chem_note2

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

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•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. Polymer
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This note was uploaded on 12/01/2010 for the course CHEM yscn0027 taught by Professor Drtong during the Spring '10 term at HKU.

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

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