Ethylene-propylene materials

The minimum service temperature is determined primarily by the Tg of the soft phase component. Thus the SBS materials ctm be used down towards the Tg of the polybutadiene phase, approaching -100°C. Where polyethers have been used as the soft phase in polyurethane, polyamide or polyester, the soft phase Tg is about -60°C, whilst the polyester polyurethanes will typically be limited to a minimum temperature of about 0°C. The thermoplastic polyolefin rubbers, using ethylene-propylene materials for the soft phase, have similar minimum temperatures to the polyether-based polymers. Such minimum temperatures can also be affected by the presence of plasticisers, including mineral oils, and by resins if these become incorporated into the soft phase. It should, perhaps, be added that if the polymer component of the soft phase was crystallisable, then the higher would also affect the minimum service temperature, this depending on the level of crystallinity. 

Fluorinated ethylene propylene materials, acid resistance of, 23 785 Fluorinated heterocyclic compounds, 77 867... 

There are little or no olefins in crude oil or straight run (direct from crude distillation) products but they are found in refining products, particularly in the fractions coming from conversion of heavy fractions whether or not these processes are thermal or catalytic. The first few compounds of this family are very important raw materials for the petrochemical Industry e.g., ethylene, propylene, and butenes. 

Propellants cast into rockets are commonly case-bonded to the motors to achieve maximum volumetric loading density. The interior of the motor is thoroughly cleaned, coated using an insulating material, and then lined with a composition to which the propellant binder adheres under the environmental stresses of the system. The insulation material is generally a mbber-type composition, filled with siUca, titanium dioxide, or potassium titanate. SiUca-filled nitrate mbber and vulcanizable ethylene—propylene mbber have been used. The liner generally consists of the same base polymer as is used in the propellant. It is usually appHed in a thin layer, and may be partially or fully cured before the propellant is poured into the rocket. 

Most elastomers can be made iato either opea-ceUed or closed-ceUed materials. Natural mbber, SBR, nitrile mbber, polychloroprene, chlorosulfonated polyethylene, ethylene—propylene terpolymers, butyl mbbers, and polyacrylates have been successfuUy used (4,111,112). 

Cables are available in a variety of constmctions and materials, in order to meet the requirements of industry specifications and the physical environment. For indoor usage, such as for Local Area Networks (LAN), the codes require that the cables should pass very strict fire and smoke release specifications. In these cases, highly dame retardant and low smoke materials are used, based on halogenated polymers such as duorinated ethylene—propylene polymers (like PTFE or FEP) or poly(vinyl chloride) (PVC). Eor outdoor usage, where fire retardancy is not an issue, polyethylene can be used at a lower cost. 

Similarly, the random introduction by copolymerization of stericaHy incompatible repeating unit B into chains of crystalline A reduces the crystalline melting point and degree of crystallinity. If is reduced to T, crystals cannot form. Isotactic polypropylene and linear polyethylene homopolymers are each highly crystalline plastics. However, a random 65% ethylene—35% propylene copolymer of the two, poly(ethylene- (9-prop5lene) is a completely amorphous ethylene—propylene mbber (EPR). On the other hand, block copolymers of the two, poly(ethylene- -prop5iene) of the same overall composition, are highly crystalline. X-ray studies of these materials reveal both the polyethylene lattice and the isotactic polypropylene lattice, as the different blocks crystallize in thek own lattices. 

At this point in the process, thermoplastic and chlorosulfonated polyethylene (CSPE) membranes are complete and are ready for packaging. In the case of ethylene—propylene—diene monomer (EPDM), the curing step occurs before the membrane is ready for packaging. The curing process is accomphshed by placing the membrane in a large vulcanizer where the material is heated under pressure to complete the cure. 

Certain block copolymers have also found appHcation as surfactants (88). Eor example, AB or ABA block copolymers in which one block is hydrophilic and one block is hydrophobic have proven useful for emulsifying aqueous and non-aqueous substances and for wetting the surface of materials. Examples of such surfactants are the poly(propylene oxide- /oi / -ethylene oxide) materials, known as Pluronics (BASC Wyandotte Co.). 

Flares are mostly used for the disposal of hydrocarbons. Waste gases composed of natural gas, propane, ethylene, propylene, butadiene, and butane probably constitute over 95 percent of the material flared. Flares have been used successfully to control malodorous gases such as mercaptans and amines, but care must be taken when flaring these gases. Unless the flare is very efficient and gives good combustion, obnoxious fumes can escape unburned and cause a nuisance. 

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... 

One unfortunate characteristic property of polypropylene is the dominating transition point which occurs at about 0°C with the result that the polymer becomes brittle as this temperature is approached. Even at room temperature the impact strength of some grades leaves something to be desired. Products of improved strength and lower brittle points may be obtained by block copolymerisation of propylene with small amounts (4-15%) of ethylene. Such materials are widely used (known variously as polyallomers or just as propylene copolymers) and are often preferred to the homopolymer in injection moulding and bottle blowing applications. 

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... 

None of the polymers from unbranched olefins, other than ethylene, propylene or but-1-ene, has yet become important as a plastics material although some of them are of interest both as adhesives and release agents. One limitation of a... 

Two random copolymers of this type are of importance, ethylene-propylene copolymers and ethylene-but-l-ene copolymers. The use and properties of polypropylene containing a small quantity of ethylene in stereoblocks within the molecule has already been discussed. Although referred to commercially as ethylene-propylene copolymers these materials are essentially slightly modified polypropylene. The random ethylene-propylene polymers are rubbery and are discussed further in Section 11.9. 

These materials were first introduced by Du Pont in 1956 and are now known as Teflon FEP resins. (FEP = fluorinated ethylene-propylene.) Subsequently other commercial grades have become available (Neoflon by Daikin Kogyo and Teflex by Niitechim, USSR). These copolymers may be regarded as the first commercial attempt to provide a material with the general properties of PTFE and the melt processability of the more conventional thermoplastics. 

Whilst the ASA materials are of European origin, the AES polymers have been developed in Japan and the US. The rubber used is an ethylene-propylene terpolymer rubber of the EPDM type (see Chapter 11) which has a small amount of a diene monomer in the polymerisation recipe. The residual double bonds that exist in the polymer are important in enabling grafting with styrene and acrylonitrile. The blends are claimed to exhibit very good weathering resistance but to be otherwise similar to ABS. 

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. 

Initial materials of this super-tough type were blends of nylon 66 with an ionomer resin (see Chapter 11). More recent materials are understood to be blends of nylon 66 with a modified ethylene-propylene-diene terpolymer rubber (EPDM rubber—also see Chapter 11). One such modification involves treatment of the rubber with maleic anhydride, this reacting by a Diels—Alder or other... 

Photodegradation may involve use of inherently photo-unstable polymers or the use of photodegradant additives. An example of the former are ethylene-carbon monoxide polymers in which absorption of light by the ketone group leads to chain scission. The polymer becomes brittle and forms a powder. Such materials are marketed by Dow and by Du Pont. Other examples are the copolymers of divinyl ketone with ethylene, propylene or styrene marketed by Eco Atlantic. 

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