Rubber, syntheti

When many moleeules eombine the maeromoleeule is termed a polymer. Polymerization ean be initiated by ionie or free-radieal meehanisms to produee moleeules of very high moleeular weight. Examples are the formation of PVC (polyvinyl ehloride) from vinyl ehloride (the monomer), polyethylene from ethylene, or SBR synthetie rubber from styrene and butadiene. 

Friction modifiers inelude inorganie fiietion modifiers such as alumina, silica, magnesia, zireonia, chrome oxide, or quartz and organic fiietion modifiers sueh as synthetie rubber or eashew dust. Graphite, or molybdenum disulfide serve as solid lubrieants. Copper fiber increases the thermal conductivity of the formulation. 

The binder may, for instanee be bitumen (eoal tar or asphalt), or linseed oil (natural materials), alkyd, ehlorinated rubber, epoxy, vinyl, polyurethane ete. (synthetie organie materials), or silieate (inorganie). Some paints are hardened by reaetion with oxygen in the air (oil and aUcyd paints), others by evaporation of the... 

The wide spread use of synthetie rubbers beeame possible with the use of reinforcing fillers. The purpose of the fillers within rubber compounds is manifested in two ways ... 

For adhesive gluing, the surfaces to be joined must be adequately treated to improve adhesion. Flaming, eorona diseharge and primer are used for surface treatment. The methods for surfaee treatment are similar to those used for decorating and printing (Section 7.3). Adhesives used for bonding of PP are eontact adhesives based on polyurethanes or synthetie rubber, two-pack adhesives based on epoxy resins, polyurethanes, ete., vinyl aeetate eopolymer hot melt adhesives, pressure-sensitive adhesives and pol5mrethane eontact cements. 

Rubber, of either natural or synthetic origin, also contains becatrse of its method of production many biodegradable compounds. It is used for pirrposes in which it needs to maintain its elasticity for a long time. Generally, synthetie mbbers are more stable than natural ones. In any case, rubbers may be attacked by microorganisms. 

Use of (PCy3)2Cl2Ru=CHPh (1) in Other Synthetie Transformations. As well as finding widespread use in metathesis, (1) has found applications as a catalyst for other important reactions. These include hydrosilylation of alk3Ties dehydrogenative condensation of alcohols and hydrosilylation of carbonyls intermolecular cyclotrimerization of terminal alkynes conversion of triynes to benzene derivatives Kharasch additions (Z)-selective cross-dimerization of ary-lacetylenes with silylacetylenes and hydrogenation of natural rubber. ... 

Many environmentalists still believe that synthetie polymers eannot biodegrade in the environment. It is certainly true that some plasties may not degrade for a very long time even in sunlight. For example, properly stabiUsed PVC is widely used in out-door applications, such as window fiames which do not biodegrade for many decades, possibly centuries. At the other extreme, the poly(dienes) - for example c/s-poly(isoprene) in the form of latex rubber - biodegrades in a few months in soil (see section 12.2). The polyolefins lie somewhere between PVC and natural rubber. Biodegradable polyethylene (e.g. EPl TDPA ) shows a substantial induction period (IP) at 20 "C, whereas at 60 "C, the IP is very short. In a commercial weatherometer, the IP is even shorter." " ... 

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