Bonds

1
Bonds
URV June 2002

• Bond energies and lengths
• Repeating units

2
Polymerization
URV June 2002

• Classical free-radical polymerization
• Cationic anionic free-radical polymerization
• Living free-radical polymerization
• Copolymerization

3
Kinetic Studies of Polymerization Objectives
A kinetic model should be based on a physically
meaningful reaction mechanism
Molecular weight distribution, degree of chain
branching.
Conversion w.r.t, species concentrations,
temperature and time.
Reaction rate order w.r.t reacting species
Initial conditions (e.g., Mo, Io)
4
Polymerization Reactions

• Free-Radical Polymerization
• Classical free-radical polymerization via
  chemical initiators (illustration A)
• Free-radical illustration (illustration B)
• Monomers that can be polymerized by free-radical
  systems
• Loss of radicals
• Decomposition production of small molecules
• Radical abstraction
• Free-radical polymerization reactor schemes
• Cationic and Anionic Polymerization Reactions
• Anionic polymerization
• Cationic polymerization
• More examples of cationic anionic
  polymerization

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Classical Free-Radical Polymerization
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Initiator Decomposition
2,2-azo-bis-isobutyrylnitrile(AIBN)
Benzoyl peroxide
7
Initiation and Propagation
Note The termination steps are not shown
8
Termination by Coupling
9
Termination by Disproportionation
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Branching
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Branching Contd
12
Polystyrene

• Chain structure

13
Classical Free-Radical Polymerization Mechanism

• Kinetic mechanism and rate of polymerization
• Chain length
• Kinetic chain length
• Number-average degree of polymerization
• Chain Size Distribution
• Kinetic approach
• Statistical approach
• Cumulative average chain length

14
Free-Radical Polymerization Specific Examples

• Poly(stryrene) and poly(methyl methacrylate)
• Poly(vinyl pyrrolidone)
• Poly(vinyl acetate)

15
PVAc -Reaction Kinetics
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Fitted Rate Coefficients fkd ktrs and Rate
Ratio kis/kim
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Selected Rate Coefficients
All rate coefficients are in L/mol min
(with i trm, trEAc, or trp)
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Model Equations
Rate of Monomer Polymerization
At the regime of high initiator concentration
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Expt. Calc. Monomer Conversion Data
T50oC
T60oC
T70oC
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Copolymerization

• Copolymerization