MXPA99010163A - Composition for tire sidewalls and other rubber constructions - Google Patents

Abstract

Rubber blends of brominated isobutylene/para-methylstyrene copolymers of 9.5 to 20 weight percent aromatic monomer content and 0.2 to 1.0 mole percent benzylic bromine content. The blends have good cure characteristics, good adhesion and flex crack resistance, as well as ozone resistance. The blends are useful in tire sidewalls, and other applications.

Description

COMPOSITION FOR LATERAI-ES WALLS OF TIRES AND OTHER RUBBER CONSTRUCTIONS Field of the Invention The present invention relates to compositions for making sidewalls of tires and other rubber constructions that exhibit improved ozone resistance and improved resistance to fatigue crack propagation, as well as a reduction in staining and discoloration. The composition comprises a physical mixture of halogenated copolymer of isoolefin and para-alkylstyrene of relatively high aromatic co-monomer content and relatively low halogen content with general purpose rubbers (GPR) such as butadiene rubber (BR), natural rubber (NR) ) and / or isoprene rubber (IR). The sidewall of the tire may comprise a single layer or a coating construction wherein an outer layer comprises the physical mixture of the halogenated copolymer with one or more general purpose rubber, and an inner layer may comprise a physical mixture of general purpose rubber. BACKGROUND OF THE INVENTION Rubber tires, such as pneumatic tires, include many components, such as, for example, side walls. The side walls are continuously subjected to distortion under normal operating conditions on the road.

The alternating walls are subjected to extensive continuous bending and may crack under such conditions. In addition to flex cracking, the side walls are also subject to the chemical action of the atmosphere, such as ozone attack. The overall effect is that the side walls can erode and degrade. The side wall can even be separated from the tire casing during use, leading to tire failure. To reduce the problems caused by ozone attack and flex cracking, tire manufacturers add chemical protectors to the general-purpose rubber used in the side walls of tires. The problem with these protectors is that they tend to be fugitive and can cause staining when they are in contact with white sidewalls. In some cases, particularly in white sidewalls, physical blends of polymers have been used to achieve improvements in ozone and flexural strength. The published international application PCT / US91 / 05666, filed on August 9, 1991, discloses a tire sidewall composition comprising a single layer prepared from a physical mixture of a halogenated copolymer of isoolefin and para-alkylstyrene with one or more rubbings of general purposes. U.S. Patent No. 5,376,438 to Costemalle et al. Discloses tire sidewalls of multiple layers having an outer layer prepared from a physical mixture of halogenated copolymer of iso-monoolefin / para-alkylstyrene and rubber from general purposes The inner layer comprises rubber of general purposes. The sidewalls are said to exhibit good ozone resistance and resistance to fatigue cracking, as well as a reduction in staining and discoloration. This patent is incorporated herein by reference in its entirety. In the state of the art, the halogen content of the isoolefin / para-alkylstyrene halogenated copolymers generally varied proportionally with the para-alkylstyrene content, for example a higher content of para-methylstyrene was used to obtain a higher content of halogen. If the copolymer was excessively halogenated, some of the undesirable benzylic dihalo substitution would occur. In this way, an excess of para-methylstyrene was commonly used. In the state-of-the-art tire sidewall compositions, a relatively high level of bromine was needed to achieve adhesion and ozone resistance, but such high levels of bromine led to relatively narrow curing and crack propagation. It would be desirable to be able to use a physical rubber blend of the halogenated isoolefin / para-alkylstyrene copolymer having good adhesion and good ozone resistance, as well as good resistance to flex cracking and good curing properties. SUMMARY OF THE INVENTION It has been found that the use of physical blends of halogenated copolymers of isoolefin and para-alkylstyrene having specific contents of aromatic monomers and halogenation, with general purpose rubbers, results in tire side wall compositions having a resistance to ozone and a resistance to the propagation of fatigue cracks significantly improved. It has now been discovered that excellent curing and crack propagation resistance can be achieved simultaneously with good adhesion and ozone resistance using a relatively low halogenation content in combination with a relatively high aromatic or para-alkylstyrene content. In one aspect, the invention is a physical mixture of rubber and a brominated copolymer of an isoolefin and a para-alkylstyrene. The copolymer comprises at least 9.5, but less than 20% by weight of aromatic monomers (styrenics), and at least 0.2 but less than 1 mol% of para-bromoalkylstyrene. The physical mixture preferably comprises from 35 to 65 phr of the copolymer, and from 35 to 65 phr of the general purpose rubber. The styrenics may include para-alkylstyrene, brominated para-alkylstyrene, alpha-methylstyrene, brominated alpha-methylstyrene, or combinations thereof. The isoolefin is preferably isobutylene, while the para-alkylstyrene is preferably para-methylstyrene and the para-bromoalkylstyrene is preferably para-bromomethylstyrene. The general purpose rubber may be a natural rubber, styrene-butadiene rubber, polybutadiene rubber, and combinations thereof. The copolymer preferably comprises from 12 to 17% by weight of non-brominated styrenics, and from 0.4 to 0.8 mol% of para-bromoalkylstyrene. In another aspect, the invention provides a tire sidewall comprising a layer of the physical mixture described above. The physical mixture can also be used in a sidewall of a coating tire where an outer layer comprises the physical mixture described above and an inner layer comprises a highly unsaturated rubber or physical mixture of unsaturated rubbers. In a further aspect, the invention provides an improvement in a tire sidewall comprising at least one outer layer comprising a physical mixture of a copolymer of an isoolefin and a para-alkylstyrene and an unsaturated rubber, and an inner layer comprising optionally a highly saturated rubber or physical mixture of unsaturated rubbers. The improvement is that the copolymer comprises from 9.5 to 20% by weight of aromatic monomers and from 0.2 to 1.0 mol% of para-bromoalkylstyrene. Preferably, the physical mixture contains amounts of bromoalkylstyrene and para-alkylstyrene that satisfy the following formula: X = [1.91- (0.094 x Y)] + 0.1 where "X" is the molar percentage of bro-alkylstyrene and "Y" is the weight percent para-alkylstyrene (between the proposed limits of 9.5 to 20% by weight). "+0.1", as used herein, indicates that the value X can be any number within the range of 0.1 over 0.1 below [1.91 - (0.094 x Y)]. Bromoalkylstyrene is preferably para-bromomethylstyrene and para-alkylstyrene is preferably para-methylstyrene. More preferably, the physical mixture of the present invention has 0.96 mol% para-bromomethylstyrene and 10% by weight para-methylstyrene. Alternatively, the physical mixture of the present invention preferably has 0.84 mol% para-bromomethylstyrene and 12.5% para-methylstyrene. In the preferred embodiment, the polymerized para-alkylstyrene comonomer unit is characterized by the formula H where R and R1 are independently selected from the group consisting of hydrogen, alkyl groups having from 1 to 5 carbon atoms, and primary and secondary alkyl halides-1-having from 1 to 5 carbon atoms, and X is selected from halogen group consisting mainly of bromine, chlorine and their mixtures. The greater the boiling, the para-alkylstyrene halogenated unit is shown as being pendant from the polymeric isoolefin chain, represented by the wavy lines in the formula. The tire sidewall composition and the layers of the present invention may be compounded by means of the methods generally known in the art, such as mixing with uncured polymers of various fillers, such as titanium dioxide, carbon black, when black side walls, or non-black fillings and pigments are desired; spreaders such as rubber processing oils; cured adjuvants such as zinc oxide, sulfur; accelerators or retarders and other additives, such as anti-oxidants and anti-ozonants. Detailed Description of the Invention The main advantages achieved by the practice of the present invention derive from the fact that by employing a physical mixture of a copolymer of an isoolefin and para-alkylstyrene with general purpose rubbers (GPR), where the copolymer has a low content of halogen but high content of aromatics, superior resistance to ozone and resistance to fatigue cracking of superior bending and adhesion can be achieved at the same time.

The invention, in one embodiment, involves the construction of a multilayer tire side wall, the outer layer of which comprises a physical mixture of a copolymer of an isoolefin and para-alkylstyrene with one or more unsaturated rubbers (GPR). The side wall also comprises one or more layers constructed of conventional side wall compositions such as those discussed in "The Vanderbilt Rubber Handbook," p. 605 (1990). The outer layer of the side wall is made of a physical blend composition comprising at least one highly unsaturated rubber selected from the group consisting of natural rubber, SBR rubber, polyisoprene and polybutadiene rubber; and a halogenated copolymer of an isoolefin and a para-alkylstyrene unit. In a particularly preferred composition useful in side walls of tires, the halogenated copolymer comprises about 35 to 65 parts, for example 40 parts, and the unsaturated rubber desirably comprises from 35 to 65 parts of natural rubber and / or polybutadiene rubber. The physical mixture of the eternal layer may also optionally include from about 1 to about 90, preferably from about 5 to about 20 parts per hundred ethylene-propylene-diene rubber (EPDM). The highly unsaturated rubber component of the outer layer may consist of a physical mixture or a mixture of two or more highly unsaturated rubbers. These optional rubbers can also contain aromatic monomers to improve their compatibility.

When white side walls are desired, particularly preferred outer layer compositions comprise the halogenated para-alkylstyrene copolymer and natural rubber in a weight ratio of para-alkylstyrene halogenated copolymer to natural rubber ranging from about 0.28: 1 to about 3: 1, preferably around 0.67: 1 to about 1: 1. The preferred para-alkylstyrene halogenated copolymer for outer layers of soft side walls preferably comprises about 9.5 to 20, more preferably about 12 to about 17 weight percent para-alkylstyrene moieties and preferably from about 0.2 to about 1.0 mol%, more preferably 0.4 to 0.8 mol%, of para-alkylstyrene halogenated. In a multi-layered construction, the inner layer (s) comprises (s) one or more unsaturated rubbers selected from the group comprising natural rubber, styrene-butadiene rubber, polybutadiene rubber. Typically, such compositions comprise physical mixtures of natural rubber and polybutadiene rubber or physical mixtures of styrene-butadiene rubber and polybutadiene rubber. The inner layer may also comprise fillers such as oils and anti-ozonants and other additives well known in the art. The highly unsaturated rubbers are selected from the group consisting of natural rubbers, polyisoprene rubbers, styrene-butadiene rubber (SBR) and polybutadiene rubber, and mixtures thereof. Natural rubbers are selected from the group consisting of Malaysian rubber such as SMR CV, SMR 5, SMR 10, SMR 20 and SMR 50, and mixtures thereof, where the natural rubbers have a Mooney viscosity at 100 ° C (ML 1 + 4 ) from about 30 to about 120, more preferably from about 40 to about 65. Comparable Indonesian fluids, with SIR prefixes, can also be used. The Mooney viscosity test referred to herein is in accordance with ASTM D-1646. The Mooney viscosity of the polybutadiene rubber, measured at 100 ° C (ML 1 + 4) can vary from about 40 to about 70, more preferably from about 45 to about 65, and most preferably about 50 to about of 60. When both natural rubber and polybutadiene rubber are used, ranges of 100 to 1 to 1 to 100, more preferably 5 to 1 to 1 to 5, and most preferably 2 to 1 to 1 to 2 are suggested. EPDM is the ASTM designation for a terpolymer of ethylene, propylene and an unconjugated diolefin. In such terpolymers, ethylene and propylene form a backbone fully saturated with methylene linkages with the unconjugated diolefin, for example dicyclopentadiene or a substituted norbornene, attached so as to provide unsaturated side chains with readily available crosslinking sites for sulfur curing . EPDM elastomers in a manner contain a fully saturated backbone that provides remarkable resistance to oxidation, ozone and cracking, as well as excellent flexibility at low temperature. The Mooney viscosity of the EPDM terpolymer, measured at 125 ° C, is from about 20 to 80, more preferably from about 25 to 75, and most preferably from about 40 to about 60. The ethylene content of EPDM terpolymers can vary from about 20 to about 90% by weight, preferably from about 30 to about 85, most preferably from about 35 to about 80% by weight. The total content of the diene monomer in the EPDM terpolymers can suitably vary from about 0.1 to about 15% by weight, preferably from about 0.5 to about 12% by weight. The non-conjugated dienes can be straight chain or cyclic hydrocarbon diolefins having from 6 to 15 carbon atoms, such as dicyclopentadiene, including 5-methylene-2-norbornene, 5-vinyl-2-norbornene, 2-methylnorbornadiene, 2, 4-dimethyl-2,7-octadiene, 1,4-hexadiene and 5-ethylidene-2-norbornene. More preferred compounds include 5-methylene-2-norbornene, dicyclopentadiene, 1,4-hexadiene and 5-ethylidene, dicyclopentadiene, 1,4-hexadiene, and 5-ethylidene-2-norbornene. A preferred EPDM terpolymer is Vistalon® 6505, manufactured by Exxon Chemical Company. The term "butyl rubber", as used herein, is intended to refer to a vulcanizable rubberized copolymer containing, by weight, about 85 to 99.5% isoolefin combined having 4 to 8 carbon atoms. Such copolymers and their preparation are well known. The butyl rubber can be halogenated by means known in the art. The Mooney viscosity of the halobutyl rubs useful in the present invention measured at 125 ° C (ML 1 + 4) is from about 20 to about 80, more preferably from about 25 to about 55, and most preferably around 30 to about 50. The suitable halogen-containing copolymers of an iso-monoolefin C4 to C7 and a para-alkylstyrene, for use as a component of the present physical blends and tire sidewall compositions, comprise at least 9.5% by weight of the para-alkylstyrene fraction. For elastomeric copolymer products, the para-alkylstyrene fraction can vary from about 9.5 to about 20% by weight, preferably from about 12 to about 17% by weight of the copolymer. The halogenated content of the copolymers can vary from about 0.2 to about 1.0 mole%, preferably from about 0.4 to about 0.8 mole%. Halogen can be bromine, chlorine, and mixtures thereof. Preferably, the halogen is bromine. The major portion of the halogen is chemically linked to the para-alkyl group, ie the halogen-containing copolymer comprises para-haloalkyl groups. The iso-monoolefin and para-alkylstyrene copolymers useful for preparing the halogen-containing copolymers as a component of the tire sidewall composition of the present invention include iso-monoolefin copolymers having from 4 to 7 carbon atoms and a para-alkylstyrene, such as those described in U.S. Patent No. 5,162,445. The preferred iso-monoolefin comprises isobutylene. The preferred para-alkylstyrene comprises para-methylstyrene. Other aromatic and styrenic monomers, for example alkylstyrenes such as alpha-methylstyrene and meta-methylstyrene, may be employed in place of some para-alkylstyrene, provided that the total aromatic content of the copolymer is in the range of 9.5 to 20. % by weight, preferably 12 to 17% by weight. Of course, sufficient amounts of para-alkylstyrene should be used to obtain the halogenated copolymer with the para-alkyl halogenated groups. Preferably, the physical mixture of the present invention contains amounts of bromoalkylstyrene and para-alkylstyrene satisfying the following formula: X = fl.91- (0.094 x Y)] ± 0.1 where "X" is the molar percentage of bromoalkylstyrene and ??? "is the weight percentage of para-alkylstyrene (between the proposed limits of 9.5 to 20% by weight)." ± 0.1", as used herein, indicates that the value X can be any number within from the range of 0.1 to 0.1 below [1.91 - (0.094 x Y)]. Bromoalkylstyrene is preferably para-bromomethylstyrene and para-alkylstyrene is preferably para-methylstyrene.

More preferably, the physical mixture of the present invention has 0.96 mol% para-bromomethylstyrene and 10% by weight para-methylstyrene. Alternatively, the physical mixture of the present invention preferably has 0.84 mol% para-bromomethylstyrene and 12.5% para-methylstyrene. Suitable copolymers of an iso-monoolefin and a para-alkylstyrene include copolymers having a weight average molecular weight (Mw) of at least about 100,000, preferably at least about 300,000, and a number average molecular weight (Mn) of at least around 100,000. The copolymers preferably also have a heavy to numeric weight average molecular weight ratio, ie Mw / Mn, of less than about 6, preferably less than about 4. The brominated copolymer of isoolefin and para-alkylstyrene obtained by the polymerization of these particular monomers under certain specific polymerization conditions now allows to produce copolymers comprising the direct reaction product (ie, in its form as it is polymerized) and having uniform, unexpectedly homogeneous compositional distributions. In this way, using the polymerization and bromination methods set forth herein, copolymers suitable for the practice of the present invention can be produced. These copolymers, as determined by gel permeation chromatography (GPC), show narrow distributions of molecular weights and substantially homogeneous compositional distributions, or compositional uniformity throughout the range of their compositions. At least about 95% by weight of the copolymer product has a para-alkylstyrene content within about 7% by weight, the average para-alkylstyrene content for the overall composition, and preferably at least about 97% by weight. The weight of the copolymer product has a para-alkylstyrene content within about 7% by weight of the average para-alkylstyrene content for the overall composition. This substantially homogeneous compositional uniformity in this way is particularly related to the inter-compositional distribution. That is, with the specified copolymers, as between any selected molecular weight fraction, the percentage of para-alkylstyrene in it, or the ratio of para-alkylstyrene to isoolefin, will be substantially the same, in the manner indicated above. In addition, since the relative reactivity of para-alkylstyrene with isoolefin, such as isobutylene, is close to one, the inter-compositional distribution of these copolymers will also be substantially homogeneous. That is, these copolymers are essentially random copolymers and in any particular polymer chain, the para-alkylstyrene and isoolefin units will be distributed essentially randomly throughout the chain. The halogen-containing copolymers useful in the practice of the present invention have a substantially homogeneous compositional composition and include the para-alkylstyrene moiety represented by the formula wherein R and R1 are independently selected from the group consisting of hydrogen, alkyl having preferably 1 to 5 carbon atoms, primary haloalkyl, secondary haloalkyl preferably having 1 to 5 carbon atoms, and mixtures thereof, and X is selected from the group consisting of bromine, chlorine and mixtures thereof, as disclosed in U.S. Patent No. 5,162,445, the teachings of which are incorporated by reference. Various methods can be used to produce the copolymers of iso-monoolefin and para-alkylstyrene, as is known in the art. Preferably, the polymerization is carried out continuously in a typical continuous polymerization process using a tank-type reactor with baffles equipped with efficient agitation means such as a turbo or propeller mixer., and drift tube, external cooling jacket and internal cooling coils or other means for removing the polymerization heat, inlet tubes for monomers, catalyst and diluents, temperature sensing means and an overflow of effluent to a holding drum or sudden cooling tank. The reactor is purged of air and moisture and charged with dry, purified solvent, or a mixture of solvents before introducing the monomers and catalysts. Reactors that are typically used in butyl rubber polymerization are generally suitable for use in polymerization reactions to produce the desired para-alkylstyrene copolymers suitable for use in the present invention. The polymerization temperature may vary from about -35 to about -100 ° C, preferably from about -40 to about -80 ° C. The processes for producing the copolymers can be carried out in the form of a polymer slurry formed in the diluents employed, or as a homogeneous solution process. However, the use of a slurry process is preferred, since in that case mixtures of lower viscosity are produced in the reactor and slurry concentrations of up to 40% by weight of the polymer are possible. However, a solution process is preferred for higher levels of PMS. The copolymers of iso-monoolefins and para-alkylstyrene can be produced by mixing iso-monoolefin and para-alkylstyrene in a copolymerization reactor under copolymerization conditions in the presence of a diluent and a Lewis acid catalyst. Typical examples of diluents that may be employed alone or in a mixture include propane, butane, pentane, cyclopentane, hexane, toluene, heptane, isooctane, etc., and various halohydrocarbon solvents which are particularly advantageous herein, including methylene, chloroform, carbon tetrachloride and methyl chloride, with methyl chloride being particularly preferred. An important element for producing the copolymer is the exclusion of the impurities from the polymerization reactor, namely impurities which, if present, will result in the complex formation with the catalyst or the copolymerization with the iso-monoolefins or the para-alkylstyrene. , which in turn will prevent the para-alkylstyrene-useful copolymer product from being produced in the practice of the present invention. More particularly, these impurities include catalyst poisons, moisture and the like. These impurities must be kept out of the system. In producing suitable copolymers, it is preferred that the para-alkylstyrene be at least 95.0% by pure weight, preferably 97.5% by pure weight, most preferably 99.5% by pure weight, that the iso-monoolefin be at least 99.5% by weight. in pure weight, preferably at least 99.8% by pure weight, and that the diluents employed are at least 99% by weight pure, and preferably at least 99.8% by weight pure. The most preferred Lewis acid catalysts are ethyl aluminum dichloride and preferably mixtures of ethyl aluminum dichloride with diethyl aluminum chloride. The amount employed of such catalysts will depend on the desired molecular weight and the desired molecular weight distribution of the copolymer being produced, but will generally vary from about 20 ppm to 1% by weight and preferably from about 0.001 to 0.2% by weight. weight, based on the total amount of the monomer to be polymerized. The halogenation of the polymer can be carried out in the bulk phase (eg, molten phase) or either in solution or in a finely dispersed slurry. The bulk halogenation can be carried out in an extruder, or other internal mixer, suitably modified to provide adequate mixing and for the handling of the halogen and the corrosive by-products of the reaction. The details of such bulk halogenation processes are set forth in U.S. Pat. No. 4, 548,995, which is incorporated herein by reference. Suitable solvents for halogenating solution include hydrocarbons (C4 to C7) and halogenated hydrocarbons of low boiling. As the high boiling point of para-methylstyrene makes its removal by conventional distillation impractical, and since it is difficult to completely avoid the halogenation of the solvent, it is extremely important where halogenation is to be used in solution or slurry than the diluent and halogenation conditions are selected to avoid halogenation of the diluent, and that the residual para-methylstyrene has been reduced to an acceptable level. With halogenation of para-methylstyrene / isobutylene copolymers, it is possible to halogenate the ring carbons, but the products are rather inert and of little interest. However, it is possible to introduce desired halogen functionality into the para-methylstyrene / isobutylene copolymers in high yields and under practical conditions without obtaining excessive polymer breakdown, excessive crosslinking or other undesirable side reactions. It should be noted that the radical bromination of the para-methylstyryl fraction chained in the copolymers useful for the "practice of this invention can be made highly specific with almost exclusive substitution occurring in the para-methyl group, to result in the benzylic bromine functionality. The specificity of the bromination reaction can thus be maintained in a wide range of reaction conditions; however, with the proviso that the factors that would promote the ionic reaction pathway (ie, polar diluents, Friedel-Crafts catalysts, etc.) are avoided. In this manner, solutions of suitable para-methylstyrene / isobutylene copolymers in hydrocarbon solvents such as pentane, hexane or heptane can be selectively brominated using light, heat or selected radical initiators (according to the conditions, i.e. particular radical initiator must be selected, which has a half life appropriate for the particular temperature condition being used, with longer half lives generally preferred at hotter halogenation temperatures) as radical halogenation promoters, to result benzylic bromine functionality desired almost exclusively, via substitution in the para-methyl group, and without appreciable chain cut and / or cross-linking. This reaction can be initiated by the formation of a bromine atom, either photochemically or thermally (with or without the use of sensitizers), or the radical initiator used can be one that preferentially reacts with a bromine molecule rather than one that react indiscriminately with bromine atoms, or solvents or polymer (ie, via hydrogen extraction). The sensitizers referred to are those photochemical sensitizers that themselves absorb photons of lower energy and dissociate, thereby causing in turn dissociation of the bromine, including materials such as iodine. In this way, it is preferred to use an initiator that has a half-life of between about 0.5 and 2,500 minutes under the desired reaction conditions, more preferably about 10 to 300 minutes. The amount of initiator used will usually vary between 0.02 and 1% by weight of the copolymer, preferably between about 0.02 and 0.3%. Preferred initiators are bis azo compounds such as azo bis-isobutyronitrile (AIBN), azo bis (2,4-dimethylvalero) nitrile, azo bis (2-methylbutyryl) nitrile, and the like. Other radical initiators may also be used, but it is preferred to use a radical initiator that is relatively poor in hydrogen extraction, so that it preferentially reacts with the bromine molecules to form bromine atoms more than with the copolymer or solvent to form radicals I rent. In those cases, it would then tend to be the molecular weight loss of the resulting copolymer, and the promotion of undesirable side reactions, such as crosslinking. The radical bromination reaction of the copolymers of para-methylstyrene and isobutylene is highly selective, and almost exclusively produces the desired benzylic bromine functionality. In fact, the only major side reaction that seems to occur is disubstitution in the para-methyl group to result in the di-bromo derivative, but even this does not occur until more than about 60% of the para-methylstyryl chained fractions have been mono-replaced. Therefore, any desired amount of benzylic bromine functionality in the mono-bromine form can be introduced into the aforementioned copolymers to about 60 mol% of the para-methylstyrene content.

Stated differently, the para-methylstyrene content should preferably be at least twice the desired content of para-bromomethylstyrene to avoid di-bromination. It is desirable that the termination reactions be minimized during bromination, so that reactions of long, fast radical chains occur and so that many benzylic bromides are introduced for each start, with a minimum of secondary reactions resulting from the termination. Therefore, the purity of the system is important, and stable-state radical concentrations must be kept low enough to avoid extensive recombination and possible cross-linking. The reactions must also be quenched suddenly once the bromine is consumed, so that the continued production of radicals does not occur with the resulting side reactions (in the absence of bromine). Sudden cooling can be achieved by cooling, turning off the light source, adding dilute caustic soda, the addition of a radical trap, or combinations thereof. As one mole of HBr is produced per mole of bromine reacted with or substituted in the para-methylstyryl chained fraction, it is also desirable to neutralize or otherwise remove this HBr during the reaction, or at least during the recovery of the polymer in order to prevent it from becoming involved in or catalyzing undesirable side reactions. Such neutralizations and removal can be achieved with a caustic post-reaction wash, generally using a molar excess of caustic soda over HBr. Alternatively, neutralization can be achieved by having a particulate base (which is relatively non-reactive with bromine) such as calcium carbonate powder present in dispersed form during the bromination reaction to absorb HBr when produced. The removal of HBr can also be achieved by stripping with an inert gas (eg, N2), preferably at elevated temperatures. Brominated, quenched, and neutralized para-methylstyrene / isobutylene copolymers can be recovered and terminated using conventional means with appropriate stabilizers added to yield functional, highly desirable and versatile saturated copolymers. In sum, the halogenation to produce a copolymer useful in the present invention is preferably achieved by halogenating an isobutylene / para-methylstyrene copolymer using bromine in a solution in normal alkane (e.g., pentane, hexane or heptane), using a initiator bis az, for example AIBN or Vazo® 52: 2, 2 '-azobis (2,4-dimethyl-pentane nitrile), at about 55 to 80 ° C, for a period of time varying from about 4.5 to 30 minutes, followed by a sudden caustic cooling. The halogen content is generally controlled by limiting the amount of reactive halogen. The recovered polymer is washed in basic water and in water / isopropanol washes, recovered, stabilized and dried.

The aromatic halomethyl groups allow for easy crosslinking in a variety of ways, for example, either directly through the halomethyl group or by conversion to other functional groups, as indicated above, to allow the desired crosslinking reactions to be employed. Direct crosslinking can be effected with a variety of polyfunctional groups, as indicated above, to allow employing the desired crosslinking reactions. Direct cross-linking can be carried out with a variety of polyfunctional nucleophilic reagents, such as ammonia, amines or polyamines; metal dicarboxylates; metal dithiolates; Promoted metal oxide (for example, ZnO + zinc and / or dithiocarbamate stearates), etc. The crosslinking can also be carried out via polyalkylation reactions. The aromatic halomethyl groups in this manner provide a wide selection of crosslinking reactions that can be used. Various fillers may also be used in the single layer or outer and / or inner layer physical blend compositions of the present invention., and these include a variety of carbon blacks, silicas, carbonates, oils, resins and waxes. Preferred carbon blacks for use in tire black side wall compositions of this invention include those types designated N339, N774, N660, N351 and N375. Alternatively, they can be used for white sidewalls of filled tires and non-black pigments.

The physical mixtures are cured with conventional curing agents for unsaturated or chlorobutyl rubbers, including sulfur, alkylphenol disulphide, zinc oxide, sulfenamide derivatives, guanidines, benzothiacylbisulfide (MBTS) and mercaptobenzothiazole (MBT). When constructing tires employing the sidewalls of the invention, the sidewalls can be made of the physical blend composition, or the physical blend composition herein can be used as an outer layer or coating on an inner layer. The thickness of the inner and outer layers will vary, depending on the type and size of the tires being manufactured. Typically for passenger car tires, the thickness of the outer layer may vary from about 0.8 to about 2.0 mm. The inner layer may vary from around 1.0 to about 2.0 mm. For example, a tire size 185/60-HR-14 would have a sidewall width of about 95 mm and an overall length of about 1,210 mm. The single-ply or multi-ply tire side wall compositions of the present invention can be vulcanized by subjecting them to heat and / or light or radiation, according to any vulcanization process. The single-ply or multi-ply tire side wall of the present invention can be used as a side wall for motor vehicle tires such as ti-truck tires, bus tires, passenger car tires, motorcycle tires, and similar. Suitable tire sidewall layer compositions can be prepared using conventional mixing techniques, including, for example, kneading, roller mixing, extruder mixing, internal mixing (such as with a Banbury® mixer), etc. The mixing sequence and the temperatures used are well known to the technicians in the formation of rubbers, the objective being the dispersion of fillers, activators and curatives in the polymeric matrix without excessive heat accumulation. A useful mixing method uses a Banbury mixer in which the rubber components, fillers and plasticizer are added and the composition mixed for the desired time at a particular temperature to achieve adequate dispersion of the ingredients. Alternatively, the rubbers and a portion of the fillings (for example, a third to two thirds) are mixed for a short time (for example, around 1 to 3 minutes), followed by the rest of the fillings and oil. The mixing is continued for about 5 to 10 minutes at a high rotor speed during which the mixed components reach a temperature of about 150 ° C. After cooling, the components are mixed in a second step in a rubber mill or in a Banbury mixer, during which the curing agent and the optional accelerator are dispersed intensively and uniformly at a relatively low temperature, for example around 80 at around 105 ° C. Variations in mixing will be apparent to those skilled in the art and the present invention is not limited to any specific mixing procedure. The mixing is carried out to disperse all the components of the composition intensively and uniformly. The tires are generally constructed on a drum from at least three layers, namely an outer layer comprising a tread portion and side walls comprising the inner and outer layers of this invention, an intermediate layer, and a lining internal. After the uncured pneumatic tire has been built on the construction drum, the uncured tire can be placed in a hot mold to shape and heat it to vulcanization temperatures and, thereby, produce a unitary, cured tire, from multiple layers. The vulcanization of the molded tire, typically, is carried out in hot presses under conditions well known to those skilled in the art. The curing time will be affected by the thickness of the tire to be molded and the concentration and type of curing agent, as well as the halogen content of the halogenated copolymer. However, the vulcanization parameters can be easily established with a few experiments using, for example, a laboratory characterization device well known in the art, the Monsanto oscillating disc curing rheometer (ODR, described in detail in American Society for Testing and Materials, ASTM D 2084). Tires produced in accordance with the present invention offer tires with black or white side walls "improved adhesion and ozone resistance characteristics, as well as good curing and good resistance to flex cracking." In the present tire, using the halogenated copolymer in The sidewall of the tire, or only in the outer layer, is achieved good resistance to ozone.In addition, the outer layer acts as a barrier that prevents the migration of additives in protectors from the inner layer to the outside, thus eliminating the problem of staining and discoloration discussed above The following examples are presented to illustrate the invention: All parts and all percentages herein are by weight, unless otherwise indicated.

TABLE 1 Test compositions were combined using three pass mixing conditions to physically mix the master filler components and curing additives listed in Table 2. The compositions were cured at 150 ° C (18 minutes for stress and fatigue tests; 21 minutes for Demattia bending tests and outdoors), and 175 ° C (11 minutes for stress and fatigue tests, 14 minutes for Demattia flexion tests and outdoors).

TABLE 2 The test compositions (IA to H) were tested for curing characteristics, tensile strength, flexural fatigue, adhesion and ozone resistance. The results are presented in Table 3 below. The following descriptors are used in it to refer to ISO cracking types and qualifications: Descriptor Excel Meaning. No cracking Good Edge cracking only Regular Minor or major cracking Poor Deep cracking, tearing or separation 0 No cracking 1 Minor cracking 2 Major cracking 3 Deep cracking 4 Tearing 5 Separation 6 Edge cracking TABLE 3 -3d Physical mixtures ID at 1H exhibited curing characteristics similar to physical mixtures IA, IB and 1C, and similar tensile properties. The physical mixtures ID and 1F had better resistance to fatigue to failure and propagation of cracks by bending, and a comparable resistance to ozone. EXAMPLE 2 Physical mixtures of rubber with a high bromine copolymer, low para-methylstyrene, and a low bromine copolymer, high para-methylstyrene, were prepared in varying proportions. The high bromine, low para-methylstyrene copolymer was Exxpro 93-4 copolymer, comprising 7.5% by weight of para-methylstyrene and 1.2% molar of benzylic bromine. It had a Mooney viscosity ML (1 + 8) at 125 ° C of 38 ± 5. The low bromine, high para-methylstyrene copolymer (copolymer 2) comprised 13.6% by weight of para-methylstyrene and 0.56% molar of benzylic bromine ( 0.78% by weight of bromine). It had a Mooney viscosity ML (1 + 8) at 125 ° C of 37 + 5. The physical mixtures were combined as described in Example 1 and cured at 180 ° C for 15 minutes. The physical mixtures had the compositions of Table 4.

TABLE 4 15 20 D • * The physical mixtures were evaluated in terms of curing characteristics and hardness properties, resistance to the propagation of cracks due to bending, strain fatigue to failure, static and dynamic resistance to ozone, and resistance to bending in exteriors. The results are presented in Table 5, using the same meanings of descriptors as in Table 3.

TABLE 5 fifteen 25 or 10 fifteen 25 15 20 15 20 fifteen 25 These results show that the physical mixtures with the copolymer 2 had comparable or slightly better cure characteristics than the physical mixtures with Exxpro 93-4, better tensile properties, comparable hardness, resistance to the propagation of cracks by substantially better bending, better fatigue to failure, and better static and dynamic resistance to ozone. EXAMPLE 3 Master charges of brominated copolymers of isobutylene / para-methylstyrene of varying bromination level, variable co-monomer content and variable molecular weight were prepared. The copolymers had the properties listed in Table 6. TABLE 6 The test compositions were combined to physically mix the components of the masterbatch and curing additives listed in Table 7. Three-pass mixing conditions were used for samples 1W, 1Z and 1Y. Two-pass mixing conditions were used for sample 1Z. Budene 1207 is a branded butadiene rubber available from Goodyear. Flexon 641 is a naphthenic oil of petroleum. Flexon 815 is a petroleum paraffinic oil.

TABLE 7 The test compositions (1W to 1Z) were tested for curing characteristics, tensile strength, flex fatigue, adhesion and ozone resistance. The results are presented in Table 8.

TABLE 8 Physical mixtures IX and 1Y exhibited superior flexural strength in exteriors and ozone over physical mixtures 1 and 1Z. The test compositions (1W to 1Z) were used to coat the sides of the tires. Tests were conducted on the tires to measure wear and ozone resistance. The results are presented in Table 9. TABLE 9 Physical mixtures IX and 1Y exhibited wear characteristics superior to physical mixtures 1W and 1Z. Physical mixtures IX and 1Y also exhibited superior ozone resistance over the 1W and 1Z physical mixtures.

Claims (5)

1. CLAIMS 1. A free physical mixture of hydrazide compounds, the physical mixture comprising rubber and a copolymer of isoolefin, para-alkylstyrene and bromo-alkylstyrene, wherein the copolymer comprises more than 9.5 but less than 20% by weight of styrenics, comprising alkylstyrene, brominated para-alkylstyrene, alpha-methylstyrene, brominated alpha-methylstyrene.
2. 2. The physical mixture of claim 1, wherein the copolymer comprises from 35 to 65 parts by weight per hundred of total rubber.
3. 3. The physical mixture of claim 1, wherein the isoolefin is isobutylene and the bromo-alkylstyrene is para-bromomethylstyrene.
4. 4. The physical mixture of claim 1, wherein the rubber is selected from the group consisting of natural rubber, styrene-butadiene rubber, polybutadiene rubber, polyisoprene rubber, and combinations thereof. The physical blend of claim 1, wherein the copolymer comprises from 12.0 to 17.0% by weight of aromatic monomer and from 0.4 to 0.8% molar of bromo-alkylstyrene. 6. A physical mixture of 35 to 65 parts by weight of a rubber selected from the group consisting of natural rubber, styrene-butadiene rubber, polybutadiene rubber, polyisoprene rubber, and combinations thereof, and from 35 to 65 parts by weight of a copolymer of isobutylene, of more than 9.5 to 20% by weight para-methylstyrene and 0.2 to 1% molar of para-bromomethylstyrene. The physical mixture of claim 6, wherein the copolymer comprises from 12.0 to 17.0 wt% of para-methylstyrene and from 0.4 to 0.8 mol% of para-bromomethylstyrene. 8. A pneumatic tire side wall, comprising the physical mixture of claim 1. 9. A pneumatic tire sidewall, comprising: (a) an outer layer comprising the physical mixture of claim 1; and (b) an inner layer comprising a highly unsaturated rubber or physical mixture of unsaturated rubbers. 10. A multi-ply pneumatic tire side wall, comprising: (a) an outer layer comprising a physical mixture of an unsaturated rubber and a copolymer of an isoolefin and a para-alkylstyrene __; __; and (b) an inner layer that optionally comprises a highly unsaturated rubber or physical mixture of unsaturated rubbers, wherein the copolymer comprises more than 9.5 to 20% by weight of aromatic monomers and 0.2 to 1.0 mol% of para-bromoalkylstyrene. 11. The physical mixture of claim 1, wherein the amounts of said bromoalkylstyrene and said para-alkylstyrene meet the following formula: X = [1.91 - (0.094 x Y)] + 0.1 where "X" is the molar percentage of bromo-alkylstyrene and "Y" is the weight percent para-alkylstyrene between the limits of 9.5 to 20% by weight. The physical mixture of claim 11, wherein said bromoalkylstyrene is para-bromomethylstyrene and said para-alkylstyrene is para-methylstyrene. The physical mixture of claim 12, wherein the molar percentage of para-bromomethylstyrene is 0.96 and the molar percentage of para-methylstyrene is 10. 14. The physical mixture of claim 12, wherein the molar percentage of para-bromomethylstyrene is 0.84 and the weight percent para-methylstyrene is 12.
5. 5.