Polymers classifying

From the point of view of technology, it is convenient to classify polymers as thermosetting and thermoplastic. The former set by chemical crosslinks introduced during fabrication and hence do not change appreciably in their deformability with changes in temperature. Thermoplastics, on the other hand, soften and/or melt on heating and can therefore be altered in shape by heating... 

There are a number of methods of classifying polymers. One is to adopt the approach of using their response to thermal treatment and to divide them into thermoplastics and thermosets. Thermoplastics are polymers which melt when heated and resolidify when cooled, while thermosets are those which do not melt when heated but, at sufficiently high temperatures, decompose irreversibly. This system has the benefit that there is a useful chemical distinction between the two groups. Thermoplastics comprise essentially linear or lightly branched polymer molecules, while thermosets are substantially crosslinked materials, consisting of an extensive three-dimensional network of covalent chemical bonding. 

Classifying polymers in their crosslinked state according to end-use properties, polymer networks include vulcanized rubbers, crosslinked thermosetting materials, protective coatings, adhesives, polymeric sorbents, microelectronics materials, soft gels, etc. Polymer networks in contrast to uncrosslinked polymers,... 

Polymers are a pretty complicated subject. Thats why they re treated in three successive chapters. In this one you ll find a number of ways people classify polymers. It s quite an inventory ... 

In a more practical way, Carswell and Nason have classified polymers on the basis of modulus into five categories, as shown in Figure 5.6 (a) soft... 

It is possible to classify polymers by their structure as linear, branched, cross-linked, and network polymers. In some polymers, called homopolymers, merely one monomer (a) is used for the formation of the chains, while in others two or more diverse monomers (a,p,y,...) can be combined to get different structures forming copolymers of linear, branched, cross-linked, and network polymeric molecular structures. Besides, on the basis of their properties, polymers are categorized as thermoplastics, elastomers, and thermosets. Thermoplastics are the majority of the polymers in use. They are linear or branched polymers characterized by the fact that they soften or melt, reversibly, when heated. Elastomers are cross-linked polymers that are highly elastic, that is, they can be lengthened or compressed to a considerable extent reversibly. Finally, thermosets are network polymers that are normally rigid and when heated do not soften or melt reversibly. 

The most common way of classifying polymers is outlined in the figure below where they are first separated into three groups thermoplastics, elastomers and thermosets. Thermoplastics are then further separated into those which are crystalline and those which are amorphous (i.e., non-crystalline). 

Polymers can be classified in many ways. An easy way to classify polymers is based on the processing used to make them. There are two main types of polymerization process ... 

We can also classify polymers based on their structure. The basic structural unit of a polymer is a flexible macromolecular chain (Fig. 3.1a). When there is no long-range molecular order and the flexible molecular chains are arranged... 

The chemist classifies polymers in several ways. There are thermosetting plastics such as Bakelite and melamine and the much larger category of thermoplastic materials, which can be molded, blown, and formed after polymerization. There are the arbitrary distinctions made among plastics, elastomers, and fibers. And there are the two broad categories formed by the polymerization reaction itself (1) addition polymers (e.g., vinyl polymerizations), in which a double bond of a monomer is transformed into a single bond between monomers, (2) condensation poly-... 

Ranbyf has appropriately classified polymers into four generations that are available as commercial products and summarized in Table 1. 

The term plastic is also used in classifying polymers and includes all polymers which are not considered to be elastomers (rubbers) and fibers, i.e., which show neither the elastic properties of elcistomers nor the high crystallinity and strength of fibers, but rather fall in between them in these respects. 

Classification by Decomposition Behavior. The decomposition mechanism is a reasonable way to classify polymers. They can either depolymerize upon irradiation, for example, poly(methylmethacrylate), or decompose into fragments such as poly-imides or polycarbonates. This method of classification is closely related to the synthesis of polymers. Polymers that are produced by radical polymerization from monomers, which contain double bonds, are likely to depolymerize into monomers, while polymers that have been formed by reactions like polycondensation will not depolymerize into monomers upon irradiation, but will be decomposed into different fragments. The second group cannot be used to produce films with the same structure or molecular weight as the original material with methods such as PLD. 

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). 

For the purpose of this discussion, we will classify polymers into three broad groups addition polymers, condensation polymers, and special polymers. By convention, polymers whose main chains consist entirely of C-C bond are addition polymers, whereas those in which hetero atoms (e.g., O, N, S, Si) are present in the polymer backbone are considered to be condensation polymers. Grouped as special polymers are those products which have special properties, such as temperature and fire resistance, photosensitivity, electrical conductivity, and piezoelectric properties, or which possess specific reactivities to serve as functional polymers. 

Do we have to class all polymers as liquids, now we know that they can be neither gases nor, except rarely, crystals In the broad sense, we would — if we only regard a liquid as a dense substance that has no long-scale order in the atoms positions. However, this definition would not be terribly informative. This is why there is another, more fruitful way to classify polymers phases. A distinction is normally made between a semi-crystaUine state, a polymer glass, an elastic, and a viscous polymer. Which of the fom phases occurs depends on the kind and strength of interactions between the monomers. 

One way of classifying polymers in pharmaceutical applications is to divide them into three general categories according to their common uses (1) polymers in conventional dosage forms (2) polymers in controlled release dosage forms and (3) polymers for packaging. 

Classify polymer liquid crystals in fuiKtion of their chemical shuctures. Compare viscosities of longitudinal and orthogonal polymer liquid crystals. 

It is helpful to use a more restrictive definition that classifies polymers as those materials which are based on covalently bonded chain structures formed by repetition of similar units, in which the chains are of sufficient length to confer on the material some additional properties not possessed by the individual units. Some of these properties are morphological and have a considerable bearing on structure-conductivity relationships in polymer electrolytes, as will be discussed later. 

Another way of classifying polymers is by their behavior under heat. Thermoplastic polymers become soft when they re heated. Pol3m(iers of this type are composed of long linear or branched strands of monomer units hooked together. Have you ever left a pair of plastic sunglasses or a child s... 

For convenience, chemists classify polymers in several main groups, depending on the method of synthesis. 

Industrialists and technologists often classify polymers as either thermoplastics or thermoset plastics rather than as addition or condensation polymers. This classification takes into account their thermal properties. 

In this chapter, we describe how to classify polymers into 21 groups from their infrared spectra as outlined in Sec. 2. This is followed by a more detailed identification and characterization of selected polymers by IR and Raman methods in Sec. 3. Both sections are intended to provide an introduction to polymer analysis. 

In this section, we discuss the identification process and the chemical structures of polymers as obtained from their infrared and Raman spectra. Many polymers have common features, and it is convenient to segregate polymers into groups, such that the characterization of the polymers in a group can be discussed together. A popular method for classifying polymers is by their modes of application. For instance, some polymers, such as polyvinyl acetate, polystyrene, and nylons, are classified as thermoplastics, while urea, melamine, and epoxide resins are classified as thermosets or thermosetting resins. In this chapter we will use a different approach to classify the polymers, based on their similarity of chemical structure. This enables us to utilize the correlation between the functional groups of polymers and their characteristic infrared and Raman frequencies. 

There are various ways to classify polymers. A simple way is to distinguish polymers with respect to their origin in synthetic and natural polymers. Natural polymeric materials such as shellac, cellulose, and natural rubber have been used for centuries. Natural polymers are a class of polymers derived from renewable biomass sources, such as plants, vegetable oil, com starch, pea starch. Generally, natural polymers (or biopolymers) are used after modification reactions. Some biopolymers are designed to biodegrade. Table 2.1.1 and Fig. 2.1.1 give examples of natural polymers and modified natural polymers. 

Another way to classify polymers results from the consideration of their typical applications. Typical classes are Compression molding compounds, injection molding compounds, semi-finished products, films, fibers, foams (urethane foam, styrofoam), adhesives (synthetic adhesives are based on elastomers, thermoplastics, emulsions, and thermosets. Examples of thermosetting adhesives are Epoxy, polyurethane, cyanoacrylate, acrylic polymers), coatings, membranes, ion exchangers, resins (polyester resin, epoxy resin, vinylether resin), thermosets (polymer material that irreversibly cures), elastomers (BR, silicon rubber). 

Heller classified three types of degradation mechanism for biodegradable polymers. Type 1, 2 and 3 and classified polymers based upon the degradation mechanism they follow [10]. 

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