Lecture 7 6pp - Polymers A Typical Polymer Polyethylene...

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1 Polymers Rubber band experiment - feeling the temperature change when stretching and releasing a rubber band warmer cooler 2 A Typical Polymer - Polyethylene Typically used in household containers, electrical insulation, chemical containers, tubings, packaging, prosthetic implants etc. Chemical formula: – CH 2 – CH 2 – CH 2 – CH 2 –…, or (–C 2 H 4 –) n Polymer = many units Properties controlled by average molecular weight or average n n = degree of polymerization 3 Paraffin Boiling Point ( ° C) CH 4 ! 164 C 2 H 6 ! 89 C 3 H 8 ! 42 C 4 H 10 ! 1 C 5 H 12 36 C 6 H 14 69 4 Polymer Structures • Stereoisomers • Linear • Branched • Cross-linked • Networked 5 Stereoisomers • Start with polyethylene (–C 2 H 4 –) n • Replace one of the H atoms with Cl - polyvinyl chloride • Replace one of the H atoms with benzene ring - polystyrene • Location of the replacement species? C C 6 Stereoisomers isotactic syndiotactic atactic
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7 Linear Polymers Linear chains When the backbone consists of single- bonded carbon atoms, the chain is flexible, e.g., polyethylene When the backbone consists of ! bonded carbon atoms, the chain is much more rigid, e.g. Kevlar 8 109.5 ° carbon hydrogen Average length L of polyethylene (–C 2 H 4 –) n given by: L = d 2 n 9 network linear branched cross-linked branches Cross-linking typically with S 10 O O Can We Crosslink with Oxygen? 11 C C CH 2 OH C C C O H H OH H H OH OH OH H C C CH 2 OH O H H OH CH 2 OH C OH C H OH glucose fructose C C CH 2 OH C C C O H H O H H OH OH OH H C C CH 2 OH O H H OH CH 2 OH C C H OH sucrose – H 2 O 12 C C CH 2 OH C C C O H Cl O H H OH OH H H C C CH 2 Cl O H H OH CH 2 Cl C C H OH sucralose
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13 Effects of Branching Interferes with sliding ---> stronger Difficult to pack molecules tight --> lower
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