Temperature stable thermotropic poly(ester carbonate) containing high amounts of readily available diols

Thermotropic poly(ester carbonates) such as the terephthalate/carbonate of a mixture of hydroquinose, resorcinol, tert-butylhydroquinone and methylhydroquinone. With a major proportion of the more readily available hydroquinone and resorcinol, thermotropic properties (liquid crystallinity in the melt) are observed.

DESCRIPTION 
BACKGROUND OF THE INVENTION 
Polymers are known exhibiting liquid crystalline behavior either in 
solution or in the melt which contribute to desirable properties when 
formed into either highly ordered fibers or other fabricated structures. 
The most commonly used class are the aromatic polyamides, typified by 
poly(p-benzamide), which exhibit liquid crystalline behavior in certain 
solutions or dopes, and are thus known as lyotropic polymers. An exemplary 
disclosure of such polymers is U.S. Pat. No. 3,671,542 to Kwolek (June 20, 
1972). These polymers are relatively easy to form, but are difficult to 
handle and must be cast into derived forms (fibers and films) from 
solution. 
Certain aromatic polyesters are known which are liquid crystalline in the 
melt and are thus thermotropic. U.S. Pat. No. 4,140,846 to Jackson, Jr. et 
al. (Feb. 20, 1979), U.S. Pat. No. 3,890,256 to McFarlane et al. (June 17, 
1975), U.S. Pat. No. 3,991,013 to Pletcher (Nov. 9, 1976), U.S. Pat. No. 
4,066,620 to Kleinschuster et al (Jan. 3, 1978), U.S. Pat. No. 4,075,262 
to Schaefgen (Feb. 21, 1978), U.S. Pat. No. 4,118,372 to Schaefgen (Oct. 
3, 1978); U.S. Pat. No. 4,156,070 to Jackson, Jr. et al (May 22, 1979) and 
U.S. Pat. No. 4,159,365 to Payet (June 26, 1979) are representative of 
such thermotropic polyesters. Known polymers of this class must be formed 
by melt polymerization, and these polymers have not found wide use. These 
polyesters exhibit little, if any, solubility in most solvents. 
One such thermotropic polyester is phenylhydroquinone terephthalate, as 
described in U.S. Pat. No. 4,159,365 to Payet. While this material has 
good low temperature properties, the phenylhydroquinone monomer is 
difficult to prepare and expensive. Furthermore, all of the known 
thermotropic polyesters lose their good properties at their glass 
transition temperature which also does not generally exceed 100.degree. C. 
Poly(ester carbonates) are a known class of polymers useful in a variety of 
articles where high performance is desirable. Such polymers are not, 
however, generally formed into fibers and are not known to exhibit the 
properties of the aromatic polyamides or other liquid crystalline material 
of either the lyotropic or thermotropic type. Such poly(ester carbonates) 
conventionally include as the principle dihydric aromatic alcohol a 
bisphenol such as bisphenol-A which would be regarded in a nomenclature of 
B. P. Griffin et al., British Polymer J. 147 (1980) as a nonlinear monomer 
and include carbonate moieties which are highly flexible. 
Thermotropic poly(ester carbonates) are described in U.S. Pat. No. 
4,284,757 to Fayolle (1981) containing methylhydroquinone as the preferred 
diol (optionally replaced up to 30% by hydroquinone) and various 
proportions of terephthalate and carbonate. While the monomers forming the 
terephthalate and carbonate moieties are readily available, 
methylhydroquinone (or its alternates, the chloro, bromo or ethyl 
compounds) are generally quite expensive. Furthermore, these poly(ester 
carbonates) have low glass transition temperatures and thus lose good 
mechanical properties on heating to 100.degree. C. 
Our own allowed U.S. application Ser. No. 333,328, filed Dec. 21, 1981 now 
U.S. Pat. No. 4,398,018, describes poly(ester carbonates) with 
tert-butylhydroquinone as the major diol, with improved properties at 
100.degree. C. and above. While this monomer is more readily available and 
less expensive than methylhydroquinone, it is still not as cheap as 
hydroquinone itself. 
BRIEF DESCRIPTION OF THE INVENTION 
A class of poly(ester carbonates) has been found which can be formed using 
high proportions of the readily available diols hydroquinone and 
resorcinol by melt condensation, and which furthermore are thermotropic 
and thus produce high strength fibers. Such polymers can be spun into 
fibers from the melt and can be oriented or otherwise upgraded by drawing, 
annealing or other conventional techniques used to improve the orientation 
and crystallinity of fibers. Furthermore, the thermotropic poly(ester 
carbonates) of this invention have glass transition temperatures of at 
least about 100.degree. C., preferably at least about 130.degree. C., 
which enables them to retain mechanical properties on heating to these 
temperatures. 
Thus the present invention includes a poly(ester carbonate) polymer having 
diacyl moieties which are primarily terephthaloyl moieties, carbonate 
moieties and aromatic dihydroxy-derived moieties. In the improvement, the 
aromatic dihydroxy-derived moieties comprise a mixture of, by moles: 
(a) about 60-20% benzene-1,4-dioxy, 
(b) about 20-40% benzene-1,3-dioxy, 
(c) about 30-5% methylbenzene-2,5-dioxy, and 
(d) about 10-30% t-butylbenzene-2,5-dioxy. 
This composition enables the greatest use of the most available 
hydroquinone and resorcinol monomers, and least use of the least available 
methylhydroquinone monomer. The intermediate monomer, 
tert-butylhydroquinone, is used in modest amounts. The poly(ester 
carbonates) of the present invention are liquid crystalline in the melt at 
least up to 20.degree. C. above their melting point and have glass 
transition temperatures of at least 100.degree. C. The polymers of the 
present invention can be formed as low molecular weight oligomers or 
polymers of sufficient molecular weight to form fibers. 
DETAILED DESCRIPTION OF THE INVENTION 
The poly(ester carbonate) polymers of the present invention have diacyl 
moieties, aromatic dihydroxy moieties and carbonate moieties. The 
carbonate moieties may be formed by reacting phosgene or by exchange of 
carbonate or haloformate monomers with various oligomers as is 
conventional. The diacyl moieties are primarily terephthaloyl and can be 
formed either from terephthalic acid or from terephthaloyl halide such as 
terephthaloyl chloride. Terephthalate diesters such as dimethyl 
terephthalate or diphenyl terephthalate (preferably the latter) may be 
used if the polymer is produced by melt condensation. Although the diacyl 
moiety should be primarily terephthaloyl, other diacyl moieties may be 
used as a relatively minor component, such as substituted terephthaloyl, 
isophthaloyl, 2,6-naphthalenedicarboxyl, 1,4-cyclohexanedicarboxyl and 
1,3-cyclohexanedicarboxyl. 
The aromatic dihydroxy moieties of the polymer of the invention should be 
primarily the four moieties listed in the Brief Description. Hydroquinone 
(1,4-dihydroxybenzene) is used to provide 60-20% of the aromatic 
dihydroxy-derived moieties, with about 30 to about 40% being preferred. 
Resorcinol is used to provide 20-40% of the aromatic dihydroxy-derived 
moieties, with about 30 to about 35% being preferred. 
Tert-butylhydroquinone is used to provide 10-30% of the aromatic 
dihydroxy-derived moieties, with about 10 to about 25% being preferred. 
Methylhydroquinone is used to provide between 5 and about 30% of the 
aromatic dihydroxy-derived moieties, with about 10 to about 20% being 
preferred. 
In general, it is preferred that hydroquinone and resorcinol together 
constitute between about 55 and about 80% of the total, and that 
tert-butylhydroquinone and methylhydroquinone constitute about 20-45% of 
the total. It is also preferred that the t-butylhydroquinone represent 
30-80% of the t-butylhydroquinone plus methylhydroquinone. Other 
substituted hydroquinones and other aromatic dihydroxies (e.g., 
substituted 4,4'-dihydroxies) may be used as minor constituents. 
Where the terephthalate moieties are not the sole diacyl moieties used in 
the polymer, other aromatic dicarboxylic acid moieties may be used. 
Examples of such moieties include substituted terephthalates such as 
methyl-, chloro-, lower alkoxy (one to six carbons) or bromoterephthalate; 
isophthalate; 2,5-pyridine dicarboxylate; and 2,6-naphthalene 
dicarboxylate. Substituted forms thereof may also be used as minor 
components. While the present polymers may have solely carbonate, dihydric 
aromatic alcohol and diacyl moieties, it is contemplated to include other 
moieties, including hydroxyaromatic carboxylates such as 4-hydroxybenzoic 
acid or substituted forms thereof in minor proportions. For example, a 
polymer of t-butylhydroquinone:terephthalate:carbonate (2:1:1) can be 
modified by using hydroxybenzoic acid as a fourth component, whereby the 
ratio becomes, for example, 1.9:0.9:0.1 or 1.8:0.8:1:0.2. Hydroxyaromatic 
carboxylates are used primarily when the polymer is formed by melt 
condensation. 
The polymers of the present invention are preferably formed by melt 
condensation. In this method the diacyl moieties may be introduced as 
diesters such as diphenylterephthalate and the carbonate moieties as 
diesters such as diphenylcarbonate. The materials are mixed in the melt 
with the mixture of dihydroxy compounds and optionally a suitable 
organometal catalyst such as lithium phenolate, aluminum isopropoxide or 
sodium methylate, and optionally hydroxybenzoic acid or one of its esters 
and heated to transesterify and remove the alcohol part of the esters 
(e.g. phenol) by evaporation. 
In a modified melt condensation process, terephthalic acid is used in place 
of terephthaloyl chloride and the amount of diphenyl carbonate is 
increased by the molar amount of terephthalic acid (e.g. doubled if the 
desired final terephthalate:carbonate ratio is 1:1). By heating to one 
temperature, e.g. 200.degree. C., at which transesterification occurs, the 
terephthalic acid is converted in situ to diphenyl terephthalate by 
conversion of the additional diphenyl carbonate to carbon dioxide and 
water (both of which are vented). The temperature is then raised to a 
suitable reaction temperature, e.g. 270.degree. C., at which 
polymerization occurs or is completed, liberating phenol. 
Once the polymers are formed, they may be purified, if required, by 
conventional technology. Prior to spinning, they may be heated to a 
temperature below their melting temperatures (e.g. to 220.degree. C. or 
240.degree. C. or 250.degree. C.) for a period (e.g. 0.5, 1.0 or 2.0 
hours) to cause further increases in molecular weight. Thereafter the 
polymers can be spun or extruded into fibers, sheets or other fabricated 
forms using conventional techniques, including post-treatments such as 
drawing, heat treatments and the like. The thermotropic nature of the 
polymers increases the orientation of the fabricated forms, which 
manifests itself in improved physical properties, e.g. higher tensile 
modulurs for fibers. 
In determining liquid crystallinity, the TOT procedure described in cols. 
8-10 of U.S. Pat. No. 4,118,372 may be used. The results reported in the 
following Example 6 are based on visual observations with such a test, and 
not on quantitative measurement of light intensity. 
An important feature of the thermotropic poly(ester carbonate) polymers of 
the present invention is their retention of properties when heated to 
100.degree. C. or above. When formed into oriented fibers or films, the 
properties most notably retained at elevated temperatures are tenacity and 
tensile modulus.