Ethylene/propylene rubber

Ethylene propylene rubber (EPR, or EPDM,) is a copolymer of ethylene and propylene. It has much of the chemical resistance of the related plastics excellent resistance to heat and oxidation good resistance to steam and hot water. It is used as a standard Kning material for steam hoses widely used in chemical services as well, having a broad spectrum of resistance. 

Successful homogeneous catalyst systems were soon developed by Natta and his research team at Milan. These were anionic coordinated catalysts obtained by reaction of an alkyl aluminium compound (e.g. A1(C2Hs)2C1) with a hydrocarbon-soluble vanadium compound (e.g. VOCI3)—at least one of the components requiring a halogen in the 

Average molecular weight increases with reaction time, with decrease in reaction temperature, with decrease in catalyst concentration, with decrease in monomer concentration and with increase in the ethylene/propylene ratio. It also depends on the nature of the alkyl aluminium compound and on the Al V ratio. 

The saturated polymers obtained, designated as EPM rubbers are vulcanized by peroxides (see Section 12.2.3). 

The long established use of accelerated sulphur systems for vulcanization of general purpose rubbers has always led to a reluctance of rubber processors to accept alternative vulcanization systems unless this was absolutely necessary. This is not simply innate conservatism but as much due to the anticipation of problems of contamination of stocks during processing and of difficulties in reclaiming. For this reason modified ethylene-propylene rubbers were developed in which units from a third monomer were present and which provided unsaturation in the polymer (EPDM rubbers). These termonomers, invariably dienes, used in amounts of 3-8% of the total monomer weight are generally expensive, relative to more common monomers and adversely affect the price structure but nevertheless the EPDM type of rubber is now dominant over the EPM copolymers. 

The dienes used are selected so that rupture of a double bond on ageing, e.g. through attack by ozone, does not lead to chain scission. 

---

Polyolefins. In these thermoplastic elastomers the hard component is a crystalline polyolefin, such as polyethylene or polypropylene, and the soft portion is composed of ethylene-propylene rubber. Attractive forces between the rubber and resin phases serve as labile cross-links. Some contain a chemically cross-linked rubber phase that imparts a higher degree of elasticity. 

R. B. Blodgett, "Ethylene—Propylene Rubber and Crosslinked Polyethylene as Insulations for 90°C Rated Medium Voltage Cables," Rubber Chem. Technol, 52, 410-424 (1978). 

Polypropylene polymers are typically modified with ethylene to obtain desirable properties for specific applications. Specifically, ethylene—propylene mbbers are introduced as a discrete phase in heterophasic copolymers to improve toughness and low temperature impact resistance (see Elastomers, ETHYLENE-PROPYLENE rubber). This is done by sequential polymerisation of homopolymer polypropylene and ethylene—propylene mbber in a multistage reactor process or by the extmsion compounding of ethylene—propylene mbber with a homopolymer. Addition of high density polyethylene, by polymerisation or compounding, is sometimes used to reduce stress whitening. In all cases, a superior balance of properties is obtained when the sise of the discrete mbber phase is approximately one micrometer. Examples of these polymers and their properties are shown in Table 2. Mineral fillers, such as talc or calcium carbonate, can be added to polypropylene to increase stiffness and high temperature properties, as shown in Table 3. 

Ethylene—Propylene Rubber. Ethylene and propjiene copolymerize to produce a wide range of elastomeric and thermoplastic products. Often a third monomer such dicyclopentadiene, hexadiene, or ethylene norbomene is incorporated at 2—12% into the polymer backbone and leads to the designation ethylene—propylene—diene monomer (EPDM) mbber (see Elastomers, synthetic-ethylene-propylene-diene rubber). The third monomer introduces sites of unsaturation that allow vulcanization by conventional sulfur cures. At high levels of third monomer it is possible to achieve cure rates that are equivalent to conventional mbbers such as SBR and PBD. Ethylene—propylene mbber (EPR) requires peroxide vulcanization. 

Nistalon Ethylene—Propylene Rubber User s Guide, Exxon Chemical Co., Polymers Group. 

The cis-polybutadiene, cis-polyisoprene, and ethylene-propylene rubbers are close duphcates of natural rubber. The newer eth)aene-propylene rubbers (EPR) have excellent resistance to heat and oxidation. 

NEMA WC8/1998 Ethylene propylene rubber insulated wire and cable for the transmission and distribution of power ... 

A trade name of CEAT CAVI Ind., Turin, Italy. It is ethylene propylene rubber/chlorosulfonated polyethylene. 

Following the considerable commercial success of Ziegler-Natta polymerisation systems which made possible high density polyethylene, polypropylene, ethylene-propylene rubbers and a number of speciality materials, a considerable... 

Polyethylene is sometimes blended with ethylene-propylene rubber (see Chapter 11). In this application it is most commonly used as an additive to the rubber, which in turn is added to polypropylene to produce rubber-modified... 

In the early stages of development of polypropylene rubbers, particularly butyl rubber, were used to reduce the brittleness of polypropylene. Their use declined for some years with the development of the polypropylene copolymers but interest was greatly renewed in the 1970s. This interest has been centred largely around the ethylene-propylene rubbers which are reasonably compatible in all proportions with polypropylene. At first the main interest was with blends in which the rubber content exceeded 50% of the blend and such materials have been designated as thermoplastic polyolefin elastomers (discussed in Section 11.9.1). There is also increasing interest in compounds with less than 50% rubber, often referred to as elastomer-modified thermoplastics. It is of interest to note... 

In consequence ethylene-propylene rubbers were introduced with a small amount (3-8%) of a third, diene, monomer which provided a cross-link site for accelerated sulphur vulcanisation. Such ethylene-propylene-diene monomer ternary copolymers are designated as EPDM rubbers. 

The use of ABS has in recent years met considerable competition on two fronts, particularly in automotive applications. For lower cost applications, where demands of finish and heat resistance are not too severe, blends of polypropylene and ethylene-propylene rubbers have found application (see Chapters 11 and 31). On the other hand, where enhanced heat resistance and surface hardness are required in conjunction with excellent impact properties, polycarbonate-ABS alloys (see Section 20.8) have found many applications. These materials have also replaced ABS in a number of electrical fittings and housings for business and domestic applications. Where improved heat distortion temperature and good electrical insulation properties (including tracking resistance) are important, then ABS may be replaced by poly(butylene terephthalate). 

Whilst the aliphatic nylons are generally classified as being impact resistant, they are affected by stress concentrators like sharp comers which may lead to brittle failures. Incorporation of mbbers which are not soluble in the nylons and hence form dispersions of rubber droplets in the polyamide matrix but which nevertheless can have some interaction between mbber and polyamide can be most effective. Materials described in the literature include the ethylene-propylene rubbers, ionomers (q.v.), polyurethanes, acrylates and methacrylates, ABS polymers and polyamides from dimer acid. 

A manufacturer considering using a thermoplastic elastomer would probably first consider one of the thermoplastic polyolefin rubbers or TPOs, since these tend to have the lowest raw polymer price. These are mainly based on blends of polypropylene and an ethylene-propylene rubber (either EPM or EPDM) although some of the polypropylene may be replaeed by polyethylene. A wide range of blends are possible which may also contain some filler, oil and flame retardant in addition to the polymers. The blends are usually subject to dynamic vulcanisation as described in Section 11.9.1. 

Add side groups such as methyl or chlorine. The methyl group (for instance in ethylene-propylene rubber) prevents neighbouring chain segments from aligning perfectly. 

Els and McGill [48] reported the action of maleic anhydride on polypropylene-polyisoprene blends. A graft copolymer was found in situ through the modifier, which later enhanced the overall performance of the blend. Scott and Macosko [49] studied the reactive and nonreactive compatibilization of nylon-ethylene-propylene rubber blends. The nonreactive polyamide-ethylene propylene blends showed poor interfacial adhesion between the phases. The reactive polyamide-ethylene propylene-maleic anhydride modified blends showed excellent adhesion and much smaller dispersed phase domain size. 

Greco et al. [50] studied the effect of the reactive compatibilization technique in ethylene propylene rubber-polyamide-6 blends. Binary blends of polyamide-6-ethylene propylene rubber (EPR) and a ternary blend of polyamide-6-EPR-EPR-g-succinic anhydride were prepared by the melt mixing technique, and the influence of the degree of grafting of (EPR-g-SA) on morphology and mechanical properties of the blends was studied. 

ATBN - amine terminated nitrile rubber X - Flory Huggins interaction parameter CPE - carboxylated polyethylene d - width at half height of the copolymer profile given by Kuhn statistical segment length DMAE - dimethyl amino ethanol r - interfacial tension reduction d - particle size reduction DSC - differential scanning calorimetry EMA - ethylene methyl acrylate copolymer ENR - epoxidized natural rubber EOR - ethylene olefin rubber EPDM - ethylene propylene diene monomer EPM - ethylene propylene monomer rubber EPR - ethylene propylene rubber EPR-g-SA - succinic anhydride grafted ethylene propylene rubber... 

The main use of ethylene-propylene rubber is to produce automotive parts such as gaskets, mechanical goods, wire, and cable coating. It may also be used to produce tires. 

Thermoplastic polyolefin rubbers are usually blends based on polypropylene and ethylene-propylene rubbers. They are not resistant to hydrocarbons. 

Butyl rubber, halogenated butyl rubber linings and ethylene propylene rubber linings have excellent chemical resistance at temperatures up to 120°C. There are cases where butyl rubber linings have been subjected to temperatures down to —65°C without deterioration. Linings based on these polymers do not exhibit good abrasion resistance, which can only be rated as fair. 

---