NO164420B - PROCEDURE FOR THE MANUFACTURE OF MELTABLE FULLY AROMATIC OXYBENZOYL POLYESTERS. - Google Patents

Description

The present invention relates to an improved method for the production of copolyesters. More particularly, the invention relates to a method for producing melt-processable fully aromatic oxybenzoyl polyesters from aromatic dicarboxylic acids, dihydroxyphenols and p-hydroxybenzoic acid compounds as starting materials.

It is known that such polyester resins can be produced by various polymerization processes including suspension polymerization and mass polymerization. Of these, the mass polymerization process is possibly the most desirable process in terms of economics. However, since the aromatic polyesters have a high melting point compared to aliphatic polyesters, such as polyethylene terephthalate, a higher temperature is required to maintain the aromatic polyesters in their molten state. Consequently, the polymers are often colored and degraded in terms of properties.

Furthermore, difficulties have arisen when it comes to achieving uniformity for the molding properties of the resin from material lot to material lot. Variations in casting conditions are obviously undesirable in commercial operations, and can result in operational inefficiencies and unacceptable differences in the cast articles.

Great efforts have therefore been devoted to the development of a method which eliminates the above-mentioned disadvantages, and which provides a polyester molding material, from which objects with an appealing and uniform appearance and properties can be obtained.

According to the present invention, a polymer can be produced in a uniform manner which has a very low degree of discolouration and an excellent heat stability which has hitherto not been possible to achieve by means of the conventional mass polymerisation.

It is an object of the present invention to provide a method for the production of fully aromatic polyesters which have a very low degree of discoloration and an excellent heat stability.

Another object of the invention is to provide an improved method for the uniform, economic production of aromatic polyesters of acceptable quality, as well as to provide polyesters which have reproducible melting and crystallization temperatures.

Other purposes and application possibilities for the invention will be apparent from the following.

It has been found that a method which overcomes the problems encountered in carrying out the previously known methods, and which provides polyester resins whose use is not accompanied by the aforementioned disadvantages, is achieved by the improvement involving the addition of an inorganic salt, namely an alkaline earth metal salt or an alkali metal salt and preferably potassium sulfate, during the production of the resin and, in particular, to the prepolymer melt before the final product is given the desired degree of polymerization.

According to the present invention, there is thus provided a method for the production of melt-processable fully aromatic oxybenzoyl polyester from aromatic dicarboxylic acids, dihydroxyphenols, and p-hydroxy-benzoic acid compounds as starting materials, which have reproducible melting and crystallization temperatures, and which comprise repeating units with the following formulas:

where X is -o- or -SO 2 -; m is 0 or 1; n is 0 or 1;

q:r is from 10:15 5il 15:10; p:q is from 1:100 to 100:1;

p+q+r is from 3 to 600; the carbonyl groups in the part of formula VII or VIII are attached to the oxy groups in the part of formula VII or IX; and the oxy groups in the part with formula VII or IX are bound to the carbonyl groups in the part with formula VII or VIII, and this method is characterized by heat condensation mass polymerizing completely aromatic polyester precursors to form a prepolymer and then advancing the prepolymer to form a completely aromatic polyester, whereby said precursors are heat condensed in the presence of an inorganic alkali or alkaline earth metal salt in an amount of 25-500 ppm, which is effective in making the melting and crystallization temperatures of the polyester reproducible with respect to melt processing.

The location of the functional groups is preferably in the para (1,4) positions. They can also be placed in the meta (1,3) position in relation to each other. With regard to the naphtha part, the most desired positions of the functional groups are 1,4; 1.5 and 2.6. Such groups can also be in the meta position in relation to each other.

Examples of materials from which the groups or moieties of formula VII can be obtained are p-hydroxybenzoic acid, phenyl-p-hydroxybenzoate, p-acetoxybenzoic acid and isobutyl p-acetoxybenzoate. Those from which the part of formula VIII may be derived include terephthalic acid, isophthalic acid, diphenyl terephthalate, diethyl isophthalate, methyl ethyl terephthalate and the isobutyl half-ester of terephthalic acid. Among the compounds from which the portion of formula IX results are p,p<1->bisphenol; p,p'-oxybisphenol; 4,4'-dihydroxybenzophenone; resorcinol and hydroquinone.

Particularly preferred for use in carrying out the present invention are plastic materials based on oxybenzoyl polyesters.

The preferred copolyesters are those with repeating units of the formula:

The synthesis of these polyesters is described in detail in US patent 3,637,595.

The mass condensation of aromatic polyesters is described in the patent literature and broadly involves an alkanoylation step, in which a suitable dicarboxylic acid, hydroxy benzoic acid and diol are reacted with an acid anhydride, a pre-polymerisation step in the reaction product from the first step, polycondensation to form a prepolymer, and the prepolymer is then heated to produce a polycondensate of the desired degree of polymerization.

The polyesters that are useful in the present invention can also be chemically modified using various methods such as by including in the polyester monofunctional reactants, such as benzoic acid or tri- or higher functional reactants such as trimesic acid, or cyanuric chloride. The benzene rings in these polyesters are preferably unsubstituted, but may be substituted with non-disturbing substituents, examples of which include is .halogen such as chlorine or bromine, lower alkoxy such as methoxy and lower alkyl such as methyl.

The following salts are used: calcium acetate, calcium sulfate, magnesium acetate, magnesium terephthalate, potassium acetate, potassium chloride, potassium phosphate, sodium acetate, sodium sulfate, potassium bisulfate, and potassium sulfate.

While the addition of the salt at any stage of the process may be appropriate, it has been found to be particularly effective, and to provide superior properties in the articles cast from the oxybenzoyl polyester resin, if the salt is added with the monomer feed.

The salt can be added as a solid or as a solution at a temperature above the salt's melting point. It is also possible to add the salt in a solution when the incorporation is carried out at a lower temperature.

Generally, the salt has been added over a range from 25.0 ppm to 500 ppm.

The exact mechanisms by which the processability of the polyester and the appearance and properties of articles molded from the polyester are significantly improved by the addition of the defined salts are not fully understood. However, it has been observed that the retention of peak heights in repeated endothermic transitions and the achievement of uniform exothermic transitions is significantly and materially improved when the defined salts are used in the processing of the polyesters.

The aromatic oxybenzoyl polyester polymers are known to exhibit an endothermic transition corresponding to a melting of the polyester. Upon cooling, an exothermic transition or crystallization occurs. When a strong exotherm is observed, the transitions are described as reversible. Observations and the results described in the tables below demonstrate that the addition of a salt, such as potassium sulfate, has greatly improved the reversibility of the peaks detected in differential scanning calorimeters or

DSC.

When determining the peak height retention, the endotherm for the first and second heating cycles is recorded on the same scale. The distances from the baseline to the maximum points are determined, and the height of the first cycle peak is divided by the height of the second cycle peak (x 100). This value is expressed as "percent retention".

When the endotherms are measured for the aromatic oxybenzoyl polyesters which do not contain a salt, it is found that the beginning of the transition in the other cycle peaks is difficult to define, and the width of the heating curve makes it difficult to determine the peak. The change in temperature between the beginning of the transition and the occurrence of the maximum temperature is thus of a gradual nature, producing a heating curve that resembles a gentle slope or rounded hilltop. Such a peak is referred to here and especially in the examples as a broad or diffuse peak.

The other cycle peaks obtained in the cases where a salt has been incorporated in the preparation of the aromatic polyesters according to the present invention are sharp and clear with well-defined temperature curves, and where the temperatures for the beginning of the transition and for the peak maximum are easy to determine.

The invention is illustrated by the following examples, where examples 1 and 3 represent control examples which are not in accordance with the present invention.

Example 1 (control example)

A reaction vessel was charged with 121.6 kg of 4,4'-dihydroxybiphenyl, 149.6 kg of p-hydroxybenzoic acid, 108.0 kg of terephthalic acid and 365.6 kg of acetic anhydride. It was charged with nitrogen and heated under agitation to reflux, which was continued for a minimum of three hours. Distillation without reflux was then started and continued for approx. five and a half hours while the temperature of the reaction mixture was increased to 315°C. At this point 0.32 kg of distearylpentaerythritol diphosphite was added and after ten minutes the thick slurry (93.3% conversion based on distillate yield) was poured into an insulated stainless steel vessel and allowed to cool under a nitrogen atmosphere. It was then removed and ground (size < 1.2 mm, 80% < 0.5 mm) Yield of prepolymer after painting is 90%.

The prepolymer was advanced by tumbling under nitrogen in a rotary oven. The prepolymer is heated from ambient temperature to 365°C at a rate of 23°C/hour and immediately cooled. The resulting polymer is obtained as . a free-flowing powder.

Example 2

The procedure of Example 1 was repeated exactly using the same materials and procedures with the one exception of adding 57 g of potassium sulfate to the reaction vessel along with the addition of monomers.

DSC (differential scanning calorimeter) endothermic and

-exothermic peaks for the first and second heating cycles were determined and are listed below in Table 1.

Example 3 (control example)

A reaction vessel was charged with 204.0 g (1.095 mol) of 4,4'-dihydroxybiphenyl, 301.1 g (2.18 mol) of p-hydroxybenzoic acid, 181.1 g (1.09 mol) of terephthalic acid and 560.6 g ( 5.158 moles) of acetic anhydride, was added under a nitrogen atmosphere and heated with stirring to reflux, which was continued for a minimum of three hours. Distillation without reflux was then started and continued for about five and a half hours, while the temperature of the reaction mixture was increased to 315°C. At this point 0.76 g of distearylpentaerythritol diphosphite was added and after ten minutes the thick slurry (93.3% conversion based on distillate yield) was poured into a stainless steel beaker lined with aluminum foil and held at 300°C. The prepolymer was kept under a nitrogen atmosphere at 300°C for twenty hours, then removed, allowed to cool and ground (size < 1.2 mm, 80% < 0.5 mm). Yield of prepolymer after painting is 90%.

The prepolymer was advanced by tumbling under nitrogen in an aluminum drum which is rotated in an oven. The prepolymer is heated from 204 to 354°C and held at the higher temperature for one hour. Upon cooling, the resulting polymer is obtained as a free-flowing powder.

Example 4

The procedure of Example 1 was repeated in exactly the same manner using the same materials and procedures with the one exception involving the addition of 0.067 g of potassium sulfate to the reaction vessel along with the addition of monomers.

The DSC (differential scanning calorimeter) endothermic peaks for the first and second heating cycles were determined and are listed below, along with percent retention for that endothermic peak height, in Table II.

Similar comparisons were made for several other polyesters, the control being prepared in accordance with the method in Example 1, and the potassium sulphate-containing polyester being prepared according to the method in Example 2. The results are set out in Table III below.

As demonstrated, the salt-containing polyester showed a significantly improved percent retention of endothermic peak height.

Comparisons are provided in Table IV between controls prepared according to Example 1 and salt-containing polyesters prepared according to Example 2. The same control was used in Examples 10, 12 and 18, but is listed separately to provide a more immediate comparison with the polyesters of Examples 9, 11, and 17.

Similar significant improvements in percent retention compared to controls having broad or diffuse other cyclic peaks were obtained when the following salts were used instead of those specifically listed in Table III: calcium sulfate, magnesium terephthalate, potassium acetate, potassium phosphate, and potassium bisulfate.

Example 19

A reaction vessel was charged with 156.3 kg of 4,4'-dihydroxybiphenyl, 233.2 kg of p-hydroxybenzoic acid, 140.2 kg of terephthalic acid, 406.4 kg of acetic anhydride and 57.0 g of potassium sulfate. This was blanketed with nitrogen and heated with stirring to reflux, which was continued for a minimum of three hours. Distillation without reflux was then started and continued for approx. five and a half hours while the temperature of the reaction mixture was raised to 315°C. At this point, 416.0 g of distearylpentaerythritol diphosphate was added and after ten minutes the thick slurry (93.3% conversion based on distillate yield) was poured into an insulated stainless steel tray, blanketed with nitrogen and allowed to cool. It was then removed and ground (size < 1.2 mm, 80% < 0.5 mm).

The prepolymer was advanced by tumbling under nitrogen in a rotary oven. The prepolymer was heated from ambient temperature to 365°C and immediately cooled. The resulting polymer is obtained as a free-flowing powder. The polymer is characterized by first and second endothermic peaks of 416 and 418°C and by first and second exothermic points of 377 and 379°C.

Example 2 0

A series of 65 runs were made whereby polyesters were prepared according to the procedure of Example 19 using 93 ppm potassium sulfate based on the final polymer. The mean average exotherm onset for the first cycle was determined to be 377.8°C and the mean average exotherm onset for the second cycle was determined to be 378.4°C. The proximity of these points is very significant in relation to consistency and reproducibility in injection molding operations. The products obtained by injection molding the polyesters were of high quality.

In the above tables, the amount of salt used is based on ppm in the finished polymer.

The term "advancement" used here is to be understood as polymerization in the solid state.

Claims (10)

1. Process for the production of melt-processable fully aromatic oxybenzoyl polyester from aromatic dicarboxylic acids, dihydroxyphenols, and p-hydroxybenzoic acid compounds as starting materials, which have reproducible melting and crystallization temperatures, and which comprise repeating units of the following formulas: where X is -0- or -SC^-; m is 0 or 1; n is 0 or 1; q:r is from 10:15 to 15:10; p:q is from 1:100 to 100:1; p+q+r is from 3 to 600; the carbonyl groups in the part of formula VII or VIII are attached to the oxy groups in the part of formula VII or IX; and the oxy groups in the part with formula VII or IX are bound to the carbonyl groups in the part with formula VII or VIII, characterized in that fully aromatic polyester precursors are mass polymerized by heat condensation to form a prepolymer and then the prepolymer is advanced to form a fully aromatic polyester, whereby said precursors is heat condensed in the presence of an inorganic alkali or alkaline earth metal salt in an amount of 25-500 ppm, which is effective in making the melting and crystallization temperatures of the polyester reproducible w.t. melting processing. 2. Method according to claim 1, characterized in that the metal salt is added in an amount of 0.0025-0.05% by weight of the produced polyester. 3. Method according to claim 2, characterized in that a salt of potassium or magnesium is used as inorganic metal salt. 4. Method according to claim 3, characterized in that a sulfate or chloride is used as an inorganic metal salt. 5. Method according to claim 4, characterized in that calcium sulfate is used as inorganic metal salt. 6. Method according to claim 1, characterized in that precursors are used which comprise an aromatic bicarboxylic acid, a hydroxycarboxylic acid, and an aromatic diol. 7. Method according to claim 6, characterized in that precursors comprising terephthalic acid, p-hydroxybenzoic acid and dihydroxybiphenyl are used. 8. Method according to claim 7, characterized in that the precursors are used in a molar ratio of approx. 1:2:1, respectively. 9. Process according to claim 6, characterized in that the precursors are condensed by alkanoylation with an acid anhydride. 10. Method according to claim 1, characterized in that the polyester has a melting temperature of at least 378 C.