Polymers basic classes

Fig. 8. (a) The four basic classes of charge-transporting polymers, and (b) corresponding examples. Class 4 polymers may be either CJ-bonded or... 

Photo/Thermal Reactions. The fifth basic class of photopolymer chemistry that can be used in commercial applications is based more on physical changes in a polymer-based matrix than on chemical reactions. A recent application of this technology is the laser ablation (77) of an organic coating on a flat support to directly produce a printing plate. The availability of newer high energy lasers will allow more applications to be based on the photo/thermal mechanism. 

This chapter addresses three basic classes of polymers and the approaches for processing them into compounds. These classes include thermoplastic polymers, and two types of elastomers -crosslinked elastomers, and thermoplastic elastomers. Compounds prepared from each class have a range of achievable properties, and each category of compounds may have overlapping properties. Each category is prepared by different technical approaches with varying controls, energy requirements, and limitations. A brief definition of each class follows. Also included, later in the chapter, is a detailed description of how additives influence the production process. 

In the form of raw materials, polymers exhibit a wide range of compositions and properties. These properties can be enhanced or tuned to specific applications through the preparation of compounds. This section addresses three basic classes of polymers and the approaches for the preparation of compounds. 

Resists function by radiation-induced alteration of the solubility of the materials. There are two basic classes of resist materials, namely, negative and positive resists (see Fig. 4.5). Negative resists become less soluble on exposure to radiation i.e., the unexposed areas can be selectively removed by treatment with an appropriate developer solvent. Positive resists selectively undergo an increase in solubility on exposure, enabling the exposed regions to be selectively removed in the developer. Both types of resists are formulated from polymers designed to have physical and chemical properties consistent with semiconductor... 

The cellulose-to-ethanol process has five basic steps as shown in Figure I. They are feedstock handling and pretreatment, enzyme production, yeast production, simultaneous saccharification/fermentation (SSF) and ethanol recovery. Cellulose is the most abundant organic material on the earth. It is annually renewable, and not directly useful as a foodstuff. It is a polymer of glucose linked /8-1,4 as compared with the a-1,4 linked polymer starch which by contrast is easily digestible by man. There are three basic classes of potential cellulose feedstocks. These are agricultural by-products, industrial and municipal wastes, and special crops. The availability of these materials in the U.S. is shown in Table I. For economic reasons, we are concentrating our efforts on those materials that are collected for some other reason. 

Figure 2.1 Basic classes of polymers (each circle represents a monomer unit).

There are two basic classes of polymeric matrices used in FRP composites thermosetting and thermoplastic resins. Thermosetting resins are polymers which are irreversibly formed from low molecular weight precursors of low viscosity. These polymers have strong bonds both in the molecules and between the molecules. They develop a network structure that sets them in shape. If they are heated after they have been cured, they do not melt and will retain their shape until they begin to thermally decompose at high temperatures. 

Tsyurupa MP, Davankov VA (2002) Hypercrosshnked polymers basic principle of preparing the new class of polymeric materials. React Funct Polym 53 193-203... 

Before reviewing in detail the fundamental aspects of elastomer blends, it would be appropriate to first review the basic principles of polymer science. Polymers fall into three basic classes plastics, fibers, and elastomers. Elastomers are generally unsaturated (though can be saturated as in the case of ethylene-propylene copolymers or polyisobutylene) and operate above their glass transition temperature (Tg). The International Institute of Synthetic Rubber Producers has prepared a list of abbreviations for all elastomers [3], For example, BR denotes polybutadiene, IRis synthetic polyisoprene, and NBR is acrylonitrile-butadiene rubber (Table 4.1). There are also several definitions that merit discussion. The glass transition temperature (Tg) defines the temperature at which an elastomer undergoes a transition from a rubbery to a glassy state at the molecular level. This transition is due to a cessation of molecular motion as temperature drops. An increase in the Tg, also known as the second-order transition temperature, leads to an increase in compound hysteretic properties, and in tires to an improvement in tire traction... 

After identifying the main structure of a polymer, it is useful to consider the structure in more detail. As an example, if two polymers are formed by the same monomer but use two different polymerisation procednres, they are still given the same name. In this case the concept of isomer conld help to provide a more precise identification. There are three basic classes of isomerism (Kricheldorf et al., 2005) ... 

Beyond using analytical solutions, there are three basic classes of numerical techniques that are commonly used to solve complex fluid flow problems the finite difference method (FDM), the finite element method (FEM), and the boundary element method (BEM) [5]. Each of these methods has its advantages and disadvantages and, therefore, one may be preferred for a certain type of process or material. Each technique has been adapted in some form for specific problems encountered in polymer processing. Although it is not the purpose of this chapter to provide a detailed deri-... 

So far quite a number of polymers have been mentioned and the structural parameters determining the physical state of the polymer have also been described. Basically, all polymers can be used as barrier or membrane material but the chemical and physical properties differ so much that only a limited munber will be used in practice. It is beyond the scope of this book to describe the properties of all polymets in detail (the reader is referred to a number of good handbooite in this field) only some important polymers or classes of polymer related to membrane applications wiU be considered [17 19]. 

Five basic classes of polymer surfaces and interfaces can be distinguished ... 

There are two basic classes of adhesive bonding in aeronautical structures. One is structural bonding, with epoxy, phenolic, or acrylic adhesives, that transfer load between members. The other is sealants, to protect against corrosion at interfaces. The stifihesses of these classes of polymers differ greatly, but the two basic needs are remarkably. similar. The first is that the adhesive or sealant will stay stuck for the life of the structure, in aU service and storage environments, while the second is that the adhesive will not fail even when the surrounding structure has been broken. 

The words basic concepts" in the title define what I mean by fundamental." This is the primary emphasis in this presentation. Practical applications of polymers are cited frequently—after all, it is these applications that make polymers such an important class of chemicals—but in overall content, the stress is on fundamental principles. Foundational" might be another way to describe this. I have not attempted to cover all aspects of polymer science, but the topics that have been discussed lay the foundstion—built on the bedrock of organic and physical chemistry—from which virtually all aspects of the subject are developed. There is an enormous literature in polymer science this book is intended to bridge the gap between the typical undergraduate background in polymers—which frequently amounts to little more than occasional relevant" examples in other courses—and the professional literature on the subject. 

A number of basic paste types may be distinguished. The most important classes are the plastisols, the organosols, plastisols incorporating filler polymers (including the rigisols), plastigels, hot melt compounds, and compounds for producing cellular products. 

These materials differ from the previous class of resin in that the basic structure of these molecules consists of long chains whereas the cyclic aliphatics contain ring structures. Three subgroups may be distinguished, epoxidised diene polymers, epoxidised oils, and polyglycol diepoxides. 

In this section we briefly summarize a few modern applications of simulation techniques for the understanding of crystal growth of more complex materials. In principle, liquid crystals and colloids also belong to this class, but since the relative length of their basic elements in units of their diameter is still of order about unity in contrast to polymers, for example, they can be described rather well by the more conventional models and methods as discussed above. 

The dependence of polymer properties on chemical compositions is reviewed in basic polymer texts.9,10 The backbone structure of a polymer defines to a large extent the flexibility and stability of a polymer molecule. Consequently, a great range of polymer properties can be achieved within each class of step-growth polymers by varying the backbone structure using different monomers. 

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