GTP: Group Transfer Polymerization

Eric Silver

CH392N

Thursday March 12, 2009

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.

Mechanisms: Associative

Webster, O.W. Adv. Polym. Sci. 2004, 167, 1-34.

Mechanisms: Associative

Webster, O.W. Adv. Polym. Sci. 2004, 167, 1-34.

Mechanisms: Dissociative

Webster, O.W. Adv. Polym. Sci. 2004, 167, 1-34.

O

O Me

O

O Me

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

From Back-Biting to ChainTransfer

Webster, O.W. Adv. Polym. Sci. 2004, 167, 1-34.

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

Questions???