Diene-type elastomers

Manufacturer Trade Type Grade name elastomer designation Oil content (phr) Mooney viscosity (T + 8 ) at 127 C Ethylene content Diene type Diene content Molecular weight distribution classification... 

ABA triblock copolymers of the styrene-diene type are well known, and owe their unique properties to their heterophase morphology. This arises from the incompatibility between the polystyrene A blocks and the polydiene B blocks, leading to the formation of a dispersion of very small polystyrene domains within the polydiene matrix. This type of elastic network, held together by the polystyrene "junctions", results in thermoplastic elastomer properties. 

Ebonite bonding The adhesive layer in this case is unvulcanized ebonite (or hard rubber , USA) applied to the metal either as a solution or as a thin sheet" Ebonite contains 30-50 parts sulphur per hundred parts of rubber (phr), whereas soft rubber seldom has more than 3 parts phr of this vulcanizing agent. The method dates back to the mid-nineteenth century and is most closely identified with natural rubber, but can be applied to other diene-type elastomers, including nitrile rubber. 

A number of patents have emphasized acrylic elastomers as a method of rubber-toughening plastics.The latexes are crosslinked, in part, to impart mechanical stability during processing. Acrylic latexes have improved stability to light and heat over SBR or NBR, and thus offer an improvement to ABS materials. In general, saturated elastomers have proved superior to the diene types for outdoor use because of their superior weather resistance. 

Diene Types The diene elastomers are based on polymers prepared from butadiene, isoprene, their derivatives and copolymers. The oldest elastomer, natural rubber (polyisoprene), is in this class (see Section 9.2). Polybutadiene, polychloroprene, styrene-butadiene rubber (SBR), and acrylonitrile-butadiene rubber (NBR) are also in this class. 

In the following data acquisition, the same 163 standard polymer samples used in the former edition were adopted as a set of representative ones utilized in versatile fields, which include representative synthetic polymers [a) polyolefins (homopolymers) (001— 007), b) vinyl polymers with ethylene units (copolymers) (008—015), c) vinyl polymers with styrene units (016—028), d) vinyl polymers with styrene derivatives (029—035), e) acrylate-type polymers (036—049), f) chlorine-containing vinyl polymers (050-059), g) fluorine-containing vinyl polymen (060—066), h) the other vinyl polymers (067—070), i) diene-type elastomers (071—081), j) polyamides (082-090), k) polyacetals and polyethers (091—095), 1) thermosetting polymers (096—106), m) polyimides and polyamide-type engineering plastics (107—114), n) polyesters (115—126), o) the other engineering plastics with phenylene skeletons (127—138), p) sificone polymers (139—143), and q) polyurethanes (144—147)] along with some natural polymers [r) cellulose-type polymers (148-155) and s) the other some natural polymers (156-163)]. 

EPDM-Derived Ionomers. Another type of ionomer containing sulfonate, as opposed to carboxyl anions, has been obtained by sulfonating ethylene—propjlene—diene (EPDM) mbbers (59,60). Due to the strength of the cross-link, these polymers are not inherently melt-processible, but the addition of other metal salts such as zinc stearate introduces thermoplastic behavior (61,62). These interesting polymers are classified as thermoplastic elastomers (see ELASTOLffiRS,SYNTHETIC-THERMOPLASTICELASTOLffiRS). 

There are seven principal classes of accelerators and several miscellaneous products that do not fit into these classes. In addition, many proprietary blends of several accelerators are sold which are designed as cure packages for a specific appHcations. Choosing the best cure system is a responsibiUty of the mbber chemist and requites extensive knowledge of each accelerator type and its appHcabiUty in each elastomer. Table 5 shows a rule of thumb comparison of the scorch/cure rate attributes for the five most widely used classes of accelerators used in the high volume diene-based elastomers. 

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. 

Emulsion polymerisation is used in the commercial production of synthetic diene elastomers and also to produce commercial latexes of the type used in paints these paints are known incorrectly as emulsion paints and... 

Solid-state 13C NMR has been used to identify elastomers in binary blends of chloroprene (CR) and NR, CR and CSM, NR and CSM, and SBR and acrylonitrile-butadiene rubber (NBR). The type of NBR can be determined by identifying the sequences of acrylonitrile and butadiene. The tertiary blend of NR/SBR/BR was also studied [49]. High-temperature 13C solid-state NMR identified ethylene-propylene diene terpolymer (EPDM) and fluoro and nitrile rubbers [50]. 

They are based on various metals. Such as zirconium, complexed with cyclopentadienide anions. This type of compound is called a zirconocene and is used with organoalu-minum to make highly regular polymers. The catalyst has the ability to flip back and forth from making atactic to isotactic polypropylene in the same polymerization. The alternating tacticity of the polymer breaks up the crystallinity of the chains and yields an elastomer. Metallocene catalysts are currently very expensive and cannot yet polymerize dienes such as butadiene, so they have only enjoyed limited commercial success in elastomers. However, this is one of the most intense fields of polymer research and many new product breakthroughs are expected in the near future. 

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