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review

review. Finish the following reactions:. §4.2 Anionic polymerization. 1 、 Introduction. (1) History. 1877 ， Wurtz, bases, epoxy ethane 1914, Na, Bd, Ip, St 1940, Ellis, BuLi , ethylene 1952 ， Higginson, styrene, KNH 2 , kinetic study

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review

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  1. review Finish the following reactions:

  2. §4.2 Anionic polymerization 1、Introduction (1) History 1877， Wurtz, bases, epoxy ethane 1914, Na, Bd, Ip, St 1940, Ellis, BuLi, ethylene 1952， Higginson, styrene, KNH2, kinetic study 1956， Szwarc, sodium naphthalene, St, living polymerization conception 60's, commercial SDS products were available 90‘s, study on the living polymerization of polar monomers (2) Carbanion

  3. 2. Monomer (1) Olefin with polar substituent For example Nitroethene Methyl methacrylate Acrylonitrile

  4. (2) Conjugated diene styrene a-Me-styrene butadiene isoprene

  5. (3) Reactivity of monomer (Substituting constant: s) Group A: Group B: Group C: Group D:

  6. Reactivity Type of polymerization Group A only >> Group B and group C Stronger or weaker >> Group D Initiator should be stronger

  7. 3. Initiator and initiation (1) alkali metal Lithium (Li) Sodium (Na) Potassium (K) a. Species b. Initiation c. Solubility

  8. Solubility of alkali metals K: soluble in ethers Li and Na dispersion: insoluble in hydrocarbon homogeneous or heterogeneous Reaction on the surface adsorbtion reaction desorption

  9. (2) Alkali metal complex Aromatic radical-anions: Sodium naphthalene Lithium naphthalene a. Species b. Initiation c. Solubility preparation initiator Alkali metal Aromatic compound

  10. Initiation: Solubility: soluble in polar solvents only ( such as: ether)

  11. (3) Organometallic compounds Alkyl metal compound: RLi Metal amides: NaNH2, KNH2 Grignard reagent: RMgX a. Species b. Initiation c. Solubility Initiation: Solubility: Soluble in nonpolar solvents

  12. (4) Nucleophilic initiator A pair of isolated electrons on the heteroatoms For example: initiator

  13. 4. Match of initiators and monomers (1) Reactivity of initiator Li, Na, NaR, LiR RMgX, ROLi, stronger bases NR3, weaker bases, H2O Strongest weakest (2) Reactivity of monomer (3) Match of initiators and monomers Table 4-6 (in textbook page 123)

  14. 5. Mechanism of polymerization (1) Initiation a. Mechanism b. Number of carbanion Dicarbanion Single carbanion Electron transfer Electron addition d. Activation energy c. Solubility Dissolve only in polar solvents Dissolve in nonpolar solvents < 10 kJ/mol Fast initiation!

  15. (2) Propagation a. Insertion propagation Active species exist in ion pair b. Single carbanion and dicarbanion Molecular weight c. Activation energy Fast initiation! 40—80 kJ/mol

  16. (3) Termination and chain transfer a. Termination + No couple between two active centers No fraction in counterions Nonpolar monomers polymerize in nonpolar solvents

  17. No termination! Impurity

  18. b. Chain transfer The chain transfer reactions rarely happen in a system with nonpolar monomers and nonpolar solvents No chain transfer!

  19. (4) Feature of anionic polymerization Condition: nonpolar monomers, nonpolar solvent Fast initiation Slow propagation No termination No chain transfer “living” polymerization

  20. 6. Living polymerization （1）Definition （2）application • Polymer with mono-distribution of molecular weight • Block copolymer • Telechelic polymers • Theoretical studies

  21. Active center State of ion pair - + B A positive counterion, positive charge Loose ion pair Solvent-separated ion pair Covalent species Tight ion pair Contact ion pair Intimate ion pair Free ion pair

  22. Stereo structure of polymer and polymerization rate

  23. Factors influencing the state of ion pair (solvent, temperature, counterion)

  24. For example: In cyclohexane: several hours in THF: 10 min.

  25. Thank you for attention

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