Note: Descriptions are shown in the official language in which they were submitted.
-
1~5386~;
The present invention relates to the preparation of
polymeric articles having a microcellular structure. More parti-
cularly microcellular heterocyclic polymeric articles such as films
and fibers are prepared by a novel solvent/non-solvent casting
technique.
Solution cast opaque films have been conventionally pre-
pared by adding pigments, fillers, flame retardants and solubilizers
to a solution of the film-forming material which pigment acts as
an opacifying agent. Without an opacifying agent such film would
be colorless or transparent. Opacif~ing agents obviously increase
the costs of the resultant film and also most often embrittle the
film. Furthermore, such resulting films will have no greater
porosity than a film which does not have pigmentation.
Various processes have been described in the art for
preparing opaque films which rely for opacity upon the presence of
a large number of voids in the film. Such films may be prepared
by depositing a film from an emulsion i.e., either an oil-in-water
or a water-in-oil emulsion.
When a water-in-oil emulsion is used -- i.e., one in
which minute droplets of water are dispersed in a continuous phase
of a film forming material -- the emulsion is deposited as a coat-
ing and the organic solvent which comprlses the continuous phase
of the emulsion is evaporated therefrom. This causes gelation of
the film-forming material and entrapment of the dispersed water
droplets. The water is then evaporated leaving microscopic voids
throughout the film structure.
Another technique for obtaining a porous, opaque non-
pigmented film is set forth in U.S. Patent No. 3,031,328, which
.
-.. - . . , - . : ..................... . . .
.
-- 1~53866
contemplates preparing a solution of a thermoplastic polymer mat-
erial in a mixture of a volatile organic solvent and a volatile
`non-solvent liquid which has an evaporation rate substantially less
than that of the solvent. The clear homogenous solution is then
coated on a suitabie backing material and drled by evaporation to
produce an opaque blushed film which is adapted to be rendered lo-
cally transparent by heat or pressure. These films are useful as
recording films.
Other techniques for ~orming opaque, porous, non-pigmented,
microporous thermosetting films are set forth in U.S. 3,655,591.
Nevertheless, in spite of the above, the art has never
appreciated the unique articles which result when a specific type
of polymer is cast in a certain manner to produce microcellular
structures which have unique and unusual properties and are in-
cidentally opaque. The art has concentrated on techniques wherein
the opaqueness is the sine qua non of the structure and the other
properties are not of significance.
In accordance with the invention unique microcellular
heterocyclic polymeric articles such as films and fibers are pre-
pared by a novel solvent/non-solvent casting technique.
It is known that films, fibers and other structures can
be made out of the solvent cast heterocycllc polymers such as
those described in U.S. 3,661,859. Those particular polymers are
referred to as 1,3-imidazolidene-2,4,5-trione-1,3-diyl. The re-
peating heterocyclic ring structure of these polymers is shown
as follows:
,
- 3 - ,
:~ .
S3~
B `
~C~
n, where n is a number
from 10 to l,OO0
' '
Related but different polymers are polyhydantoins which ;
have been described in the art. See, for instance, Netherlands,
6809916, Belgium 723,772, German 1,807,742; 1,805,955; 1,812,002;
1,812,003; 1,905,367. Polyimides are well known and are described
in such publications as British 1,240,665, U.S. 3,486,934, U.S.
3,536,666, French 1,488,924, French 1,549,101, Russian 218,424,
German 1,301,114, Netherlands 7,001,648 and the like.
The detailed preparation of these polymers and solutions
of these polymers in suitable solvents are set forth in the above-
recited patents and others also in the art.
The preferred heterocyclic polymers which are used to
form the microcellular structures of the invention are character-
ized by high temperature thermal stability, organic petroleum sol~
vent resistance, relatively high tensile modulus,-tensile strength
and ultimate elongation with low shrinkage at high temperatures.
Furthermore, they have relatively high dielectric
strengths. These properties have been found by the present in-
ventor and his co-workers to offer outstanding commercial advant-
ages when used as films in flexible circuitry for use in air bag
circuits, light monitoring circuits, and telephone circuits, because
of their ability to be soldered. They also are useable for
-- 4 --
- .- . . . -, ,, ........ ~ , . ......... , .:, . . , . .... ~ . . . .
... .. , . . . . . , . : ; .............. . . ...... . . . ..
. . ' . .' . . ~ ' ' ' ' ' ' . '. ~ ' ' , '.
:10538~
magnetic tapes (where good dimensional stability at high temper-
atures is required), for fibers, such as tire cord fibers, where
high tenacity and modulus are required, for moldings for èlectrical
connectors and bearings where high temperatures are required, mag-
net wire insulation, coatings for sh:ip cables and cookware, gIass
fabrics, industrial belts and the li]ce.
However, in these applications the structure has a
relatively high cost per unit of weight since it is prepared from
a specialty polymer. It would be desirable to have a structural
article possessing essentially the outstanding properties of the
above articles so that it can be used for the applications listed
above, but less dense, so that it would not cost as much per unit
of weight. If products of low density and still superior properties
could be obtained, it would mean that a novel new structure of out-~
standing cost-performance utility would exist.
It has now been discovered and forms the fundamental
substance of the invention that such relatively low density struc-
tures can be prepared and are novel themselves. The technique of
preparing them is also novel and forms a portion of this invention.
If the advantages delineated above for the lower density
material were all that the material contributed, its existence
would be welcomed and its utility would be considered outstanding
in terms of cost effectiveness. Notwithstanding the outstanding
utility of the lower density material, it has been discovered that
the material has additional unique properties of its own which make
it extremely valuable in addition to those properties enumerated
above.
For purposes of convenience, the preferred heterocylic
- 5 -
::
1053~66
polymer species, 1,3-imidazolidene-2,4,5-trione, i.e. polypara-
banic acid, herein referred to as PP~, will be featured in the
following discussion. The particular conditlons, reagents and
uses are especially well suited for the PPA polymers and structures
resulting therefrom. Nevertheless, :;t must be emphasized that
other polymers of similar structures can be handled in an analogous
manner to make structures which have at least some similar pro-
perties. These latter include the soluble polyimides, polyamides,
and various soluble polyhydantoins.
In general, the heterocyclic polymers of the invention
will comprise sufficient repeating units of a special heterocyclic
ring structure to be solid at room temperature.
The heterocyclic ring will be 5-membered and will contain
carbon, and nitrogen linkages wherein at least two of the carbon
linkages will be carbonyl groups, i.e. ¦¦ which are separated by
a nitrogen atom.
The preferred heterocyclic ring can be schematically
represented as
X ..
IX/ \ IX
X X
wherein X is selected from the group consisting of:
O .,
f N- and -C- = C
and wherein a minimum of two carbonyl groups are present and
separated by a nitrogen atom. Examples of heterocyclic rings
which fall in this class are:
-- 6 --
:. -: . ~ . . . ,, ,:;
..
1~3866
~c~ f_~ /c~
Other suitable polymers have repeating units as ollows:
or
:
R ~ R--Aromatic or sub-
stitued aromat~c ::
\ / Z nucleous.
Wherein Z is a number from 50 to 2 x 107, preferably
50 to 1 x 106.
Although casting in general is a relatively welI-kDown
process, for each polymer and solvent system there are unique prob-
lems brought about by the particular solvents which must be used ;::
and the properties of the polymer itself. Very generally, PPA's -`
are soluble in moderate hydrogén bonding dipolar, aprotic solvents.
This presents a practical problem in casting, since solvents which
are available at a reasonable cost have relatively high boiling
points and are of low volatility, except at relatively high temper-
atures. The effect of theseparameters is that when PPA is cast
into even relatively thin structures, a film, for instance, it is
iO53~6
relatively difficult to remove the last small amounts of solvent
from the structure, e.g. film.
For instance, dimethylformamide (DMF) is considered to
be one of the best solvents for working with PPA solution formu-
lations. It boils at 156C and its excellent solvating effect
results in the fast dissolution of PPA along with the formation of
low viscosity solutions.
Nevertheless, this combination of low volatility and high
solvation, which characterizes a good solvent, makes the removal
of the last amounts of solvent from even thin structures such as
films very difficult. Therefore, film casting processes must be
conducted with extremely high temperatures in order to get good
solvent removal at reasonable production rates.
In order to avoid these long time intervals and high
temperatures, an attempt was made to find more practical techniques
that could be used to effect complete solvent removal within
reasonable time parameters at relatively low temperatures. As a
result of these activities, the technique of making cellular PPA
film was discovered.
Very briefly, this relatively low density PPA structure,
e.g. film, which has a microcellular structure, is prepared by -
first solvent casting of film. Then, prior to the complete drying,
which is difficult to effect anyway, one precipitates the film by
contacting the film with an antisolvent, such as water. The anti-
solvent should be miscible with the solvent in the polymer solution.
In general, there are four methods according to the
invention that can be used to form the novel cellular articles
of the invention. These are:
~353866
(a~ Method 1 - The cast article, e.g. film or
solvent extruded article, e.g. fiber, is
exposed to a relative:Ly high water humidi-
ty, followed by a direct water washing,
followed by drying. As is true of all of
the techniques, the thickness and shape of
the structure is controlled by its origin-
al cast or extruded thickness and shape
and solids content. Precipitating the
structure in a high humidity environment
rather than initial direct water contact is
important. The reason is that too rapid
precipitation and solvent removal will cause
wrinkling of the structure, which is very
undesirable.
(b) Method 2 - The structure, e.g. film or fiber,
is solvent cast or extruded; then it is par-
tially dried to a greater or lesser extent.
This serves two purposes; prevents wrinkling
and increases the density of the structure.
Then it is water washed and then dried com-
pletely. The density will vary according to
the amount of solvent removed in the initial
drying step.
(c) Method 3 - A solvent blend is prepared from a
high-boiling non-solvent and a lower-boiling
good solvent, then an article of film or fiber
film is cast extruded from this solvent blend
1~386~
and the article is subsequently dried. This
is not a precipitation as described above for
Methods 1 and 2. ~owever, the article thick-
ness would be set by the initial thickness of
the cast or extruded article.
(d) Method 4 - The structure, e.g., film or fiber,
is solvent cast or extruded onto a suitable
surface, e.g. metal, glass or vellum paper,
and is introduced directly into an anti-solvent
without either pre-exposure to humid atmosphere
as in Method 1 or pre-drying as in Method 2.
The key to this method is the solution of an
anti-solvent, with either a single solvent or
multi component mixture, which is a weak anti-
solvent relative to water. -
The precipitation thus proceeds much more slowly
and prevents surface wrinkling which would occur
if a strong anti-solvent such as water were used.
It is often highly desirable to extrude directly
into the weak anti-solvent instead of onto a suit-
able surface.
The structure is subsequently exposed to a series
of progressively stronger anti-solvents to complete
the precipitation and finally washed with water and
dryed. The density can be controlled by the choice
of anti-solvent and the percent of polymer in the
original polymer solution.
Thus, Method 1 gives a density of about 0.45 g. per cubic
centimeter, Method 2 gives a density varying from about
,, 10 --
.. - - ~ :
~ 38~6
0.5 to 1.1 g. per c~lbic centimeter, and Methods 3 and 4 can be used
to obtain a wide range of densities. When operating in the solu-
tion casting mode, the following considerations will be pertinent.
Density is largely dependent on the weight fraction of
polymer in the wet film at the instant precipitation occurs.
Solutions of PPA ranging above 30 weight percent cannot be con-
veniently handled in conventional solvent casting equipment due
to their very high viscosity associated with high molecular weight.
The Method 1 technique contemplates the use of the most
viscous solution that can be handled, i.e. ~0 to 50 weight percent
PPA depending upon molecular weight of the polymer.
Method 2 permits the use of a more dilute solution with
its concomitant easierhandling advantages, and relies upon the
evaporation of more solvent from the film after it is cast and prior
to first precipitation. This allows a wider range of densities
than can be obtained by Method 1.
The practical limit which sets the maximum density
which can be obtained in Method 2 is the minumum amount of solvent
which must remain in the polymer in order for precipitation to
occur when the cast polymer solvent structure is contacted with
water or other antisolvent.
The minimum density of Method 2 is limited by the max-
imum amount of solvent that can be left in the wet film at the
first precipitation step, which will not cause surface wrinkles
on the film or fiber surface. This will vary depending on the
choice of anti-solvent.
The range of densities can be further increased by (a)
calendering the resulting cellular film, (b) orienting the film
.~' -
-- 11 --
. .
' ' .' . ~ . ,: ' . ' .
' ' . . ..
and the fibers to elongate and reduce diameters of the cellular
portions, or (c) the use of different mechanical equipment designed
to handle the extremely viscous polymer solutions, for example slot
extruders. That latter approach would increase the density of the
microcellular material approximately proportionately to the amount
of solvent reduction in the original polymer solvent solution. Thus
when solution extrusion equipment is used, much higher polymer sol-
vent contents can be handled as compared to the ca`sting methods
described above.
In actual operation, cellular filmmade from PPA solutions
in DMF were prepared on equipment which is normaIly used to make
porous cellulose acetate film for electrophoresis''applications. The
equipment consisted of a doctor's knife applicator, a sixty-foot
continuous stainless steel belt, and four chambers equipped to con-
trol humidity, temperature and the rate of air flow.
Provisions were also incorporated to spray water onto the
moving continuous belt for the purposes of initiàl precipitation and
for washing the solvent from the film.
The technique used was that described for Method 1. And
the polymer was PPA in 20% concentration in DMF. ~The humidity was
controlled at 90-95% and the film initially precipitated due to ab-
sorption of water vapor. Additional precipitation and solvent re-
moval was effected by direct immersion in a water bath followed by
drying.
Under these conditions of high humidity'the wet film ab-
sorbs water vapor xapidly due to the hygroscropic`nature of the
DMF solvent but much slower than if directly immersed in water.
Films having a uniform cellular structure were obtained having
- . . . - - : :
.
- - , ~ : : ~
--- 10~3866
densities of about 0.5 g. per cubic centimeterO
The belt speed varied from about .50 feet per minute
to about 2.5 feet per minute. The temperature was about 100F.
The air rate was about 900 to 1,300 cu. ft. per minute. The thick~
ness of the wet film varied from about 8 mils to about 20 mils.
The total time in the oven ranged from about 6 minutes to about 15
minutes. Generally time periods above 10 minutes and less than 20
minutes appeared to be satisfactory.
Subsequent work has been done to produce cellular films
which have relatively high densities, i.e. up to l.l gms./cc.
For this, the above-described equipment was modified
somewhat to permit the use of a Method 2 type approach. It re-
quired the addition of heaters to the first chamber in order to
provide for some gradual initial solvent removal, which is a step
required to control the increase in the density of the film and
to prevent wrinkling. Equipment to spray water onto the moving
stainless steel belt was installed in the second chamber to pre-
cipitate the film. Water sprays in the third and fourth chambers
were provided in order to wash out additional solvent, e.g. N,N-
dimethylformamide (DMF) prior to stripping the film off the beltand subsequent drying.
Passage of the solvent loaded film into an irregular
water interface produced a non-uniform surface on the precipitated
film. Therefore an air knife was installed which directed an air
flow downward onto the surface of the belt and provided a relatively
uniform water interface for the wet film to pass into. -
This type of equipment is adequate to produce a wide
range of densities.
- 13 -
`- 1053866
Although it is predictable that mechanical properties
such as modulus and tensile strength will decrease with decreasing
density, it was found that these mechanical properties were not
sufficiently diminished to seriously affect the utility of the cell-
ular article for many applications. Moreover, in the case of the
film, the propagating tear strength tended to be as good as that for
the dense film.
The dielectric constant will decrease with decreasing den-
sity, and therefore the dielectric constant for the cellular prod
ucts are lower than that for the dense film products. This makes
the cellular film more attractive for use as insulation, e.g. for
microwave circuitry, especially where transmission is to be over
relatively long distances. In an analogous fashion, the lower
thermal conductivity make these structures desirable for thermal
insulation.
As in the case of the dense film, the cellular film also
withstands commercial solder bath temperatures, i.e. 500F.
One important and highly advantageous property of the
cellular film, as opposed to the dense film is that copper circuits
can be electroplated directly onto the cellular film, with much
higher peel strengths for the electroplated copper on the cellular
film than on the dense film. -
For example, peel strengths for copper electro-deposited
on the dense film were in the range of about 2.5 to 3.0 pounds per
inch. But peel strengths on copper electrodeposited onto the micro-
cellular film were in the range of about 8 pounds per inch.
This is an extremely important, aspect of the cellular
film which gives it an outstanding advantage, taken in combination
- 14 -
:, . - ~ . ~ ,.
:. 10538~i6
` with its o-ther properties, over dense film.
Not only are the adhesion values exceedingly high for
the electroplated copper circuit on dense film, and also laminates
prepared with adhesives but the use of the cellular film permits
the omission of a bothersome process step~ Thus, before copper
laminated onto plastic films which normally contain small quant-
ities of absorbed water can be soldered, the unit must be dried to
remove absorbed water. If it is not, the absorbed water tends to
be driven from the film during the soldering operation, because of
heating of the composite unit. This rapid generation of steam
causes the copper to be delaminated from the film substrate.
When the cellular film of the invention is utili~ed,
the copper does not delaminate. It is theorized that this is due
to the fact that there are numerous microcellular orifices into
which the water can expand and through which the water can escape
along the surface and through the side cross-sections of the film.
Therefore delamination is effectively prevented. This is an ex-
ceedingly useful property.
These films are much more flexible than dense film of
the same thickness, which is an advantage for thick multilayer
structures. -
Another important feature of the structures of the
invention involves selective surface etching by strong bases or
acids. This removes the film covering the micropores, either com-
pietely or in any pattern desired. The exposed micropores, can
then be electro or chemically plated with far better adhesion. In
fact, grooves can be etched into the surface into which conductive
metals can be deposited with excellent adhesion to the exposed
-~ 15
: . : , :.
~53~36~
micropores and with excellent separation and insulation from adjacent
conductor filled grooves.
All in all, cellular film because of its combination of
properties and its relatively low cost is an ideal material for
flexible circuits and flat conductor cables.
Numerous other highly effective uses can be made
of the cellular structures, e.g. film. For instance, it can be
used as is or converted to membranes Eor both liquid and gaseous
separations.
The preferred structures produced by the practice of this
invention are characterized by the presence therein of a large num-
ber of discrete closed cells. Substantially all of these cells or
voids are less than 300 microns, and preferably less than 15 microns,
in size. The average cell size and cell size distribution is
governed by the conditions under which the structures are made,
e.g., temperature solvent, anti-solvent, polymer solids content of
casting solutions, etc. The range obtainable is from about 0.1 to
300 microns.
Unless some color-forming material has been included in
the composition, such as a soluble dye, the preferred films of this
invention are opaque and white. Colored films may be obtained by
incorporating small amounts of dye.
A film having an apparent thickness of, for example,
10 mils will have a real solid thickness which is equal to the sum
of the thickness of each wall between the discrete cells lying along
a path perpendicular to the outermost planar surface of the film
which may be, for example, no more than 3 mils. This property ren-
ders the film of this invention, particularly those having an average
cell size of less than 10.0 micron, useful as vapor or liquid per-
~ l6
.
: . .
: ~ t
1(~53866
meation membranes which may be utilized for a number of applications,such as for example, in desalinization processes. Thus, the film
is of sufficient apparent thickness to provide the required amount
of strength; yet the total thickness of solid polymer through which
a molecule must pass (i.e. the cell walls) is relatively small.
Furthermore, the diffusion per unit of time of a vapor
or a liquid through a unit area of some of the films of this in-
vention is far greater than that in the case of non-porous film
heretofore available.
The preferred films of this invention reflect light of
wavelengths above 3800 angstroms which makes them useful as visible
light reflectors.
The compositions of this invention are particularly use-
ful when precipitated on fibers such as fiber glass, resinous yarns,
vegetable or cellulosic yarns and cords. When these fibers or cords
are coated with the structures of this invention, an opaque or white
fabrlc is obtained without the addition of pigments as needed in
the fabric heretofore employed. These coated fabrics have very
desirable flexibility. The fact that pigments such as TiO2 are not
needed to obtain whiteness in fibrous fabrics is quite significant
since this has been a problem in the art due to the adverse effects
these pigments have on the resulting fabrics. For example, it is
known that pigments such as Tio2 weaken the tensile strength of the
fabric.
The fibers may be coated with the compositions of this
invention by any of the first three methods described above. One
method found to be suitable is to dip the fibers into a solution
which contains resin, solvent and non-solvent in amounts indicated
- 16a -
- 1053866
hereinabove. Upon precipitation a fabric having the desired white-
ness and softness is obtained without the addition of pigments
such as TiO2.
Although the above discussion has been made with re-
ference to films as discrete articles, it is to be noted that films
in terms of surface coatings with unique and important properties
and which are bonded to a substrate can also be produced according
to the technique of the invention.
The structures of this invention may be formed as surface
coating films by techniques described in Methods 1-4 above. `Thus~
they may be applied by brushing/ spraying, dipping, roller coating,
knife coating, electrodepositing or calendering followed by pre
cipitation and drying. They can also be extrusion coated onto
substrates.
The compositions of this invention are particularly use-
ful when employed in spray applications using Method 3 due to the
presence of the non-solvent in the composition.
The compositions of the present invention containing
the non-solvent can have a lower viscosity at corresponding solids
content, thereby permitting easier atomizàtion of a higher solids
content of resinous materials than compositions not containing a non-
solvent. Therefore, fewer coats are necessary to obtain the de-
sired thickness of film by spray application using the compositions
of this invention.
As already indicated compositions of this invention may
be applied as films to various types of surfaces or substrates.
These surfaces may be of the type whereby the film is to be removed
by a suitable method or of the type where it is adhered to the ~inal
:~~
~ l[)5386~i
substrate such as the metal of an automobile. Among the more suit-
able surfaces which may be coated with the cellular structures of
this invention are steel, treated steel, galvanized steel, concrete,
glass, fabrics, fiber glass, wood, plaster board, aluminum, treated
aluminum, lead, copper, and plastics. The most preferred surfaces
are metals such as treated steel and treated aluminum.
Films formed from the compositions of this invention may -- -
be air dried, vacuum dried or bake dried at elevated temperatures.
Although considerable emphasis has been placed on cellu-
lar film formation and applications, it is an important feature ofthis invention that cellular fibers of high strength can be pro-
duced utilizing the technique of the invention.
Cellular fibers made by the conventional techniques of
the art are never left in cellular form, but are remelted and orient-
ed in order to eliminate the cellular structure which is considered
undesirable. In this invention the polymers used have such a high
modulus that the porous fibers can be used with only moderate-
orientation. This gives rise to a highly porous fiber which can
accept dyes extremely readily. Moreover, the fiber has the capacity
to absorb moisture very easily. Thus, it will be comfortable in
contact with the human body. The capability of absorbing moisture
is often the difference between synthetic fabrics which may feel
clammy and natural fabrics such as cotton, the latter being much
more comfortable because of its water absorptive capacity. Perma-
nent press fabrics can be made due to high softening temperatures
of these novel fibers.
The mi~rocellular films, fibers and other structures
can also beelectrocoated with various metals such as copper,
- - :. . .. ~ ~ :
1053~3~;6
aluminum and the like in order to form thin conductive coatings
with a minimum of coating metal.
Electrocoated structures can be used in a wide variety
of decorative and utilitarian applications. These involve auto-
motive trim, under-the-hood uses, and radiation shields.
Electrodeposition and chemical metalizing can also be
used to coat catalytic metals such as palladium, platinum, nickel,
and the like, within the porous intexstices of the structure,
so that it can be used to form an extremely high surface area,
artificial surface for conducting catalytic reactions at relatively
high temperatures. For instance, the ability of heterocyclic st-
ructures to withstand temperatures up to 300C. wauld make them
effective in automobile exhausts.
Also, when used for magnetic tape the cellular film is
exceptionally useful because the magnetic oxide can be bonded to
the surface quite readily and easily because of footholes provided
by the cellular configurations.
The cellular structures of the invention are also highly
useful for specialty applications where highly tenacious painted
surfaces are required.
The invention is further illustrated by the following
examples:
Example 1
Utilizing the technique and apparatus described above,
a series of runs was carried out in the apparatus. The solutions
used for each run were as follows:
(a) 19.7 weight percent PPA, 79 weight percent
,
- - 19 =
..... , - - ~
.. . .
866
DMF and 1.3 weight percent of octabromo-
biphenyl twhich is an excellent flame re- . .
tardant for PPA film);
(b) a polymer solution containing 18.8 weight
percent PPA, 80 weight percent DMF and 1.2
weight percent octabromobiphenyl.
All PPA utilized in these examples was prepared from di-
phenyl methane diisocyanate monomer.
The properties of the film obtained are summarized below
in Table I.
_ 20 _
105;~866
X a~ o a~
a~
I
X ~ .
O H
.
~5 ~
O U~ O
~I O ~ O
a.) Q) U~ O ~ ~ O
~1 ~1 ~ ,~ ~1 U)
~1 ta o
a
rl ~ ~I
~-ri
~ ~ ~ CO ~ O O
O
S~ ~ ~1
P~
E~
o O O O
a) u, o o o o
o o O O
-rl
a~ ~r o
~ ~ ~ ~r ~ o
a~ o ,, c~
E~
H
~ U~
~m ~ ~n O o
E~ ,y ,1
.0 ~ U~
E~
U)
~ r~ ~ ~CO ~-
a1 ~ o ~o ~ - .,
rl
'~ . ' ~
.,~ ~ m o,,
~ .
,~
o o o
~ ~
- a
~1 rl A
H Iq la Ul
O O O
.,1 O OO
.~, C~
--21-
1053866
The resulting level of octabromobiphenyl in the dense
film was about 6 weight percent. Such a level of flame retardant
resulted in an oxygen index of 32 to 34, depending on thickness and
density of the film, as can be seen above.
The microcellular structures of the invention can have
incorporated therein a wide variety of small particle additives and/
or fillers. These can be selected so as to fit within the pores.
The resulting structures are relatively non-brittle compared to a
dense structure containing a comparable amount of filler or additive.
Illustrative examples of additives are flame retardants,
antioxidants, pigments and the like.
For many uses and applications, emphasis in this application
has been placed on the cellular structure per se and its many uses.
It is to be emphasized that for many applications describe`d
herein where the unique properties of the cellular material are not
required, films, coatings, article structures, etc., composed of the
dense version of the heterocyclic polymers are useable. Some of
these specific uses and applications of the dense heterocyclics are
novel and unobvious in their own right.
The cellular structures will also be highly useful as
membranes and separators in fuel cells which do not utilize alkaline
electrolytes. The high temperature resistance, strength, perme-
ability and ability to be adhered to conductors such as metals and
carbon as wall as the ease of electroplating a strong adherent metal
film to the microporous structures make them uniquely suitable for
many fuel cell and battery component applications.
Furthermore, the ability of the dense and cellular mat-
erials described herein to both adhere tenaciously to metals, carbon
3L053866
graphite, etc., substrates as well as their high temperature solvent
and corrosion resistance to virtually all chemical substances except
aprotic solvents and alkalies makes these heterocyclic polymers
outstanding material for tank linings, pipe coatings and other thin
film protective coatings. Their low permeability properties (denser
film) are also of significance in this application.
When applied in the form of a solvent solution, the aprotic
solvent is so active with respect to many of the ordinary surface
contaminants such as oxidized metals, salts, dirt, grease, oil, etc.,
that good adhesion can be obtained without rigorous surface prepar-
ation.
Another unique and highly useful application of the film
coatings of these heterocyclics, especially PPA, relies on the un-
usual low temperature performance of these polymers. Thus, coatings
for pipes and electrical cable conduit wraps of these heterocyclics
can be used in extremely adverse low temperature, environments as
low as about -268C;, with no adverse effect. This permits use with
liquid helium and liquid nitrogen without losing flexibility and with
low dissipation factors.
This permits PPA materials (either cellular or dense), to
be used as insulating and protective materials in low temperature
conductors. Such low temperature conductors are the clear trend of
the future and PPA should play an important role in these environ-
ments.
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