Chemical structure of repeat unit

Figure 23.5 Chemical structure of repeat units of various commercial nylons a) nylon 11,b) nylon 12,c) nylon 46, d) nylon 610, and e) nylon 612...

Chart 1.3 Chemical structures of repeating units bearing naphthalene and anthracene groups contained in copolymers employed in photon-harvesting studies [13]. 

The bottom left Panel illustrates models used in dynamic density functional theory (DDFT) simulations (a) The chemical structure of repeat unit of sulfonated poly(ether ether ketone) (sPEEK) chain. Hydrophilic blocks A and hydrophobic blocks B correspond to the sulfonated and nonsulfonated monomers, respectively, (b) The atomistic model of sPEEK chain, (c) The mapping of the atomistic chain onto a coarse-grained [ABtxChain and water molecules onto mesoscale solvent particle of type C. 

Fig. 10.12 Chemical structure of repeat units for pyridine-based polybenzimidazoles...

Figure 23.5 Chemical structure of repeat units of various commerciai nylons ...

Figure 1.1 Chemical structure of repeating units of geUan.

Chart 5.17 Chemical structures of repeating units of a copolymer with backbone-bound acid generator [159]. 

Materials Materials used in this study are listed in table 1. A series of new polymer coating 20 are composed essentially of a copolymer having perfluoroalkyl chain and hydrophobic filler. Subordinate No.-l, -2 and -3 indicate 80, 100 and 200 phr of filler contents, respectively. The copolymer was synthesized by means of radical polymerization of comonomer, perfluoro (meth)acrylates and vinyltrimethoxysil-ane. Chemical structure of repeat unit is described as follows ... 

HSQC NMR spectra of the O-deacylated lipopolysaccharide and the lipid-free PS in conjunction with chemical shift predictions made by the CASPER program allows to identify the positions of O-acylation process. The new approach was successfully implemented by Widmalm et al. in the structural elucidation of the O-antigen PS of E. coli 059. The algorithm used in this methodology was demonstrated as flowchart in Fig. 2a and the top-ranked structure of repeating unit of O-deacetylated repeating unit of the O-antigen PS of E. coli 059 in Fig. 2b. 

Chart 2.1 Chemical structures ofthe repeating units of polymers shown in Figure 2.6. 

It reflects the chemical structure of a system chemical composition of repeating units, nature of co- valent bonds linking the units into a chain, nature of terminal and side groups, functionality, stereochemical structure (cis, trans, iso, syndio, etc.), arrangement of units in a chain (1-2,1-4, head-to-tail), etc., which themselves determine thermodynamic parameters of a system such as the chemical affinity of components. 

Structure of xanthan has been determined by chemical degradation and methylation analysis (335,336) it is composed of repeating units consisting of a main chain of D-glucopyranosyl residues with trisaccharide side chains made up of D-mannopyranosyl and D-glucopyranosyluronic acid residues. 

The overwhelming majority of synthetic polymers is organic in nature, and it is on these that we will concentrate. The simplest and most common synthetic polymer is polyethylene, which will be our first example. Figure 1.1 shows the basic chemical structure of polyethylene. Pairs of hydrogen atoms are attached to the carbon atoms that make up the backbone. The repeat unit in this structure contains two carbon atoms and is derived from the ethylene monomer. In the case of polyethylene, the number of monomer residues, which is known as the polymerization... 

The final class of polymers are copolymers containing one or more of the repeat units of classes 2 and 3 (15-18). Copolymer effectiveness would presumably be a function of the chemical structures of each comonomer, comonomer sequence distribution, and polymer molecular weight. The comonomer could be a relatively... 

Fig. i. Chemical structure of poly(hydroxyalkanoate) repeating unit... 

Figure 9.19 Chemical structure of poly 3-[2-((S)-2-methylbutoxy)ethyl]thiophene. Number of repeating units is 50.

Telechelic polymers rank among the oldest designed precursors. The position of reactive groups at the ends of a sequence of repeating units makes it possible to incorporate various chemical structures into the network (polyether, polyester, polyamide, aliphatic, cycloaliphatic or aromatic hydrocarbon, etc.). The cross-linking density can be controlled by the length of precursor chain and functionality of the crosslinker, by molar ratio of functional groups, or by addition of a monofunctional component. Formation of elastically inactive loops is usually weak. Typical polyurethane systems composed of a macromolecular triol and a diisocyanate are statistically simple and when different theories listed above are... 

The principal deficiency of source-based nomenclature is that the chemical structure of the monomeric unit in a polymer is not identical with that of the monomer, e.g., -CHX-CH2- versus CHX=CH2. The structure of the constitutional repeating unit (CRU) may also not be clearly identified in this scheme for example, the name polyacrylaldehyde does not indicate whether (i) the vinyl group or (ii) the aldehyde group was the locus of polymerization. 

To avoid the obviously incorrect classification of polyurethanes as well as of some other polymers as addition polymers, polymers have also been classified from a consideration of the chemical structure of the groups present in the polymer chains. Condensation polymers have been defined as those polymers whose repeating units are joined together by functional... 

Figure 7.2 Schematic representation of alginate cross-linking with divalent cations and the chemical structure of the constituent repeat units, guluronate (G) and mannuronate (M). Carboxylate groups present along the backbone (largely from the G residues) interact with multivalent cations to yield metal ion cross-linked gels.

Macromolecules are very much like the crystalline powder just described. A few polymers, usually biologically-active natural products like enzymes or proteins, have very specific structure, mass, repeat-unit sequence, and conformational architecture. These biopolymers are the exceptions in polymer chemistry, however. Most synthetic polymers or storage biopolymers are collections of molecules with different numbers of repeat units in the molecule. The individual molecules of a polymer sample thus differ in chain length, mass, and size. The molecular weight of a polymer sample is thus a distributed quantity. This variation in molecular weight amongst molecules in a sample has important implications, since, just as in the crystal dimension example, physical and chemical properties of the polymer sample depend on different measures of the molecular weight distribution. 

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