CHAPTER9 - Spring 2008 Chap 9 Chain-growth Polymerization...

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Hanyang Univ. Hanyang Univ. Spring 2008 Chap 9. Chain-growth Polymerization Chain-Growth Polymerization (Addition) Processes 1. Free radical Initiation Processes 2. Cationically Initiated Processes 3. Anionically Initiated Processes 4. Group Transfer Polymerization 5. Coordination Polymerization
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Hanyang Univ. Hanyang Univ. Spring 2008 Chain-Growth Polymerization Step-Growth Polymerization 1. Molecular weight increases steadily. 2. 2. High molecular weight polymers are found at the end. High molecular weight polymers are found at the end. 3. Long reaction time needs to synthesize high conversion and high molecular weight. 1. Only growth reaction adds repeating units one at a time to the chain 2. 2. Monomer concentration decreases steadily throughout the reaction Monomer concentration decreases steadily throughout the reaction 3. High Molecular weight polymer is formed at once; polymer molecular weight changes little throughout the reaction. 4. Long reaction times give high yields but affect molecular weight little. 5. 5. Reaction mixture contains only monomer, high polymer, and about 10 Reaction mixture contains only monomer, high polymer, and about 10 -8 -8 part of growing chains. part of growing chains.
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Hanyang Univ. Hanyang Univ. Spring 2008 (1) Initiation (1) Initiation k d : I : Initiator decomposition rate constant : 10 : 10 -4 ~ 10 ~ 10 -6 L/mole sec L/mole sec Unstable radical Unstable radical Chain Growth Polymerization Heat (60ºC) Heat (60ºC) UV UV k d Primary radical Primary radical AIBN AIBN Bond Energy Bond Energy = 46 kcal/mole = 46 kcal/mole  I M k R i i
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Hanyang Univ. Hanyang Univ. Spring 2008 (2) Propagation (2) Propagation k p : 10 : 10 2 ~ 10 ~ 10 4 L/mole sec (much faster than step-growth polymerization) L/mole sec (much faster than step-growth polymerization) (Repetition of similar reaction) Chain Growth Polymerization  M M k R p p
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Hanyang Univ. Hanyang Univ. Spring 2008 (3) Termination (3) Termination (a) Coupling or combination (a) Coupling or combination Chain Growth Polymerization
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Hanyang Univ. Hanyang Univ. Spring 2008 (b) Disproportionation (b) Disproportionation k t =k =k tc +k +k td td 10 10 6 ~ 10 ~ 10 8 L/mole sec L/mole sec (3) Termination (3) Termination Chain Growth Polymerization  2 M R M M k R t k t td k td k
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Hanyang Univ. Hanyang Univ. Spring 2008 (4) Chain Transfer (4) Chain Transfer Kinetic chain length Monomer, Polymer, Solvent or Chain transfer agent Physical chain length Chain Growth Polymerization
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Hanyang Univ. Hanyang Univ. Spring 2008 Chain Growth Polymerization Kinetic Chain Length : kinetic chain length υ of a radical chain polymerization is defined as the average number of monomer molecules consumed (polymerized) per each radical, which initiates a polymer chain. ex) Monomer # 4000 Disproportionation υ =4,000/4 =1,000 Determined by steps 1, 2, 3. (Initiation, propagation, and termination) (No chain transfer) Physical Chain Length : This condition contains Step 1, 2, 3, 4.
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  • Fall '13
  • ElizabethFrechette
  • Polymer, Chemical reaction, Polymer chemistry, Living polymerization, HANYANG UNIV

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