Ethene monomers

Table 7 Copolymerization Reactions of Lignin and Ethene Monomers...

Occasionally, monomers are added so that a chain branches. For example, an ethene monomer is sometimes added to form a side chain. A polymer with many side chains remains flexible. Such polymers are used to manufacture the plastic that wraps a variety of consumer products such as those shown in Figure 11. 

Schematically, the monomer ethene can be linked to other ethene monomers if the double bond is opened and the resulting broken bonds are linked together, in an addition reaction (Scheme 6.1). The chemical formula of the resulting polymer, called polyethylene or polythene, is ...

Tacticity is common in polymeis based on substituted ethene monomers, CH j = CHR, and the pattern of optically active sites in a polymer chain can sharply alter the properties of polymers such as polypropylene. Even in atactic polymers, the frequency of repeated, identically oriented, active sites can influence polymer properties. The fiequeney of two identically oriented sites in a row, diads, and three identically oriented sites in a row, triads, is often determined in some polymers with identical chemical composition to determine how differences in properties are produced 1 differences in spatial orientation within the polymer samples. 

Solution polymerization allows easy heat control and can be conveniently applied to ethene monomers. The solvent must be selected to dissolve both monomer and polymer and should minimize chain transfer to solvent Removal of the solvent is often impractical so the reaction mixture is ofien the desired polymerization product... 

Table 10.4 Information and data about five different plasties based on the ethene monomer... 

Ethene monomers can be made to react with each other, breaking the double bond between carbons and joining together to make a long polymer chain. 

Gas phase polymerization. Compared to the slurry process, polymerization in the gas phase has the advantage that no diluent is used which simplifies the process [74-76]. A fluidized bed that can be stirred is used with supported catalysts. The polymerization is carried out at 2 to 2.5 MPa and 85 to 100 °C. The ethene monomer eireulates, thus removing the heat of polymerization and fluidizing the bed. To keep the temperature at values below 100 °C, gas conversion is maintained at 2 to 3 per pass. The polymer is withdrawn periodically from the reaetor. 

In terms of production volume, polyethene (PE) is the most important polymer. The production capacity for PE was 94 mio. tons in 2008 and is expected to rise to 128 mio. tons in 2015 (Plastemart, 2010). Despite the simple structure of the ethene monomer, many different polyethene production processes are in operation, leading to different classes of products with specific physicochemical properties and application fields. 

Probably the most important addition reaction of the alkenes forms the basis of much of the plastics industry. Molecules of ethene, as well as other unsaturated compounds, can react with each other under the right conditions to form polymer molecules. A polymer is a long-chain molecule made up of many repeating units. The small, reactive molecules that react together to make the polymer are called monomers. Up to 10000 ethene monomers can bond together to form the polymer chains of poly(ethene). Poly(ethene) is commonly used to make carrier bags. 

Milstein, O., Gersonde, R., Huttermann, A., Chen, M.J. and Meister, J.J. (1996) Fungal Biodegradation of Lignin Graft Copolymers from Ethene Monomers,... 

In addition polymerization, all the atoms present in the monomers are retained in the polymer product. Polyethylene is an example of an addition polymer. Its chain contains all the atoms present in the ethene monomers that bonded to form it. Condensation polymerization takes place when monomers each containing at least two functional groups combine with the loss of a small by-product, usually water. Nylon is an example of a condensation polymer. 

If 4 < the overall rate will be decreased by chain transfer. This is degradative chain transfer. In fact, if is so small as to be negligible, chain transfer results in inhibition and the agent is a free-radical sink, or inhibitor. Almost all ethenic monomers are stored and shipped containing such a material to prevent adventitious polymerization. Hydroquinone and diphenylamine are compounds that at concentrations of 10-200 ppm are effective inhibitors. The radicals that result from these compounds are unreactive toward monomer. These inhibitors have many features in common with additives required for living radical polymerization, discussed later. 

This discussion of chain polymerization has centered on free-radical polymerization of an ethenic monomer. Conjugated dienes such as 1,3-butadiene often polymerize as bifunctional monomers with 1,4-addition rather than as tetrafunctional monomers. 

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