Note: Descriptions are shown in the official language in which they were submitted.
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PRODUCTION OF MODIFIED POLYALKYLENE TEREPHTHALATES
The invention relates to a process for the production of a
modified polyalkylene terephthalate in which a portion Or the tere- -
phthalic acid is replaced by an aIiphatic dicarboxylic acid.
It is known that polyesters can be prepared by reacting an
aromatic or aliphatic dicarboxylic acid or ester with an aliphatic
glycol. This reaction which proceeds with elimination of water or ~-
alcohol is usually carried out on an industrial scale~in two or more
stages.
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For example when dimethyl terephthalate is used as the starting ;
ester, this may first be reacted with ethylene glycol to Porm di-
ethylene glycol terephthalate or an oligomeric condensation product
of the same. The product obtaine~ is then polycondensed in~o a hi~h
molecular weight-reaction product batchwise or continuously with the -~
elimination of glycol.
To prepare a modified polyester which offers particular ad-
.
vantages in certain applications it is possible in principle to re-
place some of the terephthalic acid component by a suitable aliphati~
dicarboxylic acid. The methods available differ in the type of com-
ponent added and the point in time at which it is introduced.
For example it is known from German Laid-Open Specification
(DOS) No. 1,520,284 that modified polyalkylene terephthalates can be
~.
prepared by transesterifying a mixture of dimethyl te~ephthalate
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and a dialkyl ester of an aliphatic dicarboxylic acid with a glycol
in the presence of a suitable transesterification catalyst such
as a zinc, manganese or calcium compound to form the corresponding
glycol ester, the monofunctional alcohol liberated being removed
by distillation. The resulting reaction mixture of monomeric and
oligomeric glycol esters, after the addition of a suitable poly-
condensation catalyst such as an antimony or germanium compound, is
converted by a conventional method into a high molecular weight
polycondensation product.
This process may often be carried out on an industrial scale
without any particular problems. It offers advantages particularly
when the acid used for modification is difficult to purify as such
because of a high melting or boiling point and low solubility in
cheap solvents and therefo~e purification iB effected by the cumber-
some routeinvolving the corresponding dialkyl esterO When the acid
in question can be conventionally purified in free form and used
for the produetion of technical derivatives 3 as in the case o~
adipic and sebacic acids, the roundabout method via the dialkyl
ester is avoided for reasons of economyO
Furthermore it is known from German Laid-Open Specification
(DOS) No 1,520,284 that modified polyalkylene terephthalates can be
prepared by reacting dimethyl terephthalate with a suikable glycol
in the presence of a suitable transesterification catalyst, then
adding to the mixture the free acid servin~ to modify the ester and
reacting this three-component mixture finally in a conventional
manner to form a high molecular weight copolyester. The acid is added
in solid or molten form, This process does avoid the troublesome pro-
duction of the dialkyl ester concerned but it still has some serious
disadvantages. Firstly the introduction of the solid product into
the transesterification m~xture offers problems particularly when
adipic acid is used as the modi~ying agentO When adipic acid or
another aliphatic acid is added in solid form there are serious
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di~riculties because it is moistened by ascending glycol vapor, which
eventually results in troublesome stoppage of the supply members
such as star feeders or screw conveyers, The addition of adipic
acid in molten form is also fraught with problems because the acid
very readily forms byproducts in the molten condition and these
seriously impair the quality of the polyester and particularly its
color~ Another disadvantage in the acldition of free acids to the
transesterification mixture is that considerable amounts Or water
of reaction are formed in the subsequent esterification reaction and
this contaminates the methanol and glycol distilled off, limits their
applications and adds to the cost of processing. The water formed
also causes di~ficulties in the subsequent evacuation of the reaction
mixtùre because the necessary final vacuum of about 1 mm is only set
up with great delay so that polycondensation takes appreciably longer
and this again results in impairment of quality and increase in the
price of the product. The presence of large amounts of free acid in
the transesterification mixture may result in insoluble salts being
` formed with the transesterification catalyst~ which are deposited
in the reactors and pipelines, especially in continuous operation,
and may have unpleasant consequences,
Addition of free dicarboxylic acid prior to the transesteri-
; fication of the dimethyl terephthalate with the glycol in question
is ruled out in most cases because the metal-catalyzed transesteri-
fication reaction is markedly slowed down by small amounts o~
acid.
Another possibility for the production of polyalkylene tere-
phthalates modified with dicarboxylic acids consists in introducing
the bisglycol ester of the modifying acid instead of the free acid
itself into the transesterification mixture (cf. O.B. Edgar and
E. Ellery, J. Chem, Soc. 1952, page 2633). The bisglycol ester used
~or modification is prepared separately by quantitative esterification
of adipic acid with the glycol concerned in a molar ratio of 1:2.
These methods avoid some of the above disadvantages in-bhat the
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e~terification reaction is carried out at atmo~pheric pressure and
without the use of esteri~ication cataly~tsO On the other hand it is
time-consuming because o~ the complete esterification Or the free
acid and is uneconomic because of the ~airly large amount o~ glycol
us ed O
~ he object of the invention~ apart from the avoidance o~ the
disadvantages of the prior art methods, is mainly the use o~ a smaller
amount of glycol with the simultaneous shortening of reaction periods.
This object is achieved by the invention~
The invention consists in a process for the production of a modi-
fied polyalkylene terephthalate from terephthalate acid and a glycol
in whlch up to 50% molar o~ the terephthalic acid radical is replaced
by an aliphatic dicarboxylic acid radical of ~our to twelve carbon
atoms wherein an aliphatic dicarboxylic acid is esterified with the
polyester-forming glycol in a molar ratio of from 1:102 to 1:1.8
- until a degree of esterification o~ ~rom 90 to 95 mole% has been
achieved (based on the aliphatic dicarboxylic acid), the esteri-
fication mixture thus obtained is mixed with a transesteri~ication
mixture of a dialkyl terephthalate and the polyester-~orming glycol
obtained by a conventional method and this mixture is polycondensed
by a conventional method.
Aliphatic dicarboxylic acids Or four to twelve carbon atoms,
~or example glutaric acid, adipic acid, suberic acid, azelaic acid
and sebacic acid, may be used ~or modification of polyalkylene tere-
phthalates by the process according to the invention.
From 1 to 50 mole% and preferably from 3 to 40 mole% of the
; terephthalic acid in the polyalkylene terephthalate may be replaced
by the modi~ying dicarboxylic acid.
Particularly suitable glycol components are aliphatic glycols
of two to six and advantageously o~ two to four carbon atoms such
as ethylene glycol~ butanediol-1,4 or hexanediol-1,6.
It is al90 possible in principle to prepare by the process
according to the invention a copolyester which contains chemically
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combined therein, in addition to terephthalic acid, two or more
different aliphatic dicarboxylic acids and two or more difrerent
glycols~ The additional modifying components(s) may be used for
example as free glycols in the transesterification reaction or as
free dicarboxylic acids and free glycols in the esterification reac-
tion.
The esterification mixture may be prepared for example as
follows
The alipha~ic dicarboxylic acid and the glycol are placed in
10 the said molar ratio in a heatable stirred container provided with
a column or dephlegmatorO The mixture is heated at atmospheric
pressure in the course of from one hour to two hours to a temperature
which is from about 5 to 20C below the boiling point of the glycol.
During the heating up phase considerable amounts of water of reaction
develop and these are removed overheadO The reflux from the column
or the temperature of the dephlegmator is regulated so that the
water is substantially separated ~rom entrained vaporous glycolO
A reflux ratio of 1:1 or a temperature in the dephlegmator of from
lQl to 102C is generally sufficient, The reaction may be convenient-
, 20 ly monitored by the amount of distillate obtained or by determiningthe acid value in samples of the esterification mixtureO At starting
molar ratios of dicarboxylic acid to glycol of from 1:1.2 to 1~1.8 a
reaction period of from two to four hours is generally ~ufficient
' to set up the required degree of ester,ification Or from 90 to 95
; mole%, The esterification mixture contains mainly diglyool ester o~
the aliphatic dicarboxylic acid and oligomers of the same. The mean
degree of polycondensation is less than 5. The molar ratio of the
starting components: dicarboxylic acid and glycol in the production
o~ the esterification mixture is advantageously rrom 1~ to 1:1,6,
30 At a higher glycol fraction than 1:108 the proce~s becomes increasingly
uneconomic and at lower than 1:1,2 a marked prolongation of the ester-
ification period has to be tolerated.
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The production of the tran3esteri~ication mixture is carried out
by conventional methods from a dialkyl ester of terephthalic acid,
particularly dimethyl terephthalate and the appropriate ~lycol or
glycols. It is generally carried out at atmospheric pressure and at
a temperature o~ rrom 130 to 240 C0 It is generally advisable to
carry out this reaction quickly and under mlld conditions because
otherwise undesirable side reactions such as the formation of di-
glycol or possibly of tetrahydrofuran may occur. The molar ratio of
dialkyl terephthalate; to glycol is generally from 1:1,2 to 1:2
10 and preferably from 1:102 to 1:1.8. As a rule the lowest possible
glycol fraction is chosen so as to keep the cost of the substance
used low and to lessen the formation of byproducts~ The transesteri-
fication reaction is generally carried out in the presence of ~
Suitable transesterification catalyst such as a zinc, manganese,
calcium or titanium compound and the amount added is generally from
0~01 to 0.2% by weight based on dialkyl terephthalate, The trans
esterification is generally continued until at least 95% of the total
alkoxyl groups present has been eliminated. The transesteri~ication
mixture then consist~ mainly o~ diglycol terephthalate and its oligo-
20 meric precondensates. The mean degree of polycondensation is con-
veniently less than 10,
The esterification mixture and the transesterification mixture
~ may be combined immediately a~ter their separate production9 i.e.
; while still hot at temperatures of from 200 to 240C and well
~` mixed. This may be carried out on an industrial scale by means of
metering pumps which can be controlled by means of suitable flow
meters. Mixing may be carried out by conventional stirring means
or static mixers,
It is also possible however for the esterification mixture,
30 i.e. the modifying component, to be cooled for example to a temper-
' ature of for example 30 to 100C, to be kept in suitable storage
vessels and only then to be added to the transesterification mixture,
After the esterification mixture has been brought to~ether
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with the transesterification mixture the polycondensation is carried
out by a conventional method and evacuation to the neccessary reac-
tion pressure is carried out before, during or after the heating up
period.
Polycondensation of the mixture should also be carried out as
mild~y as possible~ i.e. at the lowest possible temperature and in
the shortest possible time, in order to lessen the formation of by-
products such as diglycol or tetrahydrofuran and to lessen thermal
degradation. The polycondensation is accordingly carried out generally
at a temperature of from 240 to 290 and preferably at from 250 to
280C and at a pressure of from 760 mm down to Ool mm. The reaction
is usually carried out in the presence of a suitable polycondensation
catalyst such as an antimony, germanium or titanium compound generally
in an amount'of`from OoOl to 0~2% by weight based on the polyester
in question and a stabilizer containing phosphorus such as triphenyl
phosphate, also in an amount of from OoOl to 002%. Copolyesters
having relative viscosities of more than 1.30 and particularly 1.35
(measured in 0.5% by weight solution in a mixture of phenol and o- ''
dichlorobenzene in a ratio by weight of 3:2 at 25C in an Ubbel~hde ~`
viscometer) may thus be achieved in rapidly proceeding polyconden~ ;
sation reactions,. ~ '
Modification of polyesber~ may be carried out with great advantages
according to the process of the invention; the produc~ion of the ~-~
modifying agent is simple and does not requ~re great expenditure
for apparatus, for example in apparatus operated at atmospheric
pressure and without the use of a catalyst~ The economical disadvantage
of using a large amount of glycol is avoided so that a substantial ~, ;
shortening of the reaction period required for the production of the
esterification mixture as modifying agent is possible.
It was not foreseeable that the reaction period for the esteri-
~ication o~ aliphatic dicarboxylic acids with aliphatic glycols using
a molar ratio o~ from 1:102 to 1:1.8 is only trivially di~ferent when
the degree of esterification is 1 mited to from 90 to 95% of the ,' -
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amount of dicarboxylic acid used and that the esterirication mixture
o~ monomer and oligomeric glycol esters of dicarboxylic acids can be
used for the production of modified polyesters without impairment
of product quality or processO
; The esterification mixture of aliphatic dicarboxylic acidQn~ ylyc~l
may easily be stored for a long time at slightly elevated temperature
without impairment of qualityO Metering the molten modifying agent
offers no technical problemsO Contamination o~ the alcohol and glycol
distillate with water of reaction is considerably lessened in this
10 method and this is of great advantage because these distillates other-
wise can only be supplied for further industrial use with di~ficulty
and at great expense. The process according to the invention moreover
avoids the formatlon of troublesome deposits and problems in the
- polycondensation stage by the water of reaction formedO
- The process may be carried out advantageously batchwise or con-
tinuously in conventional polyesker plant.
Polyesters obtained according to the in~ention are distinguished -~
by a low content of byproducts such as diglycol and accordingly ex-
hibit good stability. The color of the products is also éxcellent~
Conventional additives such as pigments, antistatic agents,
dyes~ glass fibers, stabilizers or fireproofing agents may be incor~
porated before, during orafter the polycondensation in the production
of modified polyesters by the process according to the invention~
Modi~ied polyalkylene terephthala~es obtained according ~o the
invention may be further processed for exarnple into fibersg fila-
ments~ threads, film, sheeting or injection moldings either imme-
diately or after conversion into chips cr` the like via a melt.
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Textile moldings even with relatively slight modi~icationg for
example with from 5 to 10 mole% of aliphatic dicarboxylic acid, ex-
~ hibit a greatly improved dyeing behavior; at a higher content ofaliphatic dicarboxylic acid, ~or example with from 10 to 30 mole%,
they may be used for example as bonding `fibers for the production
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of nonwovens. Copolyesters prepared according to the invention and
particularly modiried polybutylene terephthalates, may also be used
as hot-melt adhesives in the shoe industryO
The following Examples illustrate the inventionO The parts and
percentages are by weightO
EXAMPLE 1
; (1) PRODUCTION OF THE ESTERIFICATION MIXTURE USED FOR THE
MODIFICATION:
A mixture of 292 parts (2 kmoles) of adipic acid and 186 parts
(3 kmoles) of ethylene glycol is heated to 180C within one hour in
a stirred vessel which is combined with a packed column having a re-
flux divider and a condenser downstream of the same. The water of
reaction formed in the esterification is separated from vaporous
, entrained ethylene glycol through the rectifying column at a reflux
- ratio of 1:1 o The reaction is monitored by determination of the acid
' number of the esteri~ication mixture and with the knowledge of the
operating oapacity of the column by the amount o~ distillate. A~ter
a reaction perlod o~ three hours at 180C a reaction mixture having
a degree o~ esterification of about 93% (based on the free adipic -~
, 20 acid used) has ~ormed in the vessel. `~
CQMPARATIVE EXPERIMENT:
292 parts (2 kmoles) of adipic acid and 248 parts (4 kmoles)
o~ ethylene glycol are used ~or the production of the esterif'ication ,
mixture. I~ a substantially quantitative esterification, i.e. a degree
of esterification of about 99%, is required under otherwise the same
, conditions, the reaction period at 180 C is about eight hours.
(2) PRODUCTION OF A TRANSESTERIFICATION MIXTURE FROM DIMETHYL ~ ;
TEREPHTHALATE AND ETHYLENE GLYCOL ~
97 parts (0.5 kmole) and 62 parts (1 kmole) of ethylene - `
3 glycol are heated to about 140C with stirring in a heatable stirred
vessel with a superposed column ~or separating the methanol liber-
ated. 0.03 part of zinc acetate (2H20) and o.o8 parts of antimony
acetate dissolved in glycol are then introduced into the homogeneous
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melt and the temperature of the reaction mixture is raised in the
course o~ three hours to 230C while stirringO The methanol liberated
is removed ~rom the system by way of the rectifying column treflux
ratio R:D = 3)0
(3) PRODUCTION OF A POLYETHYLENF. TEREPHTHALATE MODIFIED WITH
ADIPIC ACID:
After the transesterification reaction is over 23 9 parts of the
esterification mixture prepared according to paragraph (1) is intro-
duced into the transesterification mixture at 230C and atmospheric
10 pressure while stirring, stirring is continued for another five minutes
and 0.05 part of triphenyl phosphite is added ror stabilization. The
stirred reaction mixture is then heated within one hour to 265 to
270C with simultaneous evacuation ~rom 760 mm to less than 1 mm and
aftercondensed in this temperature range for about three hours. The
finished polycondensate is forced outlunder nitrogen, passed through a
` waterbath, granulated and dried~ A practically colorless product is
; obtained with a relative viscosity of 1043. The material has a ` -
so~tening point of about 220C determined microscopi~ally~
EXAMPLE 2
20 (1) PRODUCTION OF THE ESTERIFICATION MIXTURE:
An esterification mixture havin~ a degree of esterification
of 95% is prepared ~rom 292 parts (2 kmoles) of adipic acid and
270 parts (3 kmoles~ of butanediol~1~4 in a three hour reaction period
at 210C in the manner described in Example 1.
(2) PRODUCTION OF A TRANSESTERIFICATION MIXTURE FROM DIMETHYL
TEREPHTHALATE AND BUTANEDIOL-(1,4):
97 parts (0.5 kmoles) of dimethyl terephthalate and 68 parts
(0~75 kmole) of butanediol are heated w~ile stirring to about 140C
in a heatable stirred vessel with a superimposed column. 0.1 part of
3 tetrabutyl o-titanate is ~radually introduced into the homogeneous
melt and the temperature o~ the reaction mixture is raised to 230C
in the course of two hours with simultaneous stirringO The methanol
liberated is removed through the columnO
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(3~ PRODUCTION OF A POLYBUTYLENE TEREPHTHALATE MODIFIED
WITH ADIPIC ACID:
82 parts of the esterification mixture prepared according to
paragraph (1) is lntroduced while sti:rring at 230C into the trans-
esterification mixture after the reaction is over and stirring is ;
continued for another five minutesO The mixture is then heated to
245 to 250C within one hour while stirring and at the same time
evacuating the vessel from 760 mm to less than 1 mm and afterconden-
sation is carried on in this temperature range for about three hours.
A substantiall~y colorless polycondensate is obtained which has
a relative viscosity of lo 360 The material has a softening point of
10 about 160C determined microscopioallv.
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