GB1576628A

GB1576628A - Manufacture of unsaturated polyesters

Info

Publication number: GB1576628A
Application number: GB2293177A
Authority: GB
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 1976-06-01
Filing date: 1977-05-31
Publication date: 1980-10-08
Also published as: DE2624509A1; NL7705817A; IT1078856B; BE855289A; FR2353587A1

Description

(54) MANUFACTURE OF UNSATURATED POLYESTERS (71) We, BASF AKTIENGESELL SHAFT, a German Joint Stock Company of 6700 Ludwigshafen, Federal Republic of Germany, do hereby declare the invention, for which we pray that a Patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following Statement: The present invention relates to a process for the manufacture of an unsaturated polyester by a 2-stage esterification process from a mixture of carboxylic acids and one or more alcohols.

In general, unsaturated polyesters are manufactured by polycondensing one or more ethylenically unsaturated dicarboxylic acids and/or their derivatives, in the presence or absence of one or more other saturated and/or unsaturated monocarboxylic acids and/or dicarboxylic acids or their derivatives, with about an equivalent amount of one or more polyalcohols, preferably glycols, by heating at from about 1600C to 220"C whilst passing inert gas through the melt.

To avoid premature gelling of unsaturated polyesters which are manufactured in the presence of dicarboxylic acids which esterify relatively slowly, it has furthermore been proposed to carry out the esterification in 2 stages. In this method, only the saturated dicarboxylic acid(s) are first esterified so that no premature polymerization can occur even if the esterification time is extremely long.

Only when the esterification of these acids has progressed sufficiently are the unsaturated dicarboxylic acid(s) added and the condensation completed, usually at from 100"C to 1500C.

It is a disadvantage of such processes that when simultaneously esterifying a mixture of saturated and unsaturated dicarboxylic acids with one or more polyols, the double bond content of the polyester is reduced by the irreversible addition reaction of the polyol with the double bond, so that when manufacturing unsaturated polyester resins, products of lower reactivity result and/or the unsaturated dicarboxylic acid(s) and/or polycondensates may polymerize and gel whilst the polycondensation is taking place. On the other hand, it is a disadvantage of the 2-stage process that within the usually short period of esterification at below 1500C adequate isomerization of maleic acid to the transform does not occur, so that once again, after dissolving the unsaturated polyester in styrene, unsaturated polyester resins which have a low reactivity and give low mechanical properties are obtained.

The present invention seeks to provide a process for the manufacture, with high space-time yields, of unsaturated polyesters which do not suffer from the above disadvantages and which, after dissolving in styrene, give unsaturated polyester resins which are very reactive and, after curing, exhibit very good mechanical properties, especially great hardness and a high heat distortion point.

According to the present invention there is provided a process for the manufacture of an unsaturated polyester by polycondensing at least one dicarboxylic acid which is not olefinically unsaturated and/or at least one derivative thereof, together with at least one ethylenically unsaturated dicarboxylic acid and/or at least one derivative thereof, with or without one or more saturated and/or unsaturated monocarboxylic acids and/or higher polycarboxylic acids or their derivatives, with at least one polyhydric alcohol, with or without one or more monohydric alcohols, by a 2-stage process, wherein the non-(olefinically unsaturated) carboxylic acid(s) and/or derivatives thereof and at least a portion of the polyhydric alcohol(s), with or without monohydric alcohol(s), are esterified to at least 60% conversion of the carboxylic groups, in a first condensation stage, thereafter the ethylenically unsatu rated carboxylic acid(s) and/or derivative(s) thereof and any further polyhydric and/or monohydric alcohol(s) are incorporated into the ester mixture and condensation is continued in a second condensation stage at from 1600C to 2500C under a pressure of from 6 to 100 bars, without removal of water, at most until the equilibrium conversion is reached, and the condensation is completed under pressures of from 5 to 0.01 bar when equilibrium has been reached and with removal of water.

The process according to the invention has the advantage that by carrying out the esterification without removal of water at most until the equilibrium conversion is reached, at from 1600C to 2500C and under pressures of from 6 to 100 bars, unsaturated polyesters can be manufactured with substantially greater space-time yields. Furthermore, the olefinic double bonds are reversibly blocked by addition reaction of water at the stated temperatures and pressures, so that the irreversible formation of adducts with alcohols, which results in a decrease in the double bond content and a lowering of the reactivity of the unsaturated polyester resin, is decisively diminished. It is a further advantage that the high proton concentration not only results in more rapid esterification but also greatly accelerates the isomerization of maleic acid to the more reactive trans-form (fumaric acid), so that this again additionally increases the reactivity of the unsaturated polyester resins.

The 2-stage esterification process ensures that, of the carboxyl end groups in the unsaturated polyesters (i.e. ignoring hydroxyl end groups) almost all are in the form of unsaturated acid half-ester units, e.g.

maleic acid half-ester and/or fumaric acid half-ester units, which are substantially more resistant to hydrolysis than half-ester units from acids lacking olefinic unsaturation, for example phthalic acid half-esters.

We have found, surprisingly, that unsaturated polyester resins which are obtained by dissolving an unsaturated polyester obtained by the process of the invention in styrene have an excellent shelf life at room temperature, so that additional temperature control to reduce the phthalic anhydride content and stabilize the polyester resins is not necessary.

This good shelf life was unexpected in view of the high double bond contents, which are from 5 to 8% above those of standard commercial products, the high fumaric acid contents and the resulting high reactivity of the unsaturated polyester resins. In addition to the great ease of curing. the crosslinked polyester resins exhibit excellent mechanical properties, in particular great hardness and dimensional stability, and a high heat distortion point.

The conventional and customary starting materials for polyesters may be used to manufacture the unsaturated polyesters by the process according to the invention.

Examples of non(olefinically unsaturated) dicarboxylic acids and their derivatives are o-phthalic acid, isophthalic acid, tetrachlorophthalic acid, tetrabromophthalic acid, hexachloroendomethylenetetrahydrophthalic acid and the corresponding anhydrides, terephthalic acid, succinic acid, glutaric acid, adipic acid, sebacic acid and dimerized fatty acids. The use of the anhydrides of the substituted or unsubstituted phthalic acids, and especially of o-phthalic anhydride, is preferred. The non-(olefinically unsaturated) dicarboxylic acids or dicarboxylic acid derivatives, especially dicarboxylic acid anhydrides, may be polycondensed either as individual compounds or in the form of mixtures with one another. In addition to the non-(olefinically unsaturated) dicarboxylic acids, small amounts of monocarboxylic acids, eg. acetic acid, butyric acid, a-ethylhexanoic acid, oleic acid and stearic acid, or of higher polycarboxylic acids, eg.

trimellitic acid or pyromellitic acid, may also be employed.

Diols are particularly suitable polyhydric alcohols for the manufacture of unsaturated polyesters by the process according to the invention. Specific examples of diols are ethylene glycol, diethylene glycol, polyethylene glycol, 1,2-and 1,3-propylene glycol, 1,3- and 1,4-butanediol, neopentylglycol, dibromoneopentylglycol, 1,6hexanediol, 2,2-(4,4'-dihydroxy-diphenyl) -propane, 2,2-(4,4'-dihydroxy-dicyclohexyl) -propane, bis-ethoxydiphenylolpropane and 1,3-dimethylolcyclohexane. The use of 1,2and 1,3-propanediol is preferred. The above diols may, for their part, be used as individual compounds or as mixtures with one another or with monoalcohols and/or with higher polyalcohols of functionality greater than two. Examples of monoalcohols are n- and isobutanol, ethylhexanol, oleyl alcohol and, preferably, methanol and propanol. Examples of higher polyalcohols of functionality greater than two, which may be present, are glycerol, trimethylolethane, trimethylolpropane, 1,2,4-butanetriol and pentaerythritol.

Examples of ethylenically unsaturated dicarboxylic acids or their derivatives are maleic acid, fumaric acid, 1,2,3,6tetrahydrophthalic acid, 3,6-endomethylene - 1,2,3 ,6-tetrahydrophthalic acid, itaconic acid, citraconic acid, mesaconic acid, maleic anhydride and citraconic anhydride. The use of maleic anhydride is preferred.

In the manufacture of the unsaturated polyesters, the starting materials may be condensed in conventional ratios. However, unsaturated polyesters in which the non (olefinically unsaturated) dicarboxylic acids and diols are condensed in a molar ratio of from : 1.3to1 : preferably from :1.5 to N '. b. , with or without addition of polyhydric alcohols or mixtures of monohydric and polyhydric alcohols, with an amount of ethy lenically unsaturated dicarboxylic acid or dicarboxylic acid mixture or derivatives of the said acid, so that the molar ratio of non (olefinically unsaturated) dicarboxylic acids to ethylenically unsaturated dicarboxylic acids is from 10 :1 to 1:10, preferably from 3 : 1 to 1: 5, and the ratio of total carboxyl to total hydroxyl is from 1:1 to 1:1.1, prefer ably 1:1.05, are particularly suitable for the manufacture of unsaturated polyester resins which, in the cured state, have excellent mechanical properties.

To manufacture an unsaturated polyester by a process within the invention, the non (olefinically unsaturated) carboxylic acids and/or their derivatives and the polyhydric alcohols, with or without monohydric alcohols, may be esterified by a conventional method until the conversion of the carboxyl groups is at least 60%, preferably from 80 to virtually 100%, especially from 85 to 97%, in the 1st condensation stage, during which an inert gas, e.g. nitrogen, may or may not be passed through the mixture. The ethyleni cally unsaturated dicarboxylic acids and/or their derivatives, with or without additional polyhydric alcohols which may or may not contains monohydric alcohols, the alcohols being added in particular to correct the molar ratios, are then added to the ester mixture obtained above. The reaction mixture is then condensed, in the 2nd condensation stage, at from 1600C to 250"C, preferably from 1700C to 2400C, under a pressure of from 6 bars to 100 bars, preferably from 8 to 25 bars, without removal of water, at most until the equilibrium conversion is reached. This usually requires condensation times of from about 4 minutes to 3 hours, preferably from 6 minutes to 60 minutes. Whether the equilib rium conversion has been reached or not can be ascertained, for example, by determining the acid number of the reaction mixture or the water content of the melt; at equilibrium conversion, both parameters reach constant values. Not later than on reaching the equilibrium conversion, the reaction mixture is let down, preferably in stages, and the polycondensation is completed, whilst removing the water of condensation, usually at from 1600C to 2500C, preferably from 1700C to 240 C, under a pressure of from 5 to 0.01 bar, preferably from 1 to 0.2 bar, usually in from 20 minutes to 4 hours, pref erably in from 30 minutes to 2 hours.

In a special and preferred embodiment of the process according to the invention, the non-(olefinically unsaturated) carboxylic acids and/or their derivatives and the polyhydric alcohols, with or without monohydric alcohols, are, in the 1st condensation sM t; 4 at elevated temRera- tures under pressure, without removal of the water of condensation, not longer than until the equilibrium conversion is reached. The details of this procedure are as follows. The non-(olefinically unsaturated) dicarboxylic acid and, preferably, the total amount of polyhydric alcohols with or without mono hydric alcohols are mixed and esterified at from 1600C to 2600C, preferably from 1700C to 240"C, under pressures of from 6 to 100 bars, preferably 8 to 25 bars, not longer than until the equilibrium conversion is reached. The equilibrium conversion is usually reached within from 8 minutes to 4 hours, preferably from 10 to 90 minutes.

After reaching this conversion, the esterifica tion mixture is, here again, let down as described for the 2nd condensation stage, and condensation of the mixture is con tinued, with removal of the water of conden sation, at from 1600C to 260"C, preferably from 1800C to 2500C, under pressures of from 5 to 0.01 bar, preferably from 1 to 0.2 bar, until the conversion df the carboxyl groups is not less than 60%. In general, con densation times of from 30 minutes to 5 hours, preferably from 45 minutes to 2.5 hours, are required to reach the above con version of carboxyl groups.

The unsaturated polyesters can be man ufactured by the process of the invention either batchwise in a pressure kettle with stirrer, or, preferably, continuously. The continuous polycondensation may be carried out, for example, in a stirred kettle cascade or in a condensation apparatus which essen tially consists of a tubular reactor with an attached delay-time vessel. Appropriate condensation apparatus is described, for example, in German Patent 916,589 and German Laid-Open Application DOS 1,958,777.

The unsaturated polyesters manufactured by the process of the invention, which have only a very pale color, generally possess molecular weights of from 600 to 2,500 pre ferred products having molecular weights from 1,200 to 1,600, and acid numbers of from 15 to 100, preferred products being from 30 to 50.

The unsaturated polyesters can be dissol ved in, and copolymerized with, monomers in the conventional manner, examples of such monomers being unsubstituted or sub stituted styrenes, eg. styrene, tertiary butyls tyrene, a-methylstyrene, vinyltoluene and divinylbenzene, acrylates and/or methacry lates, eg. methyl methacrylate, butyl acry late, tert.-butyl acrylate and ethylhexyl acry late, and diallyl phthalate. Unsaturated polyester resins obtained in this way, which have a monomer content of from 50 to 75% by weight, based on total weight, may be used, for example, to produce paint films, coatings, buttons, corrugated sheets, adhesives and containers. The particular advantage of the process according to the invention is, inter alia, that, using conventional starting materials for the manufacture of unsaturated polyesters or unsaturated polyester resins, it is possible to manufacture, with improved spacetime yields, products which after dissolving in monomers have a high shelf life, a low adduct content, greater ease of curing and a correspondingly high crosslinking density, and which after curing give moldings having very good mechanical properties and a high heat distortion point.

In the Examples, parts and percentages are by weight.

EXAMPLE 1 148 parts of o-phthalic anhydride and 190 parts of 1,2- propylene glycol are condensed, in the 1st condensation stage, in a closed pressure vessel equipped with a stirrer, for 30 minutes at 210 C under a pressure of 10 bars. The reaction vessel is then let down, the water of condensation being removed at the same time. The reaction mixture, which has an acid number of about 110 and has therefore not reached the equilibrium conversion (which corresponds to an acid number of 95), is then condensed further at 240"C for from 50 to 60 minutes, whilst distilling off the water via a distillation column, until the acid number is < 10, i.e. the conversion is in excess of 97 % based on the carboxyl groups of the o-phthalic acid.

196 parts of maleic anhydride, 47 parts of 1,2-propylene glycol and 0.03 parts of hydroquinone are added to the resulting ester mixture, whilst stirring. The reaction mixture is then condensed in the 2nd condensation stage at 210 C under a pressure of 10 bars for 30 minutes, without removing water.

After this time (when the mixture is near the equilibrium conversion) the reaction vessel is let down and the condensation is completed at 210 C and 0.3 bar in 110 minutes, whilst distilling off the water of condensation. The resulting unsaturated polyester has an acid number of 50.

EXAMPLE 2 If the instructions of Example 1 are followed, but the condensation in the 2nd condensation stage is completed in from 140 to 150 minutes whilst distilling off the water of condensation. an unsaturated polyester having an acid number of from 40 to 45 is obtained.

EXAMPLE 3 If the instructions of Example 1 are followed, but the condensation in the 2nd condensation stage is carried out at 2300 C, the equilibrium conversion under a pressure of 15 bars is reached after only 15 minutes and after letting down the reaction vessel and removing the water of condensation an unsaturated polyester of acid number 50 is obtained after only 50 minutes.

COMPARATIVE EXAMPLE 148 parts of o-phthalic anhydride, 196 parts of maleic anhydride, 237 parts of 1,2propylene glycol and 0.03 part of hydroquinone are polycondensed at 2100C whilst stirring and distilling off the water. Under these reaction conditions, it requires more than 8.5 hours to obtain a relatively darkcolored unsaturated polyester having an acid number of 50. To reduce the free o-phthalic anhydride content, the unsaturated polyester subsequently had to be heated for 2 hours at 140"C.

In order to determine the shelf life of the unsaturated polyester resins obtained from the unsaturated polyesters manufactured according to the invention and from the polyester obtained in the Comparative Example, 65% strength solutions of the unsaturated polyesters in styrene, containing 0.06 % by weight of hydroquinone, were prepared. It was found that, in contrast to the Comparative Example, the polyester resins obtained from the polyesters manufactured according to the invention showed no sedimentation after 3 months' storage.

WHAT WE CLAIM IS: 1. A process for the manufacture of an unsaturated polyester by polycondensing at least one dicarboxylic acid which is not olefinically unsaturated and/or at least one derivative thereof, together with at least one ethylenically unsaturated dicarboxylic acid and/or at least one derivative thereof, with or without one or more saturated and/or unsaturated monocarboxylic acids and/or higher polycarboxylic acids or their derivatives, with at least one polyhydric alcohol, with or without one or more monohydric alcohols, by a 2-stage process, wherein the non-(olefinically unsaturated) carboxylic acid(s) and/or derivatives thereof and at least a portion of the polyhydric alcohol(s), with or without monohydric alcohol(s), are esterified to at least 60% conversion of the carboxyl groups in a first condensation stage, thereafter the ethylenically unsaturated carboxylic acid(s) and/or derivative(s) thereof and any further polyhydric and/or monohydric alcohol(s) are incorporated into the ester mixture and condensation is continued in a second condensation stage at from 1600C to 2500C under a pressure of from 6 to 100 bars, without removal of water, at most until the equilibrium conversion is reached, and the condensation is completed under pressures of from 5 to 0.01 bar when equilibrium has been reached and with removal of water.

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Claims

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by weight, based on total weight, may be used, for example, to produce paint films, coatings, buttons, corrugated sheets, adhesives and containers. The particular advantage of the process according to the invention is, inter alia, that, using conventional starting materials for the manufacture of unsaturated polyesters or unsaturated polyester resins, it is possible to manufacture, with improved spacetime yields, products which after dissolving in monomers have a high shelf life, a low adduct content, greater ease of curing and a correspondingly high crosslinking density, and which after curing give moldings having very good mechanical properties and a high heat distortion point.

In the Examples, parts and percentages are by weight.

EXAMPLE 1

148 parts of o-phthalic anhydride and 190 parts of 1,2- propylene glycol are condensed, in the 1st condensation stage, in a closed pressure vessel equipped with a stirrer, for 30 minutes at 210 C under a pressure of 10 bars. The reaction vessel is then let down, the water of condensation being removed at the same time. The reaction mixture, which has an acid number of about 110 and has therefore not reached the equilibrium conversion (which corresponds to an acid number of 95), is then condensed further at 240"C for from 50 to 60 minutes, whilst distilling off the water via a distillation column, until the acid number is < 10, i.e. the conversion is in excess of 97 % based on the carboxyl groups of the o-phthalic acid.

196 parts of maleic anhydride, 47 parts of 1,2-propylene glycol and 0.03 parts of hydroquinone are added to the resulting ester mixture, whilst stirring. The reaction mixture is then condensed in the 2nd condensation stage at 210 C under a pressure of 10 bars for 30 minutes, without removing water.

After this time (when the mixture is near the equilibrium conversion) the reaction vessel is let down and the condensation is completed at 210 C and 0.3 bar in 110 minutes, whilst distilling off the water of condensation. The resulting unsaturated polyester has an acid number of 50.

EXAMPLE 2 If the instructions of Example 1 are followed, but the condensation in the 2nd condensation stage is completed in from 140 to 150 minutes whilst distilling off the water of condensation. an unsaturated polyester having an acid number of from 40 to 45 is obtained.

EXAMPLE 3 If the instructions of Example 1 are followed, but the condensation in the 2nd condensation stage is carried out at 2300 C, the equilibrium conversion under a pressure of 15 bars is reached after only 15 minutes and after letting down the reaction vessel and removing the water of condensation an unsaturated polyester of acid number 50 is obtained after only 50 minutes.

COMPARATIVE EXAMPLE

148 parts of o-phthalic anhydride, 196 parts of maleic anhydride, 237 parts of 1,2propylene glycol and 0.03 part of hydroquinone are polycondensed at 2100C whilst stirring and distilling off the water. Under these reaction conditions, it requires more than 8.5 hours to obtain a relatively darkcolored unsaturated polyester having an acid number of 50. To reduce the free o-phthalic anhydride content, the unsaturated polyester subsequently had to be heated for 2 hours at 140"C.

In order to determine the shelf life of the unsaturated polyester resins obtained from the unsaturated polyesters manufactured according to the invention and from the polyester obtained in the Comparative Example, 65% strength solutions of the unsaturated polyesters in styrene, containing 0.06 % by weight of hydroquinone, were prepared. It was found that, in contrast to the Comparative Example, the polyester resins obtained from the polyesters manufactured according to the invention showed no sedimentation after 3 months' storage.

WHAT WE CLAIM IS: 1. A process for the manufacture of an unsaturated polyester by polycondensing at least one dicarboxylic acid which is not olefinically unsaturated and/or at least one derivative thereof, together with at least one ethylenically unsaturated dicarboxylic acid and/or at least one derivative thereof, with or without one or more saturated and/or unsaturated monocarboxylic acids and/or higher polycarboxylic acids or their derivatives, with at least one polyhydric alcohol, with or without one or more monohydric alcohols, by a 2-stage process, wherein the non-(olefinically unsaturated) carboxylic acid(s) and/or derivatives thereof and at least a portion of the polyhydric alcohol(s), with or without monohydric alcohol(s), are esterified to at least 60% conversion of the carboxyl groups in a first condensation stage, thereafter the ethylenically unsaturated carboxylic acid(s) and/or derivative(s) thereof and any further polyhydric and/or monohydric alcohol(s) are incorporated into the ester mixture and condensation is continued in a second condensation stage at from 1600C to 2500C under a pressure of from 6 to 100 bars, without removal of water, at most until the equilibrium conversion is reached, and the condensation is completed under pressures of from 5 to 0.01 bar when equilibrium has been reached and with removal of water.
2. A process as claimed in claim 1,

wherein, in the first condensation stage, the non- (olefinically unsaturated) carboxylic acid(s) and/or derivative(s) thereof and the polyhydric alcohol(s), with or without monohydric alcohol(s), are esterified at from 1600C to 2600C under a pressure of from 6 to 100 bars, without removal of water, not longer than until the equilibrium conversion is reached, and the mixture is then further condensed under pressures of from 5 to 0.01 bar until the conversion of the carboxyl groups is not less than 60%.
3. A process as claimed in claim 1 or 2, wherein the low-pressure condensation is carried out at from 1 bar to 0.2 bar.
4. A process as claimed in any of claims 1 to 3, wherein the polycondensation is carried out continuously.
5. A process as claimed in claim 4, wherein the polycondensation is carried out continuously in a stirred kettle cascade or a condensation apparatus which essentially consists of a tubular reactor and an attached delay-time vessel.
6. A process as claimed in any of claims 1 to 5, wherein phthalic acid, terephthalic acid, adipic acid, succinic acid, glutaric acid and/or sebacic acid is used to provide the non-(olefinically unsaturated) dicarboxylic acid(s).
7. A process as claimed in any of claims 1 to 6, wherein maleic acid, fumaric acid, 1,2,3,6-tetrahydrophthalic acid, 3,6 endomethylene-1,2,3,6 -tetrahydrophthalic acid, itaconic acid, citraconic acid and/or mesaconic acid is used to provide the ethylenically unsaturated dicarboxylic acid(s).
8. A process as claimed in any of claims 1 to 5, wherein carboxylic acid anhydrides are used as derivatives of the non-(olefinically unsaturated) and/or ethylenically unsaturated dicarboxylic acids for the polycondensation.
9. A process as claimed in claim 8, wherein phthalic anhydride, 1,2,3,6tetrahydrophthalic anhydride, 3,6endomethylene- 1,2,3,6 -tetrahydrophthalic anhydride and/or maleic anhydride are used as carboxylic acid anhydrides.
10. A process as claimed in any of claims 1 to 9, wherein ethylene glycol, 1,2- and 1,3-propylene glycol, 1,3-butanediol, 1,4butanediol, neopentylglycol and 1,6hexanediol are used as polyhydric alcohols.
11. A process for the manufacture of an unsaturated polyester carried out substantially as described in any of the foregoing Examples 1 to 3.
12. Unsaturated polyesters when manufactured by a process as claimed in any of claims 1 to 11.
13. Unsaturated polyester resins comprising a solution of an unsaturated polyester as claimed in claim 12 in styrene.
14. Products obtained by curing unsaturated polyester resins claimed in claim 13 or unsaturated polyester claimed in claim 12 and other monomers.