Polymers and Polymerization

Polymers— large molecules made up of repeating units of smaller molecules called monomers— include such biologically important compounds as proteins and carbohydrates. They also include such industrially important plastics as polyethylene, poly(vinyl chloride) (PVC), and polystyrene. 

Many synthetic polymers— that is, those synthesized in the lab—are among the most widely used organic compounds in modem scx iety. Although some synthetic polymers resemble natural substances, many have different and unusual properties that make them more useful than naturally occurring materials. Soft drink bottles, plastic bags, food wrap, compact discs. Teflon, and Styrofoam are all made of synthetic polymers. Chapter 30 is devoted to a detailed discussion of the synthesis and properties of synthetic polymers. 

For example, joining ethylene monomers together forms the polymer polyethylene, a plastic used in milk containers and sandwich bags. 

Many ethylene derivatives having the general structure CH2=CHZ are also used as monomers for polymerization. The identity of Z affects the physical properties of the resulting polymer, making some polymers more suitable for one consumer product (e.g., plastic bags or food wrap) than another (e.g., soft drink bottles or compact discs). Polymerization of CH2=CHZ usually affords polymers with the Z groups on every other carbon atom in the chain. Table 15.2 lists some common monomers and polymers prepared industrially. 

Problem 15.33 (a) What polymer is formed on polymerization of CH2=C(CH3)2 (b) What monomer is used to form 

Po/ymers-Aj fiM culH iiEle 5nits of smaller molecules called 

Energy changes during the propagation steps CH2 = CH2 + HBr CH3CH2Br 

I-CH2CH2--CH2CH2--CH2CH2-I = three monomer units joined together 

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In the next group of chapters we shall discuss condensation or step-growth polymers and polymerizations in Chap. 5, addition or chain-growth polymers and polymerizations in Chap. 6, and copolymers and stereoregular polymers in Chap. 7. It should not be inferred from this that these are the only classes of polymers and polymerization reactions. Topics such as ring-opening polymeri-... 

The statistical nature of polymers and polymerization reactions has been illustrated at many points throughout this volume. It continues to be important in the discussion of stereoregularity. Thus it is generally more accurate to describe a polymer as, say, predominately isotactic rather than perfectly isotactic. More quantitatively, we need to be able to describe a polymer in terms of the percentages of isotactic, syndiotactic, and atactic sequences. 

The polymerization of tetrahydrofuran was first studied ia the late 1930s (3,4). In 1960, this work was summarized (4), and the Hterature on tetrahydrofuran polymers and polymerization has been growing ever siace. Polytetrahydrofuran with hydroxy end groups has become a large-scale commercial product, used mainly as the flexible polyether segment ia elastomeric polyurethanes and polyesters. It is commercially available under the trade names Terathane (Du Pont), Polymeg (QO Chemicals), and PolyTHF (BASF). Comprehensive review articles and monographs have been pubUshed (2,5-8). 

D. McCall and Biiefing Panel, Report of the Research Briefng Panel on High Peformance Polymers and Polymeric Composites, National Research Council, Washington, D.C., Aug. 10,1984, pp. 11-12, 16-19. 

Having examined the properties of alkenes and introduced the elements of polymers and polymerization, let s now look at some commercial applications of ethylene and propene. 

The pioneering work on polyorganosiloxanes dates back to 1863-1871, to the studies of Friedel, Crafts8 "10) and Ladenburg 11 However, it was F. S. Kipping and his coworkers who were first to demonstrate the polymeric siloxane structures in the early 1900 s12). Unfortunately, since their interest was mainly in small molecules, they did not recognize the importance of the polymers and polymerization in this field 13). 

Polymers, ceramics, and composite materials. In addition to continued growth in support for research on polymers and polymeric composites, a new thmst is recommended to establish six to eight centers for the chemical engineering of ceramic materials and composites over the next 5 years, funded at a total annual level of 4 million per year. Cross-disciplinary pioneers should also be supported in this area. 

Ogasawara, Ma Application of Pulse Radiolysis to the Study of Polymers and Polymerizations. VoLlQ5,pp. 37-80,... 

Oheme and co-workers investigated335 in an aqueous micellar system the asymmetric hydrogenation of a-amino acid precursors using optically active rhodium-phosphine complexes. Surfactants of different types significantly enhance both activity and enantioselectivity provided that the concentration of the surfactants is above the critical micelle concentration. The application of amphiphilized polymers and polymerized micelles as surfactants facilitates the phase separation after the reaction. Table 2 shows selected hydrogenation results with and without amphiphiles and with amphiphilized polymers for the reaction in Scheme 61.335... 

Polyatomic Chalcogen Polymers and Polymeric Tellurium Cations... 

Polymers and polymerization—Congresses. 2. Mark, Herman Francis, 1895-. 3. Chemists—... 

With respect to the polymeric backbone, two approaches exist for the preparation of functional polymers, the polymerization or copolymerization of monomers which carry the desired functionality, and secondly the chemical modification of preformed polymers. The former concept, the polymerization of prefunctionalized monomers, was often tested in the early days of polymer-assisted syntheses, e. g. in the preparation of polymers containing pyridine [12] or quinone [13] residues, and benzaldehyde [14] or phosphine [15] functionalities. Although the latter approach demands that the synthetic organic chemist acquires profound knowledge of polymers and polymerization, this strategy can have advantages because... 

Nuclear magnetic resonance spearoscopy—Congresses. 2. Carbon—Isotopes—Spectra—Congresses. 3. Polymers and polymerization—Spectra—Congresses. 

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