Unsaturation ethylene-propylene-diene

These polyolefin rubbers are produced in two main types the saturated co-polymers, ethylene propylene rubber (EPM), and the unsaturated ethylene-propylene diene terpolymer (EPDM). The monomers are co-polymerised in ziegler natta type catalysts. The EPDM types are capable of sulfur vulcanisation as they contain, in addition to olefins, a non coagulated diene as the third monomer. 

The natural rubber does not generally exhibit all the desired properties for use in the rubber industry. Thus, it is possible to obtain better mechanical and physical properties at a lower cost by blending natural rubber with synthetic rubbers. Normally, natural rubber is deteriorated by ozone and thermal attacks due to its highly unsaturated backbone, and it also shows low oil and chemical resistances due to its non-polarity. However, these properties can be achieved by blending it with low unsaturated ethylene propylene diene monomer rubber, styrene butadiene rubber, carboxylate styrene butadiene rubber, nitrile butadiene rubber, chloroprene rubber, chlorosulfonated polyethylene rubber, and acrylonitrile butadiene rubber. 

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. 

Ozonc-rcsjstant elastomers which have no unsaturation are an exceUent choice when their physical properties suit the appHcation, for example, polyacrylates, polysulfides, siHcones, polyesters, and chlorosulfonated polyethylene (38). Such polymers are also used where high ozone concentrations are encountered. Elastomers with pendant, but not backbone, unsaturation are likewise ozone-resistant. Elastomers of this type are the ethylene—propylene—diene (EPDM) mbbers, which possess a weathering resistance that is not dependent on environmentally sensitive stabilizers. Other elastomers, such as butyl mbber (HR) with low double-bond content, are fairly resistant to ozone. As unsaturation increases, ozone resistance decreases. Chloroprene mbber (CR) is also quite ozone-resistant. 

Ethylene—Propylene (Diene) Rubber. The age-resistant elastomers are based on polymer chains having a very low unsaturation, sufficient for sulfur vulcanization but low enough to reduce oxidative degradation. EPDM can be depicted by the following chain stmcture ... 

We have considerable latitude when it comes to choosing the chemical composition of rubber toughened polystyrene. Suitable unsaturated rubbers include styrene-butadiene copolymers, cis 1,4 polybutadiene, and ethylene-propylene-diene copolymers. Acrylonitrile-butadiene-styrene is a more complex type of block copolymer. It is made by swelling polybutadiene with styrene and acrylonitrile, then initiating copolymerization. This typically takes place in an emulsion polymerization process. 

It is evident that reactions of unsaturated polymers with bisnitrile oxides lead to cross-linking. Such a procedure has been patented for curing poly(butadiene), butadiene-styrene copolymer, as well as some unsaturated polyethers and polyesters (512-514). Bisnitrile oxides are usually generated in the presence of unsaturated polymers by dehydrochlorination of hydroximoyl chlorides. Cross-linking of ethylene-propylene-diene co-polymers with stable bisnitrile oxides has been studied (515, 516). The rate of the process has been shown to reduce in record with the sequence 2-chloroterephthalonitrile oxide > terephthalonitrile oxide > 2,5-dimethylterephthalonitrile oxide > 2,3,5,6-tetramethylterephthalo-nitrile oxide > anthracene-9,10-dicarbonitrile oxide (515). 

With larger amount of propylene a random copolymer known as ethylene-propylene-monomer (EPM) copolymer is formed, which is a useful elastomer with easy processability and improved optical properties.208,449 Copolymerization of ethylene and propylene with a nonconjugated diene [EPDM or ethylene-propylene-diene-monomer copolymer] introduces unsaturation into the polymer structure, allowing the further improvement of physical properties by crosslinking (sulfur vulcanization) 443,450 Only three dienes are employed commercially in EPDM manufacture dicyclopentadiene, 1,4-hexadiene, and the most extensively used 5-ethylidene-2-norbomene. 

Improved ABS-similar resins can be obtained by grafting SAN onto ethylene-propylene-diene terpolymers (EPDMs) which contain, usually, a much lower degree of unsaturation than polybutadiene, thus achieving hi er thermal-oxidative resis-tance However, only EPDMs containing a sufficient amount (7—10 double bonds per 1,000 C atons) of reactive unsaturations, e.g. ethylidene or isopropylidene groups, display a grafting efficiency sufiident to bring about compatibility of the ssy i se with the rubbery one and hence satisfactory final properties. 

Ethylene has been co-polymerized with virtually any conceivable a-olefin, from propylene to vinyl-terminated PE and PP macromonomers. Ethylene/propylene (E/P) copolymerization to produce saturated rubbers and ethylene/propylene/diene (EPD) terpolymerization to produce unsaturated, vulcanizable rubbers will be discussed in Section 4.09.4.1.3. 1-Butene, 1-hexene, and 1-octene are the most commonly used co-monomers for the production of LLDPE. Ethylene/octene co-polymers, developed by Dow and marketed under the Engage tradename, have been shown to have improved thermal properties compared to ethylene/butene and ethylene/hexene co-polymers.503 In ethylene/a-olefin (E/O) co-polymeriza-tions, the critical parameters are co-monomer reactivity and co-monomer distribution . The former is most conveniently described by the relative reactivity parameter, R, defined as the ratio between polymer composition and reactor medium composition. 

Recent findings indicated that this drawback can be overcome by using particular reinforcing agents, i.e. graft copolymers obtained by modifying saturated or low-unsaturated elastomers such as ethylene-propylene (EP) or ethylene-propylene-diene monomer (EPDM) rubbers and acrylic elastomers (9-16). 

Figure 15.3 Scanning electron micrographs of tensile fractured surfaces of the vulcanizates cured at 160°C (a) 75 25 unsaturated natural rubber-ethylene-propylene-diene (NR-EPDM) blend (one-stage) at 500 x (b) 75 25 NR-EPDM blend (two-stage) at 500 x (c) 50 50 NR-EPDM blend (one-stage) at 750 x (d) 50 50 NR-EPDM blend (two-stage) at 750 x. (From Reference 32 with permission from John Wiley Sons.)...

During the last few years we have developed methods for rapid cross-linking of polyethylenes, ethylene-propylene-diene elastomers (EPDM)2 and linear unsaturated polyesters using UV light for initiation. Efficient crosslinking to high gel content has been obtained for these polymer systems, which contain small amounts of UV-absorbing initiator and a multifimctional monomer (a crosslinker),... 

Copolymerization of ethylene and propylene produces an elastomeric polymer that is virtually inert because of the absence of carbon-carbon double bonds (EPM). Such polymers thus tend to be crossUnked with peroxides or by radiation. To improve the reactivity of ethylene-propylene copolymers, 1-10% of a third monomer can be added to give a terpolymer or ethylene-propylene-diene monomer (EPDM). The primary diene monomers used in EPDM are 1,4-hexadiene, dicyclopentadiene, and ethyUdene norbomene. Introduction of an unsaturated monomer such as ethylidene norbomene will enable use of sulfur-based crosslinking systems. 

Ethylene-propylene rubber is a synthetic hydrocarbon-based rubber made either from ethylene-propylene diene monomer or ethylene-propylene terpolymer. These monomers are combined in such a manner as to produce an elastomer with a completely saturated backbone and pendant unsaturation for sulfur vulcanization. As a result of this configuration, vulcanizates of EPDM elastomers are extremely resistant to attack by ozone, oxygen, and weather. 

Onizawa M. Method for crossUnking of isoprene-isobutylene rubber, ethylene-propylene-diene rubber containing ethyli-denenorbomene as unsaturated component, or mixture thereof and crosslinked rubber product obtained by said method. US patent 6403713 2002. 

Ethylene-propylene-diene terpolymer (EPDM) is an unsaturated PO rubber with wide applications. Several researchers [136,160,317] reported the results of investigations on... 

TPO materials are defined as compounds (mixtures) of various polyolefin polymers, semicrystalline thermoplastics, and amorphous elastomers. Most TPOs are composed of polypropylene and a copolymer of ethylene and propylene called ethylene—propylene rubber (EPR) [2]. A common rubber of this type is called ethylene propylene diene monomer rubber (EPDM), which has a small amount of a third monomer, a diene (two carbon-carbon double bonds in it). The diene monomer leaves a small amount of unsaturation in the polymer chain that can be used for sulfur cross-linking. Like most TPEs, TPO products are composed of hard and soft segments. TPO compounds include fillers, reinforcements, lubricants, heat stabilizers, antioxidants, UV stabilizers, colorants, and processing aids. They are characterized by high impact strength, low density, and good chemical resistance they are used when durability and reliability are primary concerns. 

Since EPR rubber molecules do not contain unsaturation, they can be vulcanized only by organic peroxide curing systems. If a third monomer is added during the polymerization, i.e., a diene monomer (wherein only one of the two double bonds takes part in the polymerization), unsaturation can be introduced into the molecule, and it can then be vulcanized by accelerated sulfur curing systems. A chemical structure for ethylene-propylene-diene-monomer (EPDM) rubbers can be expressed as follows ... 

Fourthly, avoid the use of very high cavity temperatures. These are not generally necessary to obtain short cure times, and certainly speed the rates at which residues are deposited. For natural rubber aim at a cavity temperature of 165 °C. For synthetic rubbers with low levels of unsaturation such as ethylene-propylene diene terpolymer this will need to be increased to 180 °C. The cavity temperature is usually 10 °C to 15 °C below the set point of the platens. 

Ethylene propylene diene polymers (EPDM) are basic elastomers with double bonds in the side chain. They are generated by adding small amounts of diene mmiomers in the copolymerisation of ethylene and propylene. Due to the presence of this unsaturated bond in the basic elastomer both vulcanisation with peroxides and vulcanisation with sulfur are possible. Vulcanisation with peroxides is usually chosen. This generates a product that is relatively inert and weU resistant to ageing. 

Determination of Unsaturation in Ethylene-Propylene-Diene Terpoiymers and Styrene-Butadiene Copolymers... 

Infrared spectroscopy has been used for the determination of unsaturation in ethylene-propylene-diene terpoiymers [10]. Determination of extinction coefficients for the various terpoiymers is required for quantitative w ork. 

This technique has found the following applications in addition to those discussed in Sections 10.1 (resin cure studies on phenol urethane compositions) [65], 12.2 (photopolymer studies [66-68]), and 13.3 (phase transitions in PE) [66], Chapter 15 (viscoelastic and rheological properties), and Section 16.4 (heat deflection temperatures) epoxy resin-amine system [67], cured acrylate-terminated unsaturated copolymers [68], PE and PP foam [69], ethylene-propylene-diene terpolymers [70], natural rubbers [71, 72], polyester-based clear coat resins [73], polyvinyl esters and unsaturated polyester resins [74], polyimide-clay nanocomposites [75], polyether sulfone-styrene-acrylonitrile, PS-polymethyl methacrylate (PMMA) blends and PS-polytetrafluoroethylene PMMA copolymers [76], cyanate ester resin-carbon fibre composites [77], polycyanate epoxy resins [78], and styrenic copolymers [79]. 

NR is normally blended with ethylene-propylene-diene rubber (EPDM) to improve the ageing resistance of the former without losing its good mechanical properties. However, due to the difference in unsaturation level between these components, a mutual incompatibility can exist, which decreases the mechanical performance. In addition to the poor interfacial adhesion caused by the thermodynamic incompatibility, these blends usually present cure rate incompatibility because of the differences between the reactivity of the elastomers with the curing agents and/or differences in solubilities of the curatives in each phase. In the case of NR/EPDM blends, the curing system can be consumed by the vulcanization of the NR phase, which is more rapidly vulcanizable because of the higher unsaturation level. ... 

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