Field of the Invention This invention relates to an improved amine antidegradant system for highly unsaturated polymers, e.g., natural or synthetic rubbers or elastomers, a process for its manufacture, and to its use to prevent flex cracking and heat aging while achieving substantially reduced migration staining.

Background of the Invention It is well known that ozone/oxygen causes surface cracking of conventional highly unsaturated rubber vulcanizates when the rubber is subjected to repeated flexing in an oxygen environment. The most severe deterioration occurs when a small number of cracks are formed which grow rapidly into deep, disruptive fissures. These cracks seriously shorten the serviceable life of the article. Chemical antidegradants have been developed which retard the formation of the oxygen cracks occurring under static and dynamic conditions. Examples of antidegradants in common use include: diarylamines, e.g., various alkylated diphenylamines, p-phenylene diamines, and dihydroquinolines.

The use of these well known amines has improved oxygen protection under both static and dynamic conditions, however, even the best of the class just described have a very strong tendency to both stain and discolor. The term "stain" or "staining" is herein used to describe the characteristic of a material to diffuse through a polymeric substrate and discolor the adjacent surface. This diffusion staining is highly objectionable in most light colored rubber articles. In tires the tendency towards diffusion staining of the aforementioned a ine antidegradant materials is objectionable particularly in white sidewall type tires. Even in non-white sidewall type tires, the tendency of the materials to diffuse to the surface of the tire sidewall can be objectionable in that a brown, dull surface is created on the tire sidewall. This is aesthetically objectionable and detracts from the general jet black, smooth appearance of a new tire. In a white sidewall tire, the migration of the brown discoloring material into the white sidewall is highly objectionable and difficult to remove by cleaning of the tire surface.

Waxes have been utilized to inhibit cracking in articles under stress in static conditions by incorporating the wax into the rubber compound prior to vulcanization. The wax functions by migrating to the surface of the rubber article to form a film which acts

-3- as a physical barrier to the oxygen attack. However, during dynamic flexing in service the wax film is cracked or disrupted and there is a tendency for the article to exhibit fewer and more severe oxygen cracks than if no wax had been incorporated. Therefore, for many service conditions, wax is not effective due to the dynamic conditions under which the article is expected to perform.

With the advent of the radial tire and high-speed conveyor belt, there has been an increase in the demand for improvement in the flex cracking resistance and heat aging resistance of these rubber products.

The polymerized reaction product of aniline and acetone, poly(l,2-dihydro-2,2,4-trimethyl quinoline) , is still widely used for oxygen aging resistance, not only because of its relatively low cost, but because of its wide availability. However, this material is a "staining" antidegradant.

The reaction product of diphenylamine and acetone is also widely used in rubber for flexing resistance and heat aging. This material is also a staining antidegradant. It would be very desirable to have an antidegradant which would not only reduce migration staining tendencies, but would also maintain both excellent flex cracking resistance and heat aging resistance.

The use of both substituted 1,2-dihydroquinolines

and diarylamines as antidegradants are known, each individually as well as in various combinations. In U.S. 4,158,000 to Nagasaki et al. a mixture of 2,2,4-trimethyl-l,2-dihydroquinoline monomer, a dimer thereof and more highly polymerized products of said dimer are used to prevent heat aging and flex cracking of rubber. This antidegradant is well established and commonly used in rubber compounding and is available under the trade mark Naugard™ Q from Uniroyal Chemical Company. Similarly, BLE-25 ^W is listed as an antioxidant in the above-mentioned handbook and is a trade mark of Uniroyal Chemical Company. This material is the high temperature reaction product of diphenylamine and acetone. Combinations of the above antidegradants have been made in various attempts to maximize the benefits while minimizing the drawbacks of each. An example of this is taught in U.S. 4,247,664 to Parker in which polymerized 2,2,4-trimethyl-l,2-dihydroquinoline is combined with a polyvinyl aromatic olefin to maintain the antioxidant qualities while minimizing its staining tendencies. Similarly U.S. patent 2,955,100 to Hill et al. relates to increasing effectiveness of amine antioxidants by reacting diarylamine antioxidants with l,2-dihydro-2,2,4-trimethylquinolines substituted in the 6 position by an alkyl, aryl or lower alkoxy group with

an aliphatic amine or mixed aliphatic aromatic monoamine. The combination is claimed to have a synergistic effect against aging and exposure cracking. In U.S. 2,400,500 to Gibbs, alkyl-substituted 1,2-dihydroquinolines are reacted with diarylamines. However, this is not similar to the reaction of the instant invention in that the 1,2-dihydroquinoline in Gibbs was a pure monomer reacting as an olefin with a diaryl amine to form a substituted tetra hydroquinoline antioxidant.

It is an object of the present invention to provided an antidegradant material which is highly effective in protecting highly unsaturated polymer substrates from ozone and oxygen attack. A further object is to ensure flexibility in a dynamic condition, and under conditions of extended use at elevated temperatures. Yet another object is to produce a compound which diffuses slowly and does not produce migration staining or objectionable brown bloom and provides improved peroxide scavenging in rubber compounds.

Description of the Invention It has been discovered that the reaction product of an aromatic primary amine and a dialkyl ketone with known antidegradants for rubber shows unexpected reduction or prevention of staining migration tendencies of the antidegradant while maintaining both excellent flex cracking and heat aging properties.

SUBSTITUTE SHEET

This invention is concerned with the preparation of novel antidegradants by the reaction of a first component which comprises a known antioxidant comprising the reaction product of a diarylamine and a dialkyl ketone with a second component comprising at least one primary aromatic amine and at least one dialkyl ketone. The present invention further relates to compositions of highly unsaturated polymers containing the novel antidegradants and a method of preventing flex cracking and heating aging of highly unsaturated polymers by adding the novel antidegradants thereto as well as articles made of highly unsaturated rubber vulcanizates containing the present antidegradant. Such articles are, for example, tires or conveyor belts. The antidegradant produced by this reaction process provides a maximization of the qualities of known antidegradants.

The known antioxidant first component and the other reactants second component may be present in ratios ranging from 10 to 90% of each component. Preferred ratios of the two components can range from 30-70% of each while the most preferred ratio is from 60-40% of each component.

The present antidegradants are most advantageously utilized to protect highly unsaturated polymers such as natural or synthetic elastomers or rubbers. Preferred such polymers are highly unsaturated. rubbers including natural rubber, cis-polyisoprene polybutadiene.

styrene-butadiene copolymers, polychloroprene, and acrylonitrile-butadiene copolymers and in blends with EPDM rubbers. Most preferred are formulations with natural rubber. The highly unsaturated polymers to be protected may be formulated in a conventional manner with the usual compounding ingredients for example, vulcanizing agents, accelerators, activators, retarders, antiozonants, plasticizing oils and softeners, fillers, reinforcing pigments and carbon blacks.

The antidegradant system of the present invention can be most advantageously used in a tire as a component of any or all of the thermosetting rubber-containing portions of the tire. These include the tread, sidewall and carcass portions of a truck,passenger or off-road vehicle tire which additionally contain many different reinforcing layers therein. These components typically contain more than one thermosetting rubber polymer in a blend which must be protected from oxidative attack. The method of incorporating the instant antidegradant into the tire are conventional and well known.

Unsaturated polymers may be optionally protected against both oxidative and ozone degradation by blending the antidegradant of the present invention with conventional antidegradants. For example, many classes of compounds function as antidegradants. 1982 Index of Commercial Antioxidants and Antiozonants, 3rd. Edition

SUBSTITUTE SHEET

published by the Goodyear Tire and Rubber Company lists materials commonly viewed as materials having antidegradant properties, and is incorporated herein by reference. Optimal levels of addition (PHR) for the antidegradants can be easily determined through routine experimentation and may vary widely depending upon the end use application.

The antidegradants of the instant invention may be added to an unsaturated polymer at a level of from 0.25 to about 6 parts by weight per hundred parts by weight of the unsaturated polymer (rubber hydrocarbon) (hereinafter PHR) . A more preferred addition level is from about 0.3 to about 5 parts PHR. The most preferred level is from about 0.5 to about 3 parts PHR. When the antidegradants of the invention are used in combination with other antidegradants, they may be added in a blend which totals to the ranges set forth above.

The antidegradants discussed for comparative and prior art purposes are well known to those skilled in the art. The diaryl amine/acetone condensate is superior to polymerized 1,2-dihydroquinoline promoting flexing, while the latter is superior to the former in resisting oxygen aging. While both are staining antidegradants, the diarylamine/acetone condensate is more so and has a higher migration staining tendency. The antidegradants of interest in this invention reduce or prevent staining tendencies, improve the

oxygen and heat aging, and do not suffer a reduction in flexural properties. A further advantage of the instant antidegradants is a cost savings realized by using one antidegradant ingredient rather than the need to use several additives. The antidegradants of this invention are solids which promotes ease of use. The present antidegradants are especially useful in passenger car tires, where staining of white sidewall tires is a severe problem and preventing degradation is a definite safety concern.

The diarylamine/dialkyl ketone reaction products, which are one of the starting materials used to prepare the present antidegradants, are known and are described in U.S. patent 1,915,108 to Ter Horst. The disclosure of Ter Horst is incorporated herein by reference. Ter Horst describes combining dialkyl ketone and secondary aromatic amines, specifically diphenylamine and acetone, with iodine catalyst at 220°C for 20 hours in an autoclave with or without agitation. The reaction time may be shortened by increasing the amount of iodine.

Amongst the dialkyl ketones which can preferably be used in the present invention for the preparation of this reaction component are those in which the alkyl groups of the ketone each independently contain from 1 to 4 carbon atoms. Examples of such ketones include acetone, methylethylketone, methylpropylketone, diethylketone and methylbutyl ketone. The diarylamines which may be used

include among others, diphenylamine, phenyl-alpha- naphthylamine, the ditolylamines, the phenyltolylamines, the dinaphthyl- amines, anilino tetraphenylmethane, dianilinodiphenylmethane, p-hydroxydiphenylamine, p-amino-diphenylamine, N,N'-diphenyl-p-phenylenediamine, anilino-biphenylene oxide, anilino acridine, 6-anilino-quinoline, p-chlorodiphenylamine, p-isopropoxydiphenylamine, phenylindanylamine, indanyl-alpha-naphthylamine, diindanylamine, and the like. A preferred diarylamine is diphenylamine.

In the preferred method of preparing the instant antidegradants, a primary aromatic amine is added to the diarylamine/dialkylketone reaction product and these components are reacted with an excess of a dialkyl ketone. Typical primary aromatic amines which can be employed include unsubstituted and substituted anilines, unsubstituted and substituted, and naphthylamines, unsubstituted and substituted o, m, and p-toluidines, and unsubstituted or substituted xylidenes. The dialkyl ketones which can be used are the same ketones as used in the preparation of the diarylamine/dialkyl ketone reaction products herein above.

The reaction is carried out in the presence of an acidic condensation catalyst. Among suitable catalysts are hydrogen chloride, phosphoric acid, sulphuric acid.

^SU B ^STI TUTESHEE _T

zinc chloride, aluminum chloride, boron trifluoride, hydrofluoric acid, stannic chloride, iodine and the like. In general, any of the well-known acidic condensation catalysts may be employed, that is, compounds which are strong acids, or which produce acids upon hydrolysis or upon contact with organic materials.

The reaction can usually be carried out at a temperature of from about 50° to 300°C. and at either atmospheric or elevated pressure, depending upon the reactants used. The relative proportion of the reactants employed is not critical, although it has found that the dialkyl ketone be desirably used in excess of the stoichiometric amount and it then serves as a solvent or medium for the reaction. The following examples are representative of the procedures used to synthesize the antidegradants of this invention. It is not meant to be limiting in any way and is representative of the procedure used to make other possible ratios. Example 1

448 grams of aniline, 448 grams of acetone- diphenylamine reaction product and 480 grams of 32 weight percent HC1 were charged to a reactor with the agitator set at 500 rpm. 538 grams of xylene were charged to the still reboiler, allowing the recycle line to the reactor to fill up. 326.5 grams of water was

distilled from the aqueous HC1 charge. After this distillation, 648 grams of acetone were charged to two acetone pumps which was activated at 8.4 ml/min. The reaction is carried out at a temperature of 148-150°C, and the recycled acetone was charged for 5-1/2 hours. The reaction mass was held for 1/2 hour at 150°C to drive off traces of acetone, then cooled to 105-110°C and transferred to the polymerization reactor.

The following materials were charged to the polymerizer along with the monomer just described:

147.6 grams of xylene, 467.5 grams of 32 weight % HC1. The latter was heated at 115-120°C for 3-5 hours during which time water was distilled off, then cooled to 95°. The following were added, under agitation: 492 grams of xylene, 1312 grams of hot (90°C) water, and enough 50% caustic to get pH 7-9 (250-260 grams). The mixture was then agitated for 1/2 hour, allowed to settled for 1/2 hour, and then the layer was separated and discarded. The reaction mass was then washed with 1312 grams of hot (95°C) water, agitated for 1/2 hour and allowed to settle for 1/2 hour. The wash water was separated and discarded.

The reaction mass was transferred to a stripper and then, applying full vacuum (120 mm Hg) stripped at 150°C to remove water, xylene, and any traces of aniline.

After this distillation was over, the batch was steam stripped at the same temperature and pressure conditions

for 3 hours. The batch was then vacuum σ jed at 150°C, less than 100mm Hg for one hour. The molten product was poured into aluminum pans to cool, and can be flaked when solidified. An antidegradant according to the present invention was tested in a formulation of a natural rubber trend stock using 1.0 phr of the antidegradant. The antidegradant was incorporated in the initial Banbury mix. The sulfur and MOR accelerator were added in a second Banbury mix. The stocks were cured at 300° and 320°F using an optimum and an overcure time. A typical recipe is as follows:

Components Parts by Wt.

Natural Rubber 100.00

Zinc Oxide 3.50

Carbon Black 45.00

Stearic Acid 2.00

Compound of Example 1 1.00 Naphthenic Oil 4.00

The above was mixed in a Banbury mixer at #2 speed, water on full to which was added the natural rubber, zinc oxide, antioxidant, and half the carbon black. Then the other half of carbon black, stearic acid, and processing oil was added. The mixture was dumped at 310°F.

The resulting product was further compounded with

2-(morpholinothio) benzothiazole (DELAC MOR™) accelerator 0.60 phr and sulfur (2.50 phr) to a Banbury at #1 speed with water on full to a maximum temperature of 195°F. Similar recipes using no antidegradants, and the standard antidegradants (poly(l,2-dihydro-2,2, 4-trimethyl quinoline) , (BLE 25 ^,M ) were also compounded for comparison purposes. It was found that when added separately to a natural rubber tread stock, the antidegradant of instant example 1 gives an improvement in oxygen resistance, flexing and heat aging over BLE-25™ alone. The staining migration of rubber compounds using the antidegradant of example 1 is significantly reduced as compared to the individual components, thus providing another useful and unexpected advantage.

Tables 1 and 2 contain the data indicative of the superior performance of the instant antidegradants as compared to the current antidegradant in common use, BLE-25™. Samples were also run using no antidegradant for comparative purposes.

The test formulation was compounded, mixed and cured into flat test sheets for subsequent analysis of discoloration and staining characteristics. The specific testing was conducted in accordance with

ASTM-D925-83 Method C. Method C judges the degree of staining tendency of material by determining the amount of discoloration that occurs from the substrate material

througk a white lacquer coating which has been placed on the test sample. The test formulation previously set forth for all test samples of the invention was utilized. Once the test specimen was mixed and cured, it was coated with a veneer of white lacquer in accordance with the ASTM-D925 procedure. It was then exposed to a sunlamp light source in a suitable test changer for a specified period of time. The Hunter Lab Colorimeter test apparatus was utilized to objectively determine the change in the color of the white lacquer during the four-hour exposure to the sun lamp. ASTM D2244-79 titled "Color Differences of Opaque Materials", reports a number of characteristics by the standard difference letters a, b, and L. The samples with no antidegradant have the highest L values and are therefore whiter since no staining material was present. However, the data below show that the samples formulated with antidegradant of the instant invention are whiter than those formulated with a standard antidegradant.

TABLE 1

HUNTER COLOR "L" READINGS ON WHITE DITZLER 8000 LACQUER COATINGS ON CURED STOCK

BLE-25™ Example STD 1

90 . 09 90 . 08

88 . 69 89 . 14

80 . 14 86 . 89

The antidegradants that are the subject of this invention are also superior to the standard antidegradants in common use by maintaining excellent flex cracking resistance when compounded in rubber. The following data show the flexing rating after 48 hours oxygen aging at 70°C and the flexing rating after 48 hours at 100°C aging using the ASTM Method D4482-85 entitled "Standard Test Method for Rubber Property- Extension Cycling Fatigue". The samples were prepared as discussed previously. Descriptions of the test methods used can be found in ASTM methods D572-88 entitled "Standard Test Method for Rubber-Deterioration by Heat and Oxygen", D573-88 entitled "Standard Test

Method for Rubber - Deterioration in an Air Oven". In Table 2, the value assigned to the BLE-25™ sample, which may be considered an industry standard, has arbitrarily been assigned the value 100. The values for samples with no antidegradant, with poly

(l,2-dihydro-2,2,4-trimethyl quinoline) alone and with the subject of this invention are compared to this standard.

TABLE 2

*Poly (l,2-dihydro-2,2,4-trimethyl quinoline)

The properties Of the subject of this invention are shown in the above tabulations to be superior in overall antidegradant properties to the widely used and commercially available antioxidants.

HPLC testing was conducted in order to demonstrate the present antidegradants are reaction products which are distinct from the reactants used in their formation. HPLC data shown in Table 3 demonstrates that the antidegradants of this invention are unique and structurally distinct from its reactant components.

This is evidenced by the HPLC retention times and area percents shown for various peaks for the antidegradants of this invention and BLE-25™.

The examples included with HPLC data can be defined as follows: Example 1, previously discussed, is the reaction product of a 50:50 molar ratio of BLE-25™ (reactant 1) and aniline (reactant 2) and acetone (reactant 3). Instant Example 2 is the reaction product of a 60:40 molar ratio of reactant 1 to reactant 2 and acetone, and instant Example 3 is an antidegradant in which the reactant ratio of reactant 1 and reactant 2 plus acetone is 70:40.

HPLC Conditions HPLC: Hewlett-Packard 1090 Column: Waters uBondapak C-18 10 micron,

4.2 x 300 mm Detection: Dual Wavelength UV @ 234 nm Eluent: A: 0.0025M Tetrabutylammonium Phosphate in

Water B: Acetonitrile

Gradient: 45% B to 100% B in 30 minutes

TABLE 3

Table 3 shows retention time (in minutes) and the area percent for each HPLC peak:

The chromatographic data shown in Table 3 shows that the present antidegradants of examples 1 through 3 had in common, peaks 1, 3, 4, 5, 6 and 12. However, the respective peak heights in each instance for the present invention are quite different from the heights of the peak for BLE-25™. BLE-25 ^,M did not give any peaks corresponding to peaks 7, 8, 9, 10 and 11 of examples

1, 2 and 3 (the present antidegradants) . The major peaks for BLE-25™ were peaks 1, 3, 4 and 5 while the corresponding peaks for the present antidegradants were only minor contributors to their HPLCs. On the other hand, the major HPLC peaks of the present antidegradants were 6 and 10. BLE-25™ had no peak corresponding to peak 10 and peak 6 of BLE-25™ HPLC was only a minor contributor to the overall chromotograph. The HPLC clearly shows the structural distinctness of the instant antidegradants.

The various aspects of the invention illustratively disclosed herein may be practiced in the absence of any composition or step in a method which is not specifically disclosed herein. Further, in view of the many changes and modifications that may be made without departing from principles underlying the invention, reference should be made to the appended claims for an understanding of the scope ϋf. the protection afforded the invention.