1. 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

2. 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

3. Polymerization of Monomer Reactants Mixture of oligomers and monomers is polymerized during processing PMR-15  Avg. oligomer molecular weight of 1500  Used as a standard for comparison Reactive endgroups

4. PMR Reactive Oligomers Lower softening temp (Tg, Tm), higher solubility, lower viscosity than high mw parent compounds No volatiles are generated (minimal voids)

5. Project Goals Prepare materials with increased long-term thermal stability Understand the degradation mechanism- (radical or ionic)

6. Stabilization W.B. Alston Polymer prepr.1986 Both exhibit same thermal stability Triphenylmethane group unable to form carbonyl

7. Synthesis of 4-chloro-4’,4”- diaminotriphenylmethane 0.08mol0.22mol0.0014mol ~30-40% yield

8. 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)

9. 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

10. 1 HNMR Spectra of 4-chloro-4’,4”-diaminotriphenylmethane Sample purified by flash column chromatography Sample purified by re- crystallization from toluene a bc d e f a b c d e f

11. toluene  Monomers needed to be completely dry  Removing toluene fully proved difficult  Drying 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

12. Analogous Compounds Other students have previously synthesized similar compounds FluoroBromo Trifluoromethyl Methoxy Hydroxy Nitro

13. Color Formation These diamine monomers exhibit a reversible color development UV light exposure causes color formation (surface effect) Lithium aluminum hydride treatment removes color

14. Molding Powders 3,3’,4,4’-Benzophenonetetracarboxylic dianhydride (BTDA) Nadic ester

15. 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

16. 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/k o )=  Log (K/K o )=  For ratesFor equilibria Where k o and K 0 represent the un-substituted compound

17. Hammett Plot Example Carey, F.; Sundburg, R. Advanced Organic Chemistry, 4 th Ed. 2000, Plenum Press, New York

18. 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

19. 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)

20. Acknowledgements Dr. John Droske Droske Research Group –Peter Jantz NASA-Glenn Research Center