The invention relates to a class of copolymers capable of forming an optically anisotropic melt comprising recurring structural units (a) independently each occurrence selected from the group consisting of Formula I; recurring structural units (b) independently each occurrence selected from the group consisting of Formulas II and III; recurring structural units (c) independently each occurrence selected from the group consisting of Formula IV and optionally recurring structural units (d) independently each occurrence selected from the group consisting of Formula V: ##STR1## wherein R independently each occurrence is a chemically inert substituent.

FIELD OF THE INVENTION 
The invention relates to a class of copolyesters which display optical 
anisotropy in the molten state and to the shaped articles, fibers and 
films obtained from the optically anisotropic melts. 
BACKGROUND OF THE INVENTION 
Liquid crystalline polymers (LCPs) are macro-molecules possessing 
significant orientation in either the molten state or in concentrated 
solution. The state of their solution (lyotropic) or melt (thermotropic) 
is between the boundaries of solid crystals and isotropic liquids. In the 
solid state these highly ordered polymers display exceptional strength 
properties in the direction of orientation. By designing molecules 
containing only relatively inert chemical bonds, preparation of thermally 
and oxidatively stable high-performance materials is possible. 
A review of thermotropic LCPs can be found in Kwolek et al., "Liquid 
Crystalline Polymers", "Encyclopedia of Polymer Science and Engineering" 
2nd Ed, Vol. 9, pp 23-55 (1987). Among those listed are polyesters. Many 
liquid crystalline polyesters display several of the desirable attributes 
of these compounds. Unfortunately, most have too high of a melt 
temperature for economical melt fabrication. 
There is a growing need in the thermoplastic engineering industries to 
provide for new and improved polyesters and copolyesters which possess a 
high degree of processability while concurrently exhibiting superior 
mechanical properties. 
SUMMARY OF THE INVENTION 
The invention concerns copolymers capable of forming an optically 
anisotropic melt comprising recurring structural units (a) independently 
each occurrence selected from the group consisting of Formula I; recurring 
structural units (b) independently each occurrence selected from the group 
consisting of Formulas II and III; recurring structural units (c) 
independently each occurrence selected from the group consisting of 
Formula IV and optionally recurring structural units (d) independently 
each occurrence selected from the group consisting of Formula V: 
##STR2## 
wherein R independently each occurrence is a chemically inert substituent. 
DETAILED DESCRIPTION 
Preferably, R is independently selected from the group consisting of 
hydrogen, halo, lower alkyl, methoxy and phenyl. Most preferably, R is 
each occurrence hydrogen. 
In the copolyesters of the invention the molar percent ranges for 
independently recurring units of Formulas II and III substantially equal 
the molar percent ranges of the independently recurring units of Formulas 
IV and V. 
Preferred molar percent ranges for these copolyesters are from 20 mole 
percent to 60 mole percent of independently recurring units of Formula I, 
from 20 mole percent to 40 mole percent of independently recurring units 
of Formulas II and III wherein the ratio of Formula II units to Formula 
III units varies from 20:80 to 80:20, and from 20 mole percent to 40 mole 
percent of independently recurring units of Formulas IV and V wherein the 
ratio of Formula IV units to Formula V units varies from 20:80 to 100:0. 
More preferred molar percent ranges are from 40 mole percent to 60 mole 
percent of independently recurring units of Formula I, from 20 mole 
percent to 30 mole percent of independently recurring units of Formulas II 
and III wherein the ratio of Formula II units to Formula III units varies 
from 25:75 to 75:25, and from 20 mole percent to 30 mole percent of 
independently recurring units of Formulas IV and V wherein the ratio of 
Formula IV units to Formula V units varies from 25:75 to 75:25. 
The most preferred molar percent ranges are from 45 mole percent to 55 mole 
percent of independently recurring units of Formula I, from 22.5 mole 
percent to 27.5 mole percent of independently recurring units of Formulas 
II and III wherein the ratio of Formula II units to Formula III units 
varies from 33:67 to 67:33, and from 22.5 mole percent to 27.5 mole 
percent of independently recurring units of Formulas IV and V wherein the 
ratio of Formula IV units to Formula V units varies from 33:67 to 67:33. 
The most preferred copolyesters of the invention melt below 350.degree. C. 
The copolymers may be formed by a variety of ester-forming techniques from 
difunctional organic compounds possessing functional groups which upon 
polycondensation form the requisite recurring units. For example, the 
functional groups of the organic aromatic compounds may independently 
contain carboxylic acid groups or acid halide groups and functional groups 
reactive therewith such as hydroxyl, or acyloxy groups. In a preferred 
embodiment, the organic reactants comprise lower acyloxy and carboxylic 
acid functionality. For example, lower acyl esters of 
4,4'-dihydroxybiphenyl, 1,4-dihydroxybenzene and 4-hydroxybenzoic acid 
wherein the hydroxy group is esterified are more preferred as reactants. 
The lower acyl groups preferably have from 2 to 4 carbon atoms. Most 
preferably, the acetate esters are used. 
The organic compounds may be allowed to react under anhydrous conditions in 
an inert atmosphere via a melt acidolysis procedure, in a suitable solvent 
via a solution procedure, or in a heat exchange medium via a slurry 
polymerization as described in Calundann, U.S. Pat. No. 4,067,852. 
Additional suitable reaction conditions are described in Schaefgen, U.S. 
Pat. No. 4,118,372. The teachings of the foregoing U.S. Patents are 
incorporated herein by reference. A preferable technique is the melt 
acidolysis technique. 
A catalyst may or may not be used in the polymerization process. If one is 
used, representative catalysts for use in the process include dialkyl tin 
oxides (e.g., dibutyl tin oxide), diaryl tin oxides, titanium dioxide, 
alkoxy titanium silicates, titanium alkoxides, Lewis acids, hydrogen 
halides (e.g., HCl), alkali and alkaline earth metal salts of carboxylic 
acids (e.g., sodium acetate). The quantity of catalyst utilized typically 
is from 0.001 to 1 weight percent based upon total reactant weight, and 
most commonly from 0.01 to 0.2 weight percent. In a preferred method of 
polymerization, a catalyst is not used. 
Liquid crystalline copolyester melts of this invention may be extruded into 
articles such as fibers which have outstanding strength and stiffness and 
will maintain their useful properties at elevated temperatures. Such 
fibers would be useful as tire cords, reinforcement in hoses, cables, 
conveyor belts or composite structures with matrixes prepared from other 
resinous materials. Articles may be films formed from the copolyesters 
which will have excellent solvent and chemical resistance. In addition, 
they should have low flammability and good electrical insulating 
properties. They would be useful as cable wrap, electric motor dielectric 
film and wire insulation. These copolyesters are useful for the 
manufacture of shaped articles such as those which are injection molded 
possessing high strength, stiffness, chemical resistance and low 
flammability. 
Conventional additives and processing aids can be added to the copolyester 
melts of the invention to improve the properties of articles made 
therefrom. Examples of additives are oxidation stabilizers; heat 
stabilizers; ultraviolet light (UV) stabilizers; lubricants; mold release 
agents; dyes and pigments; fibrous or powdered fillers and reinforcing 
agents; nucleating agents; and plasticizers. 
Examples of oxidation stabilizers and heat stabilizers are halides of 
metals of group I of the Periodic Table, used alone and used as a mixture 
with copper (I) halides or sterically hindered phenols in concentrations 
from 0.001 to 1 weight percent based on the weight of the copolyester 
composition. 
Examples of UV stabilizers are substituted resorcinols, salicylates, 
benzotriazoles, benzophenones and mixtures of these, which are added, for 
example, in amounts from 0.001 to 2 weight percent based on the weight of 
the copolyester composition. 
Dyes and pigments are used, for example, in amounts from 0.001 to 5 weight 
percent based on the weight of the copolyester composition. Examples are 
nigrosine, titanium dioxide, cadmium sulfide, phthalocyanine dyes, 
ultramarine blue and carbon black. 
Examples of fillers and reinforcing agents are carbon fibers, glass fibers, 
amorphous silica, calcium silicate, aluminum silicate, magnesium 
carbonate, kaolin, chalk, powdered quartz, mica and feldspar, which may be 
present in a concentration from 0.5 to 70 weight percent, based on the 
total weight of the filled material. 
Examples of nucleating agents are talc, calcium fluoride, sodium 
phenylphosphonate, alumina and finely divided polytetrafluoroethylene. 
Suitably, the nucleating agent may be present in an amount from 0.001 to 1 
percent by weight. 
Plasticizers, such as phthalates, hydrocarbon oils and sulfonamides can be 
included in an amount of from 0.0001 to 20 weight percent, based on the 
weight of the composition. 
Also included in the composition of the invention, in addition to or in 
partial replacement of the reactants of Formulas I, II, III, IV, or V are 
amounts of other aromatic polymerizable units whose presence do not 
interfere with the excellent mechanical properties of these copolyesters. 
Examples of such aromatic units comprising these additional repeating 
units are isophthalic acid, resorcinol, 4,4'-isopropylidenediphenol, 
3,4'-biphenyldicarboxylic acid and 3-hydroxybenzoic acid. 
Preparation of 4-Acetoxybenzoic Acid 
An amount of 4-hydroxybenzoic acid (92.1 grams (g), 0.67 mole) was 
dissolved in a solution of sodium hydroxide (NaOH) (53.4 g, 1.33 moles) 
and 1.33 liters (L) of water in a 4 L beaker. The solution was stirred and 
cooled to a temperature of 0.degree. C. by adding crushed ice, then acetic 
anhydride (102.1 g, 1.00 mole) was added. The temperature was maintained 
at -2.degree. C. for 1 hour by adding one killogram (Kg) of crushed ice. A 
solution of concentrated hydrochloric acid (HCl) (144.7 g, 1.42 moles) in 
267 milliliters (ml) of water was added. The slurry was stirred briefly 
and filtered. The product was washed twice by stirring it with 2 L 
portions of fresh water then filtered and dried in a vacuum oven at 
80.degree. C. for 16 hours. After recrystallization from methyl isobutyl 
ketone, the product consisted of 111 g of white crystals with a melting 
point (m.p.) of 192.degree. C. to 192.5.degree. C. 
Preparation of 1,4-Diacetoxybenzene 
The reaction was run in a 1-liter, single neck, round bottom flask equipped 
with a reflux condenser, nitrogen inlet, heating mantle and magnetic 
stirrer. Hydroquinone (88.0 g, 0.800 mole) and acetic anhydride (706 g, 
6.9 moles) were added to the flask. The reaction mixture was heated to 
reflux at which time all of the hydroquinone had dissolved. The solution 
was refluxed for 18 hours, then the volatile fraction was removed to yield 
191.2 g of crude 1,4-diacetoxybenzene. The crude product was 
recrystallized from 600 ml of methyl isobutyl ketone. The hot solution was 
filtered and allowed to cool overnight in a freezer. The clear, colorless 
crystals were isolated by filtration and dried in a vacuum oven at 
75.degree. C. for 4 hours. There remained 139.8 g of 1,4-diacetoxybenzene 
with a m.p. of 121.5.degree. C. to 122.0.degree. C. 
Preparation of 4,4'-Diacetoxybiphenyl 
An amount of 4,4'-biphenol (200 g, 1.07 moles), (Aldrich Chemical Company, 
Milwaukee, Wis.), and 1000 ml of acetic anhydride were added to a 2-liter 
boiling flask equipped with a cold water condenser and a 
polytetrafluoroethylene-coated magnetic stirring bar. The mixture was 
heated to reflux under nitrogen and all of the solid dissolved. The 
solution was refluxed for 20 hours, then cooled in a freezer at 
-15.degree. C. overnight. The white crystals that were formed were 
isolated by filtration, washed with cold acetic anhydride and dried in a 
100.degree. C. vacuum oven overnight yielding 268.4 g of 
4,4'-diacetoxybiphenyl with a m.p. of 162.7.degree. C. to 164.0.degree. C. 
Preparation of 4,4'-Biphenyldicarboxylic acid 
A 440 g portion of acetic acid, cobalt acetate tetrahydrate (1.25 g, 0.0033 
mole), manganese acetate tetrahydrate (1.23 g, 0.0033 mole), potassium 
bromide (0.6 g, 0.005 mole), potassium acetate (1.48 g, 0.015 mole) and 
4,4'-diisopropylbiphenyl (10 g, 0.042 mole) were added to a one-liter 
stirred titanium autoclave, which was then sealed. The reactor was then 
heated to 150.degree. C., and 60 pounds per square inch (psi) of oxygen 
was introduced into the reactor to bring the total reactor pressure to 
about 150 psig. The reactor temperature was then raised to 180.degree. C. 
and held for one hour. The reactor was then cooled to 50.degree. C. and 
the carbon dioxide generated from oxidation was vented. The reactor was 
heated again to 180.degree. C., then oxygen was introduced into the 
reactor which was kept at constant temperature for one hour. This 
procedure was repeated three more times. The reactor was cooled to room 
temperature and the contents filtered. A solid was obtained and washed 
with water and acetone to yield 9.4 g of a light brown solid, which was 
identical to 4,4'-biphenyldicarboxylic acid by infrared analysis.

Having described the invention, the following examples are provided as 
further illustrative and are not to be construed as limiting. 
EXAMPLE I 
Preparation of a Copolyester from 4-Acetoxybenzoic Acid, Terephthalic Acid, 
1,4-Diacetoxybenzene, 4,4'-Biphenyldicarboxylic Acid and 
4,4'-Diacetoxybiphenyl 
The polymerization was run in a 1 L, single neck, round bottom flask fitted 
with a two neck adapter upon which were mounted a paddle stirrer and a 13 
centimeter (cm) Vigreaux distillation column, distillation head, condenser 
and receiver. An amount of 4-acetoxybenzoic acid (228.5 g, 1.268 moles), 
terephthalic acid (51.89 g, 0.3123 mole) Amoco* TA-33, (Amoco Chemical 
Company, Chicago, Ill.), 4,4'-biphenyldicarboxylic acid (75.66 g, 0.3123 
mole), 1,4-diacetoxybenzene (60.65 g, 0.3123 mole) and 
4,4'-diacetoxybiphenyl (84.42 g, 0.3123 mole) were added to the reaction 
flask. The apparatus was evacuated and refilled with nitrogen. The flask 
was immersed in a molten salt bath preheated to 285.degree. C. When the 
solid reactants had melted, stirring was started and the temperature was 
slowly increased to 350.degree. C. over a 100 minute period at atmospheric 
pressure. In the next 35 minutes the pressure was reduced to 2 mm Hg and 
maintained for 85 minutes. The vacuum was then released under nitrogen and 
the reaction vessel was removed from the 350.degree. C. salt bath. The 
reaction apparatus was disassembled and the flask was broken away from the 
cooled, tan polymer plug. The plug was sawed into chunks and then ground 
in a Wiley mill. The copolyester comprised recurring units of Formulas I, 
II, III, IV and V wherein R is hydrogen. 
The inherent viscosity of the copolyester prepared as described above was 
computed from the equation, n.sub.inh =(ln n.sub.rel)/C, where ln 
n.sub.rel is the natural logarithm of the relative viscosity and C is the 
concentration in grams (g) of copolymer per deciliter (dl) of solution. 
Relative viscosity is the ratio of the polymer solution flow time to 
solvent flow time in a capillary viscometer at 45.degree. C. The solvent 
used was pentafluorophenol. The concentration was 0.1 gram copolymer per 
deciliter of solution. The copolyester had an inherent viscosity of 8.4 
dl/g. 
Melt temperature analysis was carried out using differential scanning 
calorimetry (DSC) on a 15 mg compressed pellet at a heating and cooling 
rate of 20.degree. C. per minute on a Mettler DSC-30 low temperature cell 
with a Mettler TC10A thermal analysis processor (Mettler Instrument Corp., 
Hightstown, N.J.). The copolyester showed peak melting points at 
326.degree. C. and 316.degree. C. on the first and second heating scans of 
the DSC. On cooling, the copolyester showed a crystallization exotherm at 
approximately 285.degree. C. 
The copolyester was solid-state heat treated for 12 hours at 292.degree. C. 
and at less than 0.1 mm Hg pressure to advance its molecular weight. The 
apparatus used for this treatment was a 1-liter round bottom flask 
connected to a rotating evaporator which was connected to a 
nitrogen/vacuum manifold. The apparatus was purged with nitrogen and 
evacuated. The flask was then lowered into a preheated salt bath and 
rotated for 12 hours. The melt viscosity of the copolyester at 330.degree. 
C. and 352 seconds.sup.-1 shear rate was increased from 211 poise to 1,650 
poise after solid-state heat treatment. 
The solid-state advanced copolyester was dried under vacuum for 14 hours at 
100.degree. C. and then injection molded into standard 1/8 inch tensile 
test bars using a Boy* 30-M Injection Molding Machine (Boy Machines Inc., 
Exton, Pa.). The barrel temperature was held at 330.degree. C. the mold 
temperature at 88.degree. C. and the injection pressure at 5 bars. Table I 
lists the tensile, flexural and impact properties of these bars measured 
using procedures described in ASTM Test No.'s D638, D790 and D256, 
respectively. 
Optical anisotropy of the copolyester melts can be determined by 
examination of the materials with the use of an optical microscope. The 
equipment used for determining the optical anisotropy of the copolyesters 
of the present invention included a TH 600 hot stage, (Linkham Scientific 
Instruments LTD, Surrey, England) and a Nikon Optiphot Microscope equipped 
with crossed polarizers and a 35 mm camera (Nikon Instrument Group, Nikon, 
Inc., Garden City, N.Y.). A thin film of the polymer was optically 
anisotropic above its DSC-determined melting temperature when observed 
through a polarizing microscope. 
TABLE I 
______________________________________ 
PROPERTY VALUE 
______________________________________ 
Tensile Strength 17,600 psi 
Tensile Modulus 718,000 psi 
Elongation 5.38% 
Flexural Strength 14,800 psi 
Flexural Modulus 827,000 psi 
Notched Izod Impact Strength 
9.14 ft lbs/inch 
______________________________________ 
EXAMPLE II 
Preparation of a Copolyester from 1,4-Diacetoxybenzene, Terephthalic Acid, 
4,4'-Diacetoxybiphenyl, 4,4'-Biphenyldicarboxylic Acid and 
4-Acetoxybenzoic Acid 
Terephthalic acid (51.89 g, 0.3123 mole), Amoco* TA-33, (Amoco Chemical 
Company, Chicago, Ill.), 4-acetoxybenzoic acid (228.5 g, 1.268 moles), 
1,4-diacetoxybenzene (61.40 g, 0.3162 mole), 4,4'-biphenyldicarboxylic 
acid (75.66 g, 0.3123 mole), and 4,4'-diacetoxybiphenyl (84.42 g, 0.3123 
mole) were added to a reaction flask and polymerized using the procedure 
of Example I. The copolyester comprised recurring units of Formulas I, II, 
III, IV and V wherein R is hydrogen. 
The inherent viscosity as determined using the methods of Example I was 9.2 
dl/g. The peak melt temperatures as determined using the methods of 
Example I were 328.degree. C. and 318.degree. C. on the first and second 
heating scans, respectively. The copolyester gave a crystallization 
exotherm at approximately 285.degree. C. on cooling. 
The copolyester was injection molded using the methods of Example I. It was 
dried under vacuum. The mold temperature was 90.degree. C., the barrel 
temperature was 335.degree. C. and the injection pressure was eight bars. 
Table II shows the tensile, flexural and impact properties of the bars as 
determined by ASTM Test No.s D638, D790 and D256, respectively. The heat 
distortion temperature (HDT) was determined by thermomechanical analysis. 
A 9.9 mm in diameter pellet of the copolyester was compression molded and 
sanded to a 3.2 millimeter (mm) thick flat disk. A 9900 Thermal Mechanical 
Analyzer (DuPont Chemical Company, Wilmington, Del.) with a 0.635 mm 
diameter probe loaded with a 10 g weight was used for analysis of the 
sample. The temperature was increased at 5.degree. C. per minute under 
nitrogen. The onset of the depression of the sample was taken as the HDT. 
TABLE II 
______________________________________ 
PROPERTY VALUE 
______________________________________ 
Tensile Strength 20,500 psi 
Tensile Modulus 1,110,000 psi 
Elongation 3.55% 
Flexural Strength 17,000 psi 
Flexural Modulus 1,370,000 psi 
Notched Izod Impact Strength 
3.47 ft lbs/inch 
HDT 288.degree. C. 
______________________________________ 
A thin film of the polymer was optically anisotropic above its 
DSC-determined melting temperature when observed through a polarizing 
microscope. 
Example III 
Copolyester of 4-Acetoxybenzoic Acid, Terephthalic acid, 
4,4'-Biphenyldicarboxylic Acid, 4,4'-Diacetoxybiphenyl and 
1,4-Diacetoxybenzene 
An amount of 4-acetoxybenzoic acid (19.16 g, 0.1063 mole), terephthalic 
acid (4.35 g, 0.0262 mole), 10 (Amoco), 4,4'-biphenyldicarboxylic acid 
(6.348 g, 0.0262 mole), 4,4'-diacetoxybiphenyl (9.437 g, 0.0349 mole) and 
1,4-diacetoxybenzene (3.390 g, 0.0175 mole) were melt polymerized 
according to the methods of Example I to give an opaque, tan-colored 
copolyester. The copolyester comprised recurring units of Formulas I, II, 
III, IV and V wherein R is hydrogen. The DSC analysis as used in Example 
I, showed a broad melting endotherm from 295.degree. C. to 340.degree. C. 
on the first heating scan, a crystallization exotherm at 290.degree. C. on 
cooling and a peak melting temperature of 320.degree. C. on the second 
heating scan. 
A thin film of the polymer was optically anisotropic above its 
DSC-determined melting temperature when observed through a polarizing 
microscope. 
Example IV 
Copolyester of 4-Acetoxybenzoic Acid, Terephthalic Acid, 
4,4'-Biphenyldicarboxylic Acid and 4,4'-Diacetoxybiphenyl 
An amount of 4-acetoxybenzoic acid (30.58 g, 0.1697 mole), terephthalic 
acid (6.944 g, 0.0418 mole), 4,4'-biphenyldicarboxylic acid (10.13 g, 
0.0418 mole) and 4,4'-diacetoxybiphenyl (22.59 g, 0.0836 mole) were melt 
polymerized according to the methods of Example I to give an opaque, 
tan-colored copolyester. The copolyester comprised recurring units of 
Formulas I, II, III and IV wherein R is hydrogen. The DSC analysis as used 
in Example I, showed a peak melting temperature of 338.degree. C. on the 
first heating scan, a crystallization exotherm at 295.degree. C. on 
cooling and a broad melting endotherm from 300.degree. C. to 350.degree. 
C. on the second heating scan. A thin film of the polymer was optically 
anisotropic above its DSC-determined melting temperature when observed 
through a polarizing microscope using the methods of Example I. 
Other copolyesters were prepared using the procedures of Examples I and II. 
The DSC-determined melting points (Tm) are shown in Table III. The table 
shows the mole fraction of each reactant wherein: 4-acetoxybenzoic acid 
(ABA), 4,4'-biphenyldicarboxylic acid (BPDCA), terephthalic acid (TA), 
4,4'-diacetoxybiphenyl (DABP), 1,4-diacetoxybenzene (DAB) are the 
reactants. 
TABLE III 
______________________________________ 
Mole Fraction of Each Reactant Added 
Melting Temp 
ABA BPDCA TA DABP DAB Tm(.degree.C.) 
______________________________________ 
0.504 0.124 0.124 0.000 0.248 358 
0.504 0.124 0.124 0.038 0.210 349 
0.504 0.124 0.124 0.075 0.173 331 
0.504 0.124 0.124 0.124 0.124 320 
0.504 0.124 0.124 0.165 0.083 320 
0.504 0.124 0.124 0.248 0.000 338 
______________________________________