Ethylene/propylene copolymers examples

Many cellular plastics that have not reached significant commercial use have been introduced or their manufacture described in Hterature. Examples of such polymers are chlorinated or chlorosulfonated polyethylene, a copolymer of vinyUdene fluoride and hexafluoropropylene, polyamides (4), polytetrafluoroethylene (5), styrene—acrylonitrile copolymers (6,7), polyimides (8), and ethylene—propylene copolymers (9). 

The use of TAG as a curing agent continues to grow for polyolefins and olefin copolymer plastics and mbbers. Examples include polyethylene (109), chlorosulfonated polyethylene (110), polypropylene (111), ethylene—vinyl acetate (112), ethylene—propylene copolymer (113), acrylonitrile copolymers (114), and methylstyrene polymers (115). In ethylene—propylene copolymer mbber compositions. TAG has been used for injection molding of fenders (116). Unsaturated elastomers, such as EPDM, cross link with TAG by hydrogen abstraction and addition to double bonds in the presence of peroxyketal catalysts (117) (see Elastol rs, synthetic). 

Plastics are susceptible to brittle crack-growth fractures as a result of cyclic stresses in much the same way as metals. In addition, because of their high damping and low thermal conductivity, plastics are prone to thermal softening if the cyclic stress or cyclic rate is high. Examples of the TPs with the best fatigue resistance include PP and ethylene-propylene copolymers. 

One component obeys the Bemoullian model the other two obey the enantiomorphic- site model. Similarly, the NMR data of fractionated copolymers can be used to demonstrate the presence of multiple components in the copolymers. An example is shown of ethylene-propylene copolymers where the NMR/fractionation data are used to show the presence of two or three catalytic sites. 

As an example of the use of MIXCO.TRIAD, an analysis of comonomer triad distribution of several ethylene-propylene copolymer samples will be delineated. The theoretical triad Intensities corresponding to the 2-state B/B and 3-state B/B/B mixture models are given In Table VI. Abls, et al (19) had earlier published the HMR triad data on ethylene-propylene samples made through continuous polymerization with heterogeneous titanium catalysts. The data can be readily fitted to the two-state B/B model. The results for samples 2 and 5 are shown In Table VII. The mean deviation (R) between the observed and the calculated Intensities Is less than 1% absolute, and certainly less than the experimental error In the HMR Intensity determination. 

The isoprene units in the copolymer impart the ability to crosslink the product. Polystyrene is far too rigid to be used as an elastomer but styrene copolymers with 1,3-butadiene (SBR rubber) are quite flexible and rubbery. Polyethylene is a crystalline plastic while ethylene-propylene copolymers and terpolymers of ethylene, propylene and diene (e.g., dicyclopentadiene, hexa-1,4-diene, 2-ethylidenenorborn-5-ene) are elastomers (EPR and EPDM rubbers). Nitrile or NBR rubber is a copolymer of acrylonitrile and 1,3-butadiene. Vinylidene fluoride-chlorotrifluoroethylene and olefin-acrylic ester copolymers and 1,3-butadiene-styrene-vinyl pyridine terpolymer are examples of specialty elastomers. 

For example, a PE-fe-poly(ethylene-co-propylene) diblock composed of crystalline PE and amorphous ethylene/propylene copolymer segments was synthesized from ethylene and ethylene/propylene. The addition of MAO and Ti-FI catalyst 40 (Fig. 25) to an ethylene-saturated toluene at 25 °C resulted in the rapid formation of a living PE (Mn 115,000, MJMn 1.10). The addition of ethylene/propylene (1 3 volume ratio) to this living PE formed a PE-/>poly(ethylcnc-co-propylcnc) block copolymer (Mn 211,000, MJMn 1.16, propylene content 6.4 mol%) [30], As expected, the polymer exhibits a high Tm of 123 °C, indicating that this block copolymer shows good elastic properties at much higher temperatures than the conventional random copolymers of similar densities. 

A common example of a copolymer is an ethylene-propylene copolymer. Although both monomers would result in semi-crystalline polymers when polymerized individually, the melting temperature disappears in the randomly distributed copolymer with ratios between 35/65 and 65/35, resulting in an elastomeric material, as shown in Fig. 1.19. In fact, EPDM rubbers are continuously gaining acceptance in industry because of their resistance to weathering. On the other hand, the ethylene-propylene block copolymer maintains a melting temperature for all ethylene/propylene ratios, as shown in Fig. 1.20. 

A final quantitative example is that of determining the % ethylene in ethylene-propylene copolymers (EPM). The International Institute of Synthetic Rubber Producers (IIRP) Technical/Operating Committee and the American Society for Testing and Materials (ASTM) cooperated to produce an updated standard method [56]. They also produced a set of standards with the ethylene content established by 13C NMR. Those standards were utilised by Parker and Waddell to study the photoacoustic determination of % ethylene [57]. Three of the four infrared band ratios specified by ASTM were measured, 1378/1462, 1378/722, and 1156/722. The fourth one, 1156/4255, was not used since it involves measurements in the near-IR region. Baselines were drawn by the valley-to-valley technique as illustrated in Figure 2.11. 

Things become a little more difficult in materials such as ethylene/propylene copolymers, for example, because vibrational modes in different units can couple and are then no longer associated with a particular type of monomer. Or the bands due to specific functional groups (e.g., CE or CH3) can overlap other modes or each other (e.g., in the CH stretching region of the spectrum) and be difficult to separate. Adding to this... 

Ethylene-propylene copolymers, EPR, and ter-polymers containing diene monomers, EPDM, crosslink on irradiation [Bradley, 1984 Aoshima et al, 1992]. The crosslinking can be enhanced by the use of crosslinking agents for example, EPDM containing 5-ethylidene-2-norborene, ENB, may be efficiently radiation crosslinked. Analogues of reaction (R-30) contribute to such crosslinking. 

Both on-column and post-column detection schemes have been developed for radionuclide detection for CE. The most common type used is an on-column configuration, which yields detection limits in the 10 M range for isotopes such as P. Isotachophoretic separations of C were among the first examples of online capillary radionuclide detection, performed by Kaniansky et al. The associated instmment uses 300-p,m ID fluorinated ethylene-propylene copolymer capillary tubing, and the separation eluent flows directly into a plastic scintillator cell between two PMTs. The scintillation events are detected coincidentally between the two PMTs, such that only if both PMTs receive an input within a short time will they register the count as signal. This kind of coincidence detection ensures that nonscintillation photons that come from outside the detection cell and only hit one PMT are not counted. This system exhibits a detection limit of 16 Bq for analytes, with a detector efficiency of 13-15%. 

If the suitable functionality (halogen) is not present originally in the polymer molecule, it can be introduced by suitable post-polymerization techniques. For example, polystyrene branches can be grafted onto ethylene-propylene rubber after chlorinating the rubber. Ethylene-propylene copolymer contains tertiary hydrogens which can be readily exchanged for chlorine. Subsequently the tertiary chlorines are easily activated by complexation with A1(C2H5)2C1 and the macro-cation formed is eminently suitable for the polymerization-initiation of, say, styrene. 

Common examples of miscible blends are ethylene-propylene copolymers of different composition that result in an elastomer comprising a semicrystalline, higher ethylene content and an amorphous, lower ethylene content components. These blends combine the higher tensile strength of the semicrystaUine polymers and the favorable low temperature properties of amorphous polymers. Chemical differences in miscible blends of ethylene-propylene and styrene-butadiene copolymers can also arise from differences in the distribution and the type of vulcanization site on the elastomer. The uneven distribution of diene, which is the site for vulcanization in blends of ethylene-propylene-diene elastomers, can lead to the formation of two distinct, intermingled vulcanization networks. 

Before reviewing in detail the fundamental aspects of elastomer blends, it would be appropriate to first review the basic principles of polymer science. Polymers fall into three basic classes plastics, fibers, and elastomers. Elastomers are generally unsaturated (though can be saturated as in the case of ethylene-propylene copolymers or polyisobutylene) and operate above their glass transition temperature (Tg). The International Institute of Synthetic Rubber Producers has prepared a list of abbreviations for all elastomers [3], For example, BR denotes polybutadiene, IRis synthetic polyisoprene, and NBR is acrylonitrile-butadiene rubber (Table 4.1). There are also several definitions that merit discussion. The glass transition temperature (Tg) defines the temperature at which an elastomer undergoes a transition from a rubbery to a glassy state at the molecular level. This transition is due to a cessation of molecular motion as temperature drops. An increase in the Tg, also known as the second-order transition temperature, leads to an increase in compound hysteretic properties, and in tires to an improvement in tire traction... 

If two monomers are used to make a plastics material then, the resultant product is known as a copolymer. It may be referred to by means of initials which represent the monomers used i.e. without a p for poly . For example, the copolymer (bipolymer) made from styrene and acrylonitrile, is referred to as styrene acrylonitrile copolymer or, as SAN. It is now suggested that an oblique stroke / be placed between the two monomer abbreviations e.g. E/P for an ethylene propylene copolymer. However, this suggestion is not universally adopted as SAN is still SAN the oblique strokes may be omitted when common usage so dictates according to ISO 1043-1 1987 (E). 

Nature of materials. The existence of a vulnerable sites on backbone, they are primordially modified either by bond splitting or by removing as primary radicals. An illustrative example can be found in the domain of ethylene-propylene elastomers [13]. While ethylene propylene copolymer (EPR), which is manufactured by the copolymerization of ethylene with propylene, it presents a saturated molecular structure. In contrast, ethylene-propylene ter-polymer (EPDM) is produced by copolymerization of ethylene with propylene in the presence of a third diene component (for example ethylidene 2-nor-bomene), which brings a certain unsaturation level. 

The chains must be crosslinked to form a network (cf. Fig 7.16). In most elastomers containing double bonds, covalent bonds are introduced between chains. This can be done either with sulfur or polysulfide bonds (the well known sulfur vulcanisation of natural rubber is an example), or else by direct reactions between double bonds, initiated via decomposition of a peroxide additive into radicals. Double bonds already exist in the chemical structure of polyisoprene, polybutadiene and its copolymers. When this is not the case, as for silicones, ethylene-propylene copolymers and polyisobutylene, units are introduced by copolymerisation which have the property of conserving a double bond after incorporation into the chain. These double bonds can then be used for crosslinking. This is how Butyl rubber is made from polyisobutylene, by adding 2% isoprene. Butyl is a rubber with the remarkable property of being impermeable to air. It is used to line the interior of tyres with no inner tube. 

Examples of typical elastomers include natural rubber, butyl rubber, poly(dimethyl siloxane), polyethyl acrylate, styrene-butadiene copolymer, and ethylene-propylene copolymer. Some polymers are not elastomers under normal... 

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