Applications of Polymer Blends, Grafts, and Blocks

Many properties are involved in determining a material s ultimate usefulness. For homopolymers, the temperature of the glass-rubber transition, presence or absence of crystallinity, crosslinking, molecular weight characteristics, permeability, and toughness all make a contribution. When two different polymers are mixed or joined in some fashion the mode of mixing becomes important as well. Tables 2.1-2.3 describe some of the many actual or proposed applications for two-polymer combinations. In many cases, the patent literature has been referred to, as this is an excellent source of such information. With polymer blends, blocks, and grafts, many new properties and hence uses appeared that were previously unavailable. 

Of course, in many of these applications, the mechanical behavior of the materials is paramount. In fact, many such applications, such as impact resistance, arise because of the two-phased nature of the products. In this case, the size of the rubber phase domains and their glass temperatures are 

In Table 2.1 the bicomponent fibers (which often have half the cylinder as polymer I and the other half as polymer II) are of interest because of the differences in thermal coefficients of expansion. On cooling, the differential rates of contraction cause a certain coiling or curlicue formation in the fibers. 

In Table 2.2, the polymer-impregnated wood has reduced porosity, and hence is more water resistant. It is also stronger. The ionomers are included in Table 2.3, because they phase-separate like the block copolymers, and represent the limiting case of polymer I/polymer II having opposite chemical properties. One may consider these products block copolymers where the block consists of a single mer. The thermoplastic elastomers utilize the 

Thermoplastic elastomers (no curing required) Surface-active agents Elastomeric fibers (Spandex type) 

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