Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to a process for preparing polyesters by
reacting terephthalic acid and butane-1,4-diol in the presence of the dimethyl
ester of the dicarboxylic acid used.
It is known that polytetramethylene esters can be made by ester
interchange of dimethyl esters of aromatic dicarboxylic acids with butanediol
to form the corresponding glycol esters which are then subjected to poly-
condensation. This method has numerous disadvantages: at the high conden-
sation temperatures, the butane-1,4-diol gives rise to large quantities of
tetrahydrofuran which distils over with the excess butane-1,4-diol. The
butane-1,4-diol recovered from the process is therefore contaminated and cannot
be used again directly.
It is also known to react the free dicarboxylic acid with butane-l,
4-diol, but if one wants good yields this method requires very high conden-
sation temperatures and applied pressure. A considerable proportion of the
butanediol is therefore again converted into tetrahydrofuran which leads to
the difficulties already mentioned above. In addition, very long condensation
times are required. It is therefore a matter of great economic interest to
; develop a special proceeding which avoids one step of the process and the
above mentioned disadvantages, especially the long condensation times, by
means of using the nonesterified aromatic dicarboxylic acids.
It has unexpectedly been found that the condensation times can
considerably be decreased by means of the addition of a dimethyl ester of the
dicarboxylic acid used. One skilled in the art should have expected that
the dimethyl ester should preferably be esterified by ester interchange because
of its good solubility in butane-1,4-diol and its higher reactivity, and that
therefore it should not be able to exercise an accelerating influence on the
, reaction after a short time.
- This invention therefore relates to a process for the preparation
of linear high-molecular weight polyesters by catalytic reaction of butane-l,
4-diol with an aromatic dicarboxylic acid, namely terephthalic acid, by the
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31t condensation proccSs, wh~ch ;s characterised in that the reaction is
carried ou~ in the presence of 5 - 20 percent by weight, based on the amount
of the dicarboxylic acid of the dimethyl ester of the dicarboxylic acid used,
i.e. of dimethyl terephthalate.
The process according to the invention may be carried out
continuously or intermittently, generally between 160 and 200C. 1,05 to
2,4 moles, preferably 1,1 to 1,4 moles of butane-1,4-diol, are used per
1 mole of (dicarboxylic acid I dicarboxylic acid dimethyl ester). Accord-
ing to a preferred method of carrying out the process, the starting
components are heated to not more than 200C in the first condensation
stage and kept at this temperature until all the volatile decomposition
products, as well as free butanediol, have distilled off~ This first
condensation stage is preferably carried out at an applied pressure of
4 - 5 excess atmospheres. The second stage of condensation may be
carried out in known manner under vacuum at temperatures of between
250C and 310C.
Both the first and the second stage of condensation are
preferably carried out in the presence of catalysts. Known esterific-
; ation catalysts such as compounds of zinc, manganese, cobalt, lead and
calcium and of the alkali metals may be used for accelerating the firststage of condensation. Phosphoric acid, phosphorous acid or alkyl,
aryl or alkylaryl esters of phosphoric acid are then added to the reaction
mixture to inhibit these catalysts after termination of the first stage
of condensation and to increase the stability of the end products. The
polycondensation process is catalysed with titanium compounds which may be
used together with other known polycondensation catalysts. Tetratitanic
acid esters are preferred, e.g. tetraisopropyl titanate.
The polytetramethylene esters obtained according to the
invention are distinguished by their high viscosity. In addition,
they are thermally stable and undergo only a negligable decrease in
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viscosity on prolonged heating in the melt.
The following Examples illustrate the invention:
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~ 1080394
Example 1
2,700 g of terephthalic acid and 300 g of dimethyl
terephthalate are mixed with 2,800 g butane-1,4-diol in
a 20 litre autoclave, and 0.1 % by weight (3 g) of sodium
acetate is added as esterification catalyst. The mixture
is heated to a temperature of 200C and kept at this temper-
ature for 3.5 hours at an applied pressure of 4 - 5 excess
atmospheres. At the same time, methanol, water and tetra-
hydrofuran are continuously distilled off. The reaction mix-
ture is then heated to 220C and the excess pressure is re-
leased after 1 hour. After the addition of 0.05 % by weight
of tetraisopropyl titanate ~1.5 g), the temperature is raised
to 265C and condensation is continued at a pressure of 1
Torr. After about 2 hours, the product has reached a vis-
cosity of 2200 Poises and is spun off. The resulting pro-
duct has the following properties:
n 280 C = 2200 Poises
250C = 5400 Poises
Mp = 224 - 225C
Reflection (460 nm) = 68.5 %
Example 2
The procedure is the same as in example 1 except
that the reaction is carried out without the addition of di-
methyl terephthalate. Only a low viscosity material with a
viscosity of ~ = 15 Poises at 280C is obtained after a reaction
time of 6.5 hours.
Example 3
'~ Condensation is carried out as described in example 1
except that the quantity of dimethyl terephthalate is reduced
to 5 % by weight, based on the dicarboxylic acid. The poly-
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ester then obtained as a viscosity of n 280C = 2000 Poises
Its melting point is 225C and its reflection (460 nm) is 70 %.
Example 4
Condensation is carried out as described in example 1 ex-
cept that the quantity of butane-1,4-diol is reduced to 1950 g.
The polyester ~hen obtained has a viscosity of ~ 280C = 2800
Poises. Its reflection (460 nm) is 82 %.
Example 5
The reaction may also be carried out continuously. In - -
that case, instead of adding dimethyl terephthalate, a reserve -
sump-is used (90 - 40 %) into which a paste of terephthalic acid
and butanediol (10 bis 60 percent by weight; proportion by weight
of terephthalic acid : butanediol = 1 : 0.7 to 1 : 3) heated
to a temperature of 150C is continuously introduced. For this
purpose it is suitable to use a pressure-operated overflow cas-
cade into the first stage of which is introduced the above
mentioned suspension at a temperature of 220C. The est~rified
material can be continuously discharged from the 8th stage
(eight chamber container with 20 litre capacity; throughput
20,000 - 25,000 g per hour) and continuously conveyed to a ~ -
polycondensation apparatus (two-shaft reactor). The reaction ~ -
is carried out at a steam pressure of 4 excess atmospheres.
The catalysts are continuously added with the suspension
of terephthalic acid and butanediol (sodium acetate and ti- -
tanium tetraisopropylate as indicated under 1). The eight-
chamber container (cascade) is advantageously arranged as a
back-flow assembly in which from the 7th chamber onwards 10 -
30 % of the esterification mixture is pumped into the first
chamber where it is reacted with the paste of terephthalic acid
and butanediol.
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