ENGR 240 - 9.28.07

ENGR 240 - 9.28.07 - ENGR 240 We think of the chain...

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ENGR 240 – September 28, 2007 We think of the chain configuration as a random walk You get an entangled chain (never a straight one) o Polymers are never perfectly straight Compare end-to-end distance (r) to total chain length to see how entangled the polymer is Side groups o CH 3 is side group o If the side group is large or bulky, the polymer: Becomes more rigid Degree of entanglement goes down End-to-end distance increases o Limits how freely the backbone is able to rotate about the 109º Polymer structure o Linear Structure Seen in thermoplastics – polymers that can be heated and cooled multiple times Repeat units join end to end o Branched Polymers Also seen in thermoplastics Side chains form off of main chain Polymers do not pack as well as linear Lower density than linear o Cross-linked polymer Seen mostly in thermosets Main chains are connected by branches Vulcanization process of cross-linking Rubber elastic materials are cross-linked
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This note was uploaded on 04/07/2008 for the course ENGR 240 taught by Professor Gross during the Fall '07 term at Bucknell.

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ENGR 240 - 9.28.07 - ENGR 240 We think of the chain...

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