DE1595545A1 - Process for the preparation of polyalkylene terephthalates - Google Patents

Description

Process for the preparation of polyalkylene terephthalates

It is known that polyalkylene terephthalates - for example polyethylene terephthalate - are produced from alkyl esters volatile alcohols with terephthalic acid - for example dimethyl terephthalate - and glycols in two stages, of which the first is called the transesterification reaction and the second is called the polycondensation reaction. Each of these stages is usually influenced by different types of catalysts, since the transesterification catalysts - for example in Reaction mixture soluble compounds of zinc, cadmium, manganese or calcium - either the polycondensation reaction accelerate insufficiently or in the required for the polycondensation reaction, compared to the Transesterification reaction higher concentrations not only cause the desired polycondensation reaction, but also a decomposition reaction. With increasing polycondensate content on decomposition products, however, their performance properties deteriorate. As a result, it belongs to the state of the Technique to keep the concentration of the transesterification catalyst either as low as for an undisturbed course the transesterification reaction just required, or the transesterification catalyst after the end of the transesterification by adding to deactivate organic phosphates, phosphates or phosphoric acid and the polycondensation reaction in both Cases to be carried out after adding another catalyst.

Such polycondensation catalysts are known in large numbers; one that is not state-of-the-art, however more relevant compilation can be found in the literature (R. E. Vilfong, J. Polymer Sci. 54 (1961), 388). In practice, soluble antimony compounds in particular have been introduced for this purpose.

Accordingly, it is also considered a particularly useful catalyst-stabilizer combination for the production of polyethylene terephthalate an addition of 0.03 mol- £ manganese acetate, 0.03 MoI-Jt antimony acetate and 0.06 MoI- ^ triphenyl phosphate or -phosphite (based on the dimethyl terephthalate used) ~

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recommended (Η. Ludewig: polyester fibers; Berlin 1965, p. 96).

Although soluble antimony compounds are good catalytic Activity for the: olykondensationsreaktion own and thereby Only little catalyze decomposition and side reactions, they have the disadvantage that they under the reaction conditions relatively easily reduced to metallic antimony and thereby the polycondensate more or less grayish tint discolor. The elimination of this disadvantage by using compounds of other metals as polycondensation catalysts generally entails other kinds of disadvantages. Almost all of these are metal compounds less active than antimony compounds, which is why the reaction times are longer when using the same molar amounts until a certain molecular weight is reached, the polyester has to be reckoned with, or they will be replaced by the multiple desirable addition of phosphite or phosphate stabilizers deactivated at the same time as the transesterification catalyst, or they significantly catalyze side or decomposition reactions stronger than antimony compounds.

So it is already known »soluble titanium compounds to be used as polycondensation catalysts. These are according to investigations by H. Zimmermann (fiber research, and textile techn. 13, No. 11 (1962), 481-90) antimony compounds that are comparable with regard to their catalytic activity clearly superior without side reactions occurring to a disruptive extent. However, they have the disadvantage that they discolour the polycondensates yellow-brown, except when the reaction time is kept so short that they are in the industrial Practice not adhered to, at least in the widespread discontinuous work, for reasons of apparatus can be, or when the catalyst concentration is so low is measured that the desired * degree of polycondensation cannot be achieved in technically acceptable times. The last-mentioned difficulty can be circumvented by the fact that the transesterification catalyst before the start of Pelykondensationsreaktion not deactivated, so that the

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Polycondensation reaction siareh the syaergistic effect deeeterttngs- and.f ^ lykondensstionekatalysators still in sufficient form it is possible to exercise; but the one in this White polyester produced have the disadvantage that they as a result of -during the polycondensation under the influence the catalysis taking place of the transesterification catalyst One of the side reactions is an often inadequate thermal Have stability that makes further processing difficult or impossible night.

It has now been found that this use is more soluble Titanium compounds as polycondensation catalysts Negative disadvantages can be eliminated by the fact that ■ on the reaction mixtures containing titanium catalysts additionally adds catalytically ^ quantities of such compounds or under the reaction conditions, the common characteristic of which is that they are active Have hydrogen atoms, and that their pK value is approx. 8-10 (the pK value is the negative logarithm of the Dissociation constants; see e.g. B. Fieser and Fieser, textbook the organ. Cheaie, Weinheia 195 * », p. 474). These so defined Compounds buses continue to be stable under the reaction conditions, and their active hydrogen atoms a must be retained, i.e. not by ver or Esterification reactions can be eliminated.

Hypophoaphites - those under the reaction conditions - have been found to be particularly useful compounds of this type gradually to phosphates and the discoloration of the polycondensates »preventing hydrogen phosphide are decomposed - phenolic compounds, which can also be condensed can be, like the hydrocyisophthalic acids or hydroxyterephthalic acids or their alkyl esters, Iaide more aroaatic Dicarboxylic acids and carbazole found.

The invention therefore relates to a method for production of polyalkylene terephthalates from dialkyl terephthalates and glycols in the presence of Ua-

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esterification catalysts, optionally stabilizers and of titanium catalysts which are also known per se and which are soluble in the reaction mixture and which, by means of a further addition catalytic amount «; α of hypophosphites, hydroxyisophthalic acids, Hydroxyberephthalic acids or their alkyl esters, dicarboxylic acid imides, etc. or carbazole.

The mode of action of these compounds is not detailed known, but it can be assumed that they are largely due to the displacement of vinyl alcohol or acetaldehyde from strong discolored vinyl titanates, which are formed towards the end of the reaction from hydroxyalkyl titanates and by decomposition reactions Acetaldehyde is formed as soon as the melt due to the increasing molecular weight of the macromolecules it contains is largely depleted of hydroxyl groups »

The use of certain hypophoaphites as polycondensation catalysts as well as - in combination with manganese phthalates - for light stabilization of polyesters has already been proposed. While that as a polycondensation catalyst proposed magnesium hypophosphite for the intended Purpose is practically completely ineffective at least in the presence of the usual stabilizers and according to the communicated Melting points of the polyester obtained in this way causes extensive lifting reactions, these were light-stabilizing acting, hypophosphite-containing combinations only together with the use of aatimony oxide as a polycondensation catalyst described, with the yellow-brown discoloration caused by titanium compounds from the outset does not occur. These above-described methods accordingly establish the use of hypophosphites according to the invention by no means close. The use of diethyl 2,5-dihydroxyterephthalate, optionally in combination with Salol, for the light stabilization of polyethylene terephthalate also already proposed, but these connections only added to the already condensed polyester, so they are not part of the catalyst sta-

bilizer system. £? 4λ * -

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The polyesters obtained according to the following examples were as follows for their non-sterile properties:

The "reduced viscosity" (VA for the concentration of Ig polymer in 100 ml of solution) is given as a measure of the degree of polycondensation achieved. A mixture of phenol with 2,2,4,4-tetrachloroethane in a weight ratio of 3: 2 was used as the solvent; the measurement temperature was 25 ⁰ C;

red rel -r— '* 0

where t, the flow time of the solution and t _Q that of the solvent means, determined in an Ubbelohde capillary viscometer, be.

To determine the diglycol content, the maximum des Melting point peaks - determined by means of a differential calorimeter, Model DSC-I from Perkin-Elmer - used. This maximum changes its position depending on the diglycol content as follows:

Diglycol (DEG) (£) Melting maximum ( ⁰ C)

0.4 ^! 262

0.8 260

1.2 258.5

1.6 257

2.0 255.

As can be seen from the size of the associated enthalpy of fusion (9.8 cal / g), a DEG content of up to 1.2 $ affects the achievable degree of crystallization and therefore also the associated mechanical properties, such as stress-strain behavior and modulus of elasticity, the moldings to be produced from the polyesters practically not "

Next became the carboxyl group concentration of the polyester according to H. Pohl (Analytic. Chem. 26 (1954), 1614) by titration

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tion of the polymers of a benzyl alcohol-chloroform solution certainly. The concentration of carboxyl groups gives a clue for the extent of the thermally and catalytically influenced decomposition; - Actiouen during the polycondensation reaction and therefore allows conclusions to be drawn about the thermal stability of the polyester melt during further processing. In practice, verden in polyethylene terephthalate, which is used for Manufacture of fibers is suitable and ^, values around 0.75 has carboxyl group concentrations around or below 40 meq / kg.

The thermal stability was further tested directly in such a manner that a sample under nitrogen by means of the above-mentioned Differentialcalorimeters "it at a rate of 16 ° C / heated min to 300 ⁰ C, 15 min at this temperature maintained at 130 ⁰ C cooled and this cycle was repeated three times. Occurs in the last cycle after passing through the melting peaks up to a temperature of 320 ⁰ C is no deviation of the Kurveaverlaufg from the base line to (the deviation can be on decomposition reactions close), so a sufficient thermal stability is ensured, as indicated by Vergleiehsrersnche with various polyester granules of known Processing properties was determined. The color of the molten polyesters was compared visually with aqueous solutions of the dye Pontamine Catechu 3 G (Du Pont). The comparison solutions were designated as follows:

0 - dist. water

1 »0.00025 g of dye in 100 μl of water

2 »double the amount of dye as with 1 -

3 ■ three times the amount of dye as with 1 etc.

Example 1:.

58.2 g dimethyl terephthalate, 46.5 f ethylene glycol, 0.003 l Zinc acetate, 0.0086 g butyl titanate and 0.018 g magnesium hypophosphite were under nitrogen as well as with stirring

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after 1 hour at 180 to 200 ⁰ C uageesterert, after which 20 ml of methanol were removed. Thereafter, 0.015 g of triphenylphosphite were added and the temperature was increased in the course of a further level to 270 ° C., at the same time the pressure was reduced to 0.5 torr during this time. This was followed by a further four hours at 0.1 torr and 270 ⁰ C gerühri The resulting product the following characteristics exhibited:

30 meq / kg BEGi 1.0 Jt

Color: 2

Thermal stability: good.

Wait for the comparison test to be carried out as above, but that fiagnesiuahypophosfthit omitted, the result was a stark yellow-brown discolored product, the color of which reached a value of 15, χ -. - ■ '

2:

Ea was as in Example 1, the Magnesiuabypephoephit was replaced by 0.006 g calcium hypophosphite. The product obtained had the following key figures:

[COOHJ: 24 eral / kg

DEG: 0.8 %

- Color: '2

Theraic stability: good. Example 3:

The procedure was as in Example 1, except that the magnesium hypaphosphite was replaced by 0.006 g of manganese hypophosphite. The product obtained in this way had the following characteristics:

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I COOH): 27 meq / kg

DEG: - 0.9 'Jf Color: 4

Thermal stability: good. Example 4:

The procedure was as in Example 1, except that the magnesium hypophosphite was replaced by 0.006 g of potassium hypophosphite. The product obtained had the following key figures:

7red

C COOHJ: 31 meq / kg

DEG: 1.0 Jf

Color: 3

Thermal stability: good. Example 5;

The procedure was as in Example 1, with both the zinc acetate and the magnusium hypophosphite through a total of 0.008 g of zinc hypophosphite was replaced. The transesterification time was also two hours. The «or received pro dukt had the following key figures:

red
[COOHj: 30 eval / kg

DEG: 1.0 fo

Color: 4

Thermal stability: good. Example 6:

The procedure was as in Example 1, except that the magnesium hypophosphite by 0.012 g of dimethyl hydrocyisophthalate was replaced. The product obtained in this way had the following key figures: * ■ "

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0.985

I COOH /: 25 myal / kg

DEG: not determined

Color: k

Thermal stability: good.

Example 7:

The procedure was as in Example 1, except that the magnesium hypophosphite by 0.010 g of dimethyl 2,5-dihydroxyterephthalate was replaced. The product obtained in this way had the following key figures:

7red \ 0.990

[COOH /; 30 meq / kg

DEG: not determined

Color: 3

Thermal stability: good.

The experiment was carried out with 0.006 or 0.015 g of 2,5-dihydroxyisophthalic acid dimethyl ester repeatedly, the color values were 5 and 2 »

Example 8:

The procedure was as in Example 1, except that the magnesium hypophosphite has been replaced by phthalimide in the following amounts:

a) 0.006 g; b) 0.009 g; c) 0.012 g.

The products obtained in this way had the following key figures:

a) b) c) 1.105 1.180 1.150 26 30 28 DEG; 0.8 1.0 0.8

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a)

b)

Colour: 4th 3 5 Thermal stability: Well Well Well Example 9: «

The procedure was as in Example 1, except that the magnesium hypophosphite has been replaced by carbazole in the following amounts:

a) 0.006 g;

b) 0 _s 009 g;

c) Q; 012 g.

The products obtained in this way had the following key figures:

a)

b)

) ^r

2red ^: 1.104 1,099 1,078: CcOObJ: 24 30th 28 DEG: 0.5 0.8 0.6 λ Colour: 3 5> ■ ■■. 5 Thermal stability: Well Well Well.

In the experiments mentioned, the reaction time was kept for 4 hours at 270 ^° C. and a vacuum below 0.5 Torr, because the discoloration caused by the titanium becomes more noticeable the longer the reaction time lasts. However, since the aim of the invention is to eliminate the discoloration caused by titanium catalysts regardless of the equipment available in each case, the extended reaction times also take into account the most unfavorable conditions to be expected in practice. , ·

Example 8 a) was then repeated and the time during which the temperature was 270 ^° C. and the vacuum was below 0.5 Torr was reduced from 4 hours to 3 hours. The product obtained afterwards had a color of 1-2, while the / 7 value was 0.980, that is still considerably higher than the value that comes into consideration for the production of fibers, and that at

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approx. 0.75.

The experiment was then repeated in such a way that the amount of butyl titanate used was reduced to 0.15 g and the final stage of the polycondensation reaction described in more detail above was again extended to four hours. The product thus obtained also had a color of 1-2, while the y value was determined to be 0.77.

Although only butyl titanate in the examples given was used, are Titanverbiriduagea, such as alkyl and Aryl titanates and their partial hydrolysis products, i. the polymeric titanates, titanium salts of carboxylic acids, titanium halides and others, insofar as they are soluble in the reaction mixture, can be used in the same way, since in all cases from such compounds in view of the reaction table Under the prevailing conditions, the corresponding hydroxyalkyl titanates are formed first, which at the time at which the folykondensationsresktion begins, should be practically alone. Accordingly, the scope of the invention is limited Process does not apply to the use of butyl titanate as a catalytically active compound but also extends to all of the prior art soluble titanium compounds because of their catalytic effectiveness as well as their property of discoloring the polymers produced with them, as a first approximation about net inen.

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Claims (1)

- 12 claim Process for the preparation of polyalkylene terephthalates from dialkyl terephthalates and glycols in the presence of an eich known transesterification catalysts, optionally stabilizers, as well as titanium-containing polycondensation catalysts which are also known per se and which are soluble in the reaction mixture, characterized by a further addition of catalytic amounts of hypophosphites, hydroxyisophthalic acids, Hydroxyterephthalic acids or their esters, dicarboximides or carbazole. Pat.-Dept. Dr.Ve/Br October 18, 1966 909884/1709