Chemical Categories of Polymers

We can further characterize polymers into thermoplastics and thermosets . Thermoplastics consist of linear or lightly branched chains that can slide past one another under the influence of temperature and pressure. These polymers flow at high temperatures which facilitates their molding into useful products. Thermosets consist of a network of interconnected chains whose positions are fixed relative to their neighbors. Such polymers do not flo v when heated. 

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The chemical modification techniques refer to the treatments used to modify the chemical compositions of polymer surfaces. Those can also be divided into two categories modification by direct chemical reaction with a given solution (wet treatment) and modification by covalent bonding of suitable macromolecular chains to the polymer surface (grafting). Among these techniques, surface grafting has been widely used to modify the surface of PDMS. 

IS Plastics are materials that can be heated and then molded or shaped into useful objects. More specifically, thermoplastics can be processed more than once by reheating, while thermoset resins react chemically during initial heating and molding to form a permanent network. The term plastic is often loosely used to describe all polymers, sometimes in an unfavorable way. As we can see in Table 1-2, however, several other categories of polymers exist, each with its own set of properties. 

There is a further category of polymers that are not copolymers in the sense that units of different types are chemically joined together, as in all the types considered so far, but consist of two interpenetrating networks (IPNs), one formed by each type of polymer. Thus the different types of polymer are constrained to coexist because the different types of chain would have to pass through each other for the polymers to segregate. 

Polyester is the category of polymers with ester functional group on the main chain, although there are many types of polyester, the term polyester in industries specifically refers to poly(ethylene terephthalate) (PET) and poly(butylene terephthalate) (PBT). Polyesters can be classified as thermoplastic or thermosetting depending on the chemical stmctures. Table 1 shows the industrial production of polyesters, and it is estimated that the production will exceed 50 million tonnes by the year of 2015. Polyesters are made from chemical substances found mainly in petroleum and are mainly manufactured into fibers, films, and plastics. These polyesters are abbreviated as wiGT, where m denotes the number of methylene groups for example, PET, PTT, and PBT are abbreviated as 2GT, 3GT, and 4GT, respectively. 

Responsive polymer bmshes are a category of polymer bmshes that can change the physical and chemical properties with the environmental stimulus, such as pH, temperature, light, " and salt concentration. Such polymer bmshes have potential applications in the field of biotechnology, medical analysis, and dmg delivery systems. 

The above definitions have been suggested by Karger-Kocsis and Fakirov [13] and they will be followed strictly in the current text. This means that the commercially available and widely cited [17-20] as SPC type of materials based on the homopolymer polypropylene (PP) (as reinforcement) and the random copolymer of PP [usually with polyethylene (PE)] (as a matrix) do not belong to SPCs because the two components are chemically different, i.e., such composites belong to the category of polymer-polymer composites. The same holds for thermoplastic polyester copolymers reinforced with poly(ethylene terephthalate) (PET) or with liquid crystalline polyester. Details about these PPCs can be foimd in the review by Matabolaet al. [17] as well as in a very recent review of Karger-Kocsis and Barany [20]. 

In the last section we examined some of the categories into which polymers can be classified. Various aspects of molecular structure were used as the basis for classification in that section. Next we shall consider the chemical reactions that produce the molecules as a basis for classification. The objective of this discussion is simply to provide some orientation and to introduce some typical polymers. For this purpose a number of polymers may be classified as either addition or condensation polymers. Each of these classes of polymers are discussed in detail in Part II of this book, specifically Chaps. 5 and 6 for condensation and addition, respectively. Even though these categories are based on the reactions which produce the polymers, it should not be inferred that only two types of polymerization reactions exist. We have to start somewhere, and these two important categories are the usual place to begin. 

Different categories of Zonyl polymers are studied by ToF-SIMS both in the positive and negative ion mode. Studies have shown that, for each polymer, a specific fingerprint is obtained and the peaks corresponding to the specific chemical moieties of each polymer are detected (Figure 15.4). To represent this good selectivity, Principal Component Analysis is performed on the obtained spectra. The result clearly discriminates the different polymers. ToF-SIMS is then suited to the characterization of these materials. 

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