Basic structures of polymers

Polymers can be composed from just one type of monomer (homopolymer) or from different types (copolymer). In the case of a linear copolymer consisting of two different monomers (e.g. A and B), the different monomers can basically be arranged in three different ways  

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With the basic structure of polymers of macromolecules clarified, scientists now searched for a quantitative understanding of the various polymerization processes, the action of specific catalysts, and initiation and inhibitors. In addition, they strived to develop methods to study the microstructure of long-chain compounds and to establish preliminary relations between these structures and the resulting properties. In this period also falls the origin of the kinetic theory of rubber elasticity and the origin of the thermodynamics and hydrodynamics of polymer solutions. Industrially polystyrene, poly(vinyl chloride), synthetic rubber, and nylon appeared on the scene as products of immense value and utility. One particularly gratifying, unexpected event was the polymerization of ethylene at very high pressures. 

Figure 1.24. Basic structures of polymer drug carriers with biodegradable polymer backbone poly[N -(2-hydroxyethyl)-L-glutamine] (a), poly(amido amine)s (b) and polyacetals (c).

Cyclic voltammetric experiments on polyaniline in aniline-free melt show very broad peaks and on continuous scanning the polymer film loses its electroactivity. However, when the polymer film is transferred in aqueous acidic conditions it gives useful peak potential of polyaniline, suggesting that the basic structure of polymer synthesized in melt and in an aqueous medium is the same with, of course, differences in protonation levels. 

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 fact, considering the basic structure of these materials (vide supra), it can be immediately realized that the basic features of poly(organophosphazenes) are the result of two main contributions. The first one is fixed and is basically related to the intrinsic properties of the -P=N- inorganic backbone, while the second is variable and mostly connected to the chemical and physical characteristics of the phosphorus substituent groups. Skeletal properties in phos-phazene macromolecules intrinsically due to the polymer chain are briefly summarized below. 

There are numerous variations on the basic linear structure of polymers. Returning to our example of polyethylene, we find short chain branches and long chain branches, as shown in Figs. 1.2 and 1.3, respectively. The number and type of these branches strongly influences the way that the molecules pack in the solid state, and hence affect the physical properties. Long... 

Based on Chien s research results, Collins et al. modified the basic structure of the catalysts and also achieved elastic material [8,18,19]. In both cases the elastic properties of the polymers are justified in a block structure with isotactic and atactic sequences. In 1999 Rieger et al. presented a couple of asymmetric, highly active metallocene catalysts, e.g., the dual-side catalyst rac-[l-(9-r 5-fluorenyl)-2-(5,6-cyclo-penta-2-methyl-l-q5-indenyl)ethane]zirconium dichloride (Fig. 3). These catalysts allowed building of isolated stereoerrors in the polymer chain to control the tacticity and therefore the material properties of the polymers [9],... 

In order to demonstrate the use of laser flash photolysis in elucidation of the MDI based polyurethane photolysis mechanism, three polyurethanes, two aryl biscarbamate models, an aryl monocarbamate model, and an aromatic amine were selected. Two of the polyurethanes are based on MDI while the third is based on TDI (mixture of 2,4 and 2,6 isomers in 80/20 ratio). The MDI based polyurethanes all have the same basic carbamate repeat unit. The MDI elastomer (MDI-PUE) is soluble in tetrahydrofuran (THF). The simple polyurethane (MDI-PU) based on MDI and 1,4-butanediol is used in the tert-butoxy abstraction reactions since it does not contain a polyether backbone. (See page 47 for structures of polymers and models.)... 

Fig. 8.8 The basic structure of high-performance polymer fibers (Staudinger s model [51]) and some examples of polymers and of a CNT used as building block for synthetic fibers. (Courtesy of H. Yue). With kind permission from Wiley (2006).

The material behavior of polymers is totally controlled by their molecular structure. In fact, this is true for all polymers synthetically generated polymers as well as polymers found in nature (bio-polymers), such as natural rubber, ivory, amber, protein-based polymers or cellulose-based materials. To understand the basic aspects of material behavior and its relation to the molecular structure of polymers, in this chapter we attempt to introduce the fundamental concepts in a compact and simple way. 

Fig. 7 Basic structures of the three low-dimensional phases of C60. Upper part shows the basic structures obtained by linking spherical units originally forming a fee lattice, while lower part shows the actual in-plane structures of the real polymers...

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