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