Polymer, branched Classifications

Figure 24 (a) Classification of different units in a hyperbranched polymer, branched, linear,... 

In this section, enzymes in the EC 2.4. class are presented that catalyze valuable and interesting reactions in the field of polymer chemistry. The Enzyme Commission (EC) classification scheme organizes enzymes according to their biochemical function in living systems. Enzymes can, however, also catalyze the reverse reaction, which is very often used in biocatalytic synthesis. Therefore, newer classification systems were developed based on the three-dimensional structure and function of the enzyme, the property of the enzyme, the biotransformation the enzyme catalyzes etc. [88-93]. The Carbohydrate-Active enZYmes Database (CAZy), which is currently the best database/classification system for carbohydrate-active enzymes uses an amino-acid-sequence-based classification and would classify some of the enzymes presented in the following as hydrolases rather than transferases (e.g. branching enzyme, sucrases, and amylomaltase) [91]. Nevertheless, we present these enzymes here because they are transferases according to the EC classification. 

Figure 1.55 Classification of polymers according to macroscopic stmcture (a) linear, (b) branched and (c) networked.

In discussions of structure we must limit ourselves to the case of linear polymers, for with the branched polymers so far studied their complexity has defied analysis. Here, however, as I have discussed elsewhere [11], it is possible to draw up a rational classification of the types of structure as defined by the arrangements of hydrogen bonds taken as the main element in intra- and inter-chain linking. 

Yet another type of classification of polymers is based on the type of repeating unit. A homopolymer has one type of repeat unit. Copolymers are polymers that have more than one type of monomers or repeat units. If the monomers in a copolymer are distributed randomly along the chain, it is called a regular or random copolymer. If, on the other hand, a sequence of one type of monomer is followed by a sequence of another type of monomer, it is called a block copolymer. If the main chain is one type of monomer and the branch chains are of another monomer, it is called a graft copolymer. 

Since the molecular backbone can be linear, branched, or network type, this aspect is also important for polymer structure. It is known that most polymers with a linear backbone are thermoplastics, while those with network backbone are thermosetting polymers. However, for classification from a chemical point of view, this differentiation is less significant. Many polymers with linear backbone are obtained from bifunctional monomers (e.g. terephthalic acid and glycol). If the polymer is obtained from similar monomers but with more than two functionalities (e g. terephthalic acid and ethylene glycerin), the polymer will have thermosetting characteristics. For this reason, this feature is not necessarily used for a classification from the chemical point of view. 

Wood-Adams, P. Dealy, J.M. deGroot, A.W. Redwine, O.D. Effect of molecular structure on the linear viscoelastic behavior of polyethylene. Macromolecules 2000, 33 (20), 7489-7499. Trinkle, S. Friedrich, C. Van Gurp-Palmen plot a way to characterize polydispersity of linear polymers. Rheol. Acta 2001, 40 (4), 322-328. Trinkle, S. Walter, P. Friedrich, C. Van Gurp-Palmen plot. II. Classification of long chain branched polymers by their topology. Rheol. Acta 2002, 41 (1-2), 103-113. 

Polyethylene is manufactured in various polymeric forms, differing by their molecular weight and linearity, or presence of irregularities, or branches, unsaturations, and so on. This in turn determines the density, or specific gravity of the polymer, which is nsed as the principal classification feature of polyethylenes. The main forms of polyethylenes are as follows ... 

Polymers can be classified in many ways, such as by source, method of synthesis, structural shape, thermal processing behavior, and end use of polymers. Some of these classifications have already been considered in earlier sections. Thus, polymers have been classified as natural and synthetic according to source, as condensation and addition (or step and chain) according to the method of synthesis or polymerization mechanism, and as linear, branched, and network according to the structural shape of polymer molecules. According to the thermal processing behavior, polymers are classified as thermoplastics and thermosets, while according to the end use it is convenient to classify polymers as plastics, fibers, and elastomers (Rudin, 1982). 

Classification of Polymers Properties 1223 Addition Polymers A Review and a Preview 1225 Chain Branching in Free-Radical Polymerization 1227 Anionic Polymerization Living Polymers 1230 1 Cationic Polymerization 1232... 

Non-linear polymers comprise branched, graft, star, cyclic, and network macromolecules. Polymer blends, interpenetrating networks, and polymer-polymer complexes are summarized as macromolecular assemblies. Their skeletal structure should be reflected in the name by using an italicized connective as a prefix to the source-based name of the polymer component or components to which the prefix applies. Table 5.10.1 lists aU classifications for non-Unear macromolecules and macromolecular assemblies with their corresponding prefixes [971UP2]. Examples for nomenclature are given in Table 5.10.2 (non-linear macromolecules) and Table 5.10.3 (macromolecular assemblies). 

There are several means to modify polymer properties, grafting is one of the effective methods. Grafting is a method in which monomers are covalently bonded (modified) onto the polymer backbone [16], as shown in Figure 3.2. Graft copolymers are special type of polymers that come under the classification of branched... 

In addition to copolymerization described above, there is considerable interest in the control of polymer architecture. As this may have a considerable influence on the behaviour of polymers as materials. Thus, polymers may be linear (Fig. 1.3a), or branched (Fig. 1.3b) or may for more complex structures such as a star arrangement (Fig. 1.3c) or more sophisticated dendrimer arrangements. Some of these more complex architectures pose considerable challenges to the organic chemist in terms of reagents and equipment (Hadjichristidis et al. 2000), while others, for example, the introduction of cross-links, can be achieved using technically quite simple methodologies. Cross-linked polymers are an important class of materials in themselves and provide another classification, namely thermoplastics and thermosets The former are those which melt and flow, the latter are materials which cannot melt or dissolve and are built up of cross-linked polymer chains. 

The authors of [125] registered on the AMP heat capacity curve (Figure 12) two relaxation transitions at 245.0 and 297.5 K which they marked as T i and Ty2, respectively. Based on the classification proposed in [117-119] y-relaxation is attributed to internal rotation in the side groups. If there are several side groups in a polymer ehain, several y-transitions can be observed. The mentioned transitions are absent on the C°=XT) curve for AML (Figure 11). It can be explained by peculiarities of the branched AMP strueture. 

It is clear from the literature classification of friction (usually classified as a branch of Physics or of Mechanical Engineering) and wear (for metallic systems often considered to be part of Metallurgy) that an ACS Symposium on polymer friction and wear encompasses an enormous range of traditional disciplines. 

Abstract Polymers are macromolecules derived by the combination of one or more chemical units (monomers) that repeat themselves along the molecule. The lUPAC Gold Book defines a polymer as A molecule of high relative molecular mass, the structure of which essentially comprises the multiple repetition of units derived, actually or conceptually, from molecules of low relative molecular mass. Several ways of classification can be adopted depending on their source (natural and synthetic), their structure (linear, branched and crosslinked), the polymerization mechanism (step-growth and chain polymers) and molecular forces (Elastomers, fibres, thermoplastic and thermosetting polymers). In this chapter, the molecular mechanisms and kinetic of polymer formation reactions were explored and particular attention was devoted to the main polymerization techniques. Finally, an overview of the most employed synthetic materials in biomedical field is performed. 

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