Ethylene-propylene rubber , comparative

Figure 2 shows the profile of the 27-29 ppm spectral region of three polymers which served as models (1J ) for ethylene propylene rubber. The better agreement between the observed spectrum and the five-parameter model strongly suggests the three-parameter model is less realistic as an explanation for the polymerization mechanism. Table VII compares the observed profiles of EPDM rubbers made with a Ziegler catalyst system. The ratio of... 

The static and dynamic mechanical properties, creep recovery behaviour, thermal expansion and thermal conductivity of low-density foams made of blends of LDPE and EVA were studied as a function of the EVA content of the blends. These properties were compared with those of a foam made from a blend of EVA and ethylene-propylene rubber. A knowledge of the way in which the EVA content affects the behaviour of these blend foam materials is fundamental to obtaining a wide range of polyolefin foams, with similar density, suitable for different applications. 9 refs. 

Ethylene-propylene rubber (EPR or EPDM) is, basically, a copolymer of ethylene and propylene. Because of the random arrangement of the monomers in the chain, crystallization does not occur, and the material behaves as a rubber. Just as with polyisobutylene, vulcanization with sulphur is impossible (the chain is saturated). Also here, a small amount of another monomer is incorporated, which enables the vulcanization and thus the use as a technical elastomer. EPR has a high resistance against ageing and chemical attack, and is, compared with other specialty rubbers, relatively cheap. 

A comparatively new group of materials— thermoplastic elastomers or thermoplastic rubbers —combines the ease of processing of thermoplastics with qualities of traditional vulcanized rubbers, especially elasticity. Because of convenience in processing there is much interest too in blends of plastics with elastomers, which may be modified by the inclusion of filler or glass fibre. As an example, a rubber-like material that can be processed as a thermoplastic can be made by blending and melt-mixing an ethylene-propylene rubber with polypropylene. The use of such blends may be helpful when there are needs to reclaim and re-process material, and in order to obtain products with qualities intermediate between those of the main components of the blends. 

Since compounds of the type XVII have shown comparable activity in a number of systems including cis-polybutadiene, styrene-butadiene rubber, and ethylene-propylene rubber, they have some commercial promise, and development work on these compounds is continuing. Nevertheless, they are not completely nondiscoloring, and in certain applications, particularly carboxylated styrene-butadiene latex films, yellow discoloration caused by the antioxidant is a serious drawback. We therefore turned our attention to ortho-linked compounds derived from 2,4-dialkylphenols. 

Polyolefin copolymers started with LLDPE and ethylene-propylene rubber (EPR). Today, there are polyolefin copolymers of ethylene with butene-1, hexene-1, octene, cyclopentene, and norbornene and copolymers of propylene with butene-1, pentene-1, and octene-1 in addition to ethylene. There are copolymers of butene-1 with pentene-1, 3-methylbutene-l, 4-methylpentene-1, and octene in addition to its copolymers with ethylene and propylene. There are copolymers of 4-methylpentene-1 with pentene-1 and hexene-1 in addition to its copolymers with butene-1 and propylene. The function of the comonomers is to reduce crystallinity, as compared to the homopolymers, resulting in copolymers that are highly elastomeric with very low... 

In this same article, O Donnell and Whittaker (164) compared the yields of cross-linking and scission, and other radiochemical products, in fully amorphous ethylene-propylene rubber (EPR) with the yields measured by them and reported by other workers for semicrystalline polyethylene and polypropylene. The yields of cross-linking and scission were significantly lower than those expected from extrapolation of the G-values for the homopolymers to zero crystalline content. In... 

A comparative analysis on thermal stability of two elastomers, butyl mbber and ethylene-propylene rubber, is presented in Figs. 30a - c. The CL investigations on these polymers [94J2] emphasize the differences that exist between them regarding the susceptibility upon oxidation. These results allow the proper selection of materials for particular applications. 

Figure 5.17 [5] compares the torque as a function of time in a batch intensive mixer for non-reactive and reactive blends of polystyrene/ethylene-propylene rubber. These results are typical for a relatively slow interfacial reaction. As the room temperature pellets of the blend are added to the hot mixer, the mixing torque rises rapidly in the melting regime. The torque for both blends then begins to fall as the temperature increases and the polymers soften. In the case of the non-reactive blend, the torque continues to fall and levels out to a reasonably constant value. However, in the case of the reactive blend there is a second peak in the torque due to the chemical reaction. The interfacial chemical reaction builds molecular weight, and in some cases may result in local crosslinking. This increases the viscosity of the blend relative to a non-reactive blend. 

Random copolymer addition to binary blends involving copolymers with structural units equal or similar to the blend components or with specific interacting groups capable of non-reactive interaction with one of both the blend components comprises another ternary polymer addition approach. An early example involved EPR (ethylene-propylene rubber) addition to HDPE/PP blends, where synergistic impact strength was observed. In some cases, the random copolymers have been compared to block copolymers comprised of the same units. The compatibihzation of LLDPE/PMMA and LLDPE/poly(MMA-co-4-vinyl pyri-dine(4VP)) blends with poly(ethylene-co-methacrylic acid) (EMAA) addition were compared [47]. Modest improvements in LLDPE/PMMA dispersion and strength were observed. The specific acid-base interaction allowed for much larger improvements with EMAA addition to LLDPE/PMMA-CO-4VP blends. 

Polyolefin thermoplastic elastomers are generally blends of polypropylene with up to 65% ethylene-propylene rubber and it is supposed that short propylene blocks in the latter co-crystallize with segments of the polypropylene chains to give microcrystalline regions which act as cross-links. A recent development in this field has been the use of highly cross-linked ethylene-propylene rubbers (and other rubbers) in the blends to give so-called thermoplastic vulcanizates (TPVs). In these blends the rubber is present as finely dispersed particles in a polypropylene matrix. Compared to the simple blends, these materials have generally enhanced properties. 

In addition to the diene rubbers, it is also possible to use DMA to identify blends of the other commercially available rubbers, provided that there is a sufficient difference in their glass transition temperature, and to characterise their properties. For example, Carlberg, Colombini and Maurer [44] mixed ethylene-propylene rubber and silicone rubber in a number of blend ratios and studied their morphology and viscoelastic properties. The results obtained experimentally by DMA and DSC were compared to theoretical data produced from self-consistent models, both indicating that the silicone rubber was the dispersed phase in a continuum of ethylene-propylene rubber. 

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