Crosslinkable thermotropic polyesters derived from allylically substituted hydroxybenzoic acid and a process for preparing a shaped article of the polyesters

A novel polyester is provided which is capable of forming an anisotropic melt and which, subsequent to being formed into shaped articles, is capable of crosslinking to render the article highly heat stable. The polyester preferably consists of approximately 1 to 40 mole percent of 3-allyl-4-oxybenzoyl and/or 3-methylallyl-4-oxybenzoyl moieties copolymerized with oxyaroyl moieties and/or dioxaryl and dicarboxyaryl moieties. The process comprises heating a monomer mixture of allylically substituted hydroxybenzoic acid and aromatic hydroxy acids and/or aromatic diols and diacids to prepare the polyester; melt processing the polyester to form a solid shaped article; and heating to substantially crosslink the allylic groups while substantially retaining the configuration of the solid shaped article.

BACKGROUND OF THE INVENTION 
This invention relates to thermotropic crosslinkable polyesters capable of 
forming a anisotropic melt and having approximately 1 to 40 mole percent 
of units derived from allylically substituted hydroxybenzoic acid and to a 
process for preparing a shaped article of the polyesters. 
It is known in the art to prepare polymers from ethylenically unsaturated 
hydroxybenzoate esters. U.S. Pat. No. 3,141,903 to Fertig et al discloses 
a monomer of the formula 
##STR1## 
wherein X is an ethylenically unsaturated group selected from the group 
consisting of acrylyloxy, acrylyloxyalkyl, methacrylyloxy, and 
methacrylyloxyalkyl. However, these monomers are said to undergo vinylic 
type polymerization rather than polyesterification, and therefore no 
pendant allylic groups remain and the polymer which results is therefore 
not crosslinkable. 
It is also known to produce polymers other than polyesters from allyl 
substituted phenols or phenolic derivatives. Canadian Patent No. 569,348 
to D'Alelio discloses a polymerizable allyl phenyl monomer of the formula: 
EQU CH.sub.2 .dbd.CH--CH.sub.2 --Ar--O--X, 
wherein Ar is an arylene radical and X may be epoxyalkyl, hydroxyalkyl, 
dihydroxyalkyl, chloroalkyl or --CH.sub.2 COOH. Polymers prepared from the 
monomer of D'Alelio are said to contain oxyalkylene rather than ester 
linkages, and pendant allylic groups. 
Also, Japanese Pat. No. 0082719 discloses a polyphenylene ether having 
pendant allyl groups. The modification of the polymer is said to permit 
easy graft copolymerization, epoxidation, or halogenation. However, 
neither of these patents appears to disclose polymers which have polyester 
linkages and which are capable of forming an anisotropic melt which may be 
crosslinked. 
It is also known to prepare aromatic copolyesters of hydroxynaphthoic acid 
and hydroxybenzoic acid. U.S. Pat. Nos. 4,337,190 and 4,161,470 to 
Calundann and U.S. Pat. No. 4,429,105 to Charbonneau (assigned to the 
assignee of the present application) disclose wholly aromatic copolyesters 
of the above acids which exhibit a thermotropic melt phase. However, the 
copolymers of the Calundann and Charbonneau patents contain no pendant 
allylic groups and are therefore not crosslinkable. 
It is also known to produce wholly aromatic monomers having liquid 
crystalline central portions and crosslinkable end groups. For example, 
U.S. Pat. Nos. 4,440,945 and 4,452,993 to Conciatori et al disclose wholly 
aromatic monomers which are terminated with acetylene and acrylic acid, 
respectively, and which are capable of forming an anisotropic melt which 
may be crosslinked. However, inasmuch as these oligomers are of low 
molecular weight, they have low melting temperatures and are therefore 
unstable at high temperatures. 
Accordingly, it is an object of the present invention to provide 
thermotropic crosslinkable polyesters containing recurring units derived 
from allylically substituted hydroxybenzoic acid. 
It is a further object of the present invention to provide thermotropic 
crosslinkable polyesters containing recurring units derived from 
allylically substituted hydroxybenzoic acid which exhibit anisotropy in 
the melt phase and which may be formed into a shaped article and 
crosslinked to produce an article which is heat stable at temperatures in 
excess of the melting point of the uncrosslinked polyester article. 
It is a still further object of the present invention to provide a 
thermotropic crosslinkable polyester containing recurring units derived 
from allylically substituted hydroxybenzoic acid copolymerized with 
hydroxybenzoic and/or hydroxynaphthoic acids free of allylic substitution 
and/or substantially stoichiometrically balanced amounts of aromatic diols 
and aromatic diacids. 
It is a still further object of the invention to provide a process for 
preparing a crosslinked shaped polyester article from a polyester 
containing recurring units derived from allylically substituted 
hydroxybenzoic acid. 
These and other objects, as well as the scope, nature and utilization of 
the invention, will be apparent from the following detailed description of 
the present invention and appended claims. 
SUMMARY OF THE INVENTION 
In accordance with one aspect, the present invention provides a 
thermotropic crosslinkable polyester capable of forming an anisotropic 
melt consisting essentially of 
(a) approximately 1 to 40 mole percent of the recurring moiety: 
##STR2## 
wherein R is an allylic group of the formula: 
##STR3## 
wherein R' and R" are independently selected from the group consisting of 
hydrogen, methyl, ethyl, propyl, phenyl, phenylmethyl, phenylethyl, and 
mixtures thereof, and 
(b) approximately 60 to 99 mole percent of recurring moieties selected from 
the group consisting of: 
##STR4## 
which are substantially free of allylic ring substitution, and 
substantially stoichiometrically balanced amounts of the recurring 
moieties 
##STR5## 
and mixtures thereof, wherein Ar.sub.1, Ar.sub.2 and Ar.sub.3 are 
independently selected and each represent one or more divalent radicals 
comprising at least one aromatic ring. 
In a further aspect, the present invention provides a process for preparing 
a crosslinked shaped polyester article. The process comprises 
(a) heating a monomer mixture consisting essentially of 
(i) approximately 1 to 40 mole percent of the monomer: 
##STR6## 
and/or the ester-forming derivatives thereof, wherein R is an allylic 
group of the formula: 
##STR7## 
wherein R' and R" are independently selected from the group consisting of 
hydrogen, methyl, ethyl, propyl, phenyl, phenylmethyl, phenylethyl and 
mixtures thereof, and 
(ii) approximately 60 to 99 mole percent of monomers selected from the 
group consisting of: 
##STR8## 
and/or the ester-forming derivatives thereof, which monomer B is 
substantially free of allylic ring substitution, and substantially 
stoichiometrically balanced amounts of monomers of the formulae: 
##STR9## 
and/or the ester-forming derivatives thereof, and mixtures thereof, 
wherein Ar.sub.1 Ar.sub.2 and Ar.sub.3 are independently selected and each 
represent one or more divalent radicals comprising at least one aromatic 
group, to a temperature sufficient to polyesterify the monomers to form a 
polyester; 
(b) melt processing the resulting polyester to form a solid shaped article; 
and 
(c) heating the resulting solid shaped article of (b) to a temperature 
sufficient to substantially crosslink allylic groups derived from monomer 
A of the polyester while substantially retaining the configuration of the 
solid shaped article imparted in step (b).

DESCRIPTION OF PREFERRED EMBODIMENTS 
As stated hereinabove, the present invention relates to a thermotropic 
crosslinkable polyester capable of forming an anisotropic melt and having 
approximately 1 to 40 mole percent of units of the formula: 
##STR10## 
wherein R is an allylic group of the formula: 
##STR11## 
wherein R' and R" are independently selected from the group consisting of 
hydrogen, methyl, ethyl, propyl, phenyl, phenylmethyl, phenylethyl, or 
mixtures thereof, e.g., the units 3-allyl-4-oxybenzoyl or 
3-methylallyl-4-oxybenzoyl, or mixtures thereof. These units may be 
derived from monomers of the formula: 
##STR12## 
wherein R has the same significance as above, e.g., the monomers 
3-allyl-4-hydroxybenzoic acid or 3-methylallyl-4-hydroxybenzoic acid, or 
mixtures of these. These hydroxyacid compounds may be prepared from the 
corresponding 4-carbomethoxy phenylallyl substituted ethers via a Claisen 
rearrangement reaction by techniques well known to one skilled in the art. 
In a preferred technique, 3-allyl-4-hydroxybenzoic acid may be prepared by 
heating the allyl ether to a temperature of approximately 200.degree. to 
250.degree. C. under reflux conditions for approximately 0.5 to 2 hours. 
The product may be isolated by dissolving in a sodium hydroxide solution 
(e.g., a 20 percent by weight sodium hydroxide solution), and extracted 
with petroleum ether. The resulting aqueous alkaline solution may be 
acidified, extracted with ethylether, and the ether evaporated to obtain 
the allylically substituted hydroxylbenzoic acid product. 
In a preferred embodiment, the polyester comprises moieties wherein R' is 
methyl or ethyl, inasmuch as the polymr comprising these moieties has a 
higher crosslinking temperature than the polymer comprising its 
nonsubstituted allyl analog (i.e., wherein R' is H). It is most desirable 
to employ monomers having a wide temperature differential between the 
temperature at which polyesterification occurs and the curing temperature 
(i.e., the temperature at which crosslinking of the unsaturated 
substituents occurs). When this differential is low, it is necessary to 
more carefully regulate polymerization conditions in order to prevent 
crosslinking of the allyl groups prior to melt processing into a fiber, 
film, or other shaped article. Optimally, the differential between the 
melt temperature and the curing temperature is at least approximately 
15.degree. C., and preferably at least approximately 20.degree. C. 
In addition to allylic substituents, the aromatic ring of the allylically 
substituted hydroxybenzoic acid may be substituted at any or all of the 2, 
5, and 6 positions. Suitable substituents include alkyl groups of 1 to 4 
carbon atoms, alkoxy groups of 1 to 4 carbon atoms, phenyl, halogen, and 
mixtures of the foregoing. Preferably a maximum of one of the 2, 5 and 6 
positions are substituted, and most preferably none of these positions are 
substituted. Although the present invention does not require the use of 
ring-substituted allylic hydroxybenzoic acid, use of the same may 
facilitate melt polymerization and/or melt processing at a lower 
temperature than the unsubstituted monomer, facilitating processing and 
lessening the likelihood of crosslinking in the melt. 
The polyesters of the present invention are copolymers of the 
aforedescribed allylically substituted hydroxybenzoic acids with aromatic 
hydroxy acids free of allyl and methylallyl ring substitution and/or 
aromatic diacids or diols. 
The polyester comprises approximately 1 to 40 mole percent of allylically 
substituted units and preferably between approximately 1 and approximately 
10 mole percent (e.g., approximately 5 mole percent). When the polyester 
comprises a higher percentage (i.e., 60% or more) of allylically 
substituted units, the amount of crosslinking is very high and the 
resulting polyester after crosslinking will be very brittle, and shaped 
articles prepared therefrom may show a significant decrease in mechanical 
properties (e.g., fiber tenacity). 
The polyester containing allylically substituted oxybenzoyl moieties is a 
copolymer having approximately 60 to 99 mole percent, and preferably 
approximately 90 to 99 mole percent, of aromatic moieties free of allylic 
ring substitution. Suitable such moieties include oxyaroyl moieties, 
dioxyaryl moieties, and dicarboxyaryl moieties, which are derived from 
aromatic monomers such as hydroxy acids, diols and diacids, respectively. 
Suitable oxyaroyl moieties are of the formula: 
##STR13## 
wherein Ar.sub.1 is a divalent radical comprising at least one aromatic 
ring and is free of allylic ring substitution. Suitable oxyaroyl units 
include 4-oxybenzoyl units, 6-oxy-2-naphthoyl units, and mixtures thereof, 
and their ring-substituted derivatives, wherein the aromatic rings 
optionally may include substituents including alkyl groups of 1 to 4 
carbon atoms, alkoxy groups of 1 to 4 carbon atoms, phenyl, halogen, and 
mixtures of the foregoing. Examples of such ring substituted oxyaryl units 
include 6-oxy-5-chloro-2-naphthoyl, 6-oxy-5-methyl-2-naphthoyl, 
6-oxy-5-methoxy-2-naphthoyl, 6-oxy-7-chloro-2-napthoyl, 
6-oxy-4,7-dichloro-2-naphthoyl, etc. Preferred oxyaroyl units are 
4-oxybenzoyl and 6-oxy-2-naphthoyl units. As will be apparent to one 
skilled in the art, these moieties can be readily derived from the 
corresponding hydroxy aromatic acids of the formula 
##STR14## 
wherein Ar.sub.1 has the same significance as above, e.g., 
4-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid. 
Copolymerized with the allylically substituted hydroxybenzoic acid (i.e., 
monomer A) in the polyester of the present invention, alone or in 
combination with hydroxybenzoic acid free from aromatic substitution 
(i.e., monomer B), may be substantially stoichiometrically balanced 
amounts of aromatic diols and dicarboxylic acids which contribute moieties 
of the formulae: 
##STR15## 
wherein Ar.sub.2 and Ar.sub.3 are independently selected and each 
represent one or more divalent radicals comprising at least one aromatic 
ring. 
Suitable examples of dioxyaryl moiety III include: 
##STR16## 
and mixture of the foregoing. 
The preferred moiety III is: 
##STR17## 
Suitable examples of dicarboxyaryl moiety IV include: 
##STR18## 
and mixtures of the foregoing. The preferred dicarboxyl moieties IV are: 
Each of moieties III and IV may or may not contain substituents on the 
aromatic ring(s). Where ring substitution occurs, suitable substituents 
include alkyl groups of 1 to 4 carbon atoms, alkoxy groups of 1 to 4 
carbon atoms, phenyl, halogen, and mixtures thereof. 
The polymer may also contain small amounts of nonaromatic moieties, but 
these moieties should be limited to those amounts (i.e., approximately 0 
to 10%) which do not seriously affect the advantageous characteristics of 
the polyester. Such moieties include ethylene glycol. As will be apparent 
to one skilled in the art of polymer technology, moieties III and IV may 
readily be derived from the corresponding diols and diacids, i.e., 
monomers having the formulae: 
##STR19## 
or the ester-forming derivatives thereof wherein Ar.sub.2 and Ar.sub.3 
have the same significance as above. Illustrative of the aromatic 
comonomers from which these units may be derived are bisphenol A, 
6-hydroxy-2-naphthoic acid, 2,6-naphthalene dicarboxylic acid, 
terephthalic acid, isophthalic acid, hydroquinone, ring substituted 
hydroquinone (e.g., methylhydroquinone), 2,6-naphthalene diol and mixtures 
thereof. As is well known in the art, when the polyester is to contain 
moieties III and IV, it is preferable to substantially stoichiometrically 
balance the amounts of diols and diacids to ensure a complete reaction of 
the monomers. 
Preferred comonomers to be copolymerized with allylically substituted 
hydroxybenzoic acid include 4- or 3-hydroxybenzoic acid, 
6-hydroxy-2-naphthoic acid, terephthalic acid, and hydroquinone. The most 
preferred comonomers are 4-hydroxybenzoic acid and 6-hydroxy-2-naphthoic 
acid. 
In a preferred embodiment, approximately 1 to 10 mole percent of 
allylically substituted oxybenzoyl (i.e., moiety I) moieties are present 
in the polyester, the remaining approximately 90 to 99 mole percent being 
oxyaroyl (i.e., moiety II) moieties free of allylic substitution, e.g., 
oxybenzoyl and/or oxynaphthoyl moieties. 
In another preferred embodiment, approximately 1 to 10 mole percent of 
allylically substituted oxybenzoyl (i.e. moiety I) moieties and 
approximately 45 to 49.5 mole percent each of aromatic dioxyaryl and 
dicarboxyaryl (i.e., moieties III and IV) moieties are present in the 
polyester. 
In another preferred embodiment, the polyester consists essentially of 
approximately 1 to 10 mole percent of 3-allyl-4-oxybenzoyl moieties, 
approximately 20 to 70 mole percent of 4-oxybenzoyl moieties, and 
approximately 20 to 70 mole percent of 6-oxy-2-naphthoyl moieties. In a 
most preferred embodiment, the polyester consists essentially of 
approximately 5 mole percent of 3-allyl-4-oxybenzoyl moieties, 
approximately 45 mole percent of 4-oxybenzoyl moieties, and approximately 
50 mole percent of 6-oxy-2-naphthoyl moieties. 
In another preferred embodiment, the polyester consists essentially of 
approximately 1 to 10 mole percent of 3-methylallyl-4-oxybenzoyl moieties, 
approximately 20 to 70 mole percent of 4-oxybenzoyl moieties, and 
approximately 20 to 70 mole percent of 6-oxy-2-naphthoyl moieties. In 
another most preferred embodiment, the polyester consists essentially of 
approximately 5 mole percent of 3-methylallyl-4-oxybenzoyl moieties, 
approximately 45 mole percent of 4-oxybenzoyl moieties, and approximately 
50 mole percent of 6-oxy-2-naphthoyl moieties. 
The polyesters of the present invention may be formed by a variety of 
ester-forming techniques whereby the monomers possessing functional groups 
which upon condensation form the requisite recurring moieties are reacted. 
For instance, the functional groups of the monomers may be carboxylic acid 
groups, hydroxyl groups, ester groups, acyloxy groups, acid halides, etc. 
The monomers may be reacted in the absence of a heat exchange fluid via a 
melt acidolysis procedure, or by a slurry polymerization process. 
Accordingly, the monomers may be heated initially to form a melt solution 
of the reactants with the reaction continuing as solid polymer particles 
are suspended therein. A vacuum may be applied to facilitate removal of 
volatiles formed during the final stage of the condensation (e.g., acetic 
acid or water). 
When employing either the melt acidolysis procedure or the slurry procedure 
the monomer reactants from which moieties A through D are derived may be 
initially provided in a modified form whereby the usual hydroxyl and/or 
carboxyl groups of these monomers are esterified (e.g., the usual hydroxyl 
groups may be provided as acyl esters). For instance, lower acyl esters of 
3-allyl-4-hydroxybenzoic acid, 3-methylallyl-4-hydroxybenzoic acid, 
6-hydroxy-2-naphthoic acid and p-hydroxybenzoic acid, wherein the hydroxy 
groups are esterified, may be provided as reactants. Such lower acyl 
groups preferably have from about 2 to about 4 carbon atoms. Preferably 
employed are the acetate esters of the monomers. Accordingly, particularly 
preferred reactants for the condensation reaction are 
3-allyl-4-acetoxybenzoic acid, 3-methylallyl-4-acetoxybenzoic acid, 
6-acetoxy-2-naphthoic acid and p-acetoxybenzoic acid. If other aromatic 
diols (as previously discussed) provide oxy- units within the resulting 
polymer, these too preferably are provided as the corresponding lower acyl 
esters. Likewise, any monomers which provide carboxy groups may be 
provided in a modified form whereby the carboxy groups are esterified, for 
instance, by first reacting with an aromatic monohydroxy compound such as 
phenol, m-cresol, p-cresol, etc., as described, for example, in U.S. Pat. 
No. 4,333,907. 
Preparation of the polyester is preferably carried out in the melt, i.e. by 
heating a monomer mixture as discussed above. Melt polymerization may be 
achieved by first placing the required molar amounts of the esterified 
(e.g., acetylated) monomers in a reaction vessel equipped with a 
mechanical agitator, a gas inlet and a distillation head. Since the 
presence of oxygen tends to inhibit polymerization, the reaction mixture 
is typically blanketed with an inert gas, such as nitrogen or argon to 
render the atmosphere non-oxidizing, at approximately atmospheric 
pressure. The reaction vessel is then heated for approximately 2 to 5 
hours at a temperature sufficient to polyesterify the monomers, i.e., a 
temperature ranging from approximately 240.degree. C. to 270.degree. C., 
preferably from approximately 250.degree. C. to 260.degree. C. At the end 
of this time, the vessel gradually is evacuated over a period of from 
approximately 10 to 30 minutes to a pressure of from approximately 
atmospheric to 0.1 mm. Hg to remove acetic acid from the vessel. In a 
preferred embodiment, it is desirable to maintain the temperature within a 
fairly constant range (i.e., 250.degree. C. to 260.degree. C.) throughout 
the polyesterification reaction. 
Representative catalysts which optionally may be employed in either the 
melt hydrolysis procedure or in the slurry procedure include dialkyl tin 
oxide (e.g., dibutyl tin oxide), diaryl tin oxide, titanium dioxide, 
alkoxy titanium silicates, titanium alkoxides, alkali and alkaline earth 
metal salts of carboxylic acids, the gaseous acid catalysts such as Lewis 
acids (e.g., BF.sub.3), hydrogen halides (e.g., HCl) etc. The quantity of 
catalyst utilized typically is approximately 0.001 to 1 percent by weight 
based upon the total monomer weight, and most commonly approximately 0.01 
to 0.2 percent by weight. 
The molecular weight of the previously formed polyester may be further 
increased via a solid state polymerization procedure wherein the 
particulate polymer is heated in an inert atmosphere (e.g., in a nitrogen 
atmosphere at a temperature of approximately 250.degree. C.) for 5 to 10 
hours. 
The polymerization process may be operated on a continuous, semi-continuous 
or, preferably, on a batch basis. 
An alternate process for preparing copolyesters that include allylically 
substituted oxybenzoyl units is disclosed in U.S. Pat. No. 4,067,852, the 
content of which is incorporated by reference. As is more fully described 
in the patent, the slurry polymerization technique involves the use of a 
liquid heat exchange medium which acts as a solvent for at least one of 
the reactants. The temperature of the mixture is increased and the polymer 
forms as a fine insoluble solid in the medium. Following cooling of the 
mixture, recovery of the polymer is accomplished by conventional steps 
such as decantation, centrifugation or filtration. The separated polymer 
may then be washed and dried. 
The prepared polyester is capable of forming an anisotropic melt (i.e., 
forms liquid crystals). Anisotropy can be confirmed by standard polarized 
light techniques whereby crosspolarizers are employed. Although the amount 
of light transmitted generally increases when a sample is sheared (e.g., 
by laterally moving the cover slide of a hot stage microscope), the melt 
is optically anisotropic even in the static state. 
Wide variations in melting temperature may occur depending on the type and 
amount of other constituents in the polyester. However, the melting 
temperature generally ranges from approximately 240.degree. C. to 
280.degree. C. (as determined by differential scanning calorimetry, or 
DSC). As discussed above, it is desirable to form a polyester having a 
relatively low melting temperature, i.e., between approximately 
260.degree. and 280.degree. C. 
The polyester of the present invention commonly exhibits a weight average 
molecular weight of approximately 2,000 to 200,000, and preferably 
approximately 10,000 to 50,000. Such molecular weight may be determined by 
standard techniques. 
The polyester prior to shaping and crosslinking commonly exhibits an 
inherent viscosity (I.V.) of at least approximately 0.5 dl./g, and 
preferably at least approximately 1.0 dl./g, when dissolved in a 
concentration of 0.1 percent by weight in pentafluorophenol at 60.degree. 
C. The inherent viscosity will vary depending on the constituents and the 
degree of polymerization obtained. 
Following polymerization and prior to crosslinking, the polyester of the 
present invention may be melt processed to form shaped articles having the 
desired configuration. 
To form fibers, films or other solid three dimensional shaped articles, the 
polyester of the present invention is typically melt processed by 
conventional techniques such as melt spinning, pressure molding, 
extrusion, etc. In melt processing the polyester, care must usually be 
taken to avoid thermal degradation of the polymer. That is, it is usually 
desirable to obtain a stable melt phase. This generally involves a 
selection of the components forming the polyester and a regulation of the 
process temperature and pressure. During shaping, it is essential that the 
temperature of the polyester not exceed its curing temperature, and that 
the duration of heating is sufficiently short to prevent crosslinking. 
When forming fibers and films, the extrusion orifice may be selected from 
among those commonly utilized during the melt extrusion of such shaped 
articles. For instance, the shaped extrusion orifice may be in the form of 
a rectangular slit (i.e., a slit die) when forming a polymeric film. When 
forming a filamentary material the spinneret selected may contain one and 
preferably a plurality of extrusion orifices. For instance, a standard 
conical spinneret containing 1 to 2000 holes (e.g., 6 to 1500 holes) such 
as commonly used in the melt spinning of polyethylene terephthalate, 
having a diameter of approximately 1 to 60 mils (e.g., 5 to 40 mils) may 
be utilized. Yarns of about 20 to 200 continuous filaments are commonly 
formed. The melt-spinnable polyester of the present invention is supplied 
to the extrusion orifice at a temperature above its melting point but well 
below its crosslinking temperature e.g., a temperature of approximately 
250.degree. to 295.degree. C., and preferably 260.degree. to 270.degree. 
C., depending on the melting point and crosslinking temperature of the 
polyester. 
Subsequent to extrusion through the shaped orifice, the resulting 
filamentary material or film is passed in the direction of its length 
through a solidification or quench zone wherein the molten filamentary 
material or film is transformed to a solid filamentary material or film. 
The resulting as-spun filaments commonly have a denier per filament of 
approximately 1 to 50, and preferably a denier per filament of 
approximately 1 to 20, and most preferably approximately 5 to 10. 
When molded articles are to be prepared, the polyester of the present 
invention may incorporate approximately 1 to 60 percent by weight of a 
solid filler (e.g., talc) and/or reinforcing agent (e.g., glass fibers). 
In accordance with the present invention, the polyester, which is 
originally thermoplastic in nature, is post-treated after the solid shaped 
articles is formed to crosslink the polymer chains through the reactive 
double bond in the allylic group, thus rendering the polymer in a sense 
thermosetting. This may be accomplished by heating ultraviolet radiation 
or chemical copolymerization. Preferably, crosslinking is performed by 
heating the solid shaped article formed above to a temperature in the 
range of approximately 275.degree. to 310.degree. C., and preferably 
approximately 290.degree. to 300.degree. C., depending on the specific 
monomer employed. As discussed above, it is desirable to employ monomers 
which crosslink at a temperature substantially above their melting 
temperature in order to prevent premature crosslinking. 
When the crosslinking step commences, the shaped article to be crosslinked 
is first heated to a temperature of approximately 240.degree. to 
260.degree. C., and preferably approximately 240.degree. to 250.degree. 
C., i.e., approximately 10.degree. to 15.degree. C. below the melting 
point of the uncrosslinked polyester, such that the article is retained in 
its solid state. By gradually increasing the temperature of the shaped 
article (i.e., by 10.degree. increments over 5 to 10 hours to an eventual 
temperature in the range of approximately 275.degree. to 310.degree. C. 
and preferably approximately 290.degree. to 300.degree. C.), the melting 
temperature of the polyester gradually increases as the polyester 
undergoes chain extension reaction and/or transesterification and the 
article substantially retains the configuration imparted in the shaping 
step. 
Optionally, the crosslinking step may be performed in an oven under an 
inert atmosphere in order to prevent termination of the crosslinking 
process, with individual fibers being mounted on a rack to prevent 
shrinkage. 
After the crosslinking reaction is completed, substantially all (i.e., 
above 1 to 40 percent and preferably above approximately 4 percent) of the 
allylically substituted units will be crosslinked while retaining the 
configuration of the shaped article. The resulting crosslinked shaped 
polyester article preferably is heat stable up to approximately 
450.degree. C. and most preferably to approximately 500.degree. C. 
The following Examples are given as specific illustrations of the polyester 
and process of the present invention. It should be understood, however, 
that the invention is not limited to the specific details set forth in the 
Examples. 
EXAMPLE I 
To a three-neck, 30 ml. round flask equipped with a stirrer, argon inlet 
tube, and distillation head connected to a condenser are added: 
(a) 4.2 grams 3-allyl-4-acetoxybenzoic acid (0.02 mole), 
(b) 32.4 grams 4-acetoxybenzoic acid (0.18 mole), 
(c) 46.0 grams 6-acetoxy-2-naphthoic acid (0.2 mole), and 
(d) 0.01 grams of potassium acetate catalyst. 
The charged flask is vacuum purged with argon three times and gradually 
(i.e., over one hour) brought to a temperature of 250.degree. C. As 
polymerization begins to occur, the solution is stirred rapidly under a 
stream of dry argon while acetic acid is distilled from the vessel. The 
reaction melt begins to turn opaque with suspended polymer after 
approximately 20 minutes. The polymerization mixture is stirred for one 
hour at 250.degree. C., and then for an additional hour at 260.degree. C. 
Approximately 18 ml. of acetic acid are collected. The polymerization 
temperature is next increased to 270.degree. C., at which temperature the 
polymer is held for 60 minutes under an argon flow and then subjected to a 
reduction in pressure. The argon flow is then halted and the pressure 
above the polymer melt is reduced to and held at 0.5 mm. Hg for 
approximately 15 minutes. During this stage the polymer melt continues to 
increase in viscosity and is stirred more slowly while the remaining 
acetic acid is removed from the reaction vessel. Upon cooling (i.e., to 
approximately 25.degree. C.), the resulting polymer plug is finely ground 
and dried in a forced air oven at 80.degree. C. for approximately 3 hours. 
The resulting polyester has an inherent viscosity (I.V.) of 1.5 as 
determined in a pentafluorophenol solution of 0.1 percent by weight 
concentration at 60.degree. C. where: 
EQU I.V.=ln (.eta.rel)/c, 
where c=concentration of solution (0.1 percent by weight), and 
.eta.rel=relative viscosity. The relative viscosity is measured by 
dividing flow time in a capillary viscometer of the polymer solution by 
the flow time for the pure solvent. 
When the polyester is subjected to differential scanning calorimetry (DSC), 
it exhibits a sharp melt endotherm at approximately 240.degree. C. (peak). 
The polymer melt is anisotropic. 
The polyester next is melt-extruded into a continuous filament of about 15 
denier per filament. More specifically, the polyester polymer melt while 
at a temperature of approximately 239.degree. C. is extruded through a 
spinneret provided with a single hole jet having a diameter of 20 mils and 
a length of 100 mils. The extruded filament is quenched in ambient air 
(i.e., at 72.degree. F. and 65 percent relative humidity). The as-spun 
filament is taken up at a rate of 150 meters per minute. 
Following extrusion, the polyester filament is subjected to further heating 
in order to crosslink pendant allyl groups. Crosslinking (curing) is 
achieved while mounting the filament on a rack to prevent shrinkage. The 
filament is subjected to a gradual increase in temperature, i.e., over 40 
hours time, while maintaining the filament in the solid state. 
Specifically, the filament is first heated in an inert (nitrogen) 
atmosphere to approximately 230.degree. C. (i.e., about 10.degree. C. 
below its melting temperature) for 10 hours, and the temperature gradually 
increased in 5.degree. C. increments over a total of 30 hours. After 40 
hours, crosslinking is substantially (i.e., 90 percent) completed and the 
resulting shaped article is heat stable to approximately 450.degree. C. 
EXAMPLE II 
Example I is substantially repeated with the exception that the following 
ingredients are charged to the flask: 
(a) 2.4 grams 3-methylallyl-4-acetoxybenzoic acid (0.02 mole), 
(b) 32.4 grams 4-acetoxybenzoic acid (0.18 mole), 
(c) 46.0 grams 6-acetoxy-2-naphthoic acid (0.2 mole), and 
(d) 0.01 grams of potassium acetate catalyst. 
The resulting polyester prior to extrusion has an I.V. of 3.8 as determined 
in pentafluorophenol as previously described. The polyester melt is 
anisotropic and exhibits a sharp melt endotherm at approximately 
262.degree. C. (peak) when subjected to differential scanning calorimetry 
(DSC). Following extrusion, crosslinking occurs over a period of 40 hours 
at a temperature range of 262.degree. to 310.degree. C. The resulting 
fibers are heat stable to approximately 450.degree. C. 
Although the invention has been described with preferred embodiments, it is 
to be understood that variations and modifications may be employed without 
departing from the concept of the invention as defined in the claims which 
follow.