Living Radical Polymerization Mediated by CuIBrDiazabutadiene Ligands

1
Living Radical Polymerization Mediated
byCu(I)Br/DiazabutadieneLigands

• Lindsay Ellis
• Simon Harrisson David Haddleton

2
Project Outline

• Synthesize ligands of various chain lengths
• Polymerize MMA using ligands and either CuBr or
  CuCl at various temperatures in toluene
• Investigate the usefulness of these ligands for
  ATP with MMA

3
Mechanism of Atom Transfer Polymerization

• Purpose of ligand to solubilize the
  transition-metal salt in the organic media and to
  adjust the redox potential of the metal centre
• Position of equilibrium controls polymerization

4
Ligands for ATP

• Effect of changing pyridine structure?
• Effect of changing the R group?
• (1) and (2) are effective ligands for ATP, will
  that effectiveness transpose to (3)?

5
Synthesis of 1,4-di(n-x)-2,3-dimethyl-1,4-diazabut
adiene

• (1) Propyl (2) Pentyl (3) Octyl
• Add amine dropwise to stirred solution of
  2,3-butadione in ether in ice bath. Dry with
  excess MgSO4, rotary evaporate off ether
• Distill to purify (1) and (2) Recrystallize (3)
  in methanol
• All were pure by 1H and 13C NMR and CHN analysis

6
Polymerization of Methylmethacrylate

• MMA, toluene and 21 ligand to either CuCl or
  CuBr was degassed in Schlenk tube
• The reaction was heated with stirring to desired
  temperature and ethyl 2-bromoisobutyrate was
  added as an initiator in equimolar amounts to the
  Cu species
• The polymerization was monitored using NMR and GPC

7
Polymerization of MMA with Propyl Ligand at 60oC

• CuCl
• After 4 hours
• 25 conversion
• Mn 13,400
• PDI 1.28
• CuBr
• After 4 hours
• 17 conversion
• Mn 6,200
• PDI 1.30

8
Mn PDI for Propyl Ligand at 90oC with CuCl

• Molecular weight rose rapidly during initial
  phase of reaction and then tailed off
• PDI remained fairly constant
• Conclusion Slow exchange between active (CuII)
  and dormant (CuI) species

9
Comparison of the Three Ligands with CuCl at 90oC

• Propyl Ligand
• conversion 72
• Mn 9000, PDI 1.76
• kPol 0.286
• Pentyl Ligand
• conversion 53
• Mn 8000, PDI 1.78
• kPol 0.130
• Octyl Ligand
• conversion 19
• Mn 1600, PDI 2.39
• kPol 0.079

10
Comparison of the Three Ligands with CuBr at 90oC

• Propyl Ligand
• conversion 63
• Mn 9970, PDI 1.83
• kPol 0.302
• Pentyl Ligand
• conversion 61
• Mn 9000, PDI 1.70
• kPol 0.234
• Octyl Ligand
• conversion 52
• Mn 7900, PDI 1.62
• kPol 0.164

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Summary of Results

• Propyl Ligand
• most promising
• Pentyl Ligand
• less promising
• Octyl Ligand unpromising

• Good conversions
• 65 - 85
• PDI 1.30 1.76
• Ok conversions
• 54 - 74
• PDI 1.70 2.12
• Mixed conversion
• 19 - 88
• PDI 1.71 2.55

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Conclusions

• Diimines poor ligands for ATP
• Are not electron rich enough to facilitate
  transition from CuI to CuII species
• Leads to high termination rates and loss of
  control over reaction
• Therefore high PDI and low conversions

13
Thank Yous

• Simon Harrisson
• Professor David Haddleton
• Entire Polymer Group