WO2000022015A1

WO2000022015A1 - Elastomeric polymer vehicle parts having improved low-temperature compression set

Info

Publication number: WO2000022015A1
Application number: PCT/US1999/022091
Authority: WO
Inventors: Ron Liotta; Periagaram S. Ravishankar
Original assignee: Exxon Chemical Patents Inc.
Priority date: 1998-10-09
Filing date: 1999-09-23
Publication date: 2000-04-20
Also published as: WO2000022015A9; JP2002527546A; AU4844799A; EP1121385A1; WO2000022014A1; KR20010075609A; AU6058999A

Abstract

Motor vehicle parts based on an ethylene, alpha-olefin, diene monomer elastomeric polymers exhibit excellent low temperature compression set. Previously, such compression set performance in the amorphous region was believed to be non-responsive to ethylene content once the amorphous region was reached. However, within certain ranges, ethylene content has been shown to have an effect on low temperature compression set even in the amorphous region. These motor vehicle parts are particularly useful where extremes of ambient temperatures maybe incurred. In a preferred embodiment, the invention is a vehicle part, such a brake part or belt including an ethylene, α-olefin, diene elastomeric polymer. The elastomeric polymer has a low ethylene content, and the vehicle part made from a compound based on the elastomeric polymer will have improved low temperature compression set. The vehicle part comprises the elastomeric polymer where the polymer has ethylene present in the range of from 50-60 mole percent, ethyldiene norbornene present in the range of from 0.2-5 mole percent and an α-olefin, selected from propylene, hexene-1 and octene-1, where the α-olefin makes up the remainder of the elastomeric polymer. The ethylene composition distribution of the elastomeric polymer is such that the ethylene in 90 % of the polymer fractions varies by no more than ± 4 % by weight. The Mw/Mn will be in the range of 2-4, the inherent viscosity in the range of 1.2-3.2 and the Mooney Viscosity (1+4) @ 125 °C in the range of from 10-80. The vehicle part will have an instantaneous compression set at -40 °C, less than 80 %.

Description

APPLICATION FOR U.S. PATENT

ELASTOMERIC POLYMER VEHICLE PARTS HAVING IMPROVED LOW-TEMPERATURE COMPRESSION SET

TECHNICAL FIELD

Embodiments of the present invention generally pertain to the field of molded or extruded elastomeric vehicle parts. More particularly, the present invention is directed to vehicle parts utilizing elastomeric polymer compounds displaying improved cold compression set. These elastomeric polymers are generally of the ethylene, alpha-olefin, ethylidene-norbornene type.

BACKGROUND

In recent years vehicle part performance requirements have been changing as the need for higher performance for longer periods of time becomes the norm. Additionally, as vehicle production is increasingly targeted to a global market, extremes of performance, as might be related to location in the world, become more important. As an example, in Northern latitudes, extreme low ambient temperatures will be experienced by majority of the components in the automobile. At those low temperatures, the rubber parts must retain much of their original flexibility to insure correct function. As for example, a vehicle part such as a brake seal, might be held in a compression mode while the engine is off. After an extended period at very low ambient temperature conditions, and upon startup, the part will be required to hold its seal. Upon starting and after warm-up, the engine compartment temperature, will be substantially the same in most latitudes. Accordingly, the low temperature performance specification for most automobile parts is generally fixed by the most extreme ambient conditions, while the high temperature specification usually is fixed by the running temperature of the engine or the service conditions of the part. The engine compartment temperature may reach 120° C and often may reach 140° C or even 150° C, generally when the vehicle stops after operation and no cooling is exerted from the outside air flow as would be experienced during moving operation. Such temperature extremes (high and low), whether endured for a relatively short period of time such as in daily vehicle use, or especially, endured for long periods during the vehicle life, put additional stress or demands upon all parts in an engine compartment. Elastomeric compounds for engine compartment use must first function at these temperatures and further must retain a useful life over all or a majority part of the vehicular life which may extend to 10 years or more than two hundred thousand miles.

It is these low temperatures that provide the most substantial challenge to rubber compounders and elastomeric polymer manufacturers as they attempt to meet the requirements of the auto part and auto manufacturer. Good low temperature properties are generally controlled by the degree of crystallinity of the polymer in addition to the cross-link density of the vulcanized part and the presence of ingredients in the compound such as process oil may impact the glass transition temperature (Tg) of the final part. Some of the same attributes also control other important properties such as tensile strength, elongation and tear strength. Therefore, it is important to optimize the polymer composition, compound formulation and cross-link density. Among these, polymer composition has the biggest impact on cold compression set for parts such as brake seals which tend to be polymer rich formulations.

US 5,698,651 suggests an ethylene copolymer rubber purported to have excellent extrusion moldability, thermal aging resistance and low-temperature flexibility with a high vulcanization rate. The copolymer rubber contains units from ethylene and from α-olefins of 3 to 20 carbon atoms. The copolymer contains additionally 0.1 to 10% by mol of units from the nonconjugated poiyene containing in one molecule, one carbon-to- carbon double bond polymerizable by the metallocene catalyst among carbon-to- carbon double bonds. The copolymer contains 0.1 to 3 % by mol of units from the nonconjugated poiyene containing in one molecule, two carbon-to- carbon double bonds polymerizable by the metallocene catalyst among carbon-to- carbon double bonds. This document cautions however that in the nonconjugated poiyene containing, in one molecule, one carbon to carbon double bond polymerizable by a metallocene catalyst among carbon-to- carbon double bonds, a chain poiyene having vinyl both ends is not included.

There is a commercial need, therefore, for an elastomeric polymer material which, when compounded, can provide vehicle parts which have improved resistance to low temperature compression set.

SUMMARY

We have discovered that vehicle parts made from a compound including ethylene, alpha-olefin, ethylidene norbornene elastomeric polymer, where the polymer has low ethylene content, narrow molecular weight distribution, and narrow ethylene composition distribution, will generally have improved resistance to low temperature compression set, compared to vehicle parts made from ethylene, alpha-olefin, non-conjugated diene elastomeric polymers where all of these conditions are not present. Additionally the ethylene, alpha-olefin, ethylidene norbornene elastomeric polymers and vehicle part components made from compounds based on these elastomeric polymers will show, faster cure rate, and improved (higher) cure state over the ethylene, alpha-olefin, non-conjugated diene elastomeric polymers discussed above. The invention comprises, at least in part, a vehicle part including an ethylene, α-olefin, diene elastomeric polymer, where the elastomeric polymer has a low ethylene content, wherein the vehicle part has improved low temperature compression set, comprising: a) ethylene present in the elastomeric polymer in the range of from 50-60 mole %, (40-50 weight %) based on the total moles of the elastomeric polymer; b) a diene consisting essentially of either ethylidene norbornene or vinyl norbornene, present in the elastomeric polymer in the range of from 0.1 -5 mole percent based on the total moles of the elastomeric polymer c) an α-olefin selected from the group consisting of propylene, hexene-1, octene-1 and combinations thereof, wherein the α-olefin makes up the remainder of the elastomeric polymer;

In the elastomeric polymer, the ethylene composition distribution is such that the ethylene in 90% of the polymer fractions varies by no more than ± 3% by weight, preferably ± 2 %, more preferably ± 1%, from the ethylene composition of the bulk polymer. The M_w/M_n of the elastomeric polymer is in the range of from 2-8, preferably from 2-5, more preferably from 2-4, most preferably 2.5-3.5. The inherent viscosity the elastomeric polymer, measured in Decalin @ 135 °C is in the range of from 1.2-3.2. The Mooney Viscosity (1+4) @125 °C of the elastomeric polymer is in the range of 10-80, preferably 15-40, more preferably 20-30. The vehicle part has an instantaneous compression set at -40° C less than 80%), preferably less than 75%o, more preferably less than 70%. These compression sets assume fully cured parts.

BRIEF DESCRIPTION OF THE DRAWINGS These and other features, aspects, and advantages of the present invention will become better understood with reference with the following description, appended claims, and accompanying drawings where:

Figure 1 shows polymer ethylene compositional distribution for three elastomeric polymers.

DESCRIPTION

Various embodiments of our invention concern certain classes of vehicle parts fabricated from ethylene, alpha-olefin, ethylidene norbornene elastomeric polymer compounds and their uses. These vehicle exhibit improved resistance to low temperature compression set over vehicle parts based on molded and/or extruded parts made from previously available materials, such as ethylene, alpha- olefin, non-conjugated diene, elastomeric polymers containing, for instance, higher ethylene contents, broader ethylene composition distributions, broader molecular weight distributions, combinations of these properties, and the like, and compounds derived from these elastomeric polymers.

A detailed description of certain preferred elastomeric polymers for use in fabricating such vehicle parts, that are within the scope of our invention, preferred methods of producing the elastomers, and the preferred applications of the molded or extruded parts follow. Those skilled in the art will appreciate that numerous modifications to these preferred embodiments can be made without departing from the scope of the invention. For example, although the properties of vehicle parts are used to exemplify the attributes of the elastomeric polymers of the present invention, the elastomeric polymers have numerous other uses and will provide the same improved low temperature compression set in other parts such as building gaskets, insulation in electrical devices and the like. To the extent that our description is specific, this is solely for the purpose of illustrating preferred embodiments of our invention and should not be taken as limiting our invention to these specific embodiments. The use of subheadings in the description is intended to assist and is not intended to limit the scope of our invention in any way. Introduction

We have discovered that the ethylene content of narrow molecular weight distribution, narrow ethylene composition distribution elastomeric polymers can have a substantial effect upon an elastomeric polymer's low temperature compression set, or the low temperature compression set of a compound based on the elastomeric polymer, or vehicle parts based on either. Conventionally, once an elastomeric polymer's ethylene content went below 70 mole percent, the amorphous region being reached, performance in tests such as low temperature compression set have been considered defined by the "amorphous" region and have been perceived as largely unchanging with ethylene content within this region. This amorphous region can be established, for example through the absence of a melting or freezing peak in a Differential Scanning Calorimeter (DSC) trace. However, we have discovered that not only is the ethylene content in the amorphous region a key to low temperature performance, but there is a range of ethylene content and ethylene composition distribution wherein the low temperature properties reach their optimum values. Ethylene Content

Specifically, we have found that maintaining the ethylene content below 80 mole percent, preferably below 70 mole percent, more preferably below 60 mole percent is among the key attributes necessary to improve and maintain low temperature compression set. More specifically, an ethylene content in the range of from 40 to 50 weight percent (50-60 mole percent) is most preferable. Conventionally, low temperature compression set of ethylene, α-olefin, non- conjugated diene elastomeric polymers is controlled by the glass transition temperature (T_g). T_g is in turn known to be a function of crystallinity, which in turn is controlled by ethylene content of these polymers. Crystalline polymers have well defined melting and freezing behavior (peaks) generally determinable DSC. These peaks generally tend to reach insignificant levels at ethylene contents less than 60 weight percent. Elastomeric polymers below these ethylene contents are, and have been generally thought to be amorphous, and the ethylene content thought to not have any appreciable effect as it might be varied below the amorphous threshold.

By contrast, we have discovered that the low temperature properties, most especially the low temperature compression set, are influenced to a great extent by both the ethylene content and its distribution, even in the amorphous region. Ethylene Compositional Distribution

The ethylene composition distribution is traditionally obtained by a solvent/non-solvent titration method, described below: Five g of the polymer is dissolved with gentle agitation in 500 ml of hexane or cyclohexane at room temperature. The insoluble portion is filtered out and dried by pouring the entire solution through a 150 mesh stainless steel screen. To the soluble portion (the supernatent solution) is added 2-propanol dropwise until the solution becomes turbid. Approximately one more ml of 2-propanol is added and the solution is allowed to stand for 5 minutes. The entire solution is filtered through a 150 mesh stainless steel screen and the residue is separated and dried. If further fractionation is desired, the above process is repeated to generate additional fractions (normally up to 5 or 6) until most of the polymer is precipitated. The insoluble portion and the residues are analyzed by FTIR for composition (ethylene and diene) and compared to the composition of the bulk sample.

The narrowness of the compositional distribution will mean generally 90% of the fractions thus generated will have a composition within ±4, preferably within ±3, more preferably within ±2, most preferably within ±1 percent of the ethylene content of the bulk polymer. Inherent Viscosity

The inherent viscosity of elastomeric polymers of the present invention, as measured in Decalin @ 135 °C will be in the range of from 1.2-3.2, more preferably in the range 1.5-2.5 and most preferably in the range 1.7-2.3. Mooney Viscosity

The Mooney Viscosity (1+4) @125 °C of the elastomeric polymer is in the range of from 10-80, preferably 15-40, more preferably 20-30. The Ethylene, Alpha-OIefin, Ethylidene Norbornene, Elastomeric Polymer Component

The ethylene, alpha-olefin, ethylidene norbornene, elastomeric polymer component contains ethylene in the range of from 40 -90 mole percent ethylene, preferably in the range of from 40 - 70 mole percent, more preferably in the range of from 50 - 60 mole percent, based on the total moles of the polymer. The elastomeric polymer contains a diene, in the range of 0.1-5 mole percent, preferably 0.2 - 5.0 mole percent, more preferably in the range of from 1.0 - 2.5 mole percent, even more preferably in the range of from 1.3 - 2.0 mole percent, most preferably 1.4 - 1.8 percent. The diene will consist essentially of ethylidene norbornene or vinyl norbornene a mixture of these dienes is not contemplated as an embodiment of this invention. The balance of the elastomeric polymer will generally be made up of an alpha-olefin, selected from the group consisting of propylene, butene-1, hexene-1, 4-methyl-l pentene, octene-1, decene-1, combinations thereof and the like. The preferred alpha-olefins are propylene, hexene-1, octene-1 and combinations thereof. The alpha-olefin or alpha-olefins maybe present in the elastomeric polymer in the range of from 10 to 50 mole percent, preferable 30 to 50 mole percent, more preferably 40 to 60 mole percent.

Definition of Terms and Tests:

* ethylene, alpha-olefin, diene monomer elastomeric polymer 1 Fourier Transfer ** daN.m Other Vehicle Compound Ingredients

Vehicle parts manufactured based on the elastomeric polymers of various embodiments of the present invention are made using ingredients, in addition to the elastomeric polymer or polymers, that will be well known to those of ordinary skill in the art. Such ingredients include but are not limited to carbon black, process aids, plasticizer, waxes, reinforcing short fibers, antioxidants, accelerators, curatives, and the like. The combination of these ingredients are known generally as compounds. Use of the term compound in this document will refer to the elastomeric polymer as well as these other common ingredients. The elastomeric polymer can be extended with an oil; aromatic, naphthenic or paraffinic, preferably paraffinic. The content of oil may vary from 0 % to 200%, preferably 0% to 100%, more preferably 0% to 50%.

Use of the terms parts per hundred parts rubber (phr) and the term parts per hundred elastomeric polymer (pphep), are considered equivalent for purposes of this application. Use of the term "compound" for purposes of this application includes the Elastomeric polymer and one or more of the following ingredients.

• Carbon black used in the reinforcement of rubber, generally produced from the combustion of a gas and/or a hydrocarbon feed and having a particle size from 20 nm to 100 nm for the regular furnace or channel black or from 150 to 350 nm for the thermal black. Level in the compound may range from 30 to 100 parts per 100 parts of elastomeric polymer (phr). Fillers other than Carbon Black, such as, silica, talc and the like are also contemplated.

• Processing oil, preferably paraffinic, can be added for the power transmission belts to adjust the viscosity of the compound for good processing and the hardness in the range of 70 Shore A. Level in the compound may vary from 0 to 100 parts per hundred of elastomeric polymer(phr).

• Process aids as used in such compounds can be a mixture of fatty acid ester or calcium fatty acid soap bound on a mineral filler. They are used to help the mixing of the compound and the injection of the compound into a mold. Levels range from 0.5 to 5 (phr). • Other types of process aid can be low molecular weight polyethylene (copolymer) wax or paraffin wax. Level may range from 0.5 to 5 phr.

• Antioxidants can be added to improve the long term heat aging, for instance a quinolein (TMQ : tri methyl hydroxyquinolene) and imidazole (ZMTI : Zincmercapto toluyl imidazole). Level ranges from 0.5 to 5 phr.

• Coagents are those used to improve the peroxide cross link density by acting: either through an addition mechanism like sulfur, thiuram (TMTDS or DPPT) (0.3 phr typically) or methacrylate (EDMA or TMPTM) or modified methacrylate (zinc diacrylate or zinc dimethacrylate) and maleimide (HVA) (0.5 to 5 phr typically). or by transfer mechanism like the 1,2 polybutadiene or the alkyl cyanurate (TAC) (typically 0.5 to 5 phr) and combinations thereof.

• Short fiber may be added in power transmission belts to improve their modulus and the belt's ability to be grinded by a rotating tool to precisely form the V-shape. The fiber may be cotton, polyamide, polyester or aramid or the like. Cotton is the most popular today in fabrication of belts. Compatibilization agent like phenolic resin or polar polyolefins might be used to enhance the cohesion between the polymer and polar short fiber. Level of fiber may be between 1 and 50 phr, more preferably 15phr. • Curative(s)

To resist to high temperature aging effects, peroxides are used to cure the ethylene, alpha-olefin, ethylidene norbornene, elastomeric polymer and the most commonly used are the butyl peroxy benzene, butyl peroxy-hexane, dicumyl peroxide, butyl peroxy-valerate, butyl peroxy methyl-cyclohexane or combinations thereof, and the like. Typical quantity ranges from 1 to 5 phr calculated on a 100 percent active base. The level of peroxide is adjusted to obtain the desired cure rate and state (cross-link density). These have a direct impact on compression set, as well as other properties such as tensile strength, elongation and tear resistance. Compound Characteristics

TABLE I

TYPICAL FORMULA USED IN VEHICLE PARTS APPLICATION

(1) Sterling Cabot

(2) PPG Co

(3) R.T. Vanderbilt Co.

(4) Sartomer Co.

(5) R.T. Vanderbilt Co

Method of Producing Ethylene, Alpha-Olefin Ethylidene Norbornene, Elastomeric Polymer Component

Elastomeric polymers that may meet the parameters of the present invention may be produced in at least two types of catalyst systems, and in a variety of reactor schemes in each of these catalyst systems. Conventional Ziegler Polymerization

Conventional Ziegler-Natta (Z-N) polymerization may be carried out with VC1₄ or VOC1-, as the catalyst and ethyl aluminum sesqui chloride (SESQUI) as the co-catalyst. A modifier such as an amine or ammonia can be used to introduce the desired level of long chain branching in the polymer chain. This catalyst system is known to be a single-sighted catalyst system. Generally this catalyst system will produce a narrow composition distribution and a narrow MWD, but these may be broadened by utilization of reactor schemes. Practical limitations of lower ethylene incorporation in such a catalyst system is 45%, by weight. Below this level, conversion of the α-olefin becomes economically unsound. Metallocene Polymerization

Metallocene based catalysts systems may be used additionally to produce narrow CD, narrow MWD polymers that may also be broadened by use of reactor schemes. Single sighted metallocene catalyst systems offer the additional advantage of ability to synthesize any ethylene composition desired, without the economic penalty associated with the Z-N polymerization schemes.

The synthesis of ethylene, alpha-olefin, ethylidene norbornene elastomeric polymers are conducted a laboratory pilot unit (output 4 Kg/day), or in a semi- works pilot unit (output 1 ton/day). Metallocene catalysis of the above monomers is also contemplated including a compound capable of activating the Group 4 transition metal compound of the invention to an active catalyst state is used in the invention process to prepare the activated catalyst. Suitable activators include the ionizing noncoordinating anion precursor and alumoxane activating compounds, both well known and described in the field of metallocene catalysis.

Additionally, an active, ionic catalyst composition comprising a cation of the Group 4 transition metal compound of the invention and a noncoordinating anion result upon reaction of the Group 4 transition metal compound with the ionizing noncoordinating anion precursor. The activation reaction is suitable whether the anion precursor ionizes the metallocene, typically by abstraction of R\ or R2, by any methods inclusive of protonation, ammonium or carbonium salt ionization, metal cation ionization or Lewis acid ionization. The critical feature of this activation is cationization of the Group 4 transition metal compound and its ionic stabilization by a resulting compatible, noncoordinating, or weakly coordinating (included in the term noncoordinating), anion capable of displacement by the copolymerizable monomers of the invention. See, for example, EP-A-0 277,003, EP-A-0 277,004, U.S. Patent No. 5,198,401, U.S. Patent No. 5,241,025, U.S. Patent No. 5,387,568, WO 91/09882, WO 92/00333, WO 93/11172 and WO 94/03506 which address the use of noncoordinating anion precursors with Group 4 transition metal catalyst compounds, their use in polymerization processes and means of supporting them to prepare heterogeneous catalysts. Activation by alumoxane compounds, typically, alkyl alumoxanes, is less well defined as to its mechanism but is none-the-less well known for use with Group 4 transition metal compound catalysts, see for example U.S. Patent No. 5,096,867. Each of these U.S. documents are incorporated herein by reference, for purposes of U.S. patent practice.

Included in the vehicle parts contemplated by various embodiments of the present invention are brake parts including, but not limited to cups, coupling disks, diaphragm cups, boots, tubing, sealing gaskets, parts of hydraulically or pneumatically operated apparatus, o-rings, pistons, valves, valve seats, valve guides, and other elastomeric polymer based parts or elastomeric polymers combined with other materials such as metal, plastic combination materials which will be known to those of ordinary skill in the art.

Also contemplated are transmission belts including V-belts, toothed belts with truncated ribs containing fabric faced V's, ground short fiber reinforced V's or molded gum with short fiber flocked V's. The cross section of such belts and their number of ribs may vary with the final use of the belt, the type of market and the power to transmit. They also can be flat made of textile fabric reinforcement with frictioned outside faces. Vehicles contemplated where these parts will find application include, but are not limited to passenger autos, motorcycles, trucks, boats and other vehicular conveyances. Examples

The following examples are presented for illustration of the invention, but are not intended to limit the scope in any way.

Synthesis of Example 1 is carried out in a semi-works pilot unit with an output of 1 ton/day. Synthesis of Examples 2 and 3 is carried out in a laboratory pilot unit with an output of 4 Kg/day. The polymerizations are carried out in a continuous stirred tank reactor or two of the tanks in series. In the case of series reactors the polymer and the unreacted monomers from the first reactor are fed, with additional monomers to a second reactor where the polymerization is continued. The fraction of the polymer made in the first reactor (polysplit) is varied between 20-95 %. The residence time in each reactor is 7-14 minutes. Example 1 Example 1 is a ethylene, propylene, and ethylidene norbornene elastomeric polymer made, using VCI4 (vanadium tetrachloride). The co-catalyst chosen is ethyl aluminum sesqui chloride (SESQUI). Two polymerizations are carried out, the first (Example 1A) utilizes a single reactor, the second (Example IB) uses a series reactor scheme. The polymerization is carried out in continuous stirred tank reactors at 20-40° C at a residence time of 6-15 minutes at a pressure of 7 kg/cm2. The molar concentration of vanadium to alkyl is from 1 to 4 to 1 to 10. About 0.3 to 1.5 kg of polymer is produced per gm of catalyst fed to the reactor. The polymer concentration in the hexane solvent is in the range of 3 - 7% by weight. The resulting polymers had the following molecular characteristics: The intrinsic viscosity measured in decalin at 135° C are in the range of

0.5 - 5.0 dl/g. The molecular weight distribution (M_w/M_n) is greater than or equal to 2.5.:

(i) weight average molecular weight (M_W,LALLS) ^measure using a low angle light scattering (LALLS) technique subsequent to a gel permeation chromatograph (GPC)

(ii) number average molecular weight (Mn,rjRI using a differential refractive index detector (DRI) (with GPC) and (iii) inherent viscosity (IV) measured in decalin at 135° C. The first two measurements are obtained in a GPC using a filtered dilute solution of the polymer in tri-chlorobenzene. Example 2

Examples 2A and 2B are polymerized using a metallocene dihalide compound alkylated with an activator such as N,N-Dimethylanilinium tetrakis(pentaflurophenyl) boron or N,N- Dimethylanilinium tetrakis(heptafluronapthyl) boron to yield metallocenes such as dimethylsilyl bis (indenyl) hafnium dimethyl compound or

[Cyclopentadienyl(fluorenyl)diphenylmethane]hafhium dimethyl compound using a series reactor scheme. The process is controlled to polymers at overall ethylene compositions similar to Example 1. Examples 2A and 2B differ in the conposition of the polymer made in the second reactor. Example 2A has a substantial portion of the polymer at 61 weight percent ethylene, similar to comparative example 4. Example 2B by contrast, maintains nearly constant ethylene content in both reactors. Example 3 Example 3 is polymerized as Example 2, except it is made at a lower ethylene content than Examples 2, and in a single reactor. Comparative Example 4

Comparative Example 4 uses a commercially available ethylene, alpha- olefin, ethylidene norbornene, elastomeric polymer (Vistalon® 2504 available from Exxon Chemical Company). Vistalon 2504 has an ethylene content of approximately 56 weight percent, an ENB content of approximately 4 to 5 weight percent, with the remainder being propylene. This product has a typical Mooney Viscosity ML 1+4,125° C of 26 (See Table II). Comparative Example 5 Comparative example 5 uses a commercially available ethylene, alpha- olefin ethylidene norbornene elastomeric polymer from Uniroyal, Royalene 521. Compounding of Examples

All the materials are compounded as per the compound shown in Table I. Physical properties are then run on the samples, including Mooney viscosity, Mooney scorch time, and oscillating disk rheometer (ODR) data. Other physical properties such as Hardness, 100% Modulus, Tensile strength, Elongation, Trouser tear and Compression Set at high and low temperatures were measured on pads cured in a press at 180° C for 10 minutes. The results for the inventive and comparative examples are shown in Table III and IV. Comparing examples 1A and IB with comparative examples 4 and 5, the low temperature compression set of the inventive examples are substantially better. Example 3 shows that lowering the ethylene composition of a single reactor polymer further from example 1A produces a slight improvement in cold compression set. Comparing examples 2A and 2B with the other examples, it is observed that though both polymers have the same overall ethylene composition, only example 2B, where the composition is uniform results in good compression set. Presence of a higher ethylene fraction in example 2A results in much worse cold compression set. Conclusion

The present invention has been described in considerable detail with reference to certain preferred versions thereof, other versions are possible. For example, while brake parts and power transmission belt have been exemplified, other uses are also contemplated. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred versions contained herein.

TABLE II

*Polysplit refers to the percentage of the polymer made in reactor 1, where applicable.

TABLE HI

Comparativ Comparative Example Example e Example 5 Example 6 1A IB

Compound ML (1+4) @ 100°C (MU) 96 100 97 93

Mooney Scorch, Ms(15) @ 125°C (MU) 10.3 21.2 22.7 22.4

Minimum Viscosity* 36 35 34 33

ODR, 180°C, 3 Arc, 8 min motor

(200 in-lb full scale)

ML (daN.m) 11 12 11 11

MH (daN.m) 115 102 119 120

Ts2 (minutes) 0.62 0.67 0.87 0.91

T90 (minutes) 4.80 5.90 6.30 6.40

T98 (minutes) 5.70 7.50 7.60 7.60

Rate (daN.m/min.) 48 43 44 39

MH-ML (daN.m) 104 90 108 109

Press Cure 10 min @ 180°C

Hardness (Shore A) 77 78 77 77

100% Modulus (M Pa) 7 6 6 6

Tensile Strength (M Pa) 18.2 18.8 15.7 15.7

Elongation (%) 213 269 218 203

Trouser Tear (Pk. Value) (N/mm) 5.6 7.7 5.1 5.2

Compression Set, press cure 12 min

22 hrs/150°C/25% deflection (%) 8 12 12 13

Cold Compression Set, press cure 12 m iπiπtti

24 hrs/-40°C/25 % Defin (Akron Rubber

Labs)

Instantaneous (%) 96.0 83.2 72.0 73.7

3 min (%) 92.1 75.6 58.7 59.4

5 min (%) 91.3 73.4 56.3 38.9

30 min (%) 85.4 80.9 46.8 42.5

''(compound) Ts5, 125 ° C, in minutes

TABLE IV

Comparative Comparative Example Example Example

Example 5 Example 6 2A 2B 3

Compound ML (1+4) @ 100°C (MU) 106 96 120 120 123

Mooney Scorch, Ms(15) @ 125°C (MU) 10.6 18.5 16.9 19.0 14.2

Minimum Viscosity* 37 33 41 40 41

ODR, 180°C, 3 Arc, 8 min motor

(200 in-lb full scale)

ML (daN.m) 14 12 14 14 13

MH (daN.m) 82 82 110 141 131

Ts2 (minutes) 0.85 0.97 0.86 1.00 0.77

T90 (minutes) 4.96 5.11 5.03 6.00 6.00

T98 (minutes) 5.76 5.80 5.78 7.50 7.50

Rate (daN.m/min.) 21 19 26 63 58

MH-ML (daN.m) 68 70 96 127 1 18

Press Cure 10 min @ 180°C

Hardness (Shore A) 78 75 ^' 78 80 79

100% Modulus (M Pa) 5 4 5 8 7

Tensile Strength (M Pa) 17.6 17.3 18.0 16.8 17.7

Elongation (%) 228 279 254 192 218

Trouser Tear (Pk. Value) (N/mm) 5.1 6.7 5.1 4.2 4.3

Compression Set, press cure 12 min

22 hrs/150°C/25% deflection (%) 19 15 18 8 8

Cold Compression Set, press cure 12 min

24 hrs/-40°C/25 % Defin (Akron Rubber

Labs)

Instantaneous (%) 88.7 87.4 93.3 73.5 68.5

3 min (%) 86.3 81.0 89.6 54.5 48.4

5 min (%) 85.5 79.5 88.5 51.9 45.3

30 min (%) 80.6 73.8 87.3 39.4 36.7

''(compound) Ts5, 125 ° C, in minutes

Claims

CLAIMS;

1. A vehicle part including an ethylene, α-olefin diene elastomeric polymer, where the elastomeric polymer has a low ethylene content, and wherein the vehicle part has improved low temperature compression set, comprising:

a) ethylene present in said elastomeric polymer in the range of from 50- 60- mole %, based on the total moles of said elastomeric polymer;

b) a diene consisting essentially of ethylidene norbornene, present in the elastomeric polymer in the range of from 0.2 -5 mole percent based on the total moles of said elastomeric polymer;

c) an α-olefin selected from propylene, hexene- 1 , and octene- 1 , wherein said α-olefin makes up the remainder of said elastomeric polymer;

wherein the ethylene composition distribution of said elastomeric polymer is such that the ethylene in 90% of the polymer fractions varies by no more than + 4% by weight,

wherein the M M_n of the elastomeric polymer is in the range of from 2-4;

wherein the inherent viscosity of said elastic polymer, measured in Decalin @ 135 °C in the range of from 1.2-3.2;

wherein the Mooney Viscosity (1+4) @125 °C of said elastomeric polymer is in the range of from 10-80; and

wherein said vehicle part has an instantaneous compression set, at -40° C, less than 80%.

2. The vehicle part of claim 1 wherein the ethylene composition distribution of said elastomeric polymer is such that the ethylene in 90% of the polymer fractions varies by no more than ± 3 % by weight, wherein the Mooney Viscosity (1+4) @125 °C of said elastomeric polymer is in the range of from 15-40, and wherein said vehicle part has an instantaneous compression set, at -40° C, less than 75%.

3. The vehicle part of claim 1 wherein the ethylene composition distribution of said elastomeric polymer is such that the ethylene in 90% of the polymer fractions varies by no more than ± 2 % by weight, wherein the Mooney Viscosity (1+4) @125 °C of said elastomeric polymer is in the range of from 20-30, and wherein said vehicle part has an instantaneous compression set, at -40° C, less than 70%.

4. The vehicle part of any of claims 1 , 2, or 3 wherein the part is a brake part.

5. The vehicle part of claim 4 wherein the brake is selected from the group consisting of cups, coupling disks, diaphragm cups, boots, tubing, sealing gaskets, and combinations thereof.

6. The vehicle part of claim 5 wherein said part is selected from the group consisting of hydraulically operated and pneumatically operated apparatus.

7. The vehicle part of claim 5 wherein said part is selected from the group consisting of o-rings, pistons, valves, valve seats, valve guides, and combinations thereof.

8. The vehicle part of claims 1, 2, or 3 wherein said part is selected from the group consisting of V-belts, flat belts, and toothed belts.

9. A vehicle including the vehicle part of claim 5.

10. A vehicle including the vehicle part of claim 8.

1. A vehicle part including an ethylene, α-olefin, diene elastomeric polymer, where the elastomeric polymer has a low ethylene content, and wherein the vehicle part has improved low temperature compression set, comprising:

a) ethylene present in said elastomeric polymer in the range of from 50-60- mole %, based on the total moles of said elastomeric polymer;

b) a diene consisting essentially of ethylidene norbornene, present in the elastomeric polymer in the range of from 1.4 -1.8 mole percent based on the total moles of said elastomeric polymer;

wherein the ethylene composition distribution of said elastomeric polymer is such that the ethylene in 90% of the polymer fractions varies by no more than + 3% by weight,

wherein the M^M,, of the elastomeric polymer is in the range of from 2.5-

3.5;

wherein the inherent viscosity of said elastomeric polymer, measured in Decalin @ 135 °C in the range of from 1.2-3.2;

12. An ethylene, alpha-olefin, diene elastomeric polymer where the elastomeric polymer has:

a) ethylene present in said elastomeric polymer in the range of from 50- ^'60 mole percent based on the total moles of said elastomeric polymer;

b) a diene consisting essentially of ethylidene norbornene, present in the elastomeric polymer in the range of from 1.4-1.8 mole percent, based on the total moles of said elastomeric polymer;

c) propylene making up the remainder of said elastomeric polymer;

wherein the ethylene composition distribution of said elastomeric polymer is such that the ethylene in 90% of the polymer fractions varies by no more than +1% by weight from the ethylene composition of the bulk polymer;

wherein the M^/M,, of the elastomeric polymer is in the range of from 2.5

- 3.5;

wherein the inherent viscosity of said elastomeric polymer, measured in

Decalin @ 135 °C in the range of from 1.7-2.3; and

wherein the Mooney Viscosity (1+4) @125 °C of said elastomeric polymer is in the range of from 10-80.

13. The ethylene, alpha-olefin, diene elastomeric polymer of claim 12, wherein said elastomeric polymer has Mooney viscosity in the range of from 15 - 40.

4. The ethylene, alpha-olefin, diene elastomeric polymer of claim 12, wherein said elastomeric polymer has a Mooney viscosity in the range of from 20 - 30.