CA1205600A - Process for the production of ethylene copolymers - Google Patents

Abstract

Abstract of Disclosure A method for the production of certain ethylene copolymers which comprises saponifying a granular feedstock which includes a polymer of at least 50% ethylene, 2 to 50% of certain esters of C3 to C12 alkene carboxylic acids, 0 to 30% vinyl esters of certain aliphatic carboxylic acids having 1 to 6 carbon atoms, and up to 3% of C3 to C12 alkene carboxylic acids.
In particular, the improvement comprises maintaining the feedstock at a particle size range of 0.1 to 8.0 mm, and suspending it in 1 - 10 parts of a ketone to 1 part of the feedstock, the ketone being of the formula wherein R and R' are individually an alkyl radical having 1 to 6 carbon atoms, and carrying out the saponification at a temperature of 40° to 75°C in the presence of at least one alkaline saponifying agent. The resulting compounds are useful as adhesives and coating materials.

This Application claims the benefit of the priority of German Application P 30 46 144.0, filed December 6, 1980.

Description

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PROCESS FOR THE PRODUCTION OF ETHYLENE COPOLYMERS
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The present~ invention is directed ~o a method for the production of certain ethylene copolymers; more particularly, such copolymers containing at least 60% ethylene, 0 to 20%
5 esters of C3 to C12 alkene carboxylic acids with Cl to C8 primary alcohols, and 1 to 20% by weight of C3 to C12 alkene carboxylic acids~ It is also contemplated that minor amounts of additional conventional monomers, which are copolymerizable with ethylene, may be ~sed.

The production of copolymers containing alkene carboxylic acids is known. For example, mixtures of ethylene, alkene carboxylic acids, and additional monomers can be converted at high pressures and high temperatures by means of radical-forrning initiators (see e.g. DOS 24 00 978 and DOS 16 15; 69 685). However, there is a substantial drawback to the foregoing procedure. Specifically, the free alkene carboxylic acids are highly corrosive and will damage equipment wi~h which they come into cont3ct under the reaction conditions.
Moreover, the polymers obtained are highly discolored.

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In order to overcome this problem, other known methods have used esters of the alkene carboxylic acids as the monomers in the polyme~ization process, and subsequently split off the alcohol re~idue. In the case of esters of secondary and tertiary alcohols, this can be affected hydrolytically or pyrolytically. However, in the case of esters of primary alcohols, only hydrolytic splitting is possible.

The hydrolytic splitting takes place in solution and requires extremely long residence times. The product must, thereafter, be isolated by precipitationO This is very expensive and, as a result, the procedure is of minor importance.

It is, therefore, among the objects of the present invention to provide a process which will produce homogeneous, non cross-linked and non discolored ethylene copolymers containing alkene carboxylic acids.

It has been discovered, in accordance with the present invention, that ethylene copolymers containing more than 60% by ~:3;
weight of ethylene, 0 to 20% by weight of esters of C3 to C12 alkene carboxylic acids with Cl to C8 primary alcohols, and 1 to 20% by weight of C3 to C12 alkene carboxylic acids can be produced as hereinafter set forth.
Such copolymers may, if desired, also include minor amounts of additional conventional monomers which are copolymerizable with ethylene.

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The process of the present invention is carried out by polymerizing monomer mixtures comprising at least 50% by weight of ethylene, 2 to 50% by weight of esters of C3 to C12 alkene carboxylic acids with C1 to C8 primary alcohols, 0 to 30% by weight of vinyl esters of a saturated, monobasic, aliphatic carboxylic acid having 1 to 6 carbon atoms, and up to 3% by weight of C3 to C12 alkene carboxylic acids. Minor amounts of additional monomers which are copolymerizable with ethylene may also be included. The polymerization reaction may be advantage-ously carried out at pressures of 100 to 8,000 bars and temperatures of 110 to 350C, in the presence of catalytic amounts of radical-forming initiators to provide the feedstock of the present invention.

The feedstock is suspended in a ketone, in a ration of one part by weight of feedstock with a particle size of 0.1 to 8O0 mm, to 1 to 10 parts by wei~ht of the ketone. The preferable particle size is 1 to 5 mm and the ketones are of the formula RCR' wherein R and R' are individually a straight or branched chain alkyl radicals having 1 to 6 carbon atoms. The alkene carboxylic acid esters of primary alcohols contained in the polymer are saponified at temperatures of 40 to 75C in the presence of alkaline saponification a~ents. The granular structure is retained.

Saponi[ication agents which have been found useful in the present process include alkali metal hydroxides, such as sodium hydroxide ,~nd potassium hydroxide, and alkali metal methylates and ethylates, such as sodium ~ethylate and potassium methylate. These agents may ~e added to the polymer -uspension in solid ~orm, or as an alcoholic solution. There may be introduced all at oncè, in portions, or continuously.

Among the additional monomers copolymerizable with ethylene, which may also be contained in the polymers of the present inventionl are C3 to C8 alkenes, esters of C3 to C12 alkenecarboxylic acids with secondary or tertiary alcohols; vinyl and alkenyl esters; vinyl and alkenyl ethers;
vinyl and alkenyl alcohols; N-vinyl and N-alkenyl compounds such as N-vinylpyrrolidone, N-vinylcarbazole, N-vinylcaprolactam; acrylamide and methacrylamide;
acrylonitrile and methacrylonitrile; alkenyl halides such as vinyl fluoride and vinylidene fluoride; vinyl and alkenyl ke~ones; vinyl and alkenyl sulphones and sulphonates;
dicarbonates; acid anhydrides; and styreneO In the same manner 20 ; as ethylenically unsaturated compounds, other copolymerizable substances such as carbon monoxide and sulfur dioxide may also be incorporated by polymeriza~ion~

The preparation of the copolymers which are capable o~
being saponified in accordance with the present invention has been described in Ullmanns Encyclopadie der technischen Chemie, 3rd Edition, (1963), Vol. 14, p. 139. The process may be carried out in autoclaves or in tubular reactors. It is mos~

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desirahle that it be carried out continuously, with the unreacte-l monomer being recycled. The conversion takes place in the presence of catalytic amounts of radical-forming initiators, e~g. oxygen, in amounts of 2 to 250 mol ppm based upon the ethylene being polymerized. Peroxides such as tert.
butyl perbenzoate, dilauroyl peroxide, di-tert. butyl peroxide or azobutyric acid dinitri~e may be used in place of oxygen in amounts of 2 to 20~ mol ppm. It has been found advantageous to carry out the polymerization in the presence of moderators such as aliphatic alcohols and carbonyl compounds, satura~ed and unsaturated hydrocarbons or chlorinated hydrocarbons, and hydrogen. Since the foregoing process results in a par~icle ~ize range of 0.8 to 8.0 mmt no additional grinding processes are necessary.

An important feature of the present invention is the suspension of the starting granulate or feedstock in certain ketones. In particular, acetone, methyl ethyl ketone, and methyl isobutyl ketone are use~ul. These substances diffuse into the interior of the gra;ns and carry with them the ~ dissolved saponification agents. Normally; 1 to 10 parts by weight (preferably 2 to 6 parts by weight) of ketone are used per part by weight of copolymer. The ketones may be used as pure substances, or also as mixturesO It is important that the ketone swells - but does not dissolve - the copolymer feedstock at temperatures below the melting point range of the starting product. These temperatures are about S to 10C below the temperatures at which the melting process starts.

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The amount of saponification agent is not critical. It may be used in stoichiometric amounts based upon the alkene carboxylic acid esters being incorporated by polymerization.
It also may be used in ~reater~or less quantities. The degree of saponificat;on can be controlled depending upon the amount of catalyst used. When catalyst is used in excess, the alkene carboxylic acid esters are saponified almost quantitatively.
The use oF stoichiometric or sub-stoichiometric amounts of saponification agent results in reaction products which contain varying amounts of unsaponified alkene carboxylic acid esters.

The degree of saponification can also be influenced by controlling the residence time. This depends upon the operating temperature, granular size, and the amount of alkene carboxylic acid esters to be incorporated. It has been found that saponification time is generally 0.5 to 10 hours, especially 0.5 to 5 hours, and preferably 2 to 4 hours. It should be noted that the lower the operating temperature, the larger the particles, and the higher the proportion of alkene carboxylic acid esters, the longer the residence time required.

The saponification can be carried out very simply~ It is merely necessary to suspend the polymer in the ketone and then h~at the suspension to the desired temperature with stirring.
The saponification agent is added, and the mixture is allowed to react until the desired degree of saponifica~ion has been obtained.

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It has heen found that the polymers according to the present invention are useful as adhesives and, when ground, as coating materials, as well.

The following Examples are intended to illustrate the 5 invention:

Example 1 100 g of granulated ethylene/n-butyl acrylate copolymer containing 25% by weight (based on t~e polymer) of n-butyl ~ acrylate and having a melt index (190C/2 kg) of 8.0 g/lO
minutes~ 800 ml of methyl ethyl ketone, and 60 g of KOH (86%, four times the amount equivalent to the n-butyl.acrylate) dissolved in 200 ml of methanol, are placed in a 2 liter volume flask equipped with a stirrer, a reflux condenser and a contact thermometer. After S hours reaction time at 74C., the lS reaction mixture is cooled to about 50C, ~he granulate is suction filtered, de-ionised at the reflux temperature (74C) . with 50 ml of 32% hydrochloric acid in 500 ml of methyl ethyl . ketone, and washed four times with 500 ml of an acetone/water . mi.xture (9 : 1) at 60C. After drying at 60C in a through-circulation drying chamber, 90 g of a col.orless reaction product containing 13,4% of acrylic acid and 3.7% of n-butyl acrylate, corresponding to a degree of saponification of 85%, is obtained. The melt index (190C/2 kg) of the polymer is 3.0 g/10 minutes.

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Example 2 100 g of ~r~-nulated ethylene/2-ethylhexyl acrylate copolymer containinP~ 19% (based on the p,olymer) o 2-ethylhexyl acrylate incorporated by polymerization-and having a melt index (190C/2 k~) o~ 33 g/lO minutes, 800 ml of methyl ethyl ketone, and 20 g of KOH (86%, which is`three times the amount equivalent to the

2-ethylhexyl acrylate) dissolved in 100 ml of methanol, are placed in a 2 liter flask equipped with a stirrer, a reflux condenser and a contact thermometer. After 5 hours reaction time at 74C, the granulate is suction filtered, de-ionised at the reflux temperature (74C) with 70 ml of 32% hydrochloric acid in 500 ml of methyl ethyl ketone, and washed four times with 500 ml of an acetone/water mixture ~ : l). After drying at 60C in a through-circulation drying chamber, 89 g of colorless granulate is obtained which contains 7.7% of acrylic acid and 1.7% of 2-ethylhexyl acrylate, corresponding to a degree of saponification of 91.6%; the melt index (190C/2 kg) is 21 ~/10 minutes.

Example 3 100 g ~Jf ~ranulated ethylene/ethyl acrylate copolymer co~taining 18% by weight (based on the polymer) of ethyl acrylate incorporated by polymerization and having a melt index (190C/2 kg) of 5.2 g/lO minutes, 800 ml of methyl ethyl ketone and 47 g of KOH (86%, which is four times the amount equivalent ~5 to the ethyl acrylate) dissolved in 200 ml of methanol are !` ~

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placed in a 2 liter flask equipped with a stirrer, a reflux condenser and a contact thermometer. After 5 hours reaction time a~ 74C, the reaction mixture is cooled to about 50C, and the gratllllate is suction filtered and washed with 5G ml of 32%
hydrochl.oric acid in 500 ml~of an acetone/water mixture (9 : 1) at 60C. After drying at 6~C in a through-circula~ion drying chamber, 95 g of a colorless saponification product is obtained containing 7.1% of acrylic acid and 9.0% of ethyl acrylate, corresponding to a degree of saponification of 52%; the melt index (190C/2 kg) is 0.15 g/10 minutes.

While only a limited number of specific examples of the present invention have been expressly set forth, it is, nonetheless, to be broadly construed, and not to be limited except by the character of the claims appended hereto.

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Claims (9)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a process for the production of ethylene copolymers comprising by weight (1) more than 60% polyethylene, (2) 0 to 20% polyesters of C3to C12 alkenecarboxylic acids with Cl to C8 primary alcohols, (3) 1 to 20% C3 to C12 polyalkenecarboxylic acids, comprising saponifying a feedstock comprising by weight a granular polymer of (a) at least 50% ethylene, (b) 2 to 50% esters of C3 to C12 alkenecarboxylic acids with Cl to C8 primary alcohols, (c) 0 to 30% vinyl esters of saturated monobasic, aliphatic carboxylic acids with 1 to 6 carbon atoms, and (d) up to 3% C3 to C12 alkenecarboxylic acids, the improvement which comprises said feedstock having a particle size of 0.1 to 8.0 mm, and being suspended in a ketone, there being 1 part of said feedstock to 1 - 10 parts of said ketone, said ketone being of the formula wherein R and Rl are individually a straight or branched chain alkyl radical having l to 6 carbon atoms, and carrying out the saponification of the polyester of alkenecarboxylic acids with primary alcohols at 40° to 75°C. in the presence of at least one alkaline saponifying agent, while retaining the granular structure thereof.

2. The process of Claim 1 wherein one part of said feedstock is suspended in 2 to 8 parts by weight of said ketone.

3. The process of Claim 1 wherein said ketone is acetone, methyl ethyl ketone, methyl isobutyl ketone, or mixtures thereof.

4. The process of Claim 1 wherein said agent is an alkali metal hydroxide.

5. The process of Claim 1 wherein said particle size is 1.0 to 5.0 mm.

6. The process of Claim 1 wherein said ketone swells but does not dissolve said feedstock at a temperature below the temperature at which melting of said feedstock starts.

7. The process of Claim 1 wherein said saponification is carried out for 0.5 to 10 hours.

8. The process of Claim 7 wherein said saponification is carried out for 0.5 to 5 hours.

9. The process of Claim 8 wherein said saponification is carried out for 2 to 4 hours.