Repeat units table

For each mixture, maximum a-helix content was obtained at a characteristic ratio of amino acid residues to disaccharide repeating units (Table IV). 

As previously mentioned, the primitive unit cell is the smallest unit of a crystal that reproduces itself by translations. Figure 1-37 illustrates the difference between a primitive and a centered or nonprimitive cell. The primitive cell can be defined by the lines a and c. Alternatively, we could have defined it by the lines a and c. Choosing the cell defined by the lines a" and c" gives us a nonprimitive cell or centered cell, which has twice the volume and two repeat units. Table 1-11 illustrates the symbolism used for the various types of lattices and records the number of repeat units in the cell for a primitive and a nonprimitive lattice. The spectroscopist is concerned with the primitive (Bravais) unit cell in dealing with lattice vibrations. For factor group selection rules, it is necessary to convert the number of molecules per crystallographic unit cell Z to Z, discussed later, which is the number of molecules per primitive cell. For example,... 

GLYCOSAMINOGLYCANS GAGs are linear polymers with disaccharide repeating units (Table 7.1). Many of the sugar residues are amino derivatives. 

The combination of the repeat unit species typically used in electrochromic homopolymers such as the thiophene, furan, pyrrole, dioxythiophene and dioxypyrrole rings with one another and with other conjugated linkages (e.g., vinylenes, phenylenes, fluorenes, and carbazoles) provides color control through both the electronic character of the backbone and by steric interactions between repeat units (Table 20.6). 

Each polymer has a basic structural unit that repeats itself several times. This is also known as the polymer repeat unit. Table 2.1 gives a few examples of monomers and the polymers derived from them. 

To understand further the conjugation in the binaphthyl-based polyarylenes, compounds 39 and 40 are synthesized from the reaction of 36 with 1,4-dibromobenzene and 4,4- -dibromobiphenyl, respectively 39 is the repeat unit of polymer (/ )-22 and 40 is that of polymer (/ )-23. The UV spectrum of 39 in methylene chloride solution displays a major absorption at A = 322 nm. The emission of 39 is observed at Ag ,j = 378, 396, and 417 nm when excited at 322 nm. Comparing the UV spectrum of 39 with those of (/ )-22 and rac-22, only a very small red shift ( 6 nm) from the repeat unit to the polymers is observed. The UV spectrum of 40 in methylene chloride solution shows A ,3 = 324 nm. The red shift ( 10 nm) in the absorption maxima from the repeat unit 40 to polymers (/ )-23 and rac-23 is also very small. The emission of 40 is observed at 387, 408, and 418 nm when excited at 324 nm. The absorption spectra of 39 and 40 demonstrate that the conjugation in polymers 22 and 23 is almost the same as that of their repeat units. Table 2 summarizes the UV absorption and fiuore.scence spectroscopic data for 22, 23, 39, and 40. 

Poly(alkylene glycols) and their ethers and esters are indexed as SRUs end groups, when known, are added as substituents after the name of the repeating unit. Table 18 lists some examples. 

Table 3.4 Temperature Coordinate and Relative Height (in Parenthesis) for the Two Loss Tangent Maxima Observed in Mixtures of Isoprene-Butadiene Block Copolymers with Homopolymers of These Two Repeat Units in the Same Proportion ...

Table 4.1 lists values of as well as AH and ASf per mole of repeat units for several polymers. A variety of experiments and methods of analysis have been used to evaluate these data, and because of an assortment of experimental and theoretical approximations, the values should be regarded as approximate. We assume s T . In general, both AH and ASf may be broken into contributions Ho and So which are independent of molecular weight and increments AHf and ASf for each repeat unit in the chain. Therefore AHf = Hq + n AHf j, where n is the degree of polymerization. In the limit of n AHf = n AHf j and ASf = n ASf j, so T = AHf j/ASf j. The values of AHf j and ASf j in Table 4.1 are expressed per mole of repeat units on this basis. Since no simple trends exist within these data, the entries in Table 4.1 appear in numbered sets, and some observations concerning these sets are listed here ... 

Use Eq. (4.14), the results in Fig. 4.5, and the data in Table 4.1 to estimate a value for 7 for polyethylene. Figure 4.10 shows the unit cell of polyethylene Fig. 4.10b shows the equivalent of two chains emerging from an area 0.740 by 0.493 nm. On the basis of the calculated value of 7 and the characteristics of the unit cell, estimate the free energy of the fold surface per mole of repeat units. 

It is apparent from an examination of Table 9.2 that the Mark-Houwink a coefficients fall roughly in the range 0.5-1.0. We conclude this section with some qualitative ideas about the origin of these two limiting values for a. We consider a polymer molecule consisting of n repeat units, and two different representations of its interaction with solvent. 

Table 4. CAS Registry Numbers for Constitutional Repeat Unit...

Because no molecule is spHt out, the molecular weight of the repeating unit is identical to that of the monomer. Vinyl monomers, H2C=CHR (Table 2) undergo addition polymerization to form many important and familiar polymers. Diene (two double bonds) monomers also undergo addition polymerization. Normally, one double bond remains, leaving an unsaturated polymer, with one double bond per repeating unit. These double bonds provide sites for subsequent reaction, eg, vulcanization. 

The diphenylsulfone group is suppHed to the repeat unit of aU polysulfones by DCDPS the differentiating species between various polysulfones comes from the choice of bisphenol. There are three commercially important polysulfones referred to genericaHy by the common names polysulfone (PSF), polyethersulfone (PES), and polyphenylsulfone (PPSF). The repeat units of these polymers are shown in Table 1. 

The repeating unit is designated by using the a terms of Table 2 ( a is elided before a or o ). However, unlike the Hantzsch-Widman and replacement systems, the atoms are cited in the reverse order of Table 2 (i.e. the last listed atom is cited first). An ending -ane , or -yne is used to indicate the bonding within the unit, which is assumed to be... 

As a further illustration of the concept of polymers Table 2.1 gives the repeating units of a number of other well-known plastics. 

Table 2.1 Repeating units of some well-known polymers...

Note that in series 3 and 10 the value of n in the table is the total number of methylene groups in the glycol portion of the repeat unit. 

A vast range of symmetrical and unsymmetrieal 1,6-diene monomers has now been prepared and polymerized and the generality of the process is well established.98,1 A summary of symmetrical 1,6-dienc structures, known to give cyclopolymerization, is presented in Table 4.4 In many cases, the structure of the repeat units has not been rigorously established. Often the only direct evidence for cyclopolymerization is the solubility of the polymer or the absence of residual unsaturalion. In these cases the proposed repeat unit structures are speculative. 

The repeat unit in the Phenoxy molecule is longer by two carbon atoms than that of PC. Otherwise the molecular structures of the two polymers are similar. Eq. (7.8) should, therefore, apply also to PC, at least approximately. 8C = 8.9 pm was measured for the crack opening displacement in a Makrolon sheet (Mn = 9.5 kg/mol) by Fraser and Ward [80], An estimate of the molecular mass between entanglements according to Eq. (7.8) yields Mc = 1.7 kg/mol. This result is not very different from the value of 2.5 kg/mol for IVIC in PC as given in Table 3.2. 

The disruption of chain regularity by the introduction of lateral substituents or kinks on repeating units is a supplementary means to decrease the melting temperature of aromatic polyesters.72 This is illustrated in Table 2.9, where the melting temperatures of unsubstituted and methyl-substituted aromatic-aliphatic and aliphatic acids are reported. Regularity disruptions often cause significant... 

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