DD290552A7 - PROCESS FOR PREPARING LIQUID CRYSTALLINE COPOLYESTER FROM AROMATIC DICARBONE ACIDS, AROMATIC DIOL DIACETATE AND P-ACETOXYBENZOENA ACID - Google Patents

Abstract

The invention relates to a process for the preparation of liquid-crystalline copolyesters from p-acetoxybenzoic acid, aromatic diol diacetate and aromatic dicarboxylic acids, in which aromatic rings containing diisocyanates are added to the reaction melt. As a result, a copolyester having high mechanical characteristics is obtained after a shorter reaction time, whereby a time-consuming and energy-consuming solid-phase condensation can be dispensed with. {Liquid-crystalline aromatic copolyesters; p-acetoxybenzoic acid; aromatic diol diacetate; aromatic dicarboxylic acids; diisocyanates; solid state postcondensation}

Description

Field of application of the invention

The invention relates to a process for the preparation of liquid-crystalline copolyesters, in which the p-acetoxybenzoic acid, the aromatic dicarboxylic acid and the diol diacetate aromatic are mixed together, melted and condensed together. The resulting copolyesters show excellent flow properties and have high mechanical properties.

Characteristic of the known state of the art

Processes involving the synthesis of liquid-crystalline, thermotropic polyesters by transesterification of polyalkylene terephthalates in the presence of carboxylic acid and acetoxy-functionalized aromatics are disclosed in US Pat. Nos. 3,778,410, 3,804,805, 4,075,262, JP-A-60-186525, 60-186526, 58-84821 and US Pat in EP-PS 173752 described. In a first step, the polyalkylene terephthalates are acidolytically cleaved and, in a second step, elimination of molecular weight takes place by removal and elimination of acetic acid. The poly (ethylene terephthalate-cooxybenzoates) prepared by transesterification of polyethylene terephthalate with p-acetoxybenzoic acid have very good mechanical properties. Instead of p-acetoxybenzoic acid, an equimolar mixture of substituted hydroquinone diacetates and terephthalic acid can be used to react the polyethylene terephthalate (US Pat. No. 4,075,262).

Furthermore, ancestors for the synthesis of thermotropic, liquid-crystalline copolyesters are known in which aromatic dihydroxy compounds and hydroxycarboxylic acids or their ester derivatives are reacted in the melt. The ester derivatives of the dihydroxy compounds or hydroxycarboxylic acids are preferably acetoxy compounds which are used directly for the synthesis or are formed only in situ by the addition of acetic anhydride during the reaction. The reaction temperature is generally increased gradually, initially under nitrogen at atmospheric pressure, the majority of the liberated acetic acid is distilled off. In a subsequent vacuum stage is carried out at pressures of about Torr and smaller an increase in molecular weight. Liquid-crystalline, thermotropic copolyesters generally have a very good processing behavior and excellent mechanical properties. Wholly aromatic copolyester types

also have good heat resistance. The mechanical properties strongly depend on the molecular weight of the liquid-crystalline copolyesters. In order to reach high molecular weights, generally high temperatures must be accepted (up to 350 ° C, 5 hours and longer). Under such reaction conditions unwanted side reactions and thermal. Damage associated with deterioration of mechanical properties occur. Although the reaction time can be reduced by adding suitable catalysts, it is still too long, especially with high-melting compounds.

In addition, catalyst additions for the preparation of thermotropic, highly aromatic copolyesters at the necessary high reaction temperatures also favor polymer degradation reactions (Polym. Eng.26 [1986], 13). In thermally relatively unstable compounds, such as the poly (ethylene terephthalate-co-oxybenzoat) en, this is particularly problematic, since the synthesis temperature is in the range of temperatures for the thermal degradation of ethylene terephthalate polymers (polyester fibers, Akademie-Verlag Berlin 1975 p f.). Thus, in the case of poly (ethylene terephthalate-co-oxybenzoate) s r), _inh . Values of not more than 0.99 dl / g are achieved, which according to Acta Polymerica 38 (1987) 10,585 / 6 corresponds to an average molecular weight of 23,700. In order to suppress thermal damage, reference is made in a number of patents on the possibility of solid phase condensation (US-PS 4287332, DE-OS 3443219, DE-OS 2025971, US-PS 2600376). Here, low molecular weight condensation products are subjected to a heat treatment (annealing). The temperatures used are below the melting point of the copolyester, so that thermal damage is largely avoided. However, the annealing times are generally very long and can last for several days in extreme cases. In addition, facilities for tempering of fibers and moldings are expensive in terms of apparatus and energy. It is also known to link linear polyesters with diisocyanates for the preparation of polyurethanes or unsaturated polyester resins (Plaste and Kautschuk 15 [1968], 347). This is the formation of urethane bonds, which are no longer stable at the synthesis temperatures used for highly aromatic, liquid-crystalline copolyesters. The thermal decomposition temperatures for urethanes of aromatic isocyanates and R-OH are for different R at: R = aliphatic 200 ⁰ C, R = aromatic 130 ° C (Polyurethane, Fachbuchverlag Leipzig 1st edition 1973, p.24). According to Houben-Weyl "Methods of Organic Chemistry", Bd. E 20 III, 2201 was to assume that the possible formation of Carbonsäureamidbindungon, from the diisocyanates and the carboxy groups of the copolyester, the melt and flow properties of the copolyester by increasing the melting point or negatively affected by infusibility or partial infusibility.

According to Polym. Closely. Sci. 26 (1986), 13 the liquid crystalline structure of polyesters strongly depends on the planarity of the chain molecules. The introduction of carboxylic acid amide bonds can lead to a disruption of the thermotropic, liquid-crystalline properties. Amide bonds form strong hydrogen bonds, which generally increase the melting point to above the decomposition temperature (Houben-Weyl, Methoden der Organischen Chemie, Vol. E, 20, 111, 2201).

The introduction of such bonds should consequently lead to a deterioration in the homogeneity of the copolyester and consequently to a lowering of the orientability, which results in a deterioration of the mechanical properties.

Object of the invention

The aim of the invention is to develop an improved process for the preparation of liquid-crystalline copolyesters, in which, while substantially shortening the reaction times, identical or higher molecular weights of the copolyesters are achieved. Another object of the invention is to lower the reaction temperature necessary to achieve high molecular weights. The. Appearance damaging side reactions should be avoided as far as possible. The necessity of a costly solid phase postcondensation should be circumvented as far as possible or be severely limited in time.

Explanation of the essence of the invention The invention is based on the object, more suitable starting materials for polymer construction of liquid-crystalline copolyester

use.

The object is achieved in that in the synthesis of aromatic copolyester Melt polycondensation after a precondensation of 15 to 90 minutes at temperatures of 260 to 300 ° C the Addition of 0.5 to 5 molar proportions in%, based on the total number of moles, diisocyanates containing aromatic rings

be added with stirring and subsequent stirring. Diisocyanates of the following chemical are advantageous

Structures added

NCO · NCO

R'-fOj-R ² NCO '

wherein R ', R ^{2 is} a Η-atom, an alkyl radical with C) to C ₆ or a Cl atom, or

where X is a single bond or a radical of the formula -CHj-; -CH ₂ -CH ₂ -; -CH (CH ₃ H -C (CH ₃ I ₂ -; -O-; -S-; -SO ₂ - '), or

NCO

OCN

In a further embodiment of the invention, the reaction melt is diisocyanate-free of compounds of the chemical formula

R ³ O

R ³ O

R ^J OH

R ³ O

R ³ O

EAR ³ OCN

where R ¹ , R ^{2 is} a Η-atom, an alkyl radical having C ₁ to C ₆ or a Cl atom, X is a single bond or a radical of the formula -CH ₂ -; -CH ₂ -CH ₂ -; -CH (CH ₃ H -CH (C ₂ H ₆ H -C (CH ₃ I ₂ -; -O-; -S-; -SO ₂ - and R ^{3 is} a radical of the formula

wherein R ^{4 is} a radical having 1 to 4 carbon atoms, ι jgesetzt.

It proves to be advantageous, the addition of diisocyanates and / or diisocyanate-releasing compounds in the temperature range from 275 ° C to 285 ⁰ C, in the pressure range of 106 to 6.66 10 ~ ³ kPa, preferably at 101 kPa, while 0.1 to 30 Minutes, preferably 1 to 5 minutes, with stirring.

The diisocyanates and / or diisocyanate-releasing compounds may be added in solid or molten form or dissolved in an inert solvent.

After the addition of the diisocyanates and / or diisocyanate-releasing compounds it is still advantageous to use 15 to 90 minutes, preferably 10 to 60 minutes, at temperatures of 26O ⁰ C to 360 ° C, preferably 275 ⁰ C to 320 ° C, and in pressure range of 106 to 6.66 x 10 ^-3 kPa, 133 to 6.66 Pa, stirred.

The addition of diisocyanates and / or diisocyanate-releasing compounds can also be carried out in an extruder, preferably with degassing, in the above-mentioned temperature interval by a metering device at residence times of the polymer in the extruder of 1 to 30 minutes, preferably 5 to 10 minutes. It proves to be advantageous, the

To degas polymers after the addition of the above compounds in a vacuum of 13300 to 133 Pa. It was surprising that improve the liquid-crystalline properties, the flow behavior and the mechanical properties, such as tensile and flexural strength, tensile and flexural modulus, the polymers by the addition of diisocyanates and / or diisocyanate releasing compounds, since it is known that by introducing atypical structures , such as amide bonds, in thermotropic,

Liquid-crystalline polyesters whose liquid crystalline behavior is disturbed. Such structural defects can lead to the deterioration of the flowability of the polymers and to the reduction of the mechanical properties of molded parts and threads of such polymers.

In contrast, the aromatic copolyesters prepared with the addition of diisocyanates and / or diisocyanate-releasing compounds have excellent flow properties and mechanical properties, as well as inherent viscosities of 0.6

to 1.2 dl · g " ¹ 1 n, _inh = -) with shorter reaction times and lower reaction temperatures than the copolyesters with

comparable inherent viscosities prepared by known methods (US Pat. No. 4,153,779, US Pat. No. 4,654,412, EP Pat. No. 170,935, EP Pat. No. 169675).

The viscosities are in a mixture of phenol / tetrachloroethane (1,1,2,2) = 50/50 volume percentages at 25 ° C and

a concentration of 0.5g polymer / 100ml.

In this process, the addition of transesterification catalysts is omitted, but the use of catalysts is

in principle possible.

Exemplary embodiments The invention will be explained in more detail below with reference to several exemplary embodiments. example 1 This example describes the preparation of a high molecular weight, fully aromatic copolyester from 46 molar parts in%. Oxybenzoateinheiten, 27 molar proportions in% isophthalic acid and 27 molar proportions in% hydroquinone diacetate with the addition of

2.5 molar parts in% methylene-p.p'-diphenyl diisocyanate.

In a 3-necked flask equipped with vacuum-tight stirrer, N ₂ -EmIaB, distillation head with template and vacuum connection

become

p-acetoxybenzoic acid: 30 g = 0.161 mol,

Hydroquinone diacetate: 18.96 g ^ 0.0967 mol, Isophthalic acid: 16.25 g & 0.0967 mol

filled and mixed. Subsequently, the flask is evacuated and then filled with nitrogen. The monomers are then melted by immersing the flask in a metal bath at a temperature of 230 ° C and reacted with stirring and constant N j-stream. The temperature is gradually increased within 10 minutes to 285 ° J. After 45 minutes, most of the resulting acetic acid is distilled off. At this time, 2.19 g of A 0.00876 mole corresponding to 2.5 molar proportions in%, based on the total number of moles used, methylene-p, p'-diisocyanate (MDI) added to the melt with stirring, which is immediately highly viscous. After 0.5 hours condensation time at 300 ⁰ C and under N ₂ stream is condensed for 0.5 hours under a vacuum of 66.5 kPa and a temperature of 32O ⁰ C. The resulting liquid crystalline copolyester has an inherent viscosity of 0.71 dl g ~ ¹ and a melting point of 285 ° C. Its color is light gray. The molded article of the copolyester described has a tensile strength of 180 MPa, θμο flexural strength of 160MPa, a tensile modulus of 8GPa and a flexural modulus of 9GPa.

The molecular weight and the mechanical properties of the molded articles can be further increased by a solid-phase postcondensation 20K below the softening temperature.

Comparative Control 1 In Comparative Example 1, the preparation of a liquid-crystalline copolyester from 46 molar proportions in % Oxybenzoateinheiten,

27 molar proportions in% isophthalic acid and 27 molar proportions in% hydroquinone diacetate, for the synthesis of which no isocyanate-containing and / or -relissetzenden compounds are used.

In the apparatus described in Example 1 are the same amounts of monomers as in Example 1

filled, after evacuation and filling of the apparatus with nitrogen immersed in a metal bath at a temperature of 23O ⁰ C and brought under stirring and constant nitrogen flow to the condensation. After stepwise heating to 285 ⁰ C within 10 minutes, the main part of the resulting acetic acid is distilled off after 45 minutes. After this time, a vacuum of 66.5 kPa is applied, the temperature is raised to 35O ⁰ C and the condensation is continued with stirring.

The resulting copolyester has a comparable inherent only after 3 hours of condensation in vacuo at 35O ⁰ C. Viscosity (0.68 dl g ~ ') as in Example 1 and a melting point of 280 ⁰ C. Its color is brown, indicating thermal Decomposition indicates. Moldings of the described copolyester have a tensile strength of 96 MPa ₁ Bending strength of 123MPa, a tensile modulus of 6GPa and a flexural modulus of 5GPa. Example 2 This example describes the synthesis of a liquid-crystalline copolyester from 50 molar parts in% oxybenzoate units,

25 molar parts in% terephthalic acid and 25 molar parts in% Resorcindiacetat.

In the condensation apparatus described in Example 1 are

p-acetoxybenzoic acid: 30.00 g ^ 0.161 mol,

Resorcinol diacetate: 15.80 g & 0.0806 mol, Terephthalic acid: 13.54 g & 0.0806 mol

given and mixed. The flask is evacuated and then filled with nitrogen. The flask is then immersed in the metal bath at a temperature of 23O ⁰ C, wherein the monomials melt and the condensation begins with stirring. The

Temperature is gradually increased within 10 minutes. After 45 minutes, the main part of the resulting acetic acid

distilled off.

Now 2.013g & 0.00805 mol corresponding to 2.5 molar proportions in%, based on the used Total mol, methylene-p.p'-diphenyl diisocyanate (MDI) added with stirring. The reaction is added for 0.5 hours

300 ⁰ C with stirring and nitrogen flow continued. After this time, a vacuum of 66.5 kPa is applied and further condensed for a further 0.5 hours under these conditions.

The resulting liquid crystalline copolyester has an inherent viscosity of 0,83dl · g ~ ', and a melting point of 245 ⁰ C. Moldings of the resulting liquid-crystalline copolyester have a tensile strength of 171 MPa, a flexural strength

150IyIPa, a tensile modulus of 23GPa and a flexural modulus of 21 GPa.

Verglelchsbolsplel 2 Comparative Example 2 describes the preparation of a liquid-crystalline copolyester from 50 molar parts in% Oxybenzoate units, 25 molar parts in ° /. Terephthalic acid and 25 molar parts in% Resorcindiacetat, but without the addition of

isocyanate-containing and / or releasing compounds.

In the apparatus described in Example 1 to the same amounts of monomers as in Embodiment 2

filled, after evacuation and filling of the apparatus with nitrogen immersed in a metal bath at a temperature of 23O ⁰ C and brought under stirring and constant nitrogen flow to the condensation. After stepwise heating to 285 ⁰ C within 10 minutes, the main part of the resulting acetic acid is distilled off after 45 minutes. After this time, a vacuum of 66.5 kPa is applied, the temperature is increased to 33O ⁰ C and the condensation is continued with stirring.

The resulting copolyester is dark brown due to thermal decomposition. He has after 3 hours of condensation in vacuo at 33O ⁰ C, a comparable inherent Viskositä (0,58dl g " ¹ ) as in Embodiment 2 and a melting point of 205 ° C. The low melting point makes the implementation of a Solid phase postcondensation impossible. Moldings of the copolyester have a tensile strength of 87 MPa, a Flexural strength of 191 MPa, a tensile modulus of 20GPa, and a flexural modulus of 22.8GPa. Example 3 This example describes the synthesis of a liquid-crystalline copolyester from 50 molar parts in% oxybenzoate units,

25 molar parts in% terephthalic acid and 25 molar parts in% Resorcindiacetat.

In the condensation apparatus described in Example 1 are

p-acetoxybenzoic acid: 3O ₁ OOgA 0.161 mol,

Resorcinol diacetate: 15.80 g & 0.0806 mol, Terephthalic acid: 13.45 g. 0.0806 mol

given and mixed. The flask is evacuated and then filled with nitrogen. The piston is now in the metal bath of a

Submerged at 230 ° C, the monomers melt and the condensation begins with stirring. The Temperature is gradually increased within 10 minutes. After 45 minutes, the main part of the resulting acetic acid

distilled off.

Now 3.53 g of A 0.00805 mol corresponding to 2.5 molar proportions in%, based on the used Total mol, methylene-p, p'-diphenyldiphenylurethan added with stirring. The reaction is added for 0.5 hours

300 ⁰ C with stirring and nitrogen flow continued. After this time, a vacuum of 66.5 kPa is applied and further condensed for a further 0.5 hours under these conditions.

The resulting liquid crystalline copolyester has an inherent viscosity of 0,79dl · g ^"1 and a melting point of 25O ⁰ C. Example 4 This example describes the synthesis of a liquid-crystalline copolyester of 50 molar proportions in% oxybenzoate units ,

25 molar parts in% terephthalic acid and 25 molar parts in% Resorcindiacetat.

In the condensation apparatus described in Example 1 are

p-acetoxybenzoic acid: 30.00 g = 0.161 mol,

Resorcinol Diacetate: 15.80 gm, 0.0806 mol, Terephthalic acid: 13.54 g. 0.0806 mole

given and mixed. The flask is evacuated and then filled with nitrogen. Dar piston is now in the metal bath of a

Submerged at 230 ° C, the monomers melt and the condensation begins with stirring. The Temperature is gradually increased within 10 minutes β. After 45 minutes, the main part of the resulting acetic acid

distilled off.

Now 1.4087 g & 0.00805 mol correspond to the melt.> End 2.5 mol% in%, based on the used Total moles, 2,4-toluene diisocyanate (TDI)

NCO

added with stirring. The reaction is continued for 0.5 hours at 300 ⁰ C with stirring and nitrogen flow. After this time, a vacuum of 66.5 kPa is applied and further condensed for 0.5 hours under diosen constrictions. The resulting liquid-crystalline copolyester has an inherent viscosity of 1.05 dl e "'and a melting point of 33O ⁰ C.

Example 5 This example describes the synthesis of a liquid crystalline copolyester from SO mole fractions in% oxybenzoate inhoites,

25 molar parts in% terephthalic acid and 25 molar parts in% Resorcindiacetat.

In the condensation apparatus described in Example 1 are

p-acetoxybenzoic acid: 30.00 g, 0.161 mol,

Resorcinol diacetate: 15.80 g = 0.0806 mol, Terephthalic acid: 13.54 g & 0.0806 mol

given and mixed. The flask is evacuated and then filled with nitrogen. The piston is now in the metal bath of a

Temperature of 23O ⁰ C immersed, the monomers melt and the condensation begins with stirring. The Temperature is gradually increased within 10 minutes. After 45 minutes, the main part of the resulting acetic acid

distilled off.

Now, to the melt 1.69 g = 0.00805 mol corresponding to 2.5 molar proportions in%, based on the used Total number, 2,6-naphthalene diisocyanate un ^(he added with stirring The reaction is further 0.5 hours at 300 ^0C. Under Stirring and nitrogen flow continued. After this time, a vacuum of 66.5 kPa is applied and a further 5 hours under

these conditions further condensed.

The resulting liquid crystalline copolyester has an inherent viscosity of 0.88 dl · g ^-1 and a melting point of Moldings of the resulting liquid-crystalline copolyester have a tensile strength of 169 MPa, a flexural strength

of 138MPa, a tensile modulus of 22GPa and a flexural modulus of 20GPa.

Claims (10)

claims: 1. A process for the preparation of liquid crystalline copolyester from 0 to 70 molar proportions in% p-acetoxybenzoic acid with 35 to 15 mole percent aromatic diol diacetate and 35 to 15 mole% aromatic dicarboxylic acids, in which the p-acetoxybenzoic acid, the aromatic dicarboxylic acid and the aromatic diol diacetate mixed together, melted and condensed with each other, characterized in that a reaction melt containing diisocyanates aromatic rings at temperatures of 260 ⁰ C to 360 ⁰ C are added with stirring and subsequent stirring. 2. The method according to claim 1, characterized in that aromatic rings containing diisocyanates is a chemical structure NCO · NCO NCO
wherein R ¹ , R ^{2 is} a Η-atom, an alkyl radical with C, to C ₅ or a Cl atom, or OCN - <O> - * - / 5V-NCO where X is a single bond or a radical of the formula -CH ₂ -; -CHi-CH ₂ -; -CH (CH ₃ ) -; C (CH ₃ ) ₂ -; -; -S-; -SO ₂ - means, or NCO NCO OCN be added. 3. The method according to claim 1 and 2, characterized in that the diisocyanate-releasing compounds of the chemical structure R ³ OI R ³ O R ³ O C = O I NH NH I C = O I R ₃ O 0 H R ³ O - CN -2- 2SO 552 wherein R ¹ , R ^{2 is} a Η-atom, an alkyl radical having Ci to C ₆ or a Cl atom, X is a single bond or a radical of the formula -CH ₂ -; -CH ₂ -CH ₂ -; -CH (CH ₃ ) -; -CH (C ₂ H ₆ ) -; C (CH ₃ J ₂ -; -O-; -S-; -SO ₂ - and R ^{3 is} a radical of the formula ι 7 ⁵ ^ ι Cl NO ₂ wherein R ^{4 is} a radical having 1 to 4 carbon atoms, are used. 4. The method according to claim 1 to 3, characterized in that the diisocyanates and / or the diisocyanate-forming compounds in 0.5 to 5 molar proportions in%, based on the total number of moles, are added after a precondensation phase to the reaction melt. 6. The method according to claim 1 to 4, characterized in that the addition of diisocyanates and / or diisocyanate-releasing compounds to the reaction melt takes place after 15 to 90 minutes, preferably 10 to 60 minutes under constant nitrogen flow and stirring. 6. The method according to claim 1 to 5, characterized in that the diisocyanates and / or the diisocyanate-releasing Vorbindungen in solid or molten form or dissolved in an inert solvent are added to the reaction melt. 7. The method according to claim 1 to 6, characterized in that the addition of diisocyanates and / or diisocyanate-releasing compounds at temperatures of 275 ⁰ C to 285 ⁰ C and in the pressure range of 106 to 6.66 · 10 " ³ kPa, preferably at 101 kPa, within 0.1 to 30 minutes, preferably for 1 to 5 minutes. 8. The method according to claim 1 to 7, characterized in that after the addition of diisocyanates and / or diisocyanate-releasing compounds for 1 to 60 minutes, preferably 10 to 30 minutes, at temperatures of 260 to 36O ⁰ C, preferably 275 ⁰ C to 320 ° C, and in the pressure range of 106 to 6.66 x 10 ^-3 kPa, preferably under reduced pressure of 133 to 6.66 Pa, is stirred. 9. The method according to claim 1 to 8, characterized in that subsequent to the synthesis, a solid phase postcondensation, preferably 20 K below the softening temperature, is performed. 10. The method according to claim 1 to 9, characterized in that diisocyanates and / or diisocyanate-releasing compounds to the reaction melt in an extruder, preferably with degassing, by a metering device for 1 to 30 minutes, preferably 5 to 10 minutes residence time in the extruder, followed by degassing be added in a vacuum of 13300 to 133 Pa.