Polymers Large molecules natural

The real breakthrough came when chemists developed processes for making large molecules from their smallest units. Instead of the ten or so natural polymers and modifications of them, the engineer was suddenly presented with hundreds of new materials with remarkable and diverse properties. The number is still increasing. 

When this is done it is seen that in all cases plastics materials, before compounding with additives, consist of a mass of very large molecules. In the case of a few naturally occurring materials, such as bitumen, shellac and amber, the compositions are heterogeneous and complex but in all other cases the plastics materials belong to a chemical family referred to as high polymers. 

The remainder of this chapter will deal with natural polymers. These are large molecules, produced by plants and animals, that carry out the many life-sustaining processes in a living cell. The cell membranes of plants and the woody structure of trees are composed in large part of cellulose, a polymeric carbohydrate. We will look at the structures of a variety of different carbohydrates in Section 23.3. Another class of natural polymers are the proteins. Section 23.4 deals with these polymeric materials that make up our tissues, bone, blood, and even hair. ... 

In February 1928, Wallace H. Carothers (Figure 1.2), then an Instructor at Harvard, joined du Pont at Wilmington to set up a fundamental research group in organic chemistry. One of the first topics he chose was the nature of polymers, which he proposed to study by using synthetic methods. He intended to build up some very large molecules by simple and definite reactions in such a way that... 

In addition to the classification of liquid chromatographic enantioseparation methods by technical description, these methods could further be classified according to the chemical structure of the diverse CSPs. The chiral selector moiety varies from large molecules, based on natural or synthetic polymers in which the chirality may be based on chiral subunits (monomers) or intrinsically on the total structure (e.g., helicity or chiral cavity), to low molecular weight molecules which are irreversibly and/or covalently bound to a rigid hard matrix, most often silica gel. 

Plastic Containers Plastics are organic and polymeric in nature. A polymer is a large molecule built up by the repetition of small and simple chemical units. The repeated unit of the polymer is usually equivalent or nearly equivalent to the monomer or the starting material from which the polymer is formed. The structural units of the polymers most used to manufacture plastic containers, along with their uses for pharmaceutical purposes, are shown in Table 21. 

Polymers are large molecules formed by the repetitive bonding together of many smaller molecules, called monomers. As we ll see in the next chapter, biological polymers occur throughout nature. Cellulose and starch are polymers built from small sugar monomers, proteins are polymers built from amino acid monomers, and nucleic acids are polymers built from nucleotide monomers. The basic idea is the same, but synthetic polymers are much less complex than biopolymers because the starting monomer units are usually smaller and simpler. 

A gelatine gel is made with warm water. Gelatine is a protein. Proteins are natural polymers (Chapter 15, p. 243) and the molecules of protein are very large. The large molecules disperse in water to form a gel. 

Polymers are large molecules (macromolecules) that consist of one or two small molecules (monomers) joined to each other in long, often highly branched, chains in a process called polymerization. Both natural and synthetic polymers exist. Some examples of natural polymers are starch, cellulose, chitin (the material of which shells are made), nucleic acids, and proteins. Synthetic polymers, the subject of this chapter, include polyethylene, polypropylene, polystyrene, polyesters, polycarbonates, and polyurethanes. In their raw, unprocessed form, synthetic polymers are sometimes referred to as resins. Polymers are formed in two general ways by addition or by condensation. 

The surface forces technique measures the force between molecules (eg. surfactants, polymers) adsorbed on mica sheets. In the case of large molecules such as polymers, the measurement is most sensitive to the regions closest to the solution and provides little direct information about the region adjacent to the surface. As it is a measurement between macroscopic surfaces, it is unable to provide information on microscopic chemical differences at the interface. Infrared spectroscopy could provide additional information about the quantity of adsorbed material on the mica surface, the identity and orientation of the adsorbed species, and possibly the nature of the surface linkage. 

A large fraction of the chemical industry worldwide is devoted to polymer manufacture, which is very important in the area of hazardous wastes, as a source of environmental pollutants, in toxicology, and in the manufacture of materials used to alleviate environmental and waste problems. Synthetic polymers are produced when small molecules called monomers bond together to form a much smaller number of very large molecules. Many natural products are polymers for example, cellulose in wood, paper, and many other materials is a polymer of the sugar glucose. Synthetic polymers form the basis of many industries, such as rubber, plastics, and textiles manufacture. 

A second way to change the scale of molecules is to build up a large molecule from fragments. Nature does this and obtains, for instance, chiral DNA (if stretched out, would form very thin thread about 2 m long). Chemists prepare synthetic polymers that can be chiral and be measured in meters - fabric - or in km - tethered space elevators. 

Polymers are very large molecules made up of repeating units. A majority of the compounds produced by the chemical industry are ultimately used to prepare polymers. These human-made or synthetic polymers are the plastics (polyethylene, polystyrene), the adhesives (epoxy glue), the paints (acrylics), and the fibers (polyester, nylon) that we encounter many times each day. It is difficult to picture our lives without these materials. In addition to these synthetic polymers, natural polymers such as wood, rubber, cotton, and wool are all around us. And, of course, life itself depends on polymers such as carbohydrates, proteins, and DNA. This chapter discusses synthetic polymers. Naturally occurring polymers are presented in Chapters 25, 26, and 27. 

William Schowalter I have a question related to polymer synthesis. First, an observation. In biochemistry departments, there s been tremendous interest in the structure of large natural molecules. In chemistry departments, people have run away about as fast as they can from the synthesis of large molecules, the kinds of polymers of commerce that most of us are familiar with. I would like to address the question first to Matt. He showed us results of the physical chemistry that came out of those syntheses. The work of Ned Thomas was made possible because some clever synthetic chemists made some special kinds of molecules. I am trying to figure out how that activity can be fit in. If this research is so important, how do we make a home available for the people who do the synthesis that is necessary for it to go on I don t see that happening in our educational structure, either in chemistry departments or in chemical engineering departments. 

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