed by the scope and spirit of the appended claims.

Claims: WHAT IS CLAIMED IS: 1. A dry concentrate which comprises (I) a triorganophosphine of the formula R1R R3P, wherein each of Rl, R2, and R3 represents an alkyl radical having up to eight carbon atoms, (II) water, (III) lower alkanol, and (IV) porous inert organic solid. 2. A dry concentrate which comprises (I) a polysulfide alkoxysilane coupling agent of the formula EMI11.1 wherein X represents an alkoxy radical, Rl represents an alkyl radical having up to four carbon atoms, y has a value of from 0 to 2 inclusive, R represents a divalent bridging group selected from the group consisting of alkylene and alkyleneoxy radicals having up to seven carbon atoms, n has a value of O or 1, p has a value of O or 1, Ar represents an aryl radical containing from 6 to 12 carbon atoms, (S)x represents a divalent polysulfide radical each free valence thereof being directly bonded to an aromatic carbon atom of an Ar radical whereby each Ar radical is bonded to another Ar radical through a (S) radical, x has a value of from 2 to 6, a has a value of at least 2, b has a value of at least 1, and the ratio of a to b is a value of not more than 2, (II) a triorganophosphine of the formula R1R2R3P, wherein each of R1, * , and R3 represents an alkyl radical having up to eight carbon atomS, (III) water, (IV) lower alkanol, and (V) porous inert organic solid. 3. A composition as in claim 2 wherein the polysulfide silane coupling agent is that of the formula EMI12.1 4. A composition as in clam 1 or 2 in hich the triorganophosphine is that of the formula (n-C4H9) 3P 5. A sulphur vulcanizable formulation which comprises a major proportion of vulcanizable unsaturated polymer or copolymer selected from the group consisting of natural rubbers, polyisoprenes, polybutadienes, poly(isobutylene-co-butadiene), poly(butadiene-coacrylonitrile) and poly(butadiene-co-styrene) and which contains a composition as in claim 1 or 2. 6. A process for preparing a vulcanized rubber which comprises vulcanizing the formulation of claim 5. 7. The product of the process of claim 6.

Inventors: WILLIAMS, THOMAS CHARLES
Applicants: UNION CARBIDE CORPORATION
Application year: 1982
Main classification: C08L21
IPC codes: C08K5, C08L9, C08K7, C08L21, C08L7, C08L33