The classification of polymers

There are many possible classifications of polymers. One is according to the general types of polymerisation processes used to produce them, as considered in the following section. Two other useful classifications are the following. 

These two sets of classifications are, of course, closely related, since structure and properties are intimately linked. A brief description of the types of polymer according to classification (ii) will now be given. 

Liquid-crystal polymers (LCPs) are a subset of thermoplastics. Consider first non-polymeric liquid crystals. The simplest types are rod-like molecules with aspect ratios greater than about 6, typically something like 

In some temperature range the molecules tend to line up parallel to each other, but not in crystal register. This leads to the formation of anisotropic regions, which gives them optical properties that are useful for displays etc. Polymeric liquid-crystal materials have groups similar to these incorporated in the chains. There are two principal types. 

Liquid-crystal polymers are considered in detail in chapter 12. 

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In Sec. 1.4 we discussed the classification of polymers into the categories of addition or condensation. At that time we noted that these classifications could be based on the following ... 

The classification of polymers according to polymerization mechanism, like that by structure and composition, is not without its ambiguities. Certain polymerizations show a linear increase of molecular weight with conversion (Fig. 1-lc) when the polymerization... 

The classification of polymers for oral drug delivery can be done by using various means. To make this discipline readily accessible to the novice reader, the hydro-phobic-hydrophilic nature of the polymer was chosen to group polymers since the mechanism of biomacromolecule release from most hydrophobic polymeric devices is similar the mechanism of release from most hydrophilic polymeric devices also have similar mechanisms. Hydrophobic polymers are described first, followed by hydrophilic polymers. 

The classification of polymers from the point of view of their chemical nature considers first the chemical structure of the molecular backbone. The chemical nature of the side groups is used only as a second criterion of classification. In some cases, the position of the side groups is well known. In other cases, polymers for practical use may be... 

The classification of polymers previously described has been used in this book for the discussion of pyrolysis results. An important class of polymers that is not discussed here is that of chemically modified natural polymers (or semisynthetic polymers). Examples of such polymers are the modified celluloses (carboxymethyl cellulose, ethyl cellulose, etc ), modified starches, casein plastics (Galalith), etc. These types of compounds were discussed in the book on pyrolysis of natural organic polymers [2]. 

In Section 1.2, we review in more detail the different criteria for the classification of polymers however, at this point, it is convenient to describe some of the main types of polymers according to their use. On the basis of this, they... 

Later, in 1953, P.J. Flory divided the polymers by their reaction mechanism into chain-reaction and step-reaction, rather than by comparing the polymer s constitutional unit and the monomer. The addition polymers are generally produced by a chain reaction mechanism, and the condensation polymers produced by a step-reaction mechanism. Currently it is customary, though not scientifically correct, to refer to addition or chain-reaction polymerization and to condensation or step-reaction polymerization. Some have suggested that the classification of polymers... 

The macroscopic behavior of the polymer materials caused by the polymer architecture is the basis of the classification of polymers in thermoplastics, elastomers and thermosets. 

Lignocellulosic polymer composites refer to the engineering materials in which polymers (procured from natural/petroleum resources) serve as the matrix while the lignocellulosic fibers act as the reinforcement to provide the desired characteristics in the resulting composite material. Polymer composites are primarily classified into two types (a) fiber-reinforced polymer composites and (b) particle-reinforced polymer composites. Figure 1.5 (a) shows the classification of polymer composites depending upon the type of reinforcement. 

Polymer composites are also classified into renewable/nonrenewable polymer composites depending upon the nature of the polymer/matrix [1, 13, 16]. Figure 1.5 (b) show the classification of polymer composites depending upon the renewable/nonrenewable nature. Polymer composites in which both components are obtained from biorenewable resources are referred to as 100% renewable composites, while composites in which at least one component is from a biorenewable resource are referred to as partly renewable polymer composites 1, 13, 16]. Chapter 4 of the book presents a review on the state-of-the-art of partly renewable polymer composites with a particular focus on the hybrid vegetable/glass fiber composites. This chapter summarizes the hybridization effect on the properties of the final thermoplastic and thermoset polymer matrices... 

Polymer blends are a mixture of at least two polymers, their combination being supposed to lead to new materials with different properties. The classification of polymer blends into (1) immiscible polymer blends, (2) compatible polymer blends, and (3) miscible polymer blends is given by the thermodynamic properties of the resulting compound by means of the number of glass transition temperatures observed for the final product. To improve the compatibility between the blended polymers, some additives or fillers are used. To the same extent, rubber blends are mixtures of elastomers, which are usually combined to obtain an improved product, with properties derived from each individual component. 

While this brief chapter cannot cover all of the types of polymer blends and composites known in the literature (1-3), Rgures 13.1 (4) and 13.2 (5) categorize the more important classes of polymer blends and composites, respectively. Figure 12.30 already summarized the classification of polymer interfaces. 

The classification of polymer mesophases have been considered in many reports (P-70). On analyzing the published data there arises much controversy in the identification. In order to avoid confusion in terminology it is necessary to define the basic terms relating to polymer columnar mesophases before further discussion. Columnar polymer systems have both a correlation of the centers of gravity and molecular orientation, but have mesomorphic properties due to the conformational disorder both of the polymer back-bone and side chains. The structural unit of the polymeric columnar mesophase is a macromolecule. In columnar phases macromolecules form regular 2D-periodic arrays. The two-dimensional symmetry of the column packing and the parameters of two-dimensional lattice are strongly dependent on the form and dimensions of the cross-section of a polymer molecule. 

This chapter will mainly focus on the classification of polymers subsequent chapters deal with engineering problems of manufacturing, characterization, and the behavior of polymer solutions, melts, and solids. 

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