Indeed, applications of these materials as fibers, flexible films, adhesives, resistant paints and tough but light solids have transformed modern society. Some important examples of these substances are discussed in the following sections.
There are two general types of polymerization reactions: addition polymerization and condensation polymerization. In addition polymerization , the monomers add to one another in such a way that the polymer contains all the atoms of the starting monomers. Ethylene molecules are joined together in long chains. Many natural materials—such as proteins, cellulose and starch, and complex silicate minerals—are polymers.
Chemical reaction - Polymerization reactions | keymatgeandstenan.tk
Artificial fibers, films, plastics, semisolid resins, and rubbers are also polymers. More than half the compounds produced by the chemical industry are synthetic polymers. The polymerization can be represented by the reaction of a few monomer units:. The bond lines extending at the ends in the formula of the product indicate that the structure extends for many units in each direction.
Notice that all the atoms—two carbon atoms and four hydrogen atoms—of each monomer molecule are incorporated into the polymer structure.
Because displays such as the one above are cumbersome, the polymerization is often abbreviated as follows:. During the polymeriation of ethene, thousands of ethene molecules join together to make poly ethene - commonly called polythene. The reaction is done at high pressures in the presence of a trace of oxygen as an initiator. Note that all the monomers have carbon-to-carbon double bonds.
Many polymers are mundane e. The oxygen reacts with some of the ethene to give an organic peroxide. Organic peroxides are very reactive molecules containing oxygen-oxygen single bonds which are quite weak and which break easily to give free radicals. You can short-cut the process by adding other organic peroxides directly to the ethene instead of using oxygen if you want to. The type of the free radicals that start the reaction off vary depending on their source.
One pair is held securely on the line between the two carbon nuclei in a bond called a sigma bond. It would be helpful - but not essential - if you read about the structure of ethene before you went on. If the diagram above is unfamiliar to you, then you certainly ought to read this background material. Don't worry that we've gone back to a simpler diagram.
The sigma bond between the carbon atoms isn't affected by any of this. The other electron returns to the right hand carbon. You can show this using "curly arrow" notation if you want to:. If you aren't sure about about curly arrow notation you can follow this link.tenburbperlinir.gq
FTIR Is an Ideal Technology for Studying Polymerization Reactions
Polymerization reactions are chain reactions, and the formation of Teflon from tetrafluoroethylene is one example. In this reaction, a peroxide a compound in which two oxygen atoms are joined together by a single covalent bond may be used as the initiator. Peroxides readily form highly reactive free-radical species a species with an unpaired electron that initiate the reaction. There are a number of different ways to terminate the chain, only one of which is shown. In the following equations, the dots represent unpaired electrons, and R is a generic organic group. Chemical reaction. Article Media.
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Polymerization reactions Polymers are high-molecular-weight compounds , fashioned by the aggregation of many smaller molecules called monomers. Load Next Page.
Shipping and storage of the liquid urethanes requires preventing initiation. The removal of the blocking group — by chemical or thermal processes — yields the reactive isocyanate, initiating the reaction. Different blocking agents will eliminate at different temperatures, so research into the best adapted blockers least toxic, optimal deblocking temperature, etc. A key part of investigating blocking agents requires studying the temperature dependence of the initiation and the time-evolution of the reaction mixture.
Infrared is ideally suited to this, as the spectrum gives specific information regarding the progressing reaction. The multi-component mixture can be analyzed as a function of time, yielding an exhaustive view of the reaction kinetics. Your email address will not be published. Leave a Reply Cancel reply Your email address will not be published. Get news and research reviews on the topic of your choice, right in your inbox. Subscribe Now. I would like to receive information about content, events, products, services and promotions from Thermo Fisher Scientific and its affiliates.
Related Polymerization Reactions
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