Polymers and Elastomers

Polymer and elastomer data are typically producer-specific. Sources therefore tend to be scattered and incomplete. While no single hard-copy source is all encompassing, the following are worth consulting. 

Tables 13.4 and 13.5 contain a summary of typical stability values for a number of polymers and elastomers against typical chemical agents. As expected, condensation polymers generally exhibit good stability to nonpolar liquids while they are generally only (relatively) moderately or unstable toward polar agents and acids and bases. This is because of the polarity of the connective condensation linkages within the polymer backbone. By comparison, vinyl type of polymers exhibit moderate to good stability toward both polar and...

Figure 5.77 Comparison of idealized stress-strain diagrams for metals, amorphous polymers, and elastomers.

Since the terms rubber, polymer and elastomer are synonyms, throughout this book these terms are used interchangeably. 

This indicates that, with time, gas evolution from PTFE (mostly water vapour) becomes an increasingly important gas source. This behaviour is typical of polymers and elastomers. 

If a modulus is plotted as a function of temperature, a very characteristic curve is obtained which is different in shape for the different types of polymer amorphous (glassy) polymers, semi crystalline polymers and elastomers (cross-linked amorphous polymers). 

Polymers and elastomers comprising at least one 9-H,H-fluorene group and at least one arylene group have been prepared. These materials are suitable for use as semiconductors or charge transport materials in optical, electrooptical, or electronic devices, including field-effect transistors, electroluminescent, photovoltaic, and sensor devices. 

Over half of the remaining market for products used in the processing of rubber is made up of antioxidants, antiozonants and stabilizers, either amino compounds or phenols. Aniline is used to manufacture vulcanization accelerators, antioxidants and antidegradants. Of the latter, several are A-substituted derivatives of p-phenylenediamine and octyl dipheny-lamine. Diphenylamines terminate free-radical reactions by donating the amino hydrogen, and are used to protect a wide range of polymers and elastomers. Many synthetic rubbers incorporate alkylated diphenylamine antioxidants. Other antioxidants include aryl amine resinous products from, e.g. condensation of aniline and acetone in the presence of... 

Paraplex [Hall]. TM for polymeric plasticizers for polymers and resinous coatings. Primarily polyesters, but some are epoxidized oils that impart heat and light stability as well as plasticization. Supplied as viscous liquids in a range of molecular weights all at 100% solids. Compatible with polyvinyl chloride, polyvinyl butyral, cellulosics, and other high polymers and elastomers. 

Plasthall [Hall]. TM for a broad range of monomeric and polymeric plasticizers used in polymers and elastomers. Types include adipates, gluta-rates, trimellitates, azelates, sebacates, and tallates. 

Although bulk silicon(IV) oxide is not chlorinated by phosgene, it does slowly chlorinate the surface [866]. This phenomenon has been used to chlorinate the surfaces of chrysotile asbestos and nonexpanded vermiculite for grafting to polystyrene for use as a filler for polymers and elastomers [1383,1384]. Moreover, in the presence of aluminium(III) chloride, phosgene will convert silica gel into silicon(IV) chloride at between 400 and 700 C [208a,208b]. 

In materials science applications of NMR imaging the geometry of the object can often be chosen at liberty. For example, cylindrical samples can be used for studies of porosity by diffusion and flow in rocks and catalyst pellets [Maj2], and investigations of deterioration in polymers and elastomers. Furthermore, many biological samples show radial or close... 

Table 7.1.2 Examples of material properties for polymers and elastomers...

Using metallocene catalysts it has proved possible to tailor the microstructure of the polymers by fine-tuning of the ligands. Besides polyethylene, it is possible to co-polymerize ethylene with a-olefins such as propylene, but-l-ene, pent-l-ene, hex-l-ene, and oct-l-ene, in order to produce LLDPE. In addition, many kinds of co-polymers and elastomers, and new structures of polypropylenes, polymers and co-polymers of cyclic olefins can be obtained. Furthermore, catalysts with chiral centers can be beneficial in stereospecific polymerization to build the desired isotactic products. 

Polymers are very sensitive to the rate of testing. As the strain rate increases, polymers in general show a decrease in ductility while the modulus and the yield or tensile strength increase. Figure 13.32 illustrates this schematically. The sensitivity of polymers to strain rate depends on the type of polymer for brittle polymers the effect is relatively small, whereas for rigid, ductile polymers and elastomers, the effects can be quite substantial if the strain rate covers several decades. 

Linear viscoelasticity is valid only imder conditions where structural changes in the material do not induce strain-dependent modulus. This condition is fulfilled by amorphous polymers. On the other hand, the structural changes associated with the orientation of crystalline polymers and elastomers produce anisotropic mechanical properties. Such polymers, therefore, exhibit nonlinear viscoelastic behavior. 

These products represent additional advances made by polymer scientists and formulating chemists. They use unique molecular building blocks and polymers, sometimes of different families than strictly acrylic, leading to numerous hybrids involving other polymer and elastomer types emerging very recently. In addition to the properties noted above, HI products retain virtually all of the performance features of earlier variants. 

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