Polymerization of monomers with multiple double bonds

The polymerizations and copolymerizations of various conjugated dienes are discussed in Chapter 5. 

Propagation reactions of unconjugated dienes can proceed by an intra-intermolecular process. This usually results in ring formation or in cyclopolymerization. It can be illustrated as follows  

The intra-intermolecular propagations can result in ring structures of various sizes. For instance, three-membered rings can form from transanular polymerizations of bicycloheptadiene  

Four-membered rings form in free-radical polymerization of perfluoro-l,4-pentadiene. The size of the ring that forms depends mainly on the number of atoms between the double bonds  

Formation of many five-membered rings is also known. One example is a polymerization of 2,3-dicarboxymethyl-1,6 hexadiene  

5 Polymerization of Monomers with Multiple Double Bonds 

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These two characteristics are not always encountered, especially in the cases of addition polymerization of monomers with double bonds. Isomerization of the monomers may occur, or false bonding of monomeric units into the chain may take place during the actual step of adding monomer onto the polymer chain. Consequently the assumed chemical structure of the polymer must always be carefully verified by analytical methods. Analysis is especially important with industrial polymer production, since the preparation history is not often known exactly. The chemical names of industrial or commercial polymers are often nothing more than a kind of generic name. Commercial poly(ethylenes), for example, despite the ascribed name, are often not homopolymers, but copolymers of ethylene and propylene. As well as that, commercial polymers practically always contain additives such as antioxidants, uv absorbers, fillers, etc. In the addition polymerization of monomers with multiple bonds, head-to-head and tail-to-tail structures are always to be expected together with the normal head-to-tail bonding, as can be seen, for example, with vinyl compounds such as CH2=CHR ... 

Addition polymerization is a reaction in which monomers with double bonds are joined together through multiple addition reactions to form a polymer. Figure 2.12 illustrates the addition polymerization reaction of ethene to form polyethene. Table 2.1, on the next page, gives the names, structures, and uses of some common polymers that are formed by addition polymerization. 

The simplest example of a polymerization reaction is the formation of polyethylene from ethylene molecules (t FIGURE 12.35). In this reaction, the double bond in each ethylene molecule opens up, and two of the electrons originally in this bond are used to form new C—C single bonds with two other ethylene molecules. This type of polymerization, in which monomers are coupled through their multiple bonds, is called addition polymerization. 

Using the multiple reactive double bonds, G o can be employed as a co-monomer in an in situ polymerization process with various vinyl based monomers through addition polymerization. For example, Mourey et al. have used radical chain polymerization with Al BN as initiator in 1,2-dichlorobenzene to produce branched structures of Ca) and both PMMA [poly(methyl methacrylate)] and PS (polystyrene)... 

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