Note: Descriptions are shown in the official language in which they were submitted.
wosl/l7l37 PCT/US91/02883
20828~}0
NOVEL MONOMERS AND PROCESS TO
SYNTHESIZE LIOUID CRYSTALLINE POLYESTERS
~ACKGROUND OF ~E_~Ey~ION
In recent years, a great deal of attention has been
directed to liquid crystalline polymers. One system studied
in detail contains an aromatic ester triad with a central
terephthaloyl unit and two terminal oxybenzoyl units connected
by a flexible polymethylene spacer of varying length. Fig. 1,
which forms a portion of the instant specification,
illustrates the structure of this known aromatic ester triad.
References which related to the synthesis and evaluation of
such known structure include: C. Ober et al., Polymer J. 14,
9 (1982); G. Galli et al., Makromol. Chem. 183, 2693 (1982);
and A. Y. Bilibin et al., Makromol. Chem. 186, 1575 (1985).
The polymers just described have been shown to be
thermotropic liquid crystalline polymers which can exhibit
either a nematic or a smectic mesophase.
Liquid crystalline polyesters can be synthesized by
step-growth polymerization techniques. Two basic methods are
generally used. The first involves growing the polymer from
solution involving the reaction of a diol with a diacid
chloride. The problem of polymer solubility, however, can be
a limiting factor in the preparation of high molecular weight
polymers, especially in the case of aromatic polyesters. The
second method avoids such problems by carrying out the
reaction in the absence of solvent. Such bulk (or melt)
polymerization techniques (see V. V. Korshak et al.,
"Experimental Methods of Bulk Polymerization", Comprehensive
Polymer Science, Vol. 5, G. Allen, ed., Pergamon Press,
Oxford, 1989), usually involve either the reaction of
dicarboxylic acids (or their alkyl esters) with diols or the
reaction of diacetates with dicarboxylic acids, in the
presence or absence of a catalyst. The bulk method works best
when the reacting functionalities are directly attached to the
aromatic rings.
WO91/17137 ' PCT/US91/02~3
208'~ ~ _ .,
It has been shown by previous investigators that the
aromat:ic triad polyester, a preferred embodiment of which is
shown by structure (B) in Fig. ~ and which is more generically
depict:ed in Fig. l, exhibits a nematic crystalline phase upon
melting. A reference which discusses this type of liquid
crystalline polyester is C. Ober et al., supra. Such a
polymer has been prepared from solution but had a relatively
low molecular weight due to solubility problems.
DESCRIPTION OF THE INVENTION
The present invention relates, in one aspect, to novel
monomers which can be used as precursors in the synthesis of
the triad polymers previously described. Fig. 2 shows a
synthesis route which can be used to maXe these monomers which
are alkylene bis(p-acetoxybenzoate) compounds. It is
contemplated that the phenyl rings in these compounds can be
independently substituted with such substituents as lower
alkyl, aryl, halogen and the like.
The alkylene bis(p-acetoxybenzoate) monomers which form
one embodiment of the instant invention are, for example, of
the formula of the end product from the synthesis reaction
shown in Fig. 2 which depicts butylene bis(p-acetoxybenzoate),
when r = 4, and hexamethylene bis(p-acetoxybenzoate), when
r = 6. In general, the monomers which are intended to be the
subject of the invention can have r range from about 3 to
about 8.
The preparation of the novel monomers is exemplified in
Examples l and 2 which follow and involves the initial
reaction of an acetoxybenzoic acid (l) in Fig. 2 with thionyl
chloride to form the corresponding acetoxybenzoyl chloride (2)
which is reacted with a dihydroxy compound of the f ormula
HO(CH2)rOH, where r is as defined above, in the presence of an
acid acceptor, such as pyridine.
The instant invention, in another aspect, also relates to
preparation of the aforementioned type of aromatic triad
liquid crystalline polymer by reaction of the foregoing type
WO91/17137 2 0 8 2 8 ~PCT/US91/02~3
of alkylene bis(acetoxybenzoate) monomer with an aromatic
dicarboxylic acid monomer to form the desired aromatic triad
polyester with liberation of acetic acid by-product.
A representative alkylene bis~acetoxybenzoate) monomer is
depicted by (A) in Fig. 3 with the alkylene group being
hexamethylene, namely -(CH2)6-. If desired, the phenyl rings
can be independently substituted with such substituents as
lower alkyl, aryl, halogen, and the like. The alkylene group
can be varied in its length, as described before, and can be
generically depicted as -(CHz), with r ranging from 3 to 8.
As depicted in Fig. 3, this monomer (A) can be reacted
with a dicarboxylic acid compound, such as terephthalic acid,
in the absence of ort preferably, in the presence of a
catalyst such as zinc acetate, using heat to produce the
desired aromatic triad liquid crystalline polyester (B) with
acetic acid by-product which is easily removed. The
dicarboxylic acid reactant can have its phenyl ring
substituted by the same substituents described above.
Copolymers with mixtures of monomers, e.g., with 50 mole % of
a monomer where r is 4 and 50 mole % of a monomer where r is 6
may be prepared. These ratios can be widely varied to cover
the entire compositional range (e.g., 1%-99% to 99%-1%).
The instant process is one which is deemed to allow for
synthesis of the type of aromatic triad polyester (8) in
increased molecular weight as compared to solution methods.
Of considerable importance is that the acidolysis reaction
does not occ1~r to any extent between the carboxylic acid
function and the internal diol ester groups so that
essentially no scrambling of the units occurs. The process
produces acetic acid as a by-product which can easily be
removed under vacuum (see U.S. Patent No. 3,772,405 of F. L.
Hamb).
The instant invention is further understood by the
Examples which follow.
WO 91/17137 PCI/US91~02883
EX~PLE 1
This Example illustrates the preparation of butylene
bis(p-acetoxybenzoate) which is the final compound depicted by
3a in t:he equation shown in Fig. 2.
An amount equalling 93.5 grams of 4-acetoxybenzoic acid
(Compound 1 in the reaction shown in Fig. 2) was mixed with
150 ml of thionyl chloride and stirred at 50C for 3.5 hours.
The excess thionyl chloride was removed under reduced
pressure, and the remaining oil was vacuum distilled, and was
lo then recrystallized in hexane, giving pure 4-acetoxybenzoyl
chloride (Compound 2 in Fig. 2) with a melting point of 28C
at 75% yield. An amount equalling 40.0 grams (0.20 mole) of
Compound 2 was then dissolved in 125 ml of anhydrous
chloroform and was warmed with stirring. To this mixture was
added dropwise a solution of 1,4-butanediol (7.86 grams, 0.087
mole) in 25 ml of chloroform and 45 ml of pyridine. After the
addition was complete, the reaction mixture was heated to
reflux with stirring for twenty-four hours. At the end of
this period, the reaction mixture was cooled and was washed
with water. The organic layer was separated and was washed
with a dilute hydrochloric acid solution, then with a 5%
sodium bicarbonate solution, followed by a final water wash.
The organic layer was dried over CaCl2 and the solvent was
removed. The resulting crude solid was recrystallized once
from methanol, then once from acetonitrile, giving butylene
bis(p-acetoxybenzoate) with a melting point of 106C, as a
fine white powder in 56% yield.
Analysis for (3a, C22H2208): Calculated: C, 63.76; H,
5.3S. Found: C, 63.75; H, 5.35.
The proton NMR spectrum was consistent with the desired
structure.
WO91t17137 PCT/US91/02883
I
2 082 83 0
EXAMPLE 2
This Example shows preparation of hexamethylene
bis(acetoxybenzoate) which is compound 3b in Fig. 2.
Hexamethylene bis(acetoxybenzoate) was prepared and
purified in a manner similar to the preparation described in
Example l for the analogous butylene compound. Thus,
4-acetoxybenzoyl chloride (34.5 grams, 0.174 mole) was reacted
with hexanediol (8.92 grams, 0.075 mole), to give the desired
compound in 63% yield. It had a melting point of 84-85C.
Analysis for (3b, C24H26O8): Calculated: C, 65.15; H,
5.92. Found: C, 65.28; H, 5.93.
The proton NMR spectrum was consistent with the desired
end product.
WO9l/17l37 PC~/US91/~2~3
EXAMPLE 3
~n amount equalling 3.800 grams of the diacetate monomer,
represented by "(A)" in Fig. 3, was combined with 1.427 grams
of terephthalic acid and 0.050 gram of zinc acetate, and the
solid~s were thoroughly mixed with a mortar and pestle. The
solid mixture was then placed into a reaction tube, and
flushed with argon, and a slow stream of argon was passed
through the reaction tube. The reaction tube was then placed
in a hot salt bath at 180C, and the temperature was slowly
raised to 250C over a period of two hours. The reaction
temperature was then raised to 270C and held there for two
and one-half hours. Finally, a high vacuum was applied, and
the reaction temperature was raised to 290C for one hour.
The product was removed and ground, then treated at 215C for
twenty hours under vacuum to induce further reaction and
increase the molecular weight of the product (see German
Offen. No. 2,520,820, U.S. Patent No. 3,991,013, and H. R.
Dicke et al., J. Polym. Sci., Polym. Chem. Ed., 21, 2581,
1983). The product was then extracted with methanol and dried
in a vacuum oven, to give 2.0 grams of polymer.
The product was examined under an optical polarizing
microscope and found to display a nematic schlieren texture.
The polymer (B) exhibited a melting point of 241C, and an
isotropization temperature of 345C, as determined by DSC.
The inherent viscosity was measured to be 0.540 dl/g at 45.5C
in p-chlorophenol.
Analysis for C28H24O8: Calculated: C, 68.84; H, 4.95.
Found: C, 68.71; H, 4.79.
WO91/17137 P~T/US91/02~3
7 20~28 3
EXAMPL~ 4
This Example shows the preparation of a triad copolymer
(B) of Fig. 3, where r = 4,6 (50/50).
An amount equalling 3.020 grams of the diacetate monomer
"(A)", where r = 4, was combined with 3.224 grams of the
diacetate monomer "(A)", where r = 6, and 2.421 grams of
terephthalic acid, along with 0.050 gram of zinc acetate. The
solids were thoroughly mixed and placed into a reaction tube,
and flushed with argon, and a slow stream of argon was passed
through the reaction tube. The reaction tube was then placed
in a hot salt bath at 180C. The reaction temperature was
then slowly raised to 295C over a period of 6 hours. A high
vacuum (less than 0.1 mm Hg) was then applied to the reaction
tube with heating at 295OC for an additional hour. The
product was removed and ground, then treated at 180-192C for
six hours under vacuum to induce further reaction and increase
molecular weight. The product was then extracted with
methanol and dried in a vacuum oven, to give 2.8 grams of
polymer.
The product was examined under an optical polarizing
microscope and found to display a nematic schlieren texture.
Analysis of the polymer (B), where r = 4,6 (50/50), by DSC
revealed two endotherm peaks at 174C and 204C. The
isotropization temperature was above the decomposition
temperature, which began at 308C as determined by TGA. The
inherent viscosity was 0.42 dl/g at 45.7C in p-chlorophenol.
Analysis for C54H44O16: Calculated: C, 68.35; H, 4.67.
Found: C, 68.10; H, 4.67.
W091/17137 PCT/US91tO~883
EXAMPLE 5
This Example shows preparation of a triad polymer of the
general structure B in Fig. 3 where the repeating methylene
unit is four carbons rather than six.
An amount (4 gm) of diacetate monomer A (with r = 4) was
combined with 1.603 gm of terephthalic acid and 0.050 gm of
zinc acetate and the solids were thoroughly mixed. The solid
mixture was then placed into a reaction tube and was flushed
with argon and a slow stream of argon was passed through the
lo reaction tube. This reaction tube was then placed in a hot
salt bath at 180C, and the temperature was slowly raised to
2850C over a period of five hours. A high vacuum (less than
o.l mm Hg) was applied, and the reaction temperature was
raised to 295C for one and one-half hours. The product was
then removed, was ground and was then treated at 2500C for two
hours under a high vacuum (less than 0.1 mm Hg). The product
was then extracted with methanol and was dried in a vacuum
oven to give 3.4 gm of polymer.
The product was examined under an optical polorizing
microscope and was found to display a nematic schlieren
texture. The polymer exhibited a melting point of 243C. The
isotropization temperature, which was 340C, as determined by
TGA. The inherent viscosity was to be 0.524 dl/g at 45.6C in
p-chlorophenol.
Analytical calculations for C26H2000: C, 67.82; H, 4.38.
Found: C, 67.40; H,4.32
The foregoing Examples should not be construed in a
limiting sense since it is intended to describe only certain
embodiments of the instant invention. The scope of protection
sought is set forth in the claims which follow.
