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Chap._200002 - 2 =CH 2 key issues choosing initiator(I...

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termination T (termination agent) x I-CH 2 -CH 2 -(CH 2 -CH 2 ) -CH 2 -CH 2 -T propagation initiation CH 2 =CH 2 CH 2 =CH 2 CH 2 =CH 2 CH 2 =CH 2 CH 2 =CH 2 I-CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 * ethylene polyethylene (PE) I* active site (catalyst or initiator) vinyl monomers to vinyl polymers In normal conditions, monomers are stable, no reaction between each other. Polymerization is started by adding initiator which reacts with the first monomer, and polymer is formed by joining together of unsaturated molecules (monomers) throught double bonds. * Reaction Mechanism Involves Three Steps: initiation , in which is formed an active species capable of starting polymerization of the otherwise unreactive vinyl compound (monomer). k d k i (benzoyl peroxide) Ex. O C O CH 2 CH 2 * (I CH 2 CH 2 *) CH 2
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Unformatted text preview: 2 =CH 2 key issues: choosing initiator (I), condition to produce active site (k d ), reaction rate between active site and vinyl monomer(k i ). ( I*: free radical initiator) * 2 O C O heat O O C O O C propagation , in which high molecular weight polymer is formed. k p : rate constand of propagation k p n n CH 2 =CH 2 CH 2 =CH 2 I-CH 2-CH 2 * I-CH 2-CH 2-CH 2-CH 2 * I-CH 2-CH 2-(CH 2-CH 2 ) -CH 2-CH 2 * propagation continues until the growing long chain radical becomes deactived or exhaustion of monomer. This is the crucial step in determining rate of polymerization, polymer molecular weight termination , in which deactivation occurs to produce final stable polymer....
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