chem_note2 - A Quick Look at Polymer A polymer is a...

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43 • A polymer is a substance composed of molecules with large molecular mass composed of repeating structural units, or monomers, connected by covalent chemical bonds. Well known examples of polymers include plastics and DNA . A Quick Look at Polymer I am a monomer I am also a monomer Together, we are a polymer! 44 Polymers , the basis of plastics, comprise a large class of natural and synthetic materials with a variety of properties and purposes . Natural polymers: e.g.) cellulose, proteins, natural rubber, and resins Synthetic polymer materials: e.g.) Nylon, polyethylene, Teflon , and silicone , today find application in nearly every industry and area of life. Polymers are widely used as adhesives and lubricants, as well as structural components for products ranging from children’s toys to aircraft. A Quick Look at Polymer Insect trapped in resin 樹脂 Latex being collected from a tapped rubber tree 45 Cookware coated with Teflon (DuPont ) Polymer - a synthetic polymer - PTFE is most well known by the DuPont brand name Teflon Polytetrafluoroethylene (PTFE) 46 • Plastics can be formed into objects or films or fibers. Their name is derived from the fact that many are malleable , having the property of plasticity. • Common synthetic plastics: polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS), polyamides (PA, nylon), cellulose acetate (rayon), polyester, polyurethane (PU), etc. Polyester Rayon PE PP PVC Nylon PS 47 Polymers Thermoplastic Thermoset • are polymers that can be melted or softened • are polymers that cure into non-melting with the application of heat Thermoplastic structure Thermoset structure weak attractive forces cross links • e.g) polystyrene, polyethylene, nylon, polyester • e.g) polyurethane, silicone, polyamide Polymer cannot be melted and re-shaped after it is cured. thermosoftening plastic 48 Bulk Properties of Polymers These are the properties that dictate how the polymer actually behaves on a macroscopic scale . (1) Tensile strength The tensile strength of a material quantifies how much stress the material will endure before failing . This is very important in applications that rely upon polymer's physical strength or durability . For example, a rubber band with a higher tensile strength will hold a greater weight before snapping. In general tensile strength increases with polymer chain length. In a tensile test, a sample is held between two clamps and stretched to test how much force is required to break the sample.
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