The synthesis of polymers is discussed. It includes: (1) the synthesis of fluorine-containing crosslinked poly(ether ketones); (2) the synthesis and characterization of poly(imide amides) and their N-methylated analogues; (3) the synthesis of fluorine-containing aromatic polyethers; (4) the synthesis of novel fluorine-containing aromatic polysiloxanes; and (5) the conversion of 6F-containing polythioethers to polysulfones. It is hoped that these polymers will find use as low dielectric materials in electronic applications, function as thermal control coatings, or be suitable elastomeric sealants for extreme service conditions

Cassidy, Patrick E.

English

NASA Technical Reports Server

TRIFLUOROMETHYL-SUBSTITUTED POLYMERS
GRANT NAG-1-631
Semiannual Status Report
January 1, 1990 to June 30, 1990
To: John F. Royal
Grants Officer
Mail Stop 126
NASA-Langley Research Center
Hampton, VA 23665
From: Professor Patrick E. Cassidy, Ph. D.
Department of Chemistry
Southwest Texas State University
San Marcos, TX 78666
September 11, 1990
N91-10170
G3/27
https://ntrs.nasa.gov/search.jsp?R=19910000857 2020-03-19T20:19:53+00:00Z
INTRODUCTION
Our current research efforts at Southwest Texas State University
concern: 1) the synthesis of fluorine-containing crosslinked poly(ether
ketones), 2) the synthesis and characterization of poly(imide amides) and
their N-methylated analogues, 3) the synthesis of fluorine-containing
aromatic polyethers, 4) the synthesis of novel fluorine-containing aromatic
polysiloxanes, and 5) the conversion of 6F-containing polythioethers to
polysulfones. It is hoped that these polymers will find use as low dielectric
materials in electronic applications, function as thermal control coatings, or
be suitable elastomeric sealants for extreme service conditions. The
following is a brief summary of the research results obtained from January 1,
1990 to June 30, 1990.
1.0 Crosslinked poly(ether ketones)
Recently, a series of new aromatic poly(ether ketones) or PEKs were
synthesized in these laboratories. Due to the extreme solubility of these
polymers in common organic solvents, a project was begun to synthesize
thermally- crosslinkable PEKs in order to render them insoluble. The
propargyl group was chosen as the crosslinking functionality for this effort
because of its low curing temperature, low price, and absence of off-gas
evolution during cure.
The first attempt at synthesizing crosslinkable PEKs involved end-
capping PEK oligomers with a monofunctional propargyl compound, as is
shown in reaction Scheme I. The stoichiometry was adjusted to give an
average of 20 repeat units. A product was obtained which could be cast into
a brittle film. Upon curing at 280 °C for 1 hour, the film became brown and
creasable. The film sample swelled greatly in common organic solvents and
lost all mechanical strength. From these results it was determined that end
capping would not give the desired degree of crosslinking and the precured
polymer would be too low of a molecular weight to utilize as a tough coating
even after curing.
Step 1:
MEPBA
Step 2: '
BPA F + MEPBA
V
DMAc/toluenc
K2C03
155-160 °C
CROSSLINKED POLY(ETHER KETONE)
where: R and R' are CHj or CEj
Scheme I- Possible Synthetic Route to Crosslinked PEKs.
The current attempt at producing crosslinked PEKs involves the
incorporation of the propargyl moiety on the polymer backbone. Reaction of
the disodium salt of bisphenol A (BPA) with propargyl bromide in ethanol
gave the propargyl diether of BPA (DEBPA) in almost quantitative yield. A
Claisen rearrangement of the diether to the dipropargyl bisphenol A
(BPBPA) was attempted by heating (Scheme H).
HC=CCH20 -OCHgC^CH X
HC=CCH20
DEBPA
Scheme n- Claisen Rearrangement Attempt
It appears that the temperature required for rearrangement is above
the B-staging temperature of this bisacetylene.1 The products isolated were
extremely viscous, brown, and probably partially crosslinked.
Closely related research indicated that an alternate route to the
synthesis of the dipropargyl ether of BPA would also yield a rearranged
byproduct of BPBPA and the mono-rearranged product.2 Reaction of BPA
with propargyl bromide in aqueous sodium hydroxide at reflux was
attempted. This yielded an alkaline-soluble product and the expected
DEBPA. Further characterization by NMR indicated that the base-soluble
material is not the desired BPBPA but is MEBPA, the end-capping agent
described earlier. Research is continuing on this project and other
approaches are being designed.
2.0 Poly(imide amides)
Consistent with our research into novel low-dielectric and thermally
stable materials, we have recently synthesized a series of
hexafluoroisopropylidene-containing (6F) poly(imlde amides). Preparation
of the imide-containing monomer (Scheme III) is accomplished in a single-
95 hr. in
boiling
HOAc
o o
Scheme ffl- Synthesis of 6F-Diimide acid
step imidization reaction of p-aminobenzoic acid with 6F-dianhydride
(6FDA) in boiling glacial acetic acid. The diacid , obtained in 94% yield, is
then converted to the acid chloride by reaction with thionyl chloride.
Polymerization of this monomer is accomplished by low temperature (0 °C)
condensation with various diamines in DMAc (Scheme IV). All polymers
were obtained in 85%-95% yields with intrinsic viscosities ranging from
0.90 to 2.26 dL/g at room temperature in DMAc. These polymers all give
clear, creasable films that are readily cast from solution and are colorless to
slightly yellow in color. Thermal analysis of these materials shows thermal
stabilities above 500 °C in air and above 515 °C in nitrogen.
—' n
R =
o- -
Scheme IV- Polyamldes Derived from 6F-DUmide Acid Chloride
In order to improve the thermo-oxidative and UV resistance of these
poly(imide amides), research is under way to replace the N-hydrogen of the
amide linkage by synthesizing the N-methylated analogues of the diamines
used.
As shown in Scheme V, the AT-methylated diamines was obtained by
first producing the trifluoroacetamide analogue, followed by the synthesis of
the N-sodium salt of the diamide. Reaction of this sodium salt with methyl
iodide and subsequent cleavage of the thifluoroacetyl group yielded the
desired N-methylated diamine. At this time, methylated analogues of 6F-
diamine and 4,4'-bis-(4-aminophenoxy)biphenyl have been synthesized in
overall yields of -50%. Research is continuing on these and other N-
methylated diamines in the areas of monomer synthesis and subsequent
polymerization with diacid chlorides.
o
II
NHCCB,
NaH
HfAQrR-<Q
CH,
^Claisen's
'Alkali
CH3I
Scheme V- Synthetic Route to N-Methylated Diamines
3.0 Fluorine-containing aromatic polyethers
This research project concerns the synthesis of fluorine-containing
polyethers for use as thermal control coatings. Previous researchers have
demonstrated that bisphenates will react with hexafluorobenzene to yield
aromatic polyethers.3 In our research, we attempted the polymerization of
bisphenol AF (BPAF) with hexafluorobenzene according to reaction Scheme
VI.
PF* Fv ,*
Crosslinked
PolyetherDMAc
Scheme VI- Attempted Reaction of BPAF with Hexafluorobenzene
The polymerization proceeded at room temperature for one day to
yield a crosslinked product which was only very slightly soluble in
chloroform. Creasable films could be cast from unfilterable solutions of this
swelled product. The results indicate that hexafluorobenzene undergoes a
sufficient degree of substitution to render it unusable. Variance of the
reaction times and conditions did not decrease the degree of crosslinking
significantly.
The polymerization of BPAF with 1,2,4,5-tetrafluorobenzene failed to
yield a polymer. Evidently, the tetrafiuorobenzene is not activated enough
towards nucleophilic substitution to yield high molecular weight polymer.
This low reactivity and low boiling point (90 °C) made the monomer difficult
to work with.
Polymerization of BPAF with decafluorobenzene for 1 day at room
temperature yielded a high molecular weight linear polyether. Since no
crosslinking was evident, the reaction temperature was increased to 60 °C
for shorter reaction times, again, high molecular weight polymer, 14F-
poly(ether ether), was obtained, an indication of decafluorobenzene's
difunctionality towards nucleophilic substitutions. Films of material cast
-o-O—O-o—
14F-Poly(ether ether) 6H8F-Poly(ether ether)
from chloroform solutions were clear, colorless, tough, and creasable. A UV-
visible spectrum of the polymer showed optical transparency or >90%
transmittance from 300-900 nm as seen in Figure 1. Polymerization of BPA
with decafluorobenzene yielded a polyether, 6H8F-poly(ether ether), which
formed clear, colorless and tough films when cast from chloroform
solutions. The UV-visible spectrum of this polymer was virtually identical
the BPAF-derived polyether. These results show that the 6F group located
between the bisphenol portion of the polyether does not improve UV-visible
transmittance as compared to the 6H moiety in this series of polymers.
However, the 6F group will most likely be more resistant than the 6H group
Qp,erafcqr : 6 0 . t
"ffrace: !•
iiamp 1'9 iident i t y :
FT' ere e h t- a g e T r a r i s m i s B i o n mode
Cjlrf'd i;'riate .Ma-x i mum 1 00. 0
tprda-'riat-t? M i n i m u m 0.0
IjJfjfJer? Wa.yelenqth 6OO. O nm.
licjWer Wavelength 200.0 nm.
Scan rfp€?e?d 1OO.O n m / m i n .
Bahdwid- th l .O nm.
1" i me C o f •» s 1 3 n t u . Ji s e c
0 Peak( s ) detected
'' . ) fK -tV .
 fc»<.,ye -5 S I . o »•»•.
o
1
•¥B ^39 =»
.e
20 .8
289.
1 :8
28
U i i n -1 mUi «t 1 c y c l e s c o m p l e t e
/"
,w^
//
Figure 1- UV-vis spectrum of 14F-PE
368.8 448 .8
U ': ! : >• ! :' *'. " t I': l' V-
528 .8 .8
to intense UV radiation and thus present a gradual loss in UV transmittance
under harsh conditions.
4.0 Novel fluorine-containing aromatic polysiloxanes
Our research efforts in this area involve synthesizing polymers
containing the [C(CF3)2-O-SiR2-O] function in backbones. We are very
excited about the potential for these new backbones because we anticipate
outstanding properties. A related compound, 2,2-dimethyl-4,4,5,5-tetraJcis
(trifluoromethyl)-2-sila-l,3-dioxolane, is known4 and gives some indication
of the properties to be anticipated in the new polymers. It is stable in
boiling water, dilute acids and concentrated H2SO4, and it is unaffected
when heated in a sealed tube at 350°c for one day.
We expect our new polymers to be highly flexible, thermally stable,
high temperature elastomers. They will also be transparent, non-adherent,
and resistant to most solvents. In addition we anticipate resistance to
atomic oxygen as well as U.V. radiation. Crosslinking via siloxane linkages
should be relatively simple using well known silicone technology, and
property fine-tuning will be easily accomplished by varying the R-groups
attached to silicon and the length of the siloxane block.
The progress that has been made thus far on this polymer system has
been to study the reactivity of aromatic hexafluoropropanols by condensing
the mono- and diols with a monoaminosilane, as shown in Scheme VII.
f. „ f3 c^ ^
HO-C-(O)~C~OH +
 xN-Si-CH,
I ^ I CH,' « *
XM- /"*C OCF3 CF3
fa „ fa
CHg-Si- O-C-O-Y^^-C-O-Si-CHg
OW f*C f*C O14
"
rg V/lo Uhj VylU
Scheme VH- Reactions of 6F-carblnols with Aminosflanes
7
The 6F- and 12F-carbinols appear to be highly reactive with the
aminosilanes and the reaction may be complete in less than one hour. To
ensure completion, however, reactions have been run for at least 8 hours at
reflux. The model reactions gave quantitative yields of the siloxanes.
Spectral analysis (IR and NMR) and elemental analysis confirm the
structures of products to be the desired compounds.
Several attempts have been made to polymerize l,4-bis-(2-
hydroxyhexailuoropropyl)benzene with bis-(AT.N-dimethylamino)
dimethylsilane (Scheme VIII). The first reaction yielded a polymeric
material with an inherent viscosity of 0.14 dL/g in THF. The material swells
in chloroform and DMAc and is slightly soluble in these solvents. Recent
polymerization attempts have not met with success. Research on these
polysiloxanes is continuing with great interest.
<rF3
HO-HI
CF0
=, f3
O)-C-OH +
±X 1
CF3
^
f
f3^ CF3
°~
c
 \c/c~
k k
c
^\ ?^|yj gj |\
CH/ 1O XM
viL
fi
O p:
ChL
_l«
'CH,
Scheme VUI- 6F-ContainIng Polysiloxane
5.0 Oxidation of Poly(ketone thioethers) to Polyfketone sulfones).
We have recently synthesized a new aromatic 6F-poly(ketqne
thioether) [6F-PKT] from K2S and the 6F-bisfluoride monomer shown in
Scheme IX. This PKT was shown to be superior to Ryton® polysulfide in
solubility and glass transition temperature, and comparable in thermal
stability. 6F-PKT also presented a unique opportunity to study the chemical
oxidation of polysulfides owing to PKTs excellent solubility in common
8
organic solvents. Oxidation of 6F-PKT was carried out under a variety of
conditions using several different types of reagents.
0 "II
-it
. o .r
0 "
II
-s-
• <• 17
J
 n
Scheme IX- Synthesis and Subsequent Oxidation of 6F-PKT
A single batch of 6F-PKT was prepared and then samples were
oxidized in solution, as films, or as powders. Oxidation was conducted
under acidic, basic, phase-transfer conditions in homogeneous and
heterogeneous systems. All oxidation methods yielded to some extent the
conversion of thioether to sulfone but the most successful oxidation
occurred using tetrabutylammonium permanganate in a water/methylene
chloride solvent system.
In most cases, the reaction product was a nearly colorless material,
soluble in chloroform and readily cast into films, and still retained the high
thermal stability of the brown polysulfide (>505 °C in air). Interestingly, any
reaction conducted under basic conditions resulted in the formation of
phenolic endgroups. This is suggestive of nucleophilic attack by hydroxide
on the polysulfide linkage. Work on this study in continuing and is near
completion.
References
1. C. T. Vijayakumar, K. Lederer, and A. Kramer, J. Polvm. Sci.. Part A:
Polvm. Chem.. 27, 2723-2748, (1989).
2. S. Dirkilov and Y. Feng, Proceedings of the 3rd International SAMPE
Electronics Conference. Vol. 34, pp. 169-180, June 20-22,1990.
3. R. Kellman, D. Gerbi, R. Williams, and J. Morgan, ACS Polymer Preprints.
21 (2), 164-165, (1980).
4. R.A. Braun, U.S. Pat. 3,433,819 (1969).)
10
PRESENTATIONS AND PUBLICATIONS
The following publications were issued and presentations made on the
research work at SWT conducted under the auspices of the NASA grant
#NAG-1-631.
P.E. Cassidy, A. K. St. Clair, and G. L. Tullos, "Low Dielectric
Fluorinated Poly(ether-ketone) Film and Coating", U. S. Patent No.
4,902,769, February 20, 1990.
D. W. Reynolds, P. E. Cassidy, C. G. Johnson, and M. L Cameron,
"Exploring the Chemistry of the 2-Aryl-hexafluoro-2-propanol Group:
Synthesis and Reactions of a New, Highly Fluorinated Monomer
Intermediate and Its Derivatives", Journal of Organic Chemistry. 55, 4448-
4454, (1990).
M. L. Cameron, K. M. Kane, P. E. Cassidy, and G. L. TuUos, "Film-
forming Polymers Derived from Hexafluoroacetone" a poster presented at
the ACS Symposium on Polyimides and Other High Performance Polymers
Conference, January 21-24, 1990, in San Diego, CA.
M. L. Cameron, P. E. Cassidy, and K. N. Ludwig, "Polymers Derived
from Hexafluoroacetone: 6F Poly(ketone thioether) [6F-PKT]", a poster
presented at the April 1990 ACS National Meeting, Boston, MA. Polymer
Preprints. 31 (1), 297, 1990.
D. W. Reynolds, P. E. Cassidy, C. G. Johnson, and M. L. Cameron,
"Exploring the 2-Arylhexafluoroisopropanol Group: Synthesis and Reaction
of a New Highly Fluorinated Monomer Intermediate and Its Derivatives", a
poster presented at the April 1990 ACS National Meeting, Boston, MA.
Polymer Preprints. 31 (1), 299, 1990.
D. J. Irvin, P. E. Cassidy, and M. L. Cameron, "Copoly(imide amides)
Containing Hexafluoroisopropylidene", presented at the 4th International
SAMPE Electronics Conference, June 12-14, 1990, Albuquerque, NM.
11


Trifluoromethyl-substituted polymers

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