Structure of Some Common Polymers

An Introduction to Materials Engineering and Science For Chemical and Materials Engineers, by Brian S. Mitchell 

Source Materials Handbook, G. S. Brady and H. R. Clauser, editors, McGraw-Hill, New York, 1991. 

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In the following section examples of the actual crystal structures of some common polymers are given. 

Table 1.1. Chemical structure of some common polymers...

Chapter 1. The Constitution and Architecture of Chains Table 1.1. Chemical structure of some common polymers (continued)... 

The classical representation of a homopolymer chain, in which the end groups are disregarded and only one monomer residue is considered, allows no possibility for structural variation. However, possibilities for stercoscqucnce isomerism arise as soon as the monomer residue is considered in relation to its neighbors and the substituents X and Y are different. The chains have tacticity (Section 4,2.1). Experimental methods for tacticity determination are summarized in 4.2.2 and the tacticity of some common polymers is considered in 4.2.3. 

Triblock copolymers of ABA type, where B is the central elastomeric block and A is the rigid end-block, are well-known commercially available polymers [7,8]. The chemical structures of some common TPEs based on styrenic block copolymers are given in Eigure 5.1. Synthesis of such ABA-type polymers can be achieved by three routes [9] ... 

Addition polymerization is a reaction in which monomers with double bonds are joined together through multiple addition reactions to form a polymer. Figure 2.12 illustrates the addition polymerization reaction of ethene to form polyethene. Table 2.1, on the next page, gives the names, structures, and uses of some common polymers that are formed by addition polymerization. 

The chemical structure of a polymer usually is represented by that of the repeat unit enclosed by brackets. Thus the hypothetical homopolymern s/v-vA—A—A—A—A—A—A—Anx-s/N is represented by-[A]-n where n is the number of repeat, units linked together to form the macromolecule. Table given below shows the chemical structures of some common homopolymers together with the monomers from which they are derived and some comments upon their properties and uses. It should be evident that slight differences in chemical structure can lead to very significant differences in properties. 

Fig. 1 Structures of some common synthetic hydrophilic polymers (A) poly aery lie acid, (B) polymethacrylic acid, (C) polyhydroxyethyl methacrylate, (D) polyvinyl alcohol, (E) polyvinyl acetate, (F) PEG/PEO, (G) polyacrylamide, (H) polyvinylpyrrolidinone, (I) Nylon 6, and (J) a simple polyurethane.

Fig. 2 Structures of some common cellulose-based hydrophilic polymers (a) cellulose, (b) sodium carboxymethyl cellulose, (c) hydroxyethyl cellulose, and (d) hydroxypropyl cellulose.

Fig. 5 Structures of some common synthetic polymers used in coatings (A) a typical Pluronic surfactant, (B) a thiol-substituted PEG derivative, (C) a polymer containing a phospholipid head group analog.

FIGURE 8.1 Molecular structures of some common conjugated polymers and small molecules (a) poly(p-phenylene vinylene), (b) polythiophenes, (c) MEH-PPV, (d) P3HT, (e) copper phthalocyanine, and (f) pentacene. 

PDMS) can be anything from an oil to a rubber. PDMS is useful as a liquid (sUicone oil) whose viscosity depends on molecular weight, or as an elastomer (sUicone mbber) whose mechanical properties depend on the degree of cross-linking of the primary linear polymer chains. The structures of some common linear polymers are shown in Figure 11.5. 

The chemical structures of the repeat units of some common polymers are shown in fig. 1.2, where for simplicity of drawing the backbone bonds are shown as if they were collinear. The real shapes of polymer molecules are considered in section 3.3. Many polymers do not consist of simple linear chains of the type so far considered more complicated structures are introduced in the following section. 

Fig. 1.2 Structures of the repeating units of some common polymers.

Free-radical polymerization is the most widely practised method of chain polymerization and is used almost exclusively for the preparation of polymers from olefinic monomers of the general structure CH2=CR R, where R and R are two substituent groups which may be identical, but more often are different. The structures of some common monomers and the homopolymers derived from them are shown in Table 1.1. 

FIGURE 5.8. Structures of some common doped conductive polymers, each projected on a plane normal to the direction of the polymer chains. Cross-hatched circles indicate dopant ions, (a) The square channel structure of potassium-doped polyacetylene (other alkali-doped PA lattices show similar structures),(b) lithium-doped polyparaphenylene, (c) potassium-doped ppp,(ii3) AsFs-doped PPR In (d) the dopant species, represented by x, are probably... 

Figure 7.1 Molecular structures of some commonly utilized conducting polymers In their pristine state.

Figure 28.6 Chemical structures of some commonly used inherently conductive polymers.

Fig. 3.1 Repeating unit structures of some common conducting polymers...

Polytetrafluoroethylene, more commonly known as the trademarked brand name Teflon, is formed from the addition polymerization of tetrafluoroethylene. Tetrafluoroethylene, shown in Figure 25.4(c), is an analogue of ethylene in which fluorine atoms have replaced all four of the hydrogen atoms. Teflon is a very good electrical insulator, so it is commonly used to coat wires. It is probably best known, though, as a nonstick substance used to coat bakeware, frying pans, and pots. It is also used in films that can be inserted into threaded joints between metal pipes to make it easier to unscrew the connection when necessary. Because Teflon is chemically inert, it is not possible to cross-link the chains like an elastomer. The structures of some addition polymers, including the structures of their respective monomers and what they are typically used for, are summarized in Table 25.1. 

FIGURE 4.2 Chemical structures for some common polymers. The section of the structure shown in square brackets is repeated along the polymer chain. 

Figure 2.1 Structures of some conducting polymers commonly used in biosensors.

A semicrystalline polymer is more rigid above Tg than a comparable amorphous polymer. For example, a crystalline polymer such as polyethylene, with a Tg well below ambient temperature, will retain useful structural properties above ambient temperature. Crystallites serve as inter-chain crosslinking sites that retard the mobility of polymer chains above Tg until the crystallites begin to melt, at a temperature called the crystalline melting point, 7. Table 19.2 lists Tg of some common polymers. 

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