Alkenes addition polymerization

Alkenes undergo addition polymerization. When a Ziegler-Natta catalyst is used, the polymer is stereoregular and has a high density. 

In Chap. 4, D. P. Gates reports elegant examples of similarities that can be found between the chemistry of carbon and that of phosphorus in low coordination numbers. The analogy between P=C and C=C bonds can be extended to polymer chemistry. Recent advances in the addition polymerization of phos-pha-alkenes and the synthesis and properties of rr-conjugated poly (p- pheny-lene phosphaalkene)s are described. 

Cyclopolymerization of Nonconjugated Dienes. Cyclopolymerization is an addition polymerization that leads to introduction of cyclic structures into the main chain of the polymer. Nonconjugated dienes are the most deeply studied monomers for cyclopolymerization and for cyclocopolymerizations with alkene monomers 66 In general, (substituted and unsubstituted) dienes with double bonds that are linked by less than two or more than four atoms cannot undergo efficient cyclization and result in crosslinked materials.12 In fact, efficient cyclopolymerization processes have been described, for instance, for a,oo-dienes like 1,5-hexadiene, 2-methyl-l,5-hexadiene, 1,6-heptadiene, and 1,7-octadiene,67 73 which lead to formation of homopolymers and copolymers containing methylene-1,3-cycloalkane units. 

Ethene or ethylene is the most important organic chemical used in commercial applications. Annual production of ethylene in the United States was over twenty-five million tons in the year 2000. Propylene is also used in large quantities with an annual production of over thirteen million tons. Alkenes such as ethylene and propylene have the ability to undergo addition polymerization. In this process, multiple addition reactions take place and many molecules link together to form a polymer. A polymer is a long chain of repeating units called monomers. For example, the addition of two ethylene molecules can be represented as... 

Other examples of addition polymerization of alkenes are the production of polypropylene from propylene, polyvinyl chloride (PVC) from vinyl chloride, and Teflon from tetrafluoroethylene. The structure of the three monomers is depicted in Figure 15.2. 

The newly formed R may also add to another alkene molecule to give a trimer. The process whereby simple molecules, or monomers, are merged can continue, eventually giving high-molecular-weight molecules called polymers. This reaction of alkenes is called chain-growth (addition) polymerization. The repeating unit in the polymer is called the mer. If a mixture of at least two different monomers polymerizes, there is obtained a copolymer. 

Catalysts. Acrolein and methacrolein 1,4-addition polymerization is catalyzed by lithium complexes of quinoline. The pcracctic acid epoxidation of a wide range of alkenes is catalyzed by 8-hydroxyquinoline. 

The properties and uses of polymers are discussed in greater detail in Chapters 13 and 29. The most important alkene monomers used in addition polymerization are listed in Table 10-4 along with some names and uses of the corresponding polymers. 

Other addition polymerizations were discussed previously, including poly-l,3-cyclopentadiene, alkene polymers (Section 10-8), polyalkadienes (Section 13-4), polyfluoroalkenes (Section 14-7D), and polymethanal (Section 16-4B). 

Write the mechanism for an addition polymerization via a radical, cationic, or anionic intermediate. In each case, predict the direction of addition to the monomer if it is an unsymmetrical alkene. 

Write resonance structures for the reactive intermediate in addition polymerization, to show how it is stabilized by the alkene substituent. 

A very important reaction, especially in the plastics industry, is additional polymerization, in which alkene molecules add to themselves to form long chains. As an example, a polymerization of CH3CH=CH2 results in the production of... 

To the best of our knowledge, X-ray structural data of complexes with simple dihapto interactions between a lithium atom and the n system of an alkene or alkyne ligand are unknown, but there is some spectroscopic evidence for weak it interactions in solutions of 3-alkenyllithium compounds from 7Li-and H-NMR data (4). Interactions of this sort are presumably important in addition (polymerization) reactions between organolithium compounds and alkenes or alkynes. 

Alkenes undergo addition polymerization. Addition polymerizations are reactions where a polymer is formed from its monomers with no other molecules produced. Polyethylene is an addition polymer each unit adds to the chain without leaving any residue behind. 

Scheme (62) is based on measurements where the rates of propene polymerization were compared in the absence and presence of hydrogen (see Fig. 2). According to Natta, the re-initiation rate of the centres of alkene addition to D-H is slow. This leads to a reduced rate.

On a coulometric scale, however, the n values for reduction of 51 and 52 were found to be less than one in DMF (see Table 11), probably due to polymerization under the dry conditions [7,55], a behavior similar to but less pronounced than that found for reduction of monoactivated alkenes. Addition of alkali metal cations did not change the n value significantly for 51 [71] but led to an increase in n for 52 [7,71]. At the same time, the overall rate of reaction of 52 increased considerably [71], an effect interpreted similarly to that observed for monoactivated alkenes (Sec. II.A.7). 

Since the product of the carbocation addition to an alkene via path Ag is also a carbocation that can rearrange and/or attack another alkene molecule (polymerization), unwanted product mixtures can result. 

Significant retardation was observed with the alkene additives and particularly with acetone or acetaldehyde. It has been experimentally observed that carbon suboxide prepared by the pyrolysis of diacetyltartaric anhydride is more stable toward polymerization than that prepared by the dehydration of malonic acid. We have observed infrared impurity bands at 3.65, 5.75,... 

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