GB1576597A

GB1576597A - Process for the polymerisation or copolymerisation of halogenated vinyl monomers in aqueous suspension ormicrosuspension

Info

Publication number: GB1576597A
Application number: GB3832/78A
Authority: GB
Original assignee: Solvay SA
Current assignee: Solvay SA
Priority date: 1977-02-01
Filing date: 1978-01-31
Publication date: 1980-10-08
Also published as: LU76676A1; FR2378800B1; IT7819879A0; NZ186192A; DE2804076A1; AU508358B2; ES466491A1; BE863435A; IT1093454B; AU3232778A; FR2378800A1

Description

(54) PROCESS FOR THE POLYMERISATION OR COPOLYMERISATION OF HALOGENATED VINYL MONOMERS IN AQUEOUS SUSPENSION OR MICROSUSPENSION (71) We, SOLVAY & CIE a body corporate organised under the laws of Belgium of 33, Rue de Prince Albert, B-1050 Brussels, Belgium, 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 polymerisation or copolymerisation of one or more halogenated vinyl monomers, as herein defined e.g. vinyl chloride, in aqueous suspension or microsuspension.

Halogenated vinyl monomers are customarily polymerised in the form of droplets dispersed in water by means of mechanical stirring in the presence of dispersing agents (dispersing or emulsifying agents) and of oil-soluble polymerisation initiators (suspension polymerisation) or water-soluble polymerisation initiators (emulsion polymerisation). Polymerisation is generally conducted batchwise in pot type steel reactors provided with'a bladed stirrer and optionally baffles.

With these conventional polymerisation techniques, and more particularly suspension polymerisation, solid polymer deposits generally known as"crusts" that adhere to the inner surfaces of the reactor (body, stirrers, baffles) from during polymerisation. This phenomenon is generally known as "build-up".

Build-up is extremely harmful. In point of fact the crusts covering the interior of the reactor body reduce the amount of heat that can be removed by the heat-transporting fluid circulating in the double jacket. Consequently productivity is reduced, as it is necessary to use slower polymerisation rates than if build-up were not present.

Furthermore some of the crusts often become detached during polymerisation and contaminate the resulting polymers, which thus contain infusible nodules that are derived from the crusts and are commonly known as "fish-eyes".

Finally, build-up which always occurs in a random fashion makes it more diffiuclt to carry out and monitor the polymerisation cycles.

It is of course general practice to clean the inner surfaces of reactors after each polymerisation cycle. Cleaning is often done manually but more sophisticated techniques also exist that employ hot solvents or devices projecting jets of water at high speed. However, cleaning is always a laborious operation that is expensive in terms of labour, energy and materials and keeps the polymerisation reactor out of action for long periods.

For these reasons efforts have been made to prevent build-up by introducing a variety of additives with an inhibiting effect on build-up into the polymerisation medium. For instance, Belgian Patent 837 056 filed on 24.12.1975 in the name of the SHINETSU CHEMICAL CO. suggests treating the walls of reactors to be used for the polymerisation of vinyl chloride with (a) at least one polar organic compound such as an organic oxygen-containing compound and (b) at least one compound selected from the halides, hydroxides, oxides and lower carboxylates of metals of periods 2 to 6 of groups IIB and III to VII of the periodic table and oxy-acids derived from the same elements. A solution or dispersion of compounds (a) and/or (b) is added to the polymerisation medium to increase the effectiveness of the treatment. It is also indispensible to contact compounds (a) and (b) with each other at a temperature of at least 50"C if the treatment of the walls is to reduce build-up effectively. To do this the solutions or dispersions of these compounds are heated before application to the walls, or the said solutions or dispersions are applied cold and the coated walls then heated. In all cases the pretreatment of the walls is an operation that adversely affects the productivity of the polymerisation plant. Furthermore the treatment is not usually fully effective.

The Applicants have now found a simple and effective process for reducing build-up in the reactors used for certain polymerisations of halogenated vinyl monomers in aqueous suspension or microsuspension. This process results from the selection of a class of polar organic compounds and more particularly a class of oxygen-containing organic compounds whose effectiveness is total without the need for applying them to the reactor walls hot or using them in combination with compounds derived from metals.

The present invention accordingly relates to a process for the polymerisation or copolymerisation of one or more halogenated vinyl monomers as herein defined in aqueous suspension or microsuspension with the aid of one or more oil-soluble free radical polymerisation initiators and in the presence of an effective amount of an inhibitor of build-up, as herein defined, derived from an oxygen-containing compound, in which process the build-up inhibitor comprises one or more anions derived from an aryl carboxylic or aryl alkyl carboxylic acid.

The anions used as build-up inhibitors in the present invention may be derived from any aryl carboxylic or aryl alkyl carboxylic acid containing in its molecule at least one carboxyl group -COOH directly linked to a carbon atom of an aromatic hydrocarbon ring or at least one carboxyl group -COOH linked by an alkylene chain to a carbon atom of an aromatic hydrocarbon ring. By aryl carboxylic and aryl alkyl carbdxylic acid we therefore mean both aryl and aryl alkyl monocarboxylic acids, aryl and aryl alkyl dicarboxylic acids and aryl and aryl alkyl polycarboxylic acids. However, it is preferable to use anions derived from aryl or aryl alkyl monocarboxylic acids and aryl or aryl alkyl dicarboxylic acids, and more particularly anions derived from aryl monocarboxylic or aryl alkyl monocarboxylic acids. Anions derived from aryl monocarboxylic acids are most particularly preferred.

The aryl radical of the aryl carboxylic acids and the aryl alkyl carboxylic acids may derive equally well from a monocyclic aromatic hydrocarbon which may or may not be substituted or a polycyclic aromatic hydrocarbon which may or may not be substituted, with or without condensed rings.

If the aryl radical is derived from a substituted aromatic hydrocarbon the best results are obtained with substituents that donate electrons by an induction effect, as for example alkyl, cycloalkyl and thiol groups and more particularly alkyl groups having from 1 to 4 carbon atoms.

Furthermore the alkylene radical of the aryl alkyl carboxylic acids may derive equally well from an aliphatic hydrocarbon which may or may not be substituted. Generally speaking the number of carbon atoms in the alkylene radical does not exceed 4.

Examples of anions that can be used in the present invention are those derived from benzoic, halogenobenzoic and nitrobenzoic acids, monomethyl benzoic acids (toluic acids), dimethyl benzoic acids (xylic acids), trimethyl benzoic acids (prehnitylic acid and p and y-isodurylic acids), mono-, bis- and tris-(tertiary butyl) benzoic, formyl benzoic, benzoyl benzoic, salicylic, halogenosalicylic, biphenyl carboxylic and anthracene carboxylic acids, benzene dicarboxylic (phthalic, isophthalic and terephthalic) acids, halogenobenzene dicar boxylic nitrobenzene dicarboxylic, anthracene dicarboxylic, trimellitic, trimesic, trimesitic and phenyl acetic (a-toluic) acids, methyl-a-toluic, diphenyl acetic, diphenyl hydroxyacetic (benzylic),phenyl propanoic, diphenyl propanoic and diphenyl hydroxypropanoic acids.

The most effective of all the anions that can be used in the present invention are those derived from aryl monocarboxylic acids whose aryl radical derives from benzene or benzene substituted by groups donating electrons by an induction effect as hereinbefore defined.

Anions that are more particularly preferred are those that are derived from benzoic acid and its alkyl substituted derivatives, more particularly methyl substituted derivatives such as toluic and xylic acids.

The anions can be used in the process according to the present invention in the form of any compound that is soluble in water and dissociates therein to form the anions as hereinbefore defined. In particular the anions may be generated from the corresponding aryl carboxylic or aryl alkyl carboxylic acids and their salts. Preference is given to the alkaline earth salts and more particularly the alkali salts of potassium and sodium for example. It is advantageous to use the build-up inhibitor in the form of alkali salts of the corresponding aryl carboxylic or aryl alkyl carboxylic acids, and more particularly sodium salts.

The process according to the invention is applicable to the polymerisation of halogenated vinyl monmers. By halogenated vinyl monomers we mean all monomers polymerisable by free radical polymerisation that possess a terminal olefinic unsaturation and are substituted by at least one halogen. These monomers are preferably selected from substituted ethylene derivates and contain only two carbon atoms. Examples of such monomers include vinyl chloride, vinyl bromide, vinyl fluoride, vinylidene chloride, vinylidene fluoride, chlorotrifluorethylene and tetrafluorethylene. The invention is preferably applied to the polymerisation of fluorine-and chlorine-containing vinyl monomers. It is particularly suitable for the polymerisation of chlorine-containing vinyl monomers, more particularly vinyl chloride.

By polymerisation we mean both the homopolymerisation of the halogenated vinyl monomers and their copolymerisation with each other or with other copolymerisable monomers. Examples of the latter include vinyl esters such as vinyl acetate, acrylic esters such as methyl acrylate and glycidyl methacrylate, unsaturated nitriles such as acrylonitrile and methacrylonitrile, unsaturated diesters such as dibutyl maleate, allyl esters such as allyl acetate, unsaturated amides such as acrylamide; styrene derivatives and a-olefines such as ethylene and propylene.

However, the invention is preferably applied to the production of polymers containing at least 50% (molar), and more particularly at least 80% (molar), of units derived from halogenated vinyl monomers.

The invention can be applied equally well to the production of random copolymers and block or graft copolymers.

The problem of build-up is particularly acute in polymerisation in aqueous suspension and microsuspension in which oil-soluble polymerisation initiators are used.

Conventional dispersing agents are generally used in suspension polymerisation, as for example finely dispersed solids, gelatins, water soluble cellulose ethers, synthetic polymers such as partially saponified polyvinyl acetates, polyvinyl pyrrolidone and vinyl acetate/ maleic anhydride copolymers and mixtures thereof. Surface-active agents may also be introduced at the same time as the dispersing agents. The amount of dispersing agent used generally varies between 0.5 and 1.5% by weight calculated on the water.

In polymerisation in microsuspension, which is sometimes still known as polymerisation in homogenised aqueous dispersion, an emulsion of monomer droplets is prepared by vigorous mechanical agitation, customarily in the presence of emulsifying agents of the same type as those referred to above, and polymerisation is carried out in the presence of oil-soluble initiators.

Any oil-soluble initiator may be used in polymerisation in suspension or microsuspension.

Examples include: peroxides, such as di-tertiary butyl peroxide, lauroyl peroxide and acetyl cyclohexyl sulphonyl peroxide; azo compounds, such as azo-bis-isobutyronitrile and azo bis- 2 ,4-dimethyl valeronitrile; dialkyl peroxydicarbonates, such as diethyl, diisopropyl, dicyclohexyl and di-tertiary butyl cyclohexyl peroxydicarbonates; and alkyl borons. Generally speaking, these initiators are used in the proportion of 0.01 to 1 %by weight calculated on the monomers.

It is particularly advantageous to apply the process according to the invention to polymerisation in aqueous suspension and more particularly to polymerisation in aqueous suspension in the presence of dialkyl peroxydicarbonates alone or mixed with other oil-soluble initiators.

Dialkyl peroxydicarbonates whose alkyl radicals, which may be the same or different and may optionally be substituted, e.g with halogen atoms, contain from 1 to 6 carbon atoms, and preferably from 1 to 4 carbon atoms, are advantageously used. A peroxydicarbonate that is particularly preferred is diethyl peroxydicarbonate.

In addition to dispersing agents and oil-soluble inititators, the polymerisation medium may contain various additives normally employed in conventional processes for polymerisation in aqueous dispersion. Examples of such additives include buffer agents, particle size regulators, molecular weight regulators, stabilisers, plasticisers, colorants, reinforcing agents and processing aids.

The operating conditions for the polymerisation process according to the invention do not differ from those customarily employed. Thus in the case of the polymerisation of vinyl chloride the temperature is generally between 35 and 80"C. The absolute pressure is generally below 15 kg/cm2. The pH is generally acid, for example between 2 and 7. The amount of water used is generally such that the total weight of the monomers represents from 20 to 50% of the total weight of the water and monomers.

Generally speaking, the polymerisation of halogenated vinyl monomers is carried out batchwise in accordance with cycles in which water is introduced first of all, followed by the various components of the reaction medium (dispersing or emulsifying agents, inititators, monomers etc.). According to a preferred embodiment of the invention the build-up inhibitor is introduced into the polymerisation medium before any of the halogenated vinyl monomer, the best results being obtained when it is also introduced before any of the oil-soluble initiator. To do this it is merely necessary to add the build-up inhibitor after the water has been introduced, optionally at the same time as the dispersing or emulsifying agents.

In addition, the build-up inhibitor may be introduced into the polymerisation medium several times during polymerisation, or continuously; To initiate polymerisation, the polymerisation medium is heated, e.g. by means of the heat-transporting fluid circulating in the double jacket with which the reactors are customarily provided. The build-up inhibitor is preferably introduced into the polymerisation medium before heating starts.

When polymerisation is conducted continuously, the build-up inhibitor is preferably also introduced into the polymerisation medium continuously.

The amounts of build-up inhibitor to use may vary very widely, particularly as a function of the nature of the monomers and the state of the inner surfaces of the reactors employed. As a general rule the amount of build-up inhibitor used is such that the polymerisation medium contains at least 0.1 ppm calculated on the water. The polymerisation medium preferably contains at least 1 ppm of inhibitor calculated on the water. The best results are obtained when the polymerisation medium contains at least 5 ppm of build-up inhibitor calculated on the water.

There are no objections to using large amounts of build-up inhibitor. However, it is usually pointless for the content of build-up inhibitor in the polymerisation medium to exceed 10,000 ppm calculated on the water. An amount not exceeding 1,000 ppm will usually suffice. An amount not exceeding 100ppm is entirely satisfactory in almost all cases. Usually, an amount of at most 50 ppm is not exceeded.

According to a preferred embodiment of the invention, from about 5 to 50 ppm, and even more particularly from 5 to 25 ppm, of build-up inhibitor are used, relative to the water present in the polymerisation mixture.

It has been found that a certain amount of build-up inhibitor is adsorbed on the metallic inner surfaces of the polymerisation reactors. It is for this reason that we prefer the polymerisation medium to contain an amount of build-up inhibitor equal to at least 1 mg per m2 and preferably at least 5 mg/m2 of the metallic inner surface. This also means that a certain amount of build-up inhibitor may remain adsorbed on the metallic inner surfaces of th reactors at the end of a polymerisation cycle and still be effective in the following cycle. Its presence may be taken into account and the amount of build-up inhibitor added in the next cycle reduced accordingly.

When starting to use the process according to the invention in a given reactor, it is important to clean the inner surfaces particularly carefully beforehand. This can be done by using solvents that are particularly effective for the polymers that form the build-up, pyrolysis of the walls, scouring or polishing The build-up inhibitors forming the object of the present invention are remarkably effective, and their use does not necessitate any pretreatment of the inner walls of the reactors. They are already totally effective when used in the proportion of about 7 ppm calculated on the water. They also include a very large number of compounds that do not exhibit any harmful side effects as regards the appearance of the polymer, its colour, odour, heat and light stability, and suitability for use in packaging foodstuffs.

The polymers obtained by the present invention can be used for all the customary applications of this type of product, and more particularly for the production of aricles such as bottles or sections by conventional extrusion and extrusion blow moulding techniques for example.

The following Examples are intended to illustrate the invention and do not restrict it in any way.

Examples 1 to 5 (R) Examples 1 to 4 are carried out in accordance with the invention. Example 5 (R) is included for purposes of comparison.

A 3-litre stainless steel laboratory reactor is used which is provided with a double jacket through which a heat transporting fluid circulates, and with a conventional stainless steel bladed stirrer. The inner surfaces of the reactor are cleaned by washing them with tetrahydrofuran, followed by pyrolysis carried out by heating the wall at 400"C for 30 minutes. The reactor is then scoured with a nitrofluoride bath, and then rinsed out 5 time with demineralised water.

1500 g of demineralised water and 10 mg of the sodium salt of a carboxylic acid are introduced into the reactor in turn. 1.65 g of polyvinyl alcohol is then introduced. The stirrer is started up. The reactor is subjected twice to a vacuum (100 mm of mercury absolute) and purged with technical grade nitrogen at a pressure of 1360 mm mercury absolute between these two operations. 1.000 g of vinyl chloride followed by 500 mg of diethyl peroxydicarbonate are then introduced. The polymerisation medium is heated to 610C at a rate of 1"C per minute.

The polymerisation medium is maintained at 61 C with stirring until the pressure falls by 3.5 kg/cm2 absolute. Polymerisation is then terminated by relaxing the pressure in the reactor and evaporating the unpolymerised vinyl chloride. The whole is then cooled and the polymer recovered by centrifuging and drying.

Table 1 below gives details of the nature of the sodium carboxylate employed and the results of inspecting the inner surfaces of the reactor at the end of the polymerisation cycle.

TABLE I Example No. Sodium carboxylate Results of inspection 1 benzoate No build-up 2 ortho-bromobenzoate Slight build-up at the top of the autoclave 3 ortho-toluate No build-up 4 2,4-xylate No build-up 5 (R) acetate Considerable build-up on the walls These examples show the superiority of the anions derived from aryl carboxylic acids, and more particularly anions derived from benzoic acid and its methyl substituted derivates, over oxygen-containing organic compounds, more particularly non-aromatic carboxylic acids.

WHAT WE CLAIM IS: 1. Process for the polymerisation or copolymerisation of one or more halogenated vinyl monomers, as herein defined, in aqueous suspension or microsuspension with the aid of one or more oil-soluble free radical polymerisation initiators and in the presence of an effective amount of an inhibitor of build-up, as herein defined, derived from an oxygen-containing compound, wherein the build-up inhibitor comprises one or more anions derived from an aryl carboxylic or aryl alkyl carboxylic acid.

2. Process as in claim 1, wherein the said one or more anions are derived from one or more aryl monocarboxylic, aryl alkyl monocarboxylic, aryl dicarboxylic or aryl alkyl dicarboxylic acids.

3. Process as in claim 2, wherein the said one or more anions are derived from one or more aryl monocarboxylic or aryl alkyl monocarboxylic acids.

4. Process as in claim 3, wherein the said one or more anions are derived from one or more aryl monocarboxylic acids.

5. Process as in any of claims 1 to 4, wherein the said one or more anions are derived from one or more aryl carboxylie or aryl alkyl carboxylic acids whose aryl radical is derived from a monocyclic aromatic hydrocarbon constituted by benzene or a substituted benzene having one or more substituent groups capable of donating electrons by an induction effect.

6. Process as in claim 5, wherein the said one or more electron-donating groups are alkyl, cycloalkyl or thiol groups.

7. Process as in claim 6, wherein the said one or more electron-donating groups are alkyl groups having 1 to 4 carbon atoms.

8. Process as in claim 1, 4 or 5 wherein the said inhibitor comprises anions derived from benzoic acid.

9. Process as in claim 1, 4, 5,6 or 7, wherein the said inhibitor comprises anions derived from toluic or xylic acids.

10. Process as in any of claims 1 to 9, wherein the said one or more anions are introduced into the polymerisation medium in the form of one or mre alkali metal carboxylic acid salts.

11. Process as in any of claims 1 to 9, wherein the said one or more anions are introduced into the polymerisation medium in the form of one or more carboxylic acids.

12. Process as in any of claims 1 to 11, wherein the said one or more anions are introduced into the polymerisation medium before the halogenated vinyl monomer(s).

13. Process as in any of claims 1 to 12, wherein the said one or more anions are introduced into the polymerisation medium before the oil-soluble free radical polymerisation initiator(s).

14. Process as in any of claims 1 to 13, wherein the said one or more anions are used in a proportion of at least 1 ppm calculated on the water present in the polymerisation medium.

15. Process as in claim 14, wherein the anion proportion is at least 5 ppm calculated on

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

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reactor and evaporating the unpolymerised vinyl chloride. The whole is then cooled and the polymer recovered by centrifuging and drying.

Table 1 below gives details of the nature of the sodium carboxylate employed and the results of inspecting the inner surfaces of the reactor at the end of the polymerisation cycle.

TABLE I Example No. Sodium carboxylate Results of inspection 1 benzoate No build-up

2 ortho-bromobenzoate Slight build-up at the top of the autoclave

3 ortho-toluate No build-up

4 2,4-xylate No build-up

5 (R) acetate Considerable build-up on the walls These examples show the superiority of the anions derived from aryl carboxylic acids, and more particularly anions derived from benzoic acid and its methyl substituted derivates, over oxygen-containing organic compounds, more particularly non-aromatic carboxylic acids.

WHAT WE CLAIM IS: 1. Process for the polymerisation or copolymerisation of one or more halogenated vinyl monomers, as herein defined, in aqueous suspension or microsuspension with the aid of one or more oil-soluble free radical polymerisation initiators and in the presence of an effective amount of an inhibitor of build-up, as herein defined, derived from an oxygen-containing compound, wherein the build-up inhibitor comprises one or more anions derived from an aryl carboxylic or aryl alkyl carboxylic acid.
2. Process as in claim 1, wherein the said one or more anions are derived from one or more aryl monocarboxylic, aryl alkyl monocarboxylic, aryl dicarboxylic or aryl alkyl dicarboxylic acids.
3. Process as in claim 2, wherein the said one or more anions are derived from one or more aryl monocarboxylic or aryl alkyl monocarboxylic acids.
4. Process as in claim 3, wherein the said one or more anions are derived from one or more aryl monocarboxylic acids.
5. Process as in any of claims 1 to 4, wherein the said one or more anions are derived from one or more aryl carboxylie or aryl alkyl carboxylic acids whose aryl radical is derived from a monocyclic aromatic hydrocarbon constituted by benzene or a substituted benzene having one or more substituent groups capable of donating electrons by an induction effect.
6. Process as in claim 5, wherein the said one or more electron-donating groups are alkyl, cycloalkyl or thiol groups.
7. Process as in claim 6, wherein the said one or more electron-donating groups are alkyl groups having 1 to 4 carbon atoms.
8. Process as in claim 1, 4 or 5 wherein the said inhibitor comprises anions derived from benzoic acid.
9. Process as in claim 1, 4, 5,6 or 7, wherein the said inhibitor comprises anions derived from toluic or xylic acids.
10. Process as in any of claims 1 to 9, wherein the said one or more anions are introduced into the polymerisation medium in the form of one or mre alkali metal carboxylic acid salts.
11. Process as in any of claims 1 to 9, wherein the said one or more anions are introduced into the polymerisation medium in the form of one or more carboxylic acids.
12. Process as in any of claims 1 to 11, wherein the said one or more anions are introduced into the polymerisation medium before the halogenated vinyl monomer(s).
13. Process as in any of claims 1 to 12, wherein the said one or more anions are introduced into the polymerisation medium before the oil-soluble free radical polymerisation initiator(s).
14. Process as in any of claims 1 to 13, wherein the said one or more anions are used in a proportion of at least 1 ppm calculated on the water present in the polymerisation medium.
15. Process as in claim 14, wherein the anion proportion is at least 5 ppm calculated on

the water present in the polymerisation medium.
16. Process as in any of claims 1 to 15, wherein the said one or more anions are used in a proportion less than 50 ppm calculated on the water present in the polymerisation medium.
17. Process as in any of claims 1 to 16, being a process carried out in a reactor having a metallic inner surface, wherein the said one or more anions are used in a proportion of at least 5 mg per m2 of that metallic inner surface.
18. Process as in any of claims 1 to 17, wherein the polymerisation medium is subjected to heating to initiate the polymerisation reaction, and the said one or more anions are introduced into the polymerisation medium before that heating.
19. Process as in any of claims 1 to 18, wherein the said one or more halogenated vinyl monomers comprise one or more fluorine- or chlorine-containing monomers derived from ethylene.
20. Process as in claim 19, wherein the said one or more monomers are constituted by, or include, vinyl chloride.
21. Process as in any of claims 1 to 20, wherein the polymer or copolymer produced contains at least 80% (molar) of units derived from one or more halogenated vinyl monomers, as herein defined.
22. Process as in any of claims 1 to 21, wherein the one or more monomers are polymerised or copolymerised in aqueous suspension.
23. Process as in claim 22, wherein the one or more oil-soluble free radical polymerisation initiators employed comprise at least one dialkyl peroxydicarbonate whose alkyl radicals contain 1 to 6 carbon atoms.
24. Process as in claim 1, substantially as described in any of the foregoing Examples 1 to 4.
25. A polymer or copolymer of one or more halogenated vinyl monomers, as herein defined, produced by a process as in any preceding claim.