Elastomer additives chemical structures

Plastics. Plastics are the polymeric materials with properties intermediate between elastomers and fibers. In spite of the possible differences in chemical structure, the demarcation between fibers and plastics may sometimes be blurred. Polymers such as polypropylene and polyamides can be used as fibers and plastics by a proper choice of processing conditions. Plastics can be extruded as sheets or pipes, painted on surfaces, or molded to form countless objects. A typical commercial plastic resin may contain two or more polymers in addition to various additives and fillers. Additives and fillers are used to improve some property such as the processability, thermal or environmental stability, and mechanical properties of the final product. 

Chart I. Chemical structures and characteristics of dicyanate monomers, elastomer additives, and PES additives. 

A true synthetic natural rubber was introduced in the mid-1960s with the exact same chemical structure as latex tapped from a tree. The difference is that natural rubber comes with a variety of other ingredients in the latex that can both add and detract from performance, while polyisoprene is considered relatively pure. In addition, there are some differences in molecular weight distribution that impact performance. Available in both latex and solid forms, this elastomer can be directly substituted for natural rubber in many applications. Adhesives which are not cured tend to have higher creep values than natural rubber, but also exhibit lower tack and green strength properties. Vulcanized adhesive products perform equal to cured natural rubber adhesive products. 

In addition to changes and variation in morphology, immiscible blends show additional, more complex changes due to different chemical properties of the two-component elastomer. This difference in the chemical structure manifests as three distinct but interrelated properties. First, the dissimilar elastomers differ in the retention of the fillers (e.g., carbon black) and plasticizers (e.g.. 

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. 

Segmented poly etherurethanes contain no water-soluble additives and are characterized by a high hydrolytic resistance, good processability, and good mechanical properties in comparison with otho elastomers. Therefore, polyurethanes of this type are widely used in medicine, for example as aortic balloon pumps, catheters, and housings for artificial hearts Thus, a corrdation betweaa blood compatibiUty and the chemical structure of polyurethanes has often been reported... 

There are two types of attack by biological organisms on plastics desirable and undesirable. Although some plastics (e.g., those with ester or amide structures) md/oT additives have a chemical structure attractive to living organisms (hydrocarbons), undesirable attack is relatively rare. Nonetheless, serious problems may arise, mainly in tropical climates therefore efforts are being made to create products for use in hot climates, e.g., elastomer pipe seals. 

The commercial polyester elastomers are mostly based on poly(tetrameth-ylene oxide) (PTMO) as flexible segment and poly(butylene terephthalate) (PBT) as rigid segment. Yet, many chemical modifications of some particular segments and also segments of totally different chemical structure have been examined and applied. Thus, in addition to PTMO [1,2,11-16], poly(ethylene oxide) (PEO) [17-22], poly(aliphatic oxide) (C2-C4) copolymers [23-30], poly (butylene succinate), and other aliphatic polyesters [31-35], polycaprolac-tone (PCL), polypivalolactone (PVL) [36,37], aliphatic polycarbonates (PC) [38-41], dimerized fatty acid (DFA)-based polyesters [42-50], polyamide 66 and derivatives [47-57], polyolefins [58-60], rubbers [61-63], and polydimethyl-siloxane [64,65] are used as flexible segments of polyester elastomers. 

The incorporation of a third block into the main chain of a multiblock copolymer not only changes its chemical structure, but also influences its morphology [31]. The changes in the supermolecular structure depend on the solubility of the additional block in the amorphous phases of the two other blocks. This solubility is affected by the chemical structure, molecular weight, polydispersity and the contribution of each of the blocks in the terpolymer (Figure 15). The thermoplastic elastomers of the -(4GT- -P04- -PA12)- type have a nanostructure and possess useful properties when the molecular weights of the blocks are appropriately chosen 1500 < 2500 g/mole, 1000 < < 1500 g/mole,... 

Among elastomers, artificial rubbers have replaced natural rabber for many uses because of their high resistance to chemical attack by ozone, an atmospheric pollutant. When ozone reacts with polymer chains, it breaks CUCn bonds and introduces additional cross-linking. Breaking 7r bonds causes the rabber to sofien, and cross-linking makes it more brittle. Both changes eventually lead to rupture of the polymer structure. 

Finally, for practical reasons it is useful to classify polymeric materials according to where and how they are employed. A common subdivision is that into structural polymers and functional polymers. Structural polymers are characterized by - and are used because of - their good mechanical, thermal, and chemical properties. Hence, they are primarily used as construction materials in addition to or in place of metals, ceramics, or wood in applications like plastics, fibers, films, elastomers, foams, paints, and adhesives. Functional polymers, in contrast, have completely different property profiles, for example, special electrical, optical, or biological properties. They can assume specific chemical or physical functions in devices for microelectronic, biomedical applications, analytics, synthesis, cosmetics, or hygiene. 

An example of this type of a safer chemical is methacrylonitrile (1) compared with acrylonitrile (2) (Figure 1.1). Both compounds are a, 3-unsaturated aliphatic nitriles, and structurally very similar, but 2 causes cancer whereas 1 does not appear to do so. Among other applications, 2 is used in the production of acrylic and modacrylic fibers, elastomers, acrylonitrile-butadiene-styrene and styrene-acrylonitrile resins, nitrile rubbers, and gas barrier resins. In a study conducted by the US National Toxicology Program (NTP) in which 2 was administered orally to mice for 2 years, there was clear evidence that it caused cancer in the treated mice (in addition to causing other toxic effects), and is classified by the NTP as a probable human carcinogen [26]. 

In addition to the PDMS elastomer depicted in Fig. 2, we have produced for these investigations two series of siloxane copolymers based on dimethylsiloxane 1) copolymers of methyl trifluoropropyl (TFP) siloxane and dimethyl siloxane and 2) copolymers of diphenyl (DP) siloxane and dimethyl siloxane. Figure 4 provides structures for the oligomers, all of which had aminoethylpiperazine (AEP) end groups. Details on synthesis and chemical characterization of these modifiers will be published38). 

Ethylene (structure in Figure 13.1) is the most widely used organic chemical. Almost all of it is consumed as a chemical feedstock for the manufacture of other organic chemicals. Polymerization of ethylene to produce polyethylene is illustrated in Figure 13.4. In addition to polyethylene, other polymeric plastics, elastomers, fibers, and resins are manufactured with ethylene as one of the ingredients. Ethylene is also the raw material for the manufacture of ethylene glycol antifreeze, solvents, plasticizers, surfactants, and coatings. 

First, a common method of forming polymers by a radical reaction is discussed. After the structures of the addition polymers made by this method are examined, several other procedures that can be used to prepare these or similar polymers are presented. Next, the effect of the structure of a polymer on its physical properties is discussed. This provides a basis for understanding the properties and uses of a number of other addition polymers. Rubbers (elastomers) are then discussed followed by condensation polymers and thermosetting polymers. The chapter concludes with a brief examination of the chemical properties of polymers. 

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