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Odian Book Chapter 3-15, 5-3

Odian Book Chapter 3-15, 5-3. Living Polymerization. Living Polymerization. Neutral and Highly Reactive. or. Living Polymerizations. Living polymerizations are chain growth polymerizations which proceed in the absence of irreversible chain transfer and termination steps.*

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Odian Book Chapter 3-15, 5-3

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  1. Odian Book Chapter 3-15, 5-3

  2. Living Polymerization

  3. Living Polymerization Neutral and Highly Reactive or

  4. Living Polymerizations • Living polymerizations are chain growth polymerizations which proceed in the absence of irreversible chain transfer and termination steps.* • Diagnostic Characteristic of Living Polymerizations • The reaction proceeds until all monomer is consumed. If more monomer is introduced then the polymerization will continue • The number average molecular weight, Mn, is a linear function of conversion. • The number of propagating chains (active centers) is constant and independent of conversion. • Mn can be controlled by the reaction stoichiometry. • Sequential monomer addition results in the preparation of block copolymers. • Resulting polymers will exhibit a narrow molecular weight distribution and the polymer must exhibit a Poisson distribution in molecular weight.** * Szwarc, M., Nature, 1956, 178, 1168. ** Flory, P. J., J. Am. Chem. Soc., 1940, 62, 1561.

  5. Living Polymerization grams of monomer Moles of initiator • No termination or chain-transfer side reaction during polymerization • Control of molecular weight • Mn= • Narrow molecular weight distribution • Synthesis of block copolymers by sequential monomer addition • Control of polymer chain microstructure • End-group functionalization

  6. Initiation • Nucleophilic Initiation of Vinyl Monomers

  7. Anionic Polymerization of Styrene

  8. Anionic Polymerization of Styrene

  9. Anionic Polymerization of Styrene

  10. Anionic Polymerization of Styrene

  11. Initiators: Organolithiums g of monomer moles of initiator • Soluble in hydrocarbons • Direct nucleophilic attack • No electron transfer (RLi)N N= 6,4,2 MW=

  12. The Poisson Distribution in Molecular Weight • The constraints imposed on a living polymer require that the polymer exhibit a Poisson distribution in molecular weight.*

  13. Scale of “Livingness” • Conversion should be linear with time in semi-logrithmic coordinates • Deceleration indicates termination or deactivation of catalyst. • When chain termination cannot be completely suppressed (kt > 0): • deviation from living behavior becomes more pronounced with time • The degree to which a reaction deviates at time, t, is proportional to the ratio of the rate of propagation to termination.

  14. End Group Functionalization Carboxylic acid terminated: Primary alcohol terminated:

  15. End Group Functionalization

  16. Monomers • Generally olefin w/ EWG or delocalizing groups Methyl acrylate (MA) Methyl methacrylate (MMA) t-Butyl methacrylate (tBuMA)

  17. Ion Pair Aggregation • Need to stabilize propagating anions

  18. Ion Pair Aggregation • Need to stabilize propagating anions

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