Polymer choice, effect

Given that some of the solvent becomes an integral part of the final product and participates in the auxiliary electrode reaction, it is more than just a reaction medium. It is a reactant and should be considered as such. The solvent will also have an effect in determining the conformational nature of the polymer. This effect is analogous to that observed with other macromolecules, such as proteins, that can fold in aqueous solution to protect their hydrophobic groups but unfold in more nonpolar solvents to expose the hydrophobic groups. The choice of solvent is critical, and its role should be considered in light of the detailed polymerization mechanism. 

Reactive Flame Retardants. Reactive flame retardants become a part of the polymer by either becoming a part of the backbone or by grafting onto the backbone. Choice of reactive flame retardant is more complex than choice of an additive type. The reactive flame retardant can exert an enormous effect on the final properties of the polymer. There are also reactive halogenated compounds used as iatermediates to other flame retardants. Tables 8 and 9 Hst the commercially avaHable reactive flame retardants and iatermediates. 

Bulk Polymerization. This is the method of choice for the manufacture of poly(methyl methacrylate) sheets, rods, and tubes, and molding and extmsion compounds. In methyl methacrylate bulk polymerization, an auto acceleration is observed beginning at 20—50% conversion. At this point, there is also a corresponding increase in the molecular weight of the polymer formed. This acceleration, which continues up to high conversion, is known as the Trommsdorff effect, and is attributed to the increase in viscosity of the mixture to such an extent that the diffusion rate, and therefore the termination reaction of the growing radicals, is reduced. This reduced termination rate ultimately results in a polymerization rate that is limited only by the diffusion rate of the monomer. Detailed kinetic data on the bulk polymerization of methyl methacrylate can be found in Reference 42. 

In the same way that natural mbber is predominandy used in blends, it is also predominandy used in tire manufacture. Its excellent building tack, low heat buildup, low rolling resistance, and good low temperature performance make it the polymer of choice for many parts of tire constmction, for both passenger and tmck vehicles. The effects of radiali2ation and demand for low rolling resistance and good low temperature performance have all tended to benefit natural mbber, especially in tmck tire constmction, as shown in Table 9. 

In summary, then, design with polymers requires special attention to time-dependent effects, large elastic deformation and the effects of temperature, even close to room temperature. Room temperature data for the generic polymers are presented in Table 21.5. As emphasised already, they are approximate, suitable only for the first step of the design project. For the next step you should consult books (see Further reading), and when the choice has narrowed to one or a few candidates, data for them should be sought from manufacturers data sheets, or from your own tests. Many polymers contain additives - plasticisers, fillers, colourants - which change the mechanical properties. Manufacturers will identify the polymers they sell, but will rarely disclose their... 

Since the mid-1950s several materials have been found effective in combating ozone-initiated degradation, in particular certain p-phenylenediamine derivatives. The actual choice of such antiozonants depends on the type of polymer and on whether or not the polymer is to be subject to dynamic stressing in service. Since antiozonants are not known to have any use in plastics materials, even those which may have certain rubber particles for toughening, they will not be dealt with further here. Anyone interested further should consult references 3-5. 

By 1988, a number of devices such as a MOSFET transistor had been developed by the use of poly(acetylene) (Burroughes et al. 1988), but further advances in the following decade led to field-effect transistors and, most notably, to the exploitation of electroluminescence in polymer devices, mentioned in Friend s 1994 survey but much more fully described in a later, particularly clear paper (Friend et al. 1999). The polymeric light-emitting diodes (LEDs) described here consist in essence of a polymer film between two electrodes, one of them transparent, with careful control of the interfaces between polymer and electrodes (which are coated with appropriate films). PPV is the polymer of choice. 

We have found that proper choice of curatives and the effective modification of polymer components im-... 

The resistant properties of a lining compound depend on the choice of polymer and the compounding ingredients added to form the final material. Thus there is a diversity of choice between the base polymers and also in various compounds based on the same polymer. The ultimate choice is usually that which will be cost effective for the environment to be resisted. 

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