Chemical structures of the repeat units

The agreement between theory and experimental results has been found to depend on the chemical structure of the repeat unit. Figure 15 represents the concentration dependence of counterion activity coefficients for two polyelectrolytes, PDADMAC and MEAC/AA (50 50) copolymer, differing in chemical structure of the cationic monomer unit but having the same charge distance (0.5 nm). 

The names given to the polymers in the following table exemplify elementary aspects of nomenclature. Thus source-based nomenclature places the prefix poly before the name of the monomer, the monomer s name being contained within parentheses unless it is a simple single word. In structure-based nomenclature the prefix poly is followed in parentheses by words which describe the chemical structure of the repeat unit. 

The nomenclature of polymers is somewhat complex, due in part to the fact that the majority of polymers have more than one correct name moreover, in some cases the registered trade names are also used to denote some polymers. The criterion adopted here is to use names that most clearly and simply state the chemical structures of the polymers. The polymers in Tables 1.1a and 1.1b have been named following the basic rules of nomenclature. Thus, the prefix poly is placed before the name of the monomer, and the name of the monomer is set within parentheses unless it is a simple word. In the case of repeating units containing more than one monomer (examples in Table 1.1b), the words contained in parentheses after the prefix poly must describe the chemical structure of the repeating unit. 

Heat capacity theory permits a correlation with the chemical structure of the repeating unit (U). In the solid state, only vibrational contributions need to be considered (skeletal and group vibrations). For an approximate discussion of the skeletal vibrations, the molecule is considered to be a string of structureless beads of the given formula weight. For linear macromolecules with similar backbones, the geometry and force constants are similar so that intramolecular skeletal vibrations are fixed by the mass of the structureless bead. The inter-molecular vibrations of linear macromolecules have quite low... 

Fig. 1 Chemical structure of the repeating unit (mcmomer) in PHA macromolecules...

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. 

As mesogenic groups, 4 -trifluoromethoxy-azobenzene units are used and linked to the methacrylate main chain by alkylene spacer, where the number n of the spacer groups was varied from 2 to 6. The chemical structure of the repeating unit of the polymers PM (n=2-6) is given in Figure 1. Details of the synthesis of the monomer, the condition for the radical polymerization, and the determination of the molecular masses were reported elsewhere 19,20). The phase transition temperatures of the polymers were... 

Draw the chemical structures of the repeat units of each category of naturally occurring polymers. 

These high stiffness and superior mechanical properties for SWNTs are due to the chemical structure of the repeat unit. The repeat unit is composed completely of sp hybridized carbons and without any points for flexibility or rotation. Also, Single walled nanotubes with diameters of an order of a nanometer can be excellent conduetors for eleetrical industries. 

The most common type of structure determination is structure verification. In this case, enough information is available (perhaps on the basis of well-known synthetic reaction paths) to propose a probable structure. The structure information which is achieved using IR and Raman spectroscopy is usually sufficient here. One of the fundamental problems in polymer science is the determination of the chemical structure of the repeat unit this moiety determines all of the chemical properties such as reactivity, stability and weatherability. Vibrational spectroscopic techniques are advantageous as a method of determining structure because the methods are applicable to aU polymers regardless of the state of order. The IR and Raman spectroscopy methods are accurate, faster than chemical analysis and reduce exposure to irritating, toxic and corrosive chemicals. 

A number of polymeric materials have been used as films, fibers and fabrics for developing medical products. A brief introduction to the chemical and physical features of these is given below. The chemical structures of the repeat units of various materials considered are given in Fig. 1.9. 

Over the last 50 years, systematic investigation has established a number of structure-property relationships for polymeric materials, which allow prediction of their physical properties from a knowledge of the chemical structure of the repeat units and molar mass of the material. All polymeric materials can be divided into a series of subclasses, reflecting either their method of synthesis or some particular characteristic of the material. Using this classification, it is possible to quickly identify how the material will respond to external factors such as change of temperature, pressure, stress, impact, etc. 

Figure 1. Chemical structure of the repeat units of polymers investigated.

Electrochemical polymerization of 3-methoxyethoxy-thiophene results in a polymer which is soluble in organic solvents, but the solutions are unstable in air. The blue solutions, typical of the polymer in the doped state, change to red, characteristic of the reduced form. Solutions of the copolymer are stable in air [25]. Figure 11.4 gives the chemical structure of the repeating unit of the thiophene/3-(2-methoxy)thiophene copolymer. 

The chemical structure of the repeating unit in the copolymers is shown in Figure 11.11 where the substituents R and R on the benzene ring are ... 

In the solid state, polymer molecules pack the space with little voids either in a regular array (crystalline) or at random (amorphous). The molecules are in close contact with other polymer molecules. In solutions, in contrast, each polymer molecule is surrounded by solvent molecules. We will learn in this book about properties of the polymer molecules in this dispersed state. The large n makes many of the properties common to all polymer molecules but not shared by small molecules. A difference in the chemical structure of the repeating unit plays a secondary role. The difference is usually represented by parameters in the expression of each physical property, as we will see throughout this book. 

One of these semiempirical methods scales the volume contributions to Tg of the diffeent moieties existing in the chemical structure of the repeating unit of polymers [31, 32]. Schneider and DiMarzio [33] suggested the more simple correlation of Tg with the mass/ flexible bond of the repeating unit. 

Calculation of the Solubility Parameter. The solubility parameter of PTBA, 6ptba, has been calculated on the basis of group contribution methods, described by Hoy (77), Van Krevelen 18) and Small 19). These methods provide an estimate of the solubility parameter based on the primary chemical structure of the repeat unit which. 

The molecular structure of polyethylene chain contains connected tetrahedral sp hybridized C atoms and it can be viewed as an extension of the covalently bound molecule ethane. Thus, in this case, the chemical structure of the repeat unit is different from the structure of ethylene monomer from which the polymer is produced. 

Other modifications of the chemical structure of the repeating units of poly(aryl ether ketone)s also show potential for significant improvement. For example, the introduction of fluorinated aromatic rings and bulky groups re-... 

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