Process for coagulating and washing lyotropic polybenzazole films

A process for coagulating a polybenzazole film which includes contacting a lyotropic polybenzazole dope film that is constrained in at least two directions with a coagulant under conditions such that the polybenzazole polymer separates as a gelled moiety with the structure set such that further removal of solvent will result in no more than a 5% increase in the force necessary to constrain the film.

BACKGROUND OF THE INVENTION 
This invention relates to films containing lyotropic polybenzazole polymers 
and processes for coagulating and washing them. 
Polybenzazole polymers are typically synthesized by polymerization in 
nonoxidizing dehydrating acid solutions to form viscous dopes which are 
solutions of the polymer in the solvent acid. Uniaxially oriented film may 
be synthesized from these dopes by extruding onto a rotating drum that 
draws the film in the machine direction and rotates it down into a water 
bath to coagulate. Biaxially oriented films are synthesized by extruding 
the dope as a tube, which is blown or forced over a mandrel to impart some 
biaxial orientation, and is then immersed in water to coagulate it. 
Examples of such processes are described in: Chenevey, U.S. Pat. No. 
4,487,735 (Dec. 11, 1984); Lusignea et al.,U.S. Pat. No. 4,871,595 (Oct. 
3, 1989); Chenevey, U.S. Pat. No. 4,898,924 (Feb. 6, 1990); Harvey et al., 
U.S. Pat. No. 4,939,235 (Jul. 3, 1990); Harvey et al., U.S. Pat. No. 
4,963,428 (Oct. 16, 1990); Lusignea et al., U.S. Pat. No. 4,966,806 (Oct. 
30, 1990); and Fujiwara, Japanese Kokai 63(1988)-74612 (published Apr. 5, 
1988), which are incorporated herein by reference. 
Once the polybenzazole dope film has been formed it must undergo 
coagulation in order to separate the polybenzazole from its solvent. 
Coagulation is the process in which a polymer in solution is contacted 
with a polymer nonsolvent, known as a coagulant, causing phase separation 
of the polymer into a gelled moiety. A coagulated film has a macroscopic 
structure that is essentially fixed. After the film has been coagulated it 
can be further washed in order to remove even more of the acid solvent. 
The amount of washing the film is subjected to depends upon the desired 
level of residual acid solvent in the final film. 
The coagulated films and sheets may be used in structural materials or 
electronic components as described in U.S. Pat. No. 4,871,595 (Oct. 3, 
1989) and 11 Ency. Poly. Sci. & Eng., Polybenzothiazoles and 
Polybenzoxazoles, 601 (J. Wiley & Sons 1988), which are incorporated 
herein by reference. 
It is necessary to coagulate and wash a dope film to obtain a polybenzazole 
film with a desired level of residual solvent in order to produce 
marketplace quality polybenzazole film. 
SUMMARY OF THE INVENTION 
One aspect of the present invention is a process for coagulating a 
lyotropic polybenzazole film which includes contacting a lyotropic 
polybenzazole dope film that is constrained in at least two directions 
with a coagulant under conditions such that the polybenzazole polymer 
separates as a gelled moiety with the structure set such that further 
removal of solvent will result in no more than a 5% increase in the force 
necessary to constrain the film. 
A second aspect of the present invention is a process for coagulating a 
lyotropic polybenzazole film which includes contacting a lyotropic 
polybenzazole dope film that is constrained in at least two directions 
with a coagulant under conditions such that the polybenzazole polymer 
separates as a gelled moiety with the structure set such that further 
removal of solvent will result in no more than a 5% increase in the force 
necessary to constrain the film, and removing some of the constraint on 
the film such that the film is constrained in at most one direction; and 
subjecting the coagulated film to washing with a suitable washing medium 
under conditions such that the desired level of residual solvent in the 
film is reached while ensuring that the film is not allowed to dry out 
until said desired levels of residual solvent in the film have been 
reached. 
A third aspect of the present invention is a process for coagulating a 
lyotropic polybenzazole film which includes contacting a lyotropic 
polybenzazole dope film that is constrained in at least two directions 
with a coagulant under conditions such that the polybenzazole polymer 
separates as a gelled moiety with the structure set such that upon release 
of constraint further removal of solvent will result in no more than 5% 
shrinkage of the coagulated film. 
DETAILED DESCRIPTION OF THE INVENTION 
As used in this application, the terms listed have the following 
definitions: 
"dope" is a solution of polybenzazole polymer material in a solvent (at any 
polymer concentration), 
"dope film/sheet" is dope material formed into a film or sheet by some 
mechanical operation (i.e. cast onto a flat surface or extruded through a 
film/sheet die), 
"extruded dope film and/or sheet" is dope material which has been formed 
into a film/sheet by extrusion through a film die, 
"oriented dope film" is dope material into which orientation has been 
imparted by some stretching operation (e.g. tentering, blown film process, 
or by a counter-rotating blown film process), 
"coagulated film" means a film with a gelled structure set such that 
further removal of solvent will result in less than a 5% increase in the 
force necessary to constrain the film (i.e., less than 5% shrinkage upon 
release of the constrained film), 
"coagulant" is a polymer nonsolvent used to remove and/or displace solvent 
(acid) from the film in either the coagulation or washing phases, 
"residual solvent" is that part of the solvent acid, or associated species, 
still remaining in the polybenzazole film after the film has been 
coagulated, 
"washing" is that part of the process in which the residual solvent level 
in the coagulated polybenzazole film is reduced to the desired level for 
the final film application, 
"lyotropic" means a material that changes the phase that it is in depending 
on its concentration in solution, 
"polybenzazole" is a lyotropic liquid crystal polymer that is isotropic at 
low polymer concentrations and anisotropic beyond a certain critical 
polymer concentration, which for a given polymer is dependent on the acid 
solvent chosen and temperature. Typically, there is a broad biphasic 
region in which there is a mixture of isotropic and anisotropic material. 
An example of a lyotropic liquid crystalline polymer is polybenzoxazole 14 
wt % dissolved in polyphosphoric acid. 
The present invention uses dopes containing polybenzoxazole ("PBO") or 
polybenzothiazole ("PBT") or copolymers thereof, dissolved in a solvent. 
PBO, PBT and random, sequential and block copolymers of PBO and PBT are 
described in references such as Wolfe et al., Liquid Crystalline Polymer 
Compositions, Process and Products, U.S. Pat. No. 4,703,103 (Oct. 27, 
1987); Wolfe et al., Liquid Crystalline Polymer Compositions, Process and 
Products, U.S. Pat. No. 4,533,692 (Aug. 6, 1985); Wolfe et al., Liquid 
Crystalline Poly(2,6-Benzothiazole) Compositions, Process and Products, 
U.S. Pat. No. 4,533,724 (Aug. 6, 1985); Wolfe, Liquid Crystalline Polymer 
Compositions, Process and Products, U.S. Pat. No. 4,533,693 (Aug. 6, 
1985); Evers, Thermoxodatively Stable Articulated p-Benzobisoxazole and 
p-Benzobisthiazole Polymers, U.S. Pat. No. 4,359,567 (Nov. 16, 1982); Tsai 
et al., Method for Making Heterocyclic Block Copolymer, U.S. Pat. No. 
4,578,432 (Mar. 25, 1986); 11 Ency. Poly. Sci. & Eng., Polybenzothiazoles 
and Polybenzoxazoles, 601 (J. Wiley & Sons 1988) and W. W. Adams et al., 
The Materials Science and Engineering of Rigid-Rod Polymers (Materials 
Research Society 1989), which are incorporated herein by reference. 
POLYBENZAZOLE POLYMERS 
The polymer may contain AB-mer units, as represented in Formula 1(a), 
and/or AA/BB-mer units, as represented in Formula 1(b) 
##STR1## 
wherein: Each Ar represents an aromatic group. The aromatic group may be 
heterocyclic, such as a pyridinylene group, but it is preferably 
carbocyclic. The aromatic group may be a fused or unfused polycyclic 
system, but is preferably a single six-membered ring. Size is not 
critical, but the aromatic group preferably contains no more than about 18 
carbon atoms, more preferably no more than about 12 carbon atoms and most 
preferably no more than about 6 carbon atoms. Examples of suitable 
aromatic groups include phenylene moieties, tolylene moieties, biphenylene 
moieties and bis-phenylene ether moieties. Ar.sup.1 in AA/BB-mer units is 
preferably a 1,2,4,5-phenylene moiety or an analog thereof. Ar in AB-mer 
units is preferably a 1,3,4-phenylene moiety or an analog thereof. 
Each Z is independently an oxygen or a sulfur atom. 
Each DM is independently a bond or a divalent organic moiety that does not 
interfere with the synthesis, fabrication or use of the polymer. The 
divalent organic moiety may contain an aliphatic group, which preferably 
has no more than about 12 carbon atoms, but the divalent organic moiety is 
preferably an aromatic group (Ar) as previously described. It is most 
preferably a 1,4-phenylene moiety or an analog thereof. 
The nitrogen atom and the Z moiety in each azole ring are bonded to 
adjacent carbon atoms in the aromatic group, such that a five-membered 
azole ring fused with the aromatic group is formed. 
The azole rings in AA/BB-mer units may be in cis- or trans-position with 
respect to each other, as illustrated in 11 Ency. Poly. Sci. & Eng., 
supra, at 602. 
The polymer preferably consists essentially of either AB-PBZ mer units or 
AA/BB-PBZ mer units, and more preferably consists essentially of AA/BB-PBZ 
mer units. The polybenzazole polymer may be rigid rod, semi-rigid rod or 
flexible coil. It is preferably rigid rod in the case of an AA/BB-PBZ 
polymer or semi-rigid in the case of an AB-PBZ polymer. It preferably 
forms lyotropic liquid crystalline solutions in a suitable solvent above a 
critical concentration point. Azole rings within the polymer are 
preferably oxazole rings (Z=0). Preferred mer units are illustrated in 
Formulae 2 (a)-(g). The polymer more preferably consists essentially of 
mer units selected from those illustrated in 2(a)-(h), and most preferably 
consists essentially of a number of identical units selected from those 
illustrated in 2(a)-(d). 
##STR2## 
Each polymer preferably contains on average at least about 25 mer units, 
more preferably at least about 50 mer units and most preferably at least 
about 100 mer units. The intrinsic viscosity of rigid AA/BB-PBZ 
##STR3## 
polymers is methanesulfonic acid at 25.degree. C. is preferably at least 
about 10 dL/g, more preferably at least about 15 dL/g and most preferably 
at least about 20 dL/g. For some purposes, an intrinsic viscosity of at 
least about 25 dL/g or 30 dL/g may be best. Intrinsic viscosity of 60 dL/g 
or higher is possible, but the intrinsic viscosity is preferably no more 
than about 40 dL/g. The intrinsic viscosity of semi-rigid AB-PBZ polymers 
is preferably at least about 5 dL/g, more preferably at least about 10 
dL/g and most preferably at least about 15 dL/g. 
FORMING A POLYBENZAZOLE DOPE 
The polybenzazole polymer or copolymer is polymerized in a solvent. 
Solutions of polybenzazole in a solvent are commonly referred to as a 
dope. The polybenzazole polymer or copolymer dope can be formed into a 
shaped article such as a fiber or film and, if desired, this polybenzazole 
fiber or film can be dissolved in a solvent. 
Some polybenzoxazole and polybenzothiazole polymers are soluble in cresol, 
but the solvent is preferably an acid capable of dissolving the polymer. 
The acid is preferably nonoxidizing. Examples of suitable acids include 
polyphosphoric acid, methanesulfonic acid and 100% sulfuric acid, and 
mixtures of those acids. The acid is preferably polyphosphoric acid or 
methanesulfonic acid, and is more preferably polyphosphoric acid. The 
polybenzazole/polyphosphoric acid dopes that are used in this invention 
are lyotropic liquid crystalline solutions. 
The dope should contain a high enough concentration of polymer for the 
polymer to coagulate to form a film of the desired thickness without 
substantial flaws. When the polymer is a lyotropic polymer, then the 
concentration of polymer in the dope is preferably high enough to provide 
a dope that contains liquid crystalline domains. The concentration of the 
polymer is preferably at least about 7 weight percent, more preferably at 
least about 10 weight percent and most preferably at least about 14 weight 
percent. The maximum concentration is limited primarily by practical 
factors, such as polymer solubility and dope viscosity. The concentration 
of polymer is seldom more than 30 weight percent, and usually no more than 
about 20 weight percent. 
Suitable polymers or copolymers and dopes can be synthesized by known 
procedures, such as those described in Wolfe et al., U.S. Pat. No. 
4,533,693 (Aug. 6, 1985); Sybert et al., U.S. Pat. No. 4,772,678 (Sep. 20, 
1988); Harris, U.S. Pat. No. 4,847,350 (Jul. 11, 1989); and Ledbetter et 
al., "An Integrated Laboratory Process for Preparing Rigid Rod Fibers from 
the Monomers," The Materials Science and Engineering of Rigid-Rod Polymers 
at 253-64 (Materials Res. Soc. 1989), which are incorporated herein by 
reference. In summary, suitable monomers (AA-monomers and BB-monomers or 
AB-monomers) are reacted in a solution of nonoxidizing and dehydrating 
acid under nonoxidizing atmosphere with vigorous mixing and high shear at 
a temperature that is increased in step-wise or ramped fashion from no 
more than about 120.degree. C. to at least about 190.degree. C. Examples 
of suitable AA-monomers include terephthalic acid and analogs thereof. 
Examples of suitable BB-monomers include 4,6-diaminoresoreinol, 
2,5-diaminohydroquinone, 2,5-diamino-1,4-dithiobenzene and analogs 
thereof, typically stored as acid salts. Examples of suitable AB-monomers 
include 3-amino-4-hydroxybenzoic acid, 3-hydroxy-4-aminobenzoic acid, 
3-amino-4-thiobenzoic acid, 3-thio-4-aminobenzoic acid and analogs 
thereof, typically stored as acid salts. 
FORMING A POLYBENZAZOLE FILM 
Forming a polybenzazole film can be as simple as using hand cast methods to 
spread the polybenzazole dope out onto a relatively flat surface. It also 
can involve complex machinery that first extrudes the film through a die 
and then stretches the film to orient the polymer. (Whether the film is 
merely cast or extruded and then oriented, all lyotropic polybenzazole 
films need to be coagulated before they can be used.) 
The following is a description of a process to form an extruded and 
oriented dope film. The three-step process described in jointly owned 
co-pending U.S. patent application Ser. No. 670,135 converts polymer dopes 
into oriented dope films. In the first step, the dope is extruded as a 
dope film or sheet which is relatively thick and is relatively narrow in 
the transverse direction, as compared with the final desired film. The 
extruded dope film is preferably left as a continuous sheet, rather than 
cutting into discrete sections. 
The dope film or sheet should be thick enough that it can be stretched as 
desired without leaving flaws after coagulation. The optimum thickness 
varies considerably depending upon the desired thickness of the final 
product and the desired stretch from the second step of the process, 
keeping in mind that the thickness of the dope film as extruded will 
decrease as much as tenfold as the dope film is first oriented, then 
coagulated. For most purposes, the oriented dope film or sheet is 
preferably at least about 1 mil thick, more preferably at least about 5 
mil thick, and most preferably at least about 25 mil thick. The dope film 
or sheet is preferably no more than about 250 mil thick and more 
preferably at most about 100 mil thick. (Ordinarily, the term "film" 
refers to an article no more than about 10-15 mil thick, and the term 
"sheet" refers to an article greater than about 10-15 mil thick. This 
Application shall use the term "film" to refer to both film and sheet.) 
It may optionally be desirable to sandwich the extruded dope film between 
two layers of a stretchable polymer film which is inert with respect to 
the dope under process conditions. Examples of a suitable polymer film 
include Teflon.RTM. fluorocarbon film or amorphous polyester film. The 
outer layers of the stretchable polymer film protect the dope from the 
atmosphere and prevent it from adhering to itself or other objects if the 
dope is stored after extrusion. By being able to extrude the film directly 
between two layers of a stretchable polymer film it is possible to store a 
freshly extruded dope film rather than having to tenter a directly 
extruded dope film immediately. The process as described in jointly owned 
co-pending U.S. application Ser. No. 670,135, does allow for storage of 
the film at any stage of the process. 
TENTERING (STRETCHING) THE FILM 
In this step, which is optional, the dope film is mechanically stretched, 
this stretching process being known as tentering. This stretching process 
takes place in at least the transverse direction to form an oriented dope 
film. Tentering of a polybenzazole film is accomplished in a manner 
similar to the tentering of known thermoplastic polymers. Tentering of a 
polybenzazole film is accomplished by having a mechanical device grip the 
transverse edges of the dope film and pull these transverse edges apart. 
The dope film may also be stretched in the machine direction and/or in any 
other direction. Stretching should be carried out at a temperature and at 
a rate at which the dope film can tolerate stretching without it tearing. 
For liquid crystalline dopes containing polyphosphoric acid (this 
polyphosphoric acid being 82-85 percent phosphorus pentoxide ("P.sub.2 
O.sub.5 ")) and 14 weight percent rigid rod polybenzoxazole or 
polybenzothiazole, the temperature for tentering is preferably at least 
about 20.degree. C., more preferably at least about 50.degree. C. and most 
preferably at least about 75.degree. C. It is preferably at most about 
175.degree. C., more preferably at most about 150.degree. C. and most 
preferably at most about 125.degree. C. The optimal rate of stretching 
varies widely depending upon a number of factors such as polymer 
structure, molecular weight and concentration, solvent acid, and dope 
temperature. It can best be determined by experiment. 
COAGULATION 
In order to be used, eventually the dope film (stretched or unstretched) 
must be coagulated to yield a polybenzazole film that can be used in 
applications. Ordinarily the dope film is coagulated by contacting the 
film with a coagulant that is a nonsolvent for the polymer. 
CONSTRAINT 
It has been found that coagulation of a polybenzazole polymer dope film 
must take place while the film is constrained in order to prevent 
uncontrolled shrinkage of the coagulated film. In order to prevent 
uncontrolled shrinkage it has been found that the film must be constrained 
in at least two of the three possible dimensions (or "directions"). 
Typically the film is constrained in the machine direction ("MD") and the 
direction perpendicular to the machine direction which is known as the 
transverse direction ("TD"). As constraint of the film in two directions 
is an expensive unit operation, compared to constraining the film in only 
one direction, it is desirable for economic reasons to minimize the amount 
of time the film must be constrained in more than one direction. 
When the film is constrained to prevent shrinkage by gripping along each of 
its edges, the increase in force necessary to maintain the film at 
constant dimensions during the coagulation is an indirect measure of the 
amount of shrinkage that would occur if the film were not constrained. The 
time for the measured force to come to an equilibrium level is a direct 
measure of the time necessary to constrain the film to prevent shrinkage 
upon release. That is, if the force necessary to constrain the film is 
changing with time, then it can be inferred that there would be shrinkage 
(collapse of structure) in the film if it were not constrained. Similarly, 
if the measured force is approximately constant with time, then it can be 
inferred that there would be minimal shrinkage in the film if the 
constraints were released. 
Thus, in this coagulation process, the film must be constrained in at least 
two directions until it has coagulated for sufficient time so as to have 
no appreciable shrinkage upon release of constraint and further removal of 
solvent. Once coagulation is completed, some of the constraint on the film 
can be removed such that the film is constrained in at most one direction. 
Typically, once coagulation is complete, the constraint on the film in the 
transverse direction is removed, leaving the film constrained in only the 
machine direction. (Constraint on the film in the machine direction can be 
as simple a force as the tension imparted to the film as it is moved 
through usual film handling equipment such as rollers and winders.) 
How much coagulation has taken place in the film can be directly inferred 
by measuring the restraining force on the constrained film. As stated 
previously, one definition of a coagulated film is a film that will have 
no more than a 5% increase in the force necessary to constrain the film 
with further removal of solvent. A second definition of a coagulated film 
is a film with the structure set that upon release of constraint further 
removal of solvent will result in no more than 5% shrinkage in the film. 
COAGULANT 
The coagulating liquid must be a nonsolvent for the polybenzazole polymer. 
It may be an organic material, such as methanol, glycerol or acetone, but 
it is preferably aqueous. The aqueous coagulant can be water alone, 
mixtures of acid(s) and water, mixtures of base(s) and water or mixtures 
of salt(s) and water. The temperature of an aqueous coagulant alone is 
preferably from 5.degree.-95.degree. C., more preferably from 20.degree. 
C.-80.degree. C., and most preferably about 25.degree. C. 
Mixtures of acid and water used as a coagulant are preferably mixtures of 
phosphoric acid and water. The concentration of phosphoric acid in water 
is preferably from 1-85 percent, more preferably 5-50 percent, and most 
preferably 5-30 percent. The preferred temperature range for coagulant 
made up of acid and water is from 5.degree. C-95.degree. C., the more 
preferred temperature is 15.degree. C.-45.degree. C., and the most 
preferred temperature is about 25.degree. C. 
Exposing the uncoagulated film to one coagulant is one technique to achieve 
a coagulated film. Another such technique is to expose the uncoagulated 
film to more than one coagulant in a sequenced order. For example, it is 
possible to coagulate a film using a mixture of phosphoric acid and water 
only. It is also possible and preferable to use first a mixture of 
phosphoric acid and water and then pure water as the coagulants in a 
sequenced manner. This sequence of exposure to first different 
concentration water/acid coagulants, followed by exposure to a water 
coagulant is preferably run in a countercurrent manner. 
Coagulation of polybenzazole films can also occur with the film being 
exposed to different coagulants in a sequenced order. 
The time that the polybenzazole film must be constrained in at least two 
directions during coagulation is dependent on the thickness of the film. 
For example, an oriented polybenzazole ("PBZ") dope film with an 
uncoagulated thickness of 5 mils or less usually requires approximately 
one minute of contact with an aqueous coagulant in order for the film to 
be coagulated sufficiently so that once some of the constraint is removed 
such that the film is constrained in at most one direction the film will 
experience no more than 5% further shrinkage upon removal of residual 
solvent. A PBZ film with a thickness of from 5-8 mils usually requires 
more than one minute and less than two minutes in contact with an aqueous 
coagulant to be coagulated sufficiently so that once some of the 
constraint is removed such that the film is constrained in at most one 
direction the film will experience no more than 5% further shrinkage upon 
removal of residual solvent. A polybenzazole film thicker than 8 mils 
usually requires more than 2 minutes and less than five minutes to be 
coagulated sufficiently so that once some of the constraint is removed 
such that the film is constrained in at most one direction the film will 
experience no more than 5% further shrinkage upon removal of residual 
solvent. 
The time that the polybenzazole film must be constrained in at last two 
directions during coagulation in an acid/water coagulant is dependent on 
the acid concentration. The residence time for coagulation of a 5 mil 
oriented polybenzazole dope film in 10-30 percent phosphoric acid/water is 
usually about 2 minutes, and in 5 percent phosphoric acid/water is usually 
about 1 minute. 
For thin polybenzazole dope films (&lt;5 mils) the time for coagulation is 
approximately constant (&lt;60 sec) for any different temperature of the 
coagulant. For films thicker than 5 mils, it has been found that the time 
that the polybenzazole film must be constrained in at least two directions 
during coagulation in an acid/water mixture decreases as the temperature 
of the acid/water mixture increases. 
Further enhancement of the coagulation process can be achieved by adding a 
suitable surfactant to the coagulant to aid in contacting the film with 
the coagulant. One such suitable surfactant is sodium lauryl sulfate. The 
amount of surfactant in the coagulant is preferably less than 1000 ppm, 
more preferably less than 500 ppm and most preferably less than 100 ppm. 
The coagulation process can be further enhanced by stirring the coagulant 
to aid in contacting the film with the coagulant. Stirring methods can 
range from mechanical stirring with a simple stirring implement to 
ultrasonic stimulation of the coagulant to cause movement therein. A 
reasonable amount of time to ultrasonically stimulate the coagulant is 
preferably up to 5 minutes, more preferably up to 20 minutes and most 
preferably up to 30 minutes. 
The end of the coagulation process is defined as when the film has been 
coagulated such that further removal of solvent will result in less than a 
5% increase in the force necessary to constrain the film. A second 
definition for the end of the coagulation process is when the film has 
been coagulated such that further removal of solvent will result in less 
than 5% shrinkage in the film. The film may be contacted by the coagulant 
by either running the film through a bath of the coagulant or by spraying 
the film with coagulant or any combination of baths or sprays. After 
coagulation has been completed the coagulated film no longer needs to be 
constrained in at least two directions. 
WASHING THE COAGULATED FILM 
Once the film has been coagulated, it can be washed to remove residual 
amounts of solvent. As previously defined, "washing" is that part of the 
process in which the residual solvent level in the coagulated 
polybenzazole film is reduced to the desired level. Typically this 
residual solvent is a phosphorus containing species such as phosphoric 
acid or polyphosphoric acid. For example, a typical coagulated film still 
contains about 2500-5000 ppm phosphorus. It is desirable to have less than 
2500 ppm phosphorus in polybenzazole films in order for the films to be 
useful in certain electronics applications. 
The film may be washed by running the film through a bath, or spraying the 
film with a washing medium, or exposing the film to steam in any type of 
standard steam chamber or any combination of the above. It has been found 
that water (cold or hot), dilute acid/water mixtures (cold or hot), and/or 
steam are useful for washing residual solvent from polybenzazole film. 
Additional suitable washing materials include mixtures of dilute base(s) 
and water or dilute salt(s) and water. It is important that the 
polybenzazole film be kept wet before and during the washing process 
because it is very difficult to further remove residual solvent from the 
film once it has been allowed to dry. 
Again, as with coagulation, the film may be exposed to a staged sequence of 
different washing materials. As with coagulation there may be some acid in 
the first such washing bath or spray applied to the film, but the final 
washing baths or sprays should be acid free in order to enhance removal of 
residual solvent. 
As with coagulation, enhancement of residual solvent removal can take place 
if a surfactant is added to the washing medium or the washing medium is 
subjected to stirring. As with coagulation a suitable surfactant is sodium 
lauryl sulfate. As with coagulation a suitable stirring method is 
ultrasonic stimulation. 
The film recovered from this process contains polybenzazole polymer as 
previously described, and preferably consists essentially of polybenzazole 
polymer. It may be very thin, for instance suitable for membrane purposes, 
or thicker to be suitable for structural purposes. Once the film has been 
coagulated and washed it may optionally undergo the further unit 
operations of drying and heat treatment. 
Typically, for polyphosphoric acid used as the solvent, the residual 
phosphorus level in the finished film is preferably less than 3000 ppm, 
more preferably less than 1500 ppm, and most preferably less than 500 ppm. 
The films are useful as substrates for magnetic recording media, coatings, 
structural materials (including insulation), membranes, and parts of 
electronic components.

The process of the present invention is more specifically illustrated in 
the following Examples. 
EXAMPLE 1 
Measurement of Forces Generated During Constrained Coagulation and Washing 
of Oriented PBO Dope Film 
Polybenzobisoxazole ("PBO") dope (14% PBO in polyphosphoric acid ("PPA") is 
extruded through a film die, taken-up between rollers, sandwiched between 
Teflon.RTM. fluoropolymer sheets (3 mil) for ease of handling, and stored 
in a nitrogen purged glove box until use. The dope films are stretched 
unsupported (Teflon.RTM. fluoropolymer sheets removed), with the 
stretching always done in the simultaneous biaxial mode. The stretch 
history varies from 2x to 7x in either the machine direction ("MD") or 
transverse direction to ("TD") and the stretched films are stored between 
Teflon.RTM. fluoropolymer sheets in a nitrogen purged glove box until use 
in the coagulation frame. 
TENTER FRAME 
An instrumented tenter frame exists for the purpose of studying the forces 
necessary to dimensionally constrain PBO film during coagulation. In this 
frame there are compression load cells in both the X and Y directions 
attached by tension rods to cross-bars with clamps to hold the film in 
place. The load cells have an actual working range of 50 lbs. with .+-.0.1 
lb. accuracy. The load cells and accompanying electronics are sealed-off 
from the outside environment with Viton diaphragms and tubing. The entire 
frame assembly is constructed of 316SS with several 
poly-ether-ether-ketone and Teflon.RTM. fluoropolymer components, in order 
to be resistant to the acid/water coagulation baths. Loading the 
coagulation frame is accomplished by laying the stretched dope film 
horizontally across the frame and clamping the film in place. Six inch by 
six inch pieces of film (inside dimension) fit into the frame. After the 
film is loaded onto the frame, the cross-bar restraining screws are 
removed, releasing the cross-bars, which allow for the force to be read on 
the load cells. If the film shows any slack, the cross-bars are tightened 
until the film was taut. Typical initial load cell readings did not exceed 
1 to 2 pounds for thin films. The data recording devices are started (two 
points per second acquisition rate), and the frame is placed horizontally 
in a plastic tub filled with 12 gallons of coagulant, which completely 
covered the frame. 
CONSTRAINED COAGULATION 
The basic experiment consists of constraining the film in both the X and Y 
directions (i.e., clamping all four sides) during a 20 minute room 
temperature water coagulation and monitoring the restraining force. The 
normalized transverse direction (TD) force vs time data for films of 
varying thickness are summarized in Table 1. For simplicity only the TD 
data are shown but the same trends can be seen in the MD data. The data 
are normalized to the equilibrium force level and appear to fall roughly 
into two groups based on film thickness. The thin films (less than 5 mils) 
reach equilibrium very quickly, while the thicker films have a more 
gradual rise to equilibrium. These data show that the time to reach the 
equilibrium force plateau is a strong function of the film thickness. 
Once the equilibrium force plateau has been reached the constraint can be 
released with minimal shrinkage. This is tested by releasing films that 
have reached the equilibrium plateau and washing them an additional 24 
hrs. unconstrained. Less than 2% shrinkage in either direction is 
observed. 
TABLE 1 
______________________________________ 
Normalized Transverse Direction Force (F/Fequilibrium) as a 
Function of Coagulation Time for PBO Dope Films of Varying 
Thickness (all film thicknesses specified are the thickness 
of the film before coagulation) 
Time (sec) 
F/Feq 
______________________________________ 
2.5 mil PBO Film 
0.00 0.00 
2.00 0.0667 
3.00 0.600 
4.00 0.867 
5.00 0.933 
6.00 0.933 
7.00 0.933 
8.00 1.00 
9.00 1.00 
10.0 0.933 
11.0 1.00 
12.0 1.00 
13.0 1.00 
14.0 1.00 
15.0 1.00 
18.0 1.00 
20.0 1.07 
22.0 1.07 
24.0 1.07 
26.0 1.07 
28.0 1.07 
30.0 1.07 
35.0 1.00 
40.0 1.00 
50.0 1.07 
60.0 1.00 
70.0 1.07 
80.0 1.07 
90.0 1.00 
3 mil PBO Film 
0.00 0.00 
1.00 0.0541 
2.00 0.135 
3.00 0.270 
4.00 0.378 
5.00 0.541 
6.00 0.595 
7.00 0.649 
8.00 0.676 
9.00 0.730 
10.0 0.757 
11.0 0.784 
13.0 0.838 
15.0 0.865 
17.0 0.892 
19.0 0.919 
21.0 0.946 
26.0 0.946 
31.0 0.946 
36.0 0.946 
41.0 0.946 
51.0 0.973 
61.0 0.973 
71.0 0.973 
81.0 1.00 
91.0 1.00 
4 mil PBO Film 
0.00 0.00 
2.00 0.0250 
3.00 0.225 
4.00 0.400 
5.00 0.525 
6.00 0.600 
7.00 0.700 
8.00 0.800 
9.00 0.875 
10.0 0.925 
11.0 0.950 
12.0 0.975 
13.0 0.975 
14.0 1.00 
15.0 1.00 
16.0 1.00 
17.0 1.00 
18.0 1.00 
19.0 1.00 
20.0 1.00 
21.0 0.975 
22.0 0.975 
23.0 0.975 
24.0 0.975 
25.0 0.975 
30.0 0.950 
35.0 0.975 
40.0 0.950 
45.0 0.950 
50.0 0.950 
55.0 0.950 
60.0 0.950 
65.0 0.950 
70.0 0.925 
75.0 0.925 
80.0 0.950 
85.0 0.925 
90.0 0.925 
5 mil PBO Film 
0.00 0.00 
2.00 0.156 
3.00 0.289 
4.00 0.356 
5.00 0.422 
6.00 0.467 
7.00 0.511 
8.00 0.556 
9.00 0.578 
10.0 0.622 
11.0 0.644 
13.0 0.689 
15.0 0.733 
17.0 0.756 
19.0 0.778 
21.0 0.800 
23.0 0.822 
25.0 0.844 
27.0 0.844 
29.0 0.867 
31.0 0.867 
36.0 0.889 
41.0 0.933 
46.0 0.956 
51.0 0.956 
56.0 0.978 
61.0 0.978 
66.0 0.978 
71.0 0.978 
76.0 0.978 
81.0 0.978 
86.0 1.00 
91.0 0.978 
6 mil PBO Film 
0.00 0.00 
2.00 0.0882 
3.00 0.132 
4.00 0.206 
6.00 0.265 
8.00 0.309 
10.0 0.368 
12.0 0.412 
14.0 0.456 
16.0 0.500 
18.0 0.529 
20.0 0.559 
25.0 0.603 
30.0 0.662 
35.0 0.706 
40.0 0.750 
45.0 0.794 
50.0 0.824 
55.0 0.853 
60.0 0.868 
65.0 0.882 
70.0 0.912 
75.0 0.926 
80.0 0.941 
90.0 0.956 
100 0.971 
110 0.985 
120 1.00 
130 1.00 
140 1.01 
8 mil PBO Film 
0.00 0.00 
2.00 0.0374 
4.00 0.0935 
6.00 0.150 
8.00 0.196 
10.0 0.243 
12.0 0.290 
14.0 0.336 
16.0 0.374 
18.0 0.411 
20.0 0.449 
22.0 0.486 
24.0 0.514 
26.0 0.542 
28.0 0.570 
30.0 0.598 
32.0 0.617 
34.0 0.636 
36.0 0.664 
38.0 0.682 
40.0 0.701 
45.0 0.738 
50.0 0.776 
55.0 0.794 
60.0 0.832 
65.0 0.860 
70.0 0.879 
75.0 0.897 
80.0 0.907 
85.0 0.925 
90.0 0.935 
95.0 0.944 
100 0.953 
105 0.963 
110 0.972 
120 0.981 
11 mil PBO Film 
0.00 0.00 
2.00 0.00645 
4.00 0.0258 
6.00 0.0516 
8.00 0.0774 
10.0 0.110 
13.0 0.161 
16.0 0.213 
19.0 0.258 
22.0 0.297 
25.0 0.335 
28.0 0.368 
31.0 0.406 
34.0 0.445 
37.0 0.477 
40.0 0.503 
45.0 0.555 
50.0 0.600 
55.0 0.639 
60.0 0.677 
65.0 0.703 
70.0 0.729 
75.0 0.755 
80.0 0.774 
85.0 0.787 
90.0 0.800 
95.0 0.813 
100 0.826 
105 0.839 
110 0.845 
115 0.852 
120 0.858 
125 0.871 
130 0.871 
135 0.877 
140 0.884 
145 0.890 
150 0.890 
155 0.897 
160 0.903 
165 0.910 
170 0.916 
175 0.916 
180 0.923 
185 0.923 
190 0.929 
195 0.929 
200 0.929 
205 0.935 
210 0.935 
215 0.935 
220 0.935 
225 0.942 
230 0.942 
235 0.942 
240 0.942 
14 mil PBO Film 
0.00 0.00 
1.00 0.00510 
2.00 0.00510 
3.00 0.0318 
4.00 0.0510 
5.00 0.0764 
6.00 0.127 
7.00 0.121 
8.00 0.127 
10.0 0.153 
12.0 0.191 
14.0 0.229 
16.0 0.268 
18.0 0.306 
20.0 0.344 
22.0 0.376 
24.0 0.414 
26.0 0.446 
28.0 0.478 
30.0 0.503 
32.0 0.535 
34.0 0.561 
36.0 0.586 
38.0 0.611 
40.0 0.637 
42.0 0.656 
44.0 0.682 
46.0 0.701 
48.0 0.720 
50.0 0.739 
52.0 0.758 
54.0 0.777 
56.0 0.796 
58.0 0.815 
61.0 0.834 
64.0 0.860 
67.0 0.885 
70.0 0.904 
73.0 0.924 
76.0 0.943 
79.0 0.962 
82.0 0.975 
85.0 0.987 
88.0 1.00 
91.0 1.01 
94.0 1.02 
97.0 1.03 
100 1.03 
103 1.04 
106 1.04 
109 1.04 
112 1.04 
115 1.05 
118 1.05 
______________________________________ 
COMATIVE EXAMPLE I 
As a control experiment, several pieces of stretched film are coagulated 
unconstrained. 
A 4xMD/4xTD biaxial stretched film shrank about 8.8% in both directions 
after 20 minutes coagulation. After an additional 24 hours in water this 
film had shrunk a total of 11% in both directions. 
A 7xMD/2.5xTD stretched film shrank about 5% in the machine direction (MD) 
and 21% in the transverse direction (TD) after being coagulated for 20 
minutes. After an additional 24 hours in water the film had shrunk a total 
of 33% in the TD but showed no additional shrinkage beyond 5% in the MD. 
EXAMPLE 2 
Determination of Shrinkage during Coagulation and Washing of PBO Dope Film 
using Water and Acid/Water Coagulants 
The film is prepared in a manner similar to that described in Example 1. 
The starting dope film thickness is 50 mils, and the film is stretched 
5xMD/5xTD in the simultaneous biaxial mode, yielding a stretched dope film 
thickness of approximately 2 mils. The films are mounted on 4" squares 
(constrained coagulation) and several different coagulation schemes are 
followed to examine the film shrinkage at different times in the process. 
The two coagulants used are water and 30% H.sub.3 PO.sub.4 /H.sub.2 O. 
The following experiments are conducted on the 4" squares of 2 mil 
stretched dope film: 
a) 30 sec. in 30% H.sub.3 PO.sub.4 /H.sub.2 O.fwdarw.released from 
constraint in the transverse direction (TD).fwdarw.5 min. water.fwdarw.no 
shrinkage observed. 
b) 120 sec. in 30% H.sub.3 PO.sub.4 /H.sub.2 O.fwdarw.released from 
constraint in the transverse direction (TD).fwdarw.5 min. water.fwdarw.no 
shrinkage observed. 
c) 120 sec in 30% H.sub.3 PO.sub.4 /H.sub.2 O.fwdarw.released from 
constraint in the transverse direction (TD).fwdarw.60 min. water.fwdarw.no 
shrinkage observed. 
d) released from constraint in the transverse direction (TD).fwdarw.20 min. 
in 30% H.sub.3 PO.sub.4 /H.sub.2 O.fwdarw.approximately 12% shrinkage 
measured. 
e) released from constraint in the transverse direction (TD).fwdarw.20 min 
in water.fwdarw.approximately 19% shrinkage measured. 
f) 60 sec. in 85% H.sub.3 PO.sub.4 .fwdarw.released from constraint in the 
transverse direction (TD).fwdarw.8 days storage in Ziploc.RTM. 
bag.fwdarw.24 hrs H.sub.2 O.fwdarw.no shrinkage observed. 
A 70 mil dope film is prepared in a similar manner but was given a 
6.5xMD/6.5xTD simultaneous biaxial stretch and then mounted on a 15" 
square frame. The following coagulation and washing scheme is used: 30 
sec. in 30% PA/water.fwdarw.removed from all constraint.fwdarw.20 min. 
water.fwdarw.&lt;1% shrinkage measured in either TD or MD. 
EXAMPLE 3 
Spray Coagulation of PBO Dope Film Using Room Temperature Water in a 
Concurrent Vertical Flow Arrangement 
Polybenzobisoxazole ("PBO") dope (14% PBO in PPA) is extruded through a 
film die and taken-up between rollers. This experimental set-up includes a 
provision for drawing of the film in the machine direction between the die 
and the rollers. In this way films of varying thickness and machine 
direction (MD) orientation are obtained. The maximum drawdown was obtained 
by having the roller speed be four (4) times the extrusion speed, for the 
thinnest film studied. After passing through the rollers, the film is 
sandwiched between Teflon.RTM. fluoropolymer sheets (3 mil) for ease of 
handling, and stored in a nitrogen purged glove box until use. In the 
remainder of this Example the term film will designate a 14% PBO in PPA 
film with the Teflon.RTM. fluoropolymer sheets removed. 
The spray coagulation apparatus is opposing sprinkler heads mounted to 
impinge at the top and normal to the face of a film mounted vertically, 
with each end constrained between clips to maintain constant length. Thus, 
the fresh coagulant (in this example tap water) contacts the film at the 
top and flowed down the length of the film strip as a thin liquid stream. 
The film samples are 1" by 4" strips, which are always arranged in the 
apparatus such that the transverse direction is constrained. This 
arrangement minimizes film shrinkage during the coagulation process. The 
technique involves mounting the film in the apparatus and turning on the 
sprinklers for a designated length of time, varying between 30 sec. and 10 
min. Then, the film is removed, patted dry with a paper towel, weighed 
(wet weight), and the dimensions measured. The film is then dried 
(unconstrained) overnight (approx. 16 hrs.) in a vacuum oven at 
100.degree. C. The dry weight is measured and used to calculate the amount 
of PPA removed during the coagulation process. The results are given in 
Table 2. These results show that the removal of PPA from the PBO dope film 
is a function of both residence time in the spray and film thickness. 
TABLE 2 
______________________________________ 
Spray Coagulation of 14% PBO/PPA Films of Various Thickness 
weight % = [(final dry weight)/(initial weight)] .times. 100 
Spray 
Time Film Film Film Film 
(sec) (4-5 mils) 
(7-8 mils) 
(12-14 mils) 
(22-25 mils) 
______________________________________ 
30 17.5 39.8 74.1 92.1 
60 15.1 24.4 59.9 92.0 
120 14.4 16.2 38.1 72.1 
240 14.2 14.6 20.9 51.3 
600 14.1 14.3 15.2 22.3 
______________________________________ 
NOTE: 
weight % = 14.0 for complete removal of PPA 
EXAMPLE 4 
Comparison of PBO Dope Film Coagulation and Washing in Water and Acid/Water 
Coagulants 
The films are prepared in a manner similar to that described in Example 1. 
The starting dope film thickness is 55-65 mils, and the film is stretched 
5xMD/5xTD in the simultaneous biaxial mode, giving a stretched dope film 
thickness of approximately 2-3 mils. The films are mounted on 4" hoops and 
constrained throughout the entire process. Several different coagulation 
schemes are followed to examine the rate of removal of PPA from the dope 
film. The coagulants used are water, 5% H.sub.3 PO.sub.4 /H.sub.2 O, and 
15% H.sub.3 PO.sub.4 /H.sub.2 O. The residual phosphorous is measured 
using X-ray Fluorescence (XRF), and the data are reported as wt % P on a 
dry film basis ((wt. P/wt. PBO).times.100). The data, Table 3, show that 
most of the acid is removed very quickly (&lt;60 sec), irrespective of the 
coagulant used and that the residual solvent level is a function of the 
H.sub.3 PO.sub.4 concentration in the coagulation bath. 
TABLE 3 
______________________________________ 
PBO dope film (5 .times. MD/5 .times. TD; 2-3 mils) 
Coagulation and Washing in Water and Acid/Water Coagulants 
Phosphorous Level (wt % P) 
Time 5% 15% 
(minutes) 
H.sub.2 O H.sub.3 PO.sub.4 /H.sub.2 O 
H.sub.3 PO.sub.4 /H.sub.2 O 
______________________________________ 
.5 -- 3.5 7.2 
1 0.35 3.5 6.9 
2 0.35 -- 6.4 
4 0.32 -- 6.6 
8 0.31 -- 6.5 
15 0.28 -- 6.3 
20 0.27 3.25 -- 
2 days 0.12 2.77 -- 
Further Experiments 
1 min. 15% H.sub.3 PO.sub.4 /H.sub.2 O .fwdarw. 20 min. H.sub.2 O 
.fwdarw. 0.30% P 
8 min. 15% H.sub.3 PO.sub.4 /H.sub.2 O .fwdarw. 20 min. H.sub.2 O 
.fwdarw. 0.44% P 
______________________________________ 
EXAMPLE 5 
Coagulation and Washing of PBO Dope Film Using Water, Cold Water, and 
Various Organic Nonsolvents 
Polybenzobisoxazole ("PBO") dope (14% PBO in PPA) was extruded through a 
film die, taken-up between rollers, sandwiched between Teflon.RTM. 
fluoropolymer sheets (3 mil) for ease of handling, and stored in a 
nitrogen purged glove box until use. The film is oriented by stretching it 
in a film stretcher. The PBO dope film is tentered in an unsupported 
manner (Teflon.RTM. fluoropolymer sheets removed), to yield a thin 
(approximately 2 mils), high oriented (4-5 times biaxial stretch) PBO dope 
film for the coagulation experiment. The stretched dope film is placed 
between Teflon.RTM. fluoropolymer sheets and once again stored in a 
nitrogen purged glove box until use. 
Coagulation is carried out by suspending unconstrained 1".times.1" pieces 
of the film from a wire in a 4000 ml beaker filled with the coagulant to 
be tested. The bath is placed on a magnetic stirrer to provide continuous 
agitation of the coagulant solution. All coagulations are carried out at 
room temperature, except for the ice water experiment. The ice water 
experiment is kept at &lt;4.degree. C. (usually 1.degree.-2.degree. C.). The 
dope films are weighed before coagulation (initial weight) and then once 
again after coagulation and drying overnight in a vacuum oven at 
100.degree. C. (final dry weight). The results for the various coagulants 
examined are given in Table 4. The weight % is indicative of the amount of 
acid solvent removed from the film. The nominal solids content of the film 
is 14% PBO, which should be the level reached if all the acid solvent is 
removed. 
TABLE 4 
______________________________________ 
Coagulation and Washing of 14% 
PBO/PPA Films with Various Coagulants 
weight % = [(final dry weight)/(initial weight)] .times. 100 
Ice 
Water Water Acetone 
Methanol 
Time (2 mils) (2 mils) (2 mils) 
(2 mils) 
______________________________________ 
60 sec 13.9 14.1 26/6 14.6 
2 min 13.8 13.7 -- -- 
5 min 13.8 13.9 28.5 13.8 
10 min 13.85 13.9 -- -- 
20 min -- -- 17.7 14.0 
60 min 13/7 -- 15.7 13.9 
2 hrs -- -- 15.7 13.9 
______________________________________ 
NOTE: 
weight % = 14.0 for complete removal of PPA 
EXAMPLE 6 
Staged Coagulation and Washing of PBO Dope Film in Various Acid/Water 
Baths. Comparative Study of Washing of Stored Coagulated Films 
The film are prepared in a manner similar to that described in Example 1. 
The starting dope film thickness in 64 mils, and the film is stretched 
4xMD/4xTD in the simultaneous biaxial mode, giving a stretched dope film 
thickness of approximately 4 mils. The films are mounted on 9" hoops and 
coagulated and washed for various times in various acid/water baths. In 
some cases the films are stored wet with the coagulant in Ziploc.RTM. bags 
for one week between the coagulation and washing steps. After washing, the 
films are dried at 100.degree. C. for at least 5 hrs. and then heat 
treated for 1.5 hrs. at 300.degree. C. Unless otherwise noted the films 
are constrained at all times. The residual %P (dry film basis) levels were 
determined using X-ray fluorescence. 
______________________________________ 
PROCESS CONDITIONS % P % H.sub.3 PO.sub.4 
______________________________________ 
60 sec. 30% H.sub.3 PO.sub.4 /H.sub.2 O .fwdarw. stored 1 
0.12 0.37 
constrained .fwdarw. 30 min. H.sub.2 O 
60 sec. 30% H.sub.3 PO.sub.4 /H.sub.2 O .fwdarw. stored 1 
0.17 0.54 
not constrained .fwdarw. 30 min. H.sub.2 O 
60 sec. 85% H.sub.3 PO.sub.4 .fwdarw. stored 8 days MD 
0.044 0.14 
constrained .fwdarw. 24 hrs. H.sub.2 O 
60 sec. 30% H.sub.3 PO.sub.4 /H.sub.2 O .fwdarw. 60 sec. 
0.19 0.60 
H.sub.3 PO.sub.4 /H.sub.2 O .fwdarw. 60 sec. 5% 
H.sub.3 PO.sub.4 /H.sub.2 O .fwdarw. 27 min. H.sub.2 O 
24 hrs. 30% H.sub.3 PO.sub.4 /H.sub.2 O .fwdarw. 30 min. 
0.16b.2 O 
0.51 
30 min. H.sub.2 O 0.29 0.92 
______________________________________ 
EXAMPLE 7 
Long Term Coagulation of Oriented PBO Dope Film With and Without Steam 
Two polybenzoxazole dope films were stretched 5 times biaxially and 
coagulated on hoops in room temperature water for five months, with water 
changes frequently for the first several days and weekly thereafter. After 
5 months sample I was removed from the bath, dried, and heat treated. 
Sample II was removed from the bath (but maintained wet at all times), and 
then steam leached for 3 hours with wet steam before removing to be dried 
and heat treated in a similar manner. The residual phosphorus levels were 
measured using X-ray fluorescence, for three discs cut from each film 
(designated a, b, c). The testing was repeated to check for 
reproducibility (#1 and #2) for each disc. The steam leaching was 
effective in removing additional phosphorous from the film. 
______________________________________ 
wt. P (ppm) 
Sample No. #1 #2 
______________________________________ 
I a 400 463 
(5 months H.sub.2 O bath) 
b 454 467 
c 515 514 
AVG 456 481 
II a 316 330 
(5 months H.sub.2 O bath 
b 372 339 
and 3 hours steam) 
c 459 408 
AVG 382 360 
______________________________________ 
EXAMPLE 8 
Coagulation and Washing of PBO Dope Film with Hot Coagulants 
The films are prepared in a manner similar to that described in Example 1. 
The starting dope film thickness is 55 mils, and the film is stretched 
5xMD/5xTD in the simultaneous biaxial mode, giving a stretched dope film 
thickness of approximately 2-3 mils. The films are mounted on 9" hoops and 
coagulated and washed for different times in various acid/water baths at 
room temperature (RT), 45.degree. C., and/or 85.degree. C. After washing, 
the films are dried at 100.degree. C. for at least 5 hrs and then heat 
treated for 1.5 hrs. at 300.degree. C. The films are constrained 
throughout the process. The residual %P (dry film basis) levels are 
determined using X-ray fluorescence. 
These results are shown in Table 5. 
TABLE 5 
______________________________________ 
PROCESS CONDITIONS % P % H.sub.3 PO.sub.4 
______________________________________ 
30 min. H.sub.2 O 0.29 0.92 
30 min. H.sub.2 O at 45.degree. C. 
0.28 0.88 
30 min. H.sub.2 O at 85.degree. C. 
0.15 0.47 
1 min. 15% H.sub.3 PO.sub.4 /H.sub.2 O at 45.degree. C. 
0.2darw. 29 
0.63 
min. H.sub.2 O at 45.degree. C. 
1 min. 15% H.sub.3 PO.sub.4 /H.sub.2 O at 85.degree. C. 
0.074rw. 29 
0.23 
min. H.sub.2 O at 85.degree. C. 
1 min. 30% H.sub.3 PO.sub.4 /H.sub.2 O at 25.degree. C. 
0.13arw. 30 
0.41 
min. H.sub.2 O at 85.degree. C. 
1 min. 30% H.sub.3 PO.sub.4 /H.sub.2 O at 25.degree. C. 
0.14arw. 1 
0.44 
min. H.sub.2 O at 85.degree. C. 
1 min. 30% H.sub.3 PO.sub.4 /H.sub.2 O at 85.degree. C. 
0.096rw. 30 
0.30 
min. H.sub.2 O at 85.degree. C. 
1 min. 50% H.sub.3 PO.sub.4 /H.sub.2 O at 85.degree. C. 
0.10arw. 30 
0.32 
min. H.sub.2 O at 85.degree. C. 
______________________________________ 
EXAMPLE 9 
Coagulation with Added Surfactant 
Polybenzobisoxazole ("PBO") dope (14 wt % PBO in polyphosphoric acid 
("PPA")) is extruded through a film die, taken-up between rollers, 
sandwiched between Teflon.RTM. fluorocarbon polymers sheets (3 mil) for 
ease of handling, and stored in a nitrogen purged glove box until use. The 
starting material is a 14 wt % PBO in PPA film with the teflon sheets 
removed. A 1".times.1" unconstrained section of PBO film (15 mil thickness 
and 0.4785 g) is placed in a bottle containing 100 g of distilled water 
with 100 ppm of sodium lauryl sulfate added as a surfactant. The solution 
is continuously shaken and after 604 seconds (approximately 10 mins), the 
film is removed and then dried at 100.degree. C. in a vacuum oven for 12 
hours. The dry film weighed 0.0710 g, indicating 99.0% removal of the 
polyphosphoric acid from the film. 
EXAMPLE 10 
Ultrasonic Coagulation 
Polybenzobisoxazole ("PBO") dope (14 wt % PBO in polyphosphoric acid 
("PPA")) is extruded through a film die, taken-up between rollers, 
sandwiched between Teflon.RTM. fluorocarbon polymer sheets (3 mil) for 
ease of handling, and stored in a nitrogen purged glove box until use. The 
starting material is a 14 wt % PBO in PPA film with the teflon sheets 
removed. A 1".times.1" unconstrained section of PBO film (15 mil thickness 
and 0.4962 g) is placed in 100 g of distilled water in a bottle under 
ultrasonic agitation for 1164 seconds (approximately 20 mins). The film is 
then dried at 100.degree. C. in the vacuum oven for 12 hours. The dry film 
weighed 0.0719 g, indicating 99.4% removal of the polyphosphoric acid from 
the film. 
EXAMPLE 11 
Failure of Further Removal of Phosphorus From Dried Film 
The polybenzobisoxazole dope film sample is stretched 4.5X biaxially, 
coagulated on hoops in room temperature water for 5-6 days, and dried for 
24 hours in a vacuum oven. Three discs are cut from PBO film A (designated 
1,2,3) and then the remainder of the film is steamed leached for ten hours 
in wet steam. The film is dried once again for 24 hours in a vacuum oven , 
and another three discs are cut from PBO film A (designated 4,5,6). The 
residual phosphorus levels are measured using X-ray fluorescence, for 
three discs cut from each film. The testing is repeated to check for 
reproducibility. 
______________________________________ 
wt. P (ppm) 
Sample No. 
Coagulation/Leaching 
#1 #2 
______________________________________ 
1 5-6 days room temp. 
765 751 
2 H.sub.2 O and drying 
795 853 
3 712 757 
A 
4 5-6 days room temp. 
824 830 
5 H.sub.2 O drying followed by 
713 697 
6 10 hours steam 
690 705 
______________________________________ 
EXAMPLE 12 
Coagulation and Washing of Thick PBO Dope Film Using Sequential Temperature 
Baths 
Polybenzobisoxazole ("PBO") dope (14% PBO in PPA) is extruded through a 
film die, taken-up between rollers, sandwiched between Teflon.RTM. 
fluorocarbon polymer sheets (3 mil) for ease of handling, and stored in a 
nitrogen purged glove box until use. Various thickness films were made by 
varying the die gap. The coagulation baths are 2000 ml beakers containing 
1900 ml of deionized water. The PBO film is cut into 1".times.1" 
unconstrained samples which are suspended from a wire in the well-stirred 
bath. The samples are weighed prior to coagulation (initial weight), and 
again after coagulation and drying in a vacuum oven at 110.degree. C. for 
16 hrs (final weight). The experiments are conducted in room temperature 
(RT) water; in 80.degree.-95.degree. C. water (hot); and in a sequence of 
Hot/RT or RT/Hot baths. For the sequential baths, the total residence time 
reported is split 50/50 between the two baths. For example, in the case of 
the Hot/RT experiment at 120 sec., the sample is suspended 60 sec. in the 
hot bath then removed and immediately placed for 60 sec. in the RT bath. 
The weight loss of PPA (as measured by the weight %)as a function of bath 
residence time in either single or sequential baths, and for films of 
different thicknesses, is reported in the following table. 
______________________________________ 
Coagulation and Washing of 14% PBO/PPA Films of Various 
Thicknesses in Sequential Temperature Baths 
weight % = [(dry weight)/initial weight)] .times. 100 
36 mils Film 8.5 mils Film 
Time HOT/ RT/ HOT/ RT/ 
(secs) 
RT HOT RT HOT RT HOT RT HOT 
______________________________________ 
30 95 83.3 -- -- 60.3 31.8 -- -- 
60 90 75.4 83.3 76.8 35.8 18.5 31.3 17.5 
120 83 61.7 71.9 64.5 17 14.4 16.8 14.0 
180 75.8 55.9 65.2 53 14 13.8 15.0 13.8 
240 68.9 45 57.5 43.7 13.9 13.9 14.5 13.9 
360 54.4 33.3 46.7 27.9 
480 45 26.5 42.6 19.7 
______________________________________ 
NOTE: 
weight % .about.14.0 for complete removal of PPA.