高分子化学（北京化工大学）14 anionic polymerization (english edition)

review,Finish the following initiations:,4.2 Anionic polymerization,1. Carbanion (Zhang Yun,张赟)2. Monomer (Zhang Yun,张赟)3. Initiator and intiation4. Match of initiators and monomers5. Mechanism of anionic polymerization6. Living anionic polymerization7. Typical products,1. Carbanion,4.2 Anionic polymerization,(1) Structure of carbanion,plain,taper,Zhang Yun张 赟,(2) Reactivity of carbanion,Kd : ionization constant,碱性,4.2 Anionic polymerization,2. Monomer,(1) Olefin with polar substituent,4.3 Anionic polymerization,+,Zhang Yun张 赟,Acrylonitrile,Nitroethene,Methyl methacrylate,For example,4.2 Anionic polymerization,(2) Conjugated diene,styrene,a-Me-styrene,butadiene,isoprene,4.2 Anionic polymerization,(3) Reactivity of monomer,(Substituting constant: s),+,4.2 Anionic polymerization,Group A:,Group B:,Group C:,Group D:,4.2 Anionic polymerization,Group A,Group B and group C,Group D,Initiator should be stronger,Stronger or weaker,only,Reactivity,Type of polymerization,4.2 Anionic polymerization,3. Initiator and initiation,(1) alkali metal,Lithium (Li)Sodium (Na)Potassium (K)Rubidium(Rb)Caesium(Cs),a. Speciesb. Initiation c. Solubility,4.2 Anionic polymerization,Li and Na dispersion: insoluble in hydrocarbon,Solubility of alkali metals,homogeneous or heterogeneous,Reaction on the surface,adsorbtion,reaction,desorption,4.2 Anionic polymerization,(2) Alkali metal complex,a. Species,Aromatic radical-anions: Sodium naphthalene Lithium naphthalene,4.2 Anionic polymerization,Preparation:,initiator,4.2 Anionic polymerization,b. Initiation:,soluble in polar solvents only ( such as: ether),c. Solubility:,4.2 Anionic polymerization,(3) Organometallic compounds,Alkyl metal compound: RLiMetal amides: NaNH2, KNH2Grignard reagent: RMgX,a. Speciesb. Initiation c. Solubility,Initiation:,Soluble in nonpolar solvents,Solubility:,4.2 Anionic polymerization,Alkyl metal compound: BuLi Important position of BuLi in research and industry Special phenomenon of BuLi association,4.2 Anionic polymerization,(4) Nucleophilic initiator,A pair of isolated electrons on the heteroatoms,For example:,initiator,4.2 Anionic polymerization,(1) Reactivity of initiator,Li, Na, NaR, LiRRMgX, ROLi, stronger basesNR3, weaker bases, H2O,Strongestweakest,4. Match of initiators and monomers,Table 4-9 (in textbook page 126),(2) Reactivity of monomer,(3) Match of initiators and monomers,4.2 Anionic polymerization,5. Mechanism of anionic polymerization,(1) Initiation,Dissolve only in polar solventsDissolve in nonpolar solvents,Fast initiation,DicarbanionSingle carbanion,Electron transferElectron addition,a. Mechanism,b. Number of carbanion,c. Solubility,d. Activation energy, 10 kJ/mol,4.2 Anionic polymerization,Covalent species,Tight ion pair Contact ion pairIntimate ion pair,Loose ion pairSolvent-separated ion pair,Free ion,A,B,-,+,Active center,positive counterion, positive charge,a. state of ion pair,(2) Propagation,4.2 Anionic polymerization,Factors influencing the state of ion pair(solvent, temperature, counterion),4.2 Anionic polymerization,Polarity of solvent,Size of counterion,Temperature,（in nonpolar solvent）,Temperature,（in polar solvent）,Stereo structure of polymer and polymerization rate,4.2 Anionic polymerization,In cyclohexane: several hours in THF: 10 min.,For example:,4.2 Anionic polymerization,Active species exist in ion pair,4.2 Anionic polymerization,Microstructure of PIp,4.2 Anionic polymerization,Molecular weight,c. Single carbanion and dicarbanion,d. Activation energy,4080 kJ/mol,Slow propagation,4.2 Anionic polymerization,(3) Termination and chain transfer,a. Termination,No couple between two active centersNo fraction in counterions,Nonpolar monomers polymerize in nonpolar solvents,4.2 Anionic polymerization,Impurity,No termination,4.2 Anionic polymerization,4.2 Anionic polymerization,Polymerization of polar monomers,“backbiting”,+,The chain transfer reactions rarely happen in a system with nonpolar monomers and nonpolar solvents,No chain transfer,b. Chain transfer,4.2 Anionic polymerization,Condition: nonpolar monomers，nonpolar solvent,(4) Feature of anionic polymerization,Fast initiation Slow propagationNo termination No chain transfer,“living” polymerizatio