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Synthesis and Processing of a Chlorinated
Diaminotriphenylmethane Monomer for the Study of Linear
Free Energy Relationships in PMR-15 Resins
James S. Baker and John P. Droske
University of Wisconsin-Stevens Point
Department of Chemistry
Aromatic Polyimides
• Aromatic polyimides in general offer:– High thermal stabilities– Low dielectric constants– Good mechanical properties
• Useful for aerospace and microelectronics applications
• High molecular weight aromatic polyimides can be difficult to process due to poor solubility and limited melt flow
Polymerization of Monomer Reactants
• Mixture of oligomers and monomers is polymerized during processing
H2C
H2CN
O
O
O
N
O
O
N
O
O
n
N
O
O
navg=2.087
•PMR-15Avg. oligomer molecular weight of 1500Used as a standard for comparison
Reactive endgroups
PMR Reactive Oligomers• Lower softening temp (Tg, Tm), higher solubility, lower
viscosity than high mw parent compounds
• No volatiles are generated (minimal voids)
Project Goals
• Prepare materials with increased long-term thermal stability
• Understand the degradation mechanism- (radical or ionic)
HC
Cl
HC
Cl
N
O
O
O
N
O
O
N
O
O
n
N
O
O
navg=2.087
Stabilization
H2C
O2, C
H OOHC
OH2O+
C
HO2,
C
OOH
C
OH2O+
W.B. Alston Polymer prepr.1986
•Both exhibit same thermal stability•Triphenylmethane group unable to form carbonyl
Synthesis of 4-chloro-4’,4”-diaminotriphenylmethane
0.08mol 0.22mol 0.0014mol
~30-40% yield
HC
Cl
NH2H2N
Cl
O H
+2
NH2
150C, 4hrs
-H2O
NH2
+
.HCl
Purification
• Early synthesis attempts gave a blood red colored, glassy solid– Wouldn’t re-crystallize from benzene or toluene– Flash column chromatography was required
• Very low yields ( <10%)
• Labor intensive
• Time consuming
• Costly (solvents, silica gel)
• Small batches (1-2g crude per run)
Purification (cont)
• Reaction was being overheated during synthesis (~180ºC)
• Keeping the reaction temperature at or below 155ºC gave a dark green colored, glassy solid– Readily re-crystallized from toluene– High purity after only a few re-crystallizations– Much better yields (30-40%)
Purified 4-chloro-4’,4”-diaminotriphenylmethane
1HNMR Spectra of 4-chloro-4’,4”-diaminotriphenylmethane
Sample purified by flash column chromatography
Sample purified by re-crystallization from toluene
HC
Cl
NH2H2N
a b cd
e
f
a
b
c
d
e
f
toluene
Monomers needed to be completely dryRemoving toluene fully proved difficultDrying times were reduced to 2-3 days by re-precipitation from methanol
Sample Drying
3 days at 55ºC under high vacuum
2 days at 55ºC under high vacuum, re-precipitated from MeOH
HC
Cl
NH2H2N
Analogous Compounds
HC
F
NH2H2NHC
Br
NH2H2N
HC
OH
NH2H2N
HC
CF3
NH2H2N
HC
OCH3
NH2H2NHC
NO2
NH2H2N
•Other students have previously synthesized similar compounds
Fluoro Bromo Trifluoromethyl
Methoxy Hydroxy Nitro
Color Formation
• These diamine monomers exhibit a reversible color development• UV light exposure causes color formation (surface effect)• Lithium aluminum hydride treatment removes color
HC
Cl
NH2H2N-H-
C+
Cl
NH2H2N C
Cl
NH2+H2N
C
Cl
NH2+H2N LAH
HC
Cl
NH2H2N
Blue colorColorless
Colorless
h
Molding PowdersO
O
O
O
O
O
O
OCH3
OH
O
O3,3’,4,4’-Benzophenonetetracarboxylic dianhydride (BTDA)
Nadic ester
HC
Cl
HC
Cl
N
O
O
O
N
O
O
N
O
O
n
N
O
O
navg=2.087
Resin Disks
• Molding powders were heated to 316ºC (600ºF) under 2200 psi gauge pressure
• Resin disks are sent to NASA-Glenn Research Center for thermooxidative stability (TOS) testing
Linear Free-Energy Relationships
• Can the thermal stability of the polymer be related to the substituent effects?
• The Hammett equation quantifies substituent effects in aromatic systems
Hammett free-energy relationship
Log (k/ko)= Log (K/Ko)=
For rates For equilibria
Where ko and K0 represent the un-substituted compound
Hammett Plot Example
Carey, F.; Sundburg, R. Advanced Organic Chemistry, 4th Ed. 2000, Plenum Press, New York
Polyimide Degradation
• Radical or Ionic?• Hammett plot would aid in elucidation of mechanism
– Radical- low – Ionic- larger
• Substituent effects are less significant in radicals• Fluoro substituted polymer exhibits best thermal
stability thus far
Future Work
• Obtain TOS data for 4-chloro compound• Compile data and determine if a linear free-energy
relationship applies• Determine degradation mechanism• Run preliminary mutagenicity tests on compounds• Determine nature of color formation mechanism
(radical or ionic)
Acknowledgements
• Dr. John Droske• Droske Research Group
– Peter Jantz
• NASA-Glenn Research Center