section%205.1%20-%20Polymer%20Molecules - Chapter 5: The...

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Chapter 5: The Structure of Polymers 5.1 Molecular Structure of Polymers Objectives Describe bonding arrangements in polymers. One of the three main types of materials is plastic. The general term plastic actually covers a wide range of materials with very different properties. For example, polyethylene can be either opaque and rigid like a milk carton or translucent and flexible like a plastic bag; polystyrene is clear and brittle; epoxy glue starts off as a liquid and then hardens to become a rigid solid. We can also include rubbers such as rubber bands and car tires as a subcategory of plastics. Paints are also plastics – they consist of plastic particles suspended in a liquid. When the liquid dries the particles fuse together to form a continuous coating. When we talk about the molecular structure of plastics we refer to it as a polymer. A polymer is a molecule that is a long chain of atoms. Polymers are organic molecules because they are primarily hydrocarbons that derive from petroleum, which in turn came from organic matter (plants and animals) that died millions of years ago. Polymers have very different properties than other organic molecules like methane, gasoline, or ethanol because of their molecular structure. In fact, polymers provide a great example of how structure and properties are related, so we will spend about half this chapter learning about their structure, and then the other half figuring out how to predict properties from that structure. To begin, we need to understand the basics of what makes something a polymer. Figure 5.1.1 compares ethane and polyethylene. Polyethylene can be thought of as a bunch of ethane molecules that have been attached with covalent bonds. Figure 5.1.1: Molecular structures of ethane and polyethylene.
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section%205.1%20-%20Polymer%20Molecules - Chapter 5: The...

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