NO832044L - PROCEDURE FOR MANUFACTURING AROMATIC 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 oxybenzoyl polyesters from aromatic dicarboxylic acids, bisphenols 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 from an economic point of view. 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 have impaired properties.

A lot of work has therefore been put into the development of a method which eliminates the above-mentioned disadvantages,

and which provides a polyester molding material from which objects with a neat and uniform appearance and properties can be obtained.

According to the present invention, a polymer can be produced which has an extremely low degree of coloring and an excellent heat stability which has not hitherto been achievable by means of the conventional mass polymerization.

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

Another object of the invention is to provide an improved method for the economic production of aromatic polyesters.

Other purposes and further application possibilities of the present invention will be apparent from the following.

It has been found that a method which overcomes the problems encountered when carrying out the previously known methods and which provides polyester resins whose use is not accompanied by the aforementioned disadvantages is provided by the improvement which includes the addition of a phosphite during production of the resin, and especially to the prepolymer melt before advancing the final product to the desired degree of polymerization.

The fully aromatic polyesters whose production the present invention relates to consist of combinations of repeating units with one or more of the following formulas: where x is 0, S,

, NH, or SO 2 and n is 0 or 1, and

the sum of the whole numbers p + q + r + s + t + uide groups present is from approx. 3 to 800.

Combinations of the above listed units include

compound of the carbonyl group in the formulas I, II, IV and

V with the oxy group in formulas I, III, IV and VI. In the most general combination, all units of the above formulas may be present in a single copolymer. The simplest embodiment would be homopolymers with units I or IV. Other combinations include mixtures

of units II and III, II and VI, III and V, V and VI, and I

and IV. The location of the functional groups is preferably in the para(1,4) positions. They can also be located in the meta(1,3) position to each other. With respect to the naphthalene moiety, the most desired positions for the functional groups are 1,4; 1.5 and 2.6. Such groups can also be in the meta position to each other.

The symbols p, q, r, s, t and u are whole numbers and indicate

the number of groups present in the polymer. The sum (p+q+r+s+t+u) can vary from 3 to 800, and,

when applicable, the ratio of q/r, q/u, t/r, t/u,

q + t, q + t and t vary from approx. 10/11 to approx.

r r + u r + u

11/10, the most preferred ratio being 10/10.

Examples of materials from which the groups of formula I

can be obtained are p-hydroxybenzoic acid, phenyl-p-hydroxybenzoate, p-acetoxybenzoic acid and isobutyl-p-acetoxybenzoate. Those from which the group of formula II may be derived include terephthalic acid, isoterephthalic acid, diphenyl terephthalate, diethyl isophthalate, methyl ethyl terephthalate and the isobutyl half-ester of terephthalic acid. Among the compounds from which the group with formula III results are p,p<1->bisphenol; p,p<1->oxybisphenol; 4,4<1->dihydroxy-benzophenone; resorcinol and hydroquinone. Investigation will

show which of these materials are also suitable for providing the groups with formulas VI - VIII.

Examples of monomers represented by formula IV are 6-hydroxy-1-naphthoic acid; 5-acetoxy-1-naphthoic acid and phenyl-5-hydroxy-1-naphthoate. Monomers of formula V include 1,4-naphthalenedicarboxylic acid; 1,5-naphthalenedicarboxylic acid

and 2,6-naphthalenedicarboxylic acid. The diphenyl esters or dicarbonyl chlorides of these acids can also be used. Examples of monomers representative of formula VI are 1,4-dihydroxynaphthalene; 2,6-diacetoxynaphthalene and 1,5-dihydroxynaphthalene.

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

The oxybenzoyl polyesters which were useful in the present invention are generally the repeating units of formula

WE:

where p is an integer from approx. 3 to approx. 600.

A preferred class of oxybenzoyl polyesters are those of formula VII:

wherein R"<*>" is selected from the group consisting of benzoyl, lower-alkanoyl or preferably hydrogen; R 2 is hydrogen, benzyl, lower alkyl or preferably phenyl; and p is an integer from 3 to 600, and preferably 20 - 200. These values for p correspond to a molecular weight of approx. 1000 -72000, and preferably 3500 - 25000. The synthesis of these polyesters is described in detail in US patent application no. 619,577 regarding "Polyesters based on hydroxybenzoic acids", whose description is hereby included. Reference is made to this application in US patent no. 3,668,300.

Another preferred class of oxybenzoyl polyesters are repeating unit copolyesters of the formulas VII,

VIII and IX:

wherein X is -O or -SC^-; m is 0 or 1; n is 0 or 1; q:r=10:15 to 15:10; p:q=1:100 to 100:1; p + q + r = 3 - 600 and preferably 20-200. The carbonyl groups in the unit of formula I or III are attached to the oxy groups in a unit of formula I or IV; the oxy groups in the unit of formula I or IV are bound to the carbonyl groups in the unit of formula I or III.

The preferred copolyesters are those of repeating units of formula X:

The synthesis of these polyesters is described in detail in

US patent no. 3,637,595 which is incorporated herein by reference.

The bulk condensation of aromatic polyesters is described

in the patent literature and generally involves an alkanoylation step in which a suitable dicarboxylic acid, hydroxybenzoic acid and diol is reacted with an acid anhydride, a prepolymerization step in which the reaction product from the first step is polycondensed to form a prepolymer. and the prepolymer is then heated to form a polycondensate with the desired degree of polymerization.

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

The phosphite compound can be an organic or inorganic phosphite. However, the use of an organic phosphite, such as an alkyl phosphite, an aryl phosphite, an alkyl aryl phosphite or a di- or polyphosphite, is preferred. More particularly, the following phosphites can be used:

Diisooctyl phosphite

Distearyl phosphite (solid)

Triisodecyl phosphite

Triisooctyl phosphite

Trilauryl Phosphite

Diphenyl phosphite

Trisnonylphenyl phosphite

Triphenyl phosphite

Diphenylidodecyl phosphite

Diphenylisooctyl phosphite

Phenyldiisodecyl phosphite

Diisodecyl pentaerythritol diphosphite

Tetraphenyl dipropylene glycol diphosphite

Poly(dipropylene glycol) phenyl phosphite

Dilauryl phosphite

Ethylhexyldiphenyl phosphite

Phenyl neopentyl glycol phosphite

Diisooctyl octylphenyl phosphite

Distearyl pentaerythritol diphosphite (flake form).

While the addition of the phosphite can take place at any stage of the process, it has been found to be particularly effective and to provide significantly superior properties in the articles cast from the oxybenzoyl polyester resin, if the phosphite compound is added shortly before, e.g. about. 5 minutes before, the prepolymer is transferred to the next step, which is by dumping in an insulated container in which an intermediate step in the polymerization takes place, before the resin thus advanced is transferred to suitable equipment, e.g.

a rotating heating drum, for advancement to the desired polymerization stage.

In another method for determining the optimum point for adding the phosphite material, it has been found that the phosphite material can most advantageously be added at approx. 95% conversion as indicated by distillate yield of acetic acid.

The phosphite material can be added as solid flakes or as

a liquid melt at a temperature above the melting point of the phosphite material. It is also possible to add the phosphite material in a solution in acetic anhydride when the incorporation is effected at a lower temperature. Addition in molten form is generally preferred.

The amount of added phosphite depends on the purity of the monomer. The purer the monomer, the less phosphite needs to be added to achieve the desired result. The purity is related to the phenol and the amount of phenol used, and to the amount of ash formed. Where a higher ash content occurs, increased amounts of phosphite will be required to achieve

optimal results, which requires a balancing in the achievement of the optimal levels for the achievement of optimal results in the achievement of the desired color and the desired level of thermal stability.

Generally, the phosphite material has been added over a range from approx. 0.05 parts per 100 to approx. 0.5 parts per 100.

However, the preferred range is from approx. 0.1 to approx. 0.25 parts per 100, with 0.125 parts per 100 represents the optimal proportion.

The invention is illustrated by the following examples. The following example represents a control in which no additive is present.

Example 1.

Control.

A charge of 207.3 g (1.096 mol) 4,4'-dihydroxybiphenyl (Sample 98.5%), 307.6 g (2.23 mol) 4-hydroxybenzoic acid,

185 g (1.11 mol) of terephthalic acid and 498 g (4.88 mol, 10% excess) of acetic anhydride were refluxed with stirring for 3 hours. The contents of the reactor were then fed with nitrogen and the mixture heated at an average rate of 30°C/hour to 295°C and held for h hour at this

the temperature. At this point the reaction mixture was dumped into a pyrex dish lined with aluminum foil and the resulting prepolymer ground and passed through a 20 mesh

term.

in

The above prepolymer (5.464 g) was introduced into

a tube furnace that was already preheated to 229°C. With a

weak hydrogen flow, the temperature of the material was raised to 360°C within 4 hours and held at 360°C for 1 hour.

After cooling, the material was weighed and the weight loss from the prepolymer to the feed polymer was found to be 3.6%.

This polymer showed a peak endotherm at 417°C as determined by differential scanning calorimetry (DSC) under nitrogen.

The resin showed a total weight loss in air of 3.6% when it

was heated at 400°C for 3 hours, using thermogravimetric analysis (TGA). The rate of weight loss at 400°C in air was 1.2%/hour after the first hour.

The following example illustrates the effect of adding

0. 28 pph distearyl pentaerythritol diphosphite to the prepolymer melt prior to dumping.

Example 2.

The supply and procedure were the same as in example 1, with the exception that at a point 5 minutes before the prepolymer dumping, 1.75 g (0.28 pph based on theoretical polymer yield) of distearyl pentaerythritol diphosphite was added to the prepolymer melt.

After grinding and sieving, this prepolymer was also advanced under a stream of nitrogen by the method described in example 1. This time it was found that the weight loss from 6.184 g of the prepolymer was 5.17% from prepolymer to advanced polymer. The peak endotherm by differential scanning calorimetry was found to be at 410°C. The weight loss for this resin as determined by TGA was only 0.7% after 3 hours at 400°C in air. The rate of weight loss after

the first hour was only 0.2%/hour compared to 1.2%/

l hour as with the control sample.

The following examples compare the effectiveness

for adding distearyl pentaerythritol diphosphite to the prepolymer melt with the addition of distearyl pentaerythritol diphosphite to the prepolymer in a rotating drum prior to feed. Example 3 is a control in which no additive was added.

Example 3.

A mixture of 301.1 g (2.18 mol) 4-hydroxybenzoic acid, 181.08 g (1.09 mol) terephthalic acid, 203.98 g (1.09 mol, sample 99.5%) 4,4'- dihydroxybiphenyl and 525 g (5.15 mol, 18% excess) of acetic anhydride, was refluxed for 4 hours. Under a stream of nitrogen, the mixture was heated at a rate of 40°C/hour until 97.2% of the total theoretical distillate (including excess anhydride) was obtained.

At this point the temperature in the reactor had reached 340°C. The contents of the reactor were dumped into an aluminum pan,

allowed to cool and ground in a Wiley mill through a 1 mm sieve. A yield of 603 g was obtained.

This prepolymer was then advanced with and without the addition of distearyl pentaerythritol diphosphite in a rotating drum.

Ute n dist earyl pentaerythritol diphosphite.

in

A total of 200 g of the prepolymer was placed in the rotating drum and heated at a rate of 44°C/hour

under a nitrogen flow in a quantity of 0.17 std.m 3/hour

and a rotation of 15 rpm. When the temperature of the resin-i

then had reached 354°C, the material was held at 354°C for 1 hour and then rapidly cooled. Yield of carried forward

polymer was 96%. The resin had a peak endotherm at 420°C and showed a weight loss in air of 0.84% at 400°C after 3 hours (TGA). The weight loss rate was 0.18%/hour after the first hour.

Distearyl pentaerythritol diphosphite added to the drum.

A total of 200 g of prepolymer and 0.5 g (0.250 pph) of distearyl pentaerythritol diphosphite were placed in a rotating i

drum and performed as indicated above. Yield of advanced polymer from prepolymer was 96.5%. This advanced resin had a peak endotherm at 421°C (differential scanning

calorimetry). The total weight loss at 400°C in air after

3 hours was 0.87%, with a weight loss rate of 0.14%/hour after the first hour.

The following example illustrates the effect of adding 0.125 pph distearyl pentaerythritol diphosphite to the prepolymer melt at 95% conversion.

Example 4.

The supply and procedure were the same as in example 3 with the exception that when the total distillate yield

was 95% of theoretical, including excess acetic anhydride), 0.81g (0.125 pph based on theoretical polymer weight) of distearyl pentaerythritol diphosphite was added. (The temperature of the forge was 330°C at this point). The mixture was further heated to 45°C over 15 minutes and the reactor contents dumped into an aluminum pan. A total distillate yield of 588 g (97.4% of theoretical including excess acetic anhydride) was obtained and the prepolymer yield was 590 g.

After painting and sifting the prepolymer as in the example

3, 200 g was added to a rotating drum and brought to 354°C and held for 1 hour (as in Example 3). The resulting advanced polymer had a reversible first peak endotherm at 421°C (differential scanning calorimetry).

Total weight loss in air after 3 hours at 400°C (TGA) was 0.75% with a weight loss rate of 0.08%/hour after the

l

the first hour. This represents a 2.25% reduction in weight loss rate relative to the unstabilized polymer and a 1.75% reduction relative to that for resin made with twice as much distearyl pentaerythritol diphosphite added to the drum.

in

Example 5.

The supply and procedure were the same as in example 4 for each of the additives, and the additive levels shown in table

In below. The differences between the additives and the additive levels were the only variation from the procedure in Example 4. The additives were introduced at the point at which the total

the distillate yield was 95% of the theoretical (incl

excess acetic anhydride). The relative weight loss determined is shown in Table I.

In addition to the optimum level of phosphite for weight loss rate, too much or too little phosphite additive can affect color and homogeneity. The examples given above are based on high purity, low ash monomers.<2>Based on phosphorus content to obtain equivalent pph value for distearyl pentaerythritol diphosphite.<3>Relative weight loss rate of lead resin compared to lead resin using 0.125 distearyl pentaerythritol diphosphite, giving a 1.0 weight loss rate as standard.

Claims (6)

1. Process for the production of an aromatic polyester, comprising heat condensation of the precursors to form a prepolymer and then advancing the prepolymer to form a polymer with the required degree of polymerization, characterized in that in the course of the reaction prior to the completion of the polymerization, a phosphite compound. 2. Method according to claim 1, characterized in that the polyester contains repeating units selected from the group consisting of one or more of the formulas: 0 where x is 0, S, - C■-, NH, or SO,, and n is 0 or 1, and the sum of the whole numbers p + q + r + s + t + u in the units present is from approx. 3 to approx. 800.. 3. Method according to claim 2, k a r a k ■terized in that the phosphite compound is an organic phosphite compound. 4. Method according to claim 2, characterized in that the phosphite compound is distearyl pentaerythritol diphosphite. 5. Method according to claim 2, characterized in that the addition of the phosphite compound takes place just before transfer of the prepolymer to the polymerization step. 6. Method according to claim 2, characterized in that the addition of the phosphite compound takes place at the point of 95% conversion.