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Brief Overview
• Discovery of Method
• Synthetic Routes
• Mechanisms: Then and Now
• Applications
• Pros and Cons(Dr. Owen Webster)
http://perceco2.chem.upenn.edu/~percec/member.html
Discovery of GTP
• Webster et al at DuPont’s Central R&D
• Needed a method for controlled “living”polymerizations of acrylates and methacrylates
• Name suggested by Trost
• Aiming for methods of synthesizing “pigment dispersing agents” and “rheology control”
• Printer InksWebster, O.W. Adv. Polym. Sci. 2004, 167, 1-34.http://www.mbacasestudysolutions.com/images/Dupont.gifhttp://www.stanford.edu/group/bmtrost/bmt.html
Desired Characteristics
• Workable Temp. range (50-80ºC)
• Can synthesize blocks
• Cheap production ($5>/lb.)
• Good PDIs and MWs (~20,000 Da)
• Nontoxic, colorless, no bad odors, etc.
Webster, O.W. Adv. Polym. Sci. 2004, 167, 1-34.
Synthetic Routes
• Always start with conjugate addition of silyl ketene acetal initiators
• Monomer: Methacrylates, Acrylates, Ketones, Nitriles, Carboxamides
• Catalysts: Two choices
-Nucleophilic Anions
-Lewis Acids
Webster, O.W.; Hertler, W.R.; Sogah, D.Y.; Farnham, W.B.; RajanBabu, T.V. J. Am. Chem. Soc. 1983, 105, 5706-5708
O CH3
O
Si
Synthesis: Catalysts
• Nucleophilic Anions tried by Webster:
KHF2
TASHF2 = Tris(dimethylamino)-sulfonium
Bu4NF
TASCN
Et4NCN
TASN3
S
N
NN
CH3H3C
CH3
CH3
H3C
CH3
F
HF
Sogah, D.Y.; Hertler, W.R.; Webster, O.W.; Cohen, G.M. Macromolecules, 1987, 20, 1473-1488.
O
O Me
Si
Me
MeMe
FO
O Me
Si
Me
MeMe
F
Synthesis: Catalysts
• Nucleophilic Anions tried by Webster:
KHF2
TASHF2 = Tris(dimethylamino)-sulfonium
Bu4NF
TASCN
Et4NCN
TASN3
S
N
NN
CH3H3C
CH3
CH3
H3C
CH3
F
HF
Sogah, D.Y.; Hertler, W.R.; Webster, O.W.; Cohen, G.M. Macromolecules, 1987, 20, 1473-1488.
O
O Me
Si
Me
MeMe
FO
O Me
Si
Me
MeMe
F
Synthesis: Catalyst
• Later Variations:
• Bu4NPhCO2HO2CPh = TBA Bibenzoate
• Bis(triphenylphosphoranylidene)ammonium bifluoride
• Potassium 18-crown-6
NP P
F
HF
O
O
O
OO
O
K
Dicker, I.B.; Cohen, G.M.; Farnham, W.B.; Hertler, W.R.; Laganis, E.D.; Sogah, D.Y. Macromolecules, 1990, 23, 4034.
Martin, D.T.; Bywater, S. Makromol. Chem. 1993, 193, 1011.
Miller, J.; Jenkins, A.D.; Tsartolia, E.; Watson, D.R.M.; Stejskal, J.; Kratochvil, P. Polym. Bull. 1988, 20, 247.
Synthesis: Catalyst
• Lewis Acids tried by Webster:
ZnBr2
ZnI2ZnCl2
(i-Bu2Al)2O
i-Bu2AlCl
Et2AlCl
OAlAl
O
OCH3
Zn Cl
Sogah, D.Y.; Hertler, W.R.; Webster, O.W.; Cohen, G.M. Macromolecules, 1987, 20, 1473-1488.
Synthesis: Catalyst
• Lewis Acids tried by Webster:
ZnBr2
ZnI2ZnCl2
(i-Bu2Al)2O
i-Bu2AlCl
Et2AlCl
OAlAl
O
OCH3
Zn Cl
Sogah, D.Y.; Hertler, W.R.; Webster, O.W.; Cohen, G.M. Macromolecules, 1987, 20, 1473-1488.
Low Temps.
Elucidating the Mechanism
• Quirk used ‘bare’ enolate to both catalyze and initiate polymerization
Quirk, R.P.; Kim J-S. J. Phys. Org. Chem. 1995, 8, 242.
Elucidating the Mechanism
• Persisting paradox: too much catalyst retards the polymerization
• Initiator actually DESTROYS catalyst in absence of monomer
• Induction Period
Sitz, H-D; Bandermann, F. (1987) Group Transfer of methyl methacrylate with basic catalysts In: Fontanille M, Guyot M (eds) Recent advances in mechanistic aspects of polymerization. Reidel, p 41
Any Evidence for Associative Mechanism?
• Yes!
• Excellent Double-Label Experiment by Farnham and Sogah
Sogah, D.Y.; Farnham, W.B. Polym. Prepr. Am. Chem. Soc. Div. Polym. Chem. 1986, 27, 167.
GTP: The Truth
• So, actually an anionic living polymerization
• “Anionic initiators for MMA can act as catalysts for GTP”
• Caveat: Back-biting not an issue with this anionic living polymerization
Applications
• Pigment Dispersant
• Emulsion Stabilizers
• AB block co-polymer
A = Hydrophilic Block
B = Hydrophobic Block
Spinelli, H.J. Prog. Org. Coat. 1996, 27, 255-260.
H2OH2O
H2O
H2O
Pros and Cons
• Advantages
1. Good for making blocks of acrylates and methacrylates
2. Can be done at RT and elevated T
3. Excellent architectural control (stars, blocks, etc.)
4. Low PDIs (can get down to 1.03!)
5. No metallic or halide impurities left over
6. No bad odors!
• Disadvantages
1. Cannot be done in presence of water
2. Initiator still costly
3. Cannot use monomers with acidic or active hydrogen functional groups
Conclusion
• Relatively new ‘living’ polymerization technique
• Full of potential, still room for improvement
• Best method around for block polymers of methacrylate derivatives
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