GB1578805A - Vinyl halide polymerisation process and reactor and coating composition - Google Patents

Description

(54) VINYL HALIDE POLYMERISATION PROCESS AND REACTOR, AND COATING COMPOSITION (71) We, ICI AUSTRALIA LIMITED, of 1 Nicholson Street, Melbourne, Victoria, Australia, a Company organised and existing under the laws of the State of Victoria, Australia, 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 of vinyl halide monomers such as vinyl chloride in aqueous dispersion, to a reactor wherein such a polymerisation process may be carried out, and to a composition suitable for coating such a reactor.

By polymerisation in aqueous dispersion is meant polymerisation in aqueous emulsion or aqueous suspension (including aqueous microsuspension), optionally in the presence of colloids such as polyvinyl alcohol and/or surfactants.

When the reaction is carried out in the usual manner it is well known that a problem arises in that the surfaces inside the reactor become coated with tenaciously adhering polymeric material known as build-up. The formation of tenaciously adhering build-up is undesirable from the point of view of achieving efficient heat transfer for cooling and heating the reactor contents, effective usage of monomer, effective control and monitoring of the polymerisation reaction, and acceptable polymer quality (in view of contamination by dislodged particles of the build-up).

This deposit, which varies in thickness, hardness and degree of adhesion to the surfaces of the reactor is composed of polymer in several different physical forms. The main type, particularly from the standpoint of routine cleaning, is a hard film over the whole surface of the reactor. The thickness of this film varies from batch but is normally a few thousandths of an inch thick. The other types are hard or soft lumps which accumulate locally in the reactor or powder which is more generally distributed. The soft lumps are composed of material that has escaped the washing out process and are comparatively easy to remove. The hard lumps are believed to originate as soft material that has allowed to stay in the reactor for more than one batch or simply by polymerization of vinyl chloride in an area of very high or very low agitation, i.e. an area where the normal droplet protection of the granulating agent is ineffective. They are normally found in roof ports, on staging brackets, on the impeller, or indeed any area where there is a severe discontinuity to the surface in the reactor. They are very difficult to remove, normally requiring a hammer and chisel. A somewhat similar type of buildup can be formed, when a reactor is inadequately cleaned, by growth on the skin buildup remaining. This type of build-up along with lumps from impellers can detach itself from the reactor wall during a batch and has to be removed manually from the reactor at frequent intervals, otherwise blockage of the valve or slurry transfer lines will result. It is known that the amount of build-up produced is much larger if the reactor is inadequately cleaned.

Powder type build.up is often quite firmly attached to the surface and is at its thickest at or above the liquid level in the reactor where it has been deposited by splashing.

Because of the problems in respect of heat transfer, polymerisation control and polymer quality, it is necessary to clean the reactor between each polymerisation cycle wherein the deposited material is removed as completely as possible, e.g. by scraping by hand, solvent cleaning or pressure-washing. This is wasteful in terms of the expense of the equipment and manpower required to carry out such cleaning and also in terms of the loss of productivity for a given reactor arising from the time taken to effect the cleaning operation.

This formation of build-up, which increases with polymerisation time, is also a major difficulty in the development of a trouble-free continuous process for the aqueous dispersion polymerisation of vinyl halide monomers such as vinyl chloride.

We have now discovered a process whereby vinyl halide monomers such as vinyl chloride may be polymerised in aqueous dispersion without any or with very much reduced formation of build-up.

According to the present invention there is provided a process for the polymerisation of vinyl halide monomers in aqueous dispersion wherein the polymerisation is carried out in a reactor having deposited on the interior surfaces thereof a coating composition, said coating composition being prepared by reacting together at least one compound (A) chosen from the group consisting of azo compounds; with at least one compound (B) chosen from the group consisting of aliphatic and aromatic amines; and with at least one compound (C) chosen from the group consisting of oxy-group substituted aromatic compounds and quinone type compounds.

Typical (A) compounds are p-aminoazobenzene, p-hydroxyazobenzene, phenylazo-2naphthol, and diazoaminobenzene. The preferred compound is p-aminoazobenzene.

The amines of group (B) may be monomeric amino compounds or polymeric amino compounds. Examples of suitable monomeric compounds include aliphatic amines, such as monoalkylamines and dialkylamines and compounds structurally derived therefrom and aromatic primary and secondary amines and compounds structurally derived therefrom. Preferably, the amino compound contains at least two amino groups per molecule as, e.g. in a polyamino monomeric compounds such as triethylene tetramine or in a polymeric amino compound. If such amino compounds contain three or more amino groups per molecule, they tend to yield extended branched or crosslinked product molecules which are particularly effective in the invention.

Typical amines suitable for use in the process of this invention are p-aminobenzoic acid, triethanolamine, tributylamine; phenothiazine and diphenylamine. Preferred (B) compounds are diphenylamine and tetraethylenepentamine.

Typical (C) compounds are hydroquinone, benzoquinones and substituted benzoquinones, pyrogallol, phenol and para and metal substituted phenols, cresols, p-tertiary-btityl catechol, picric acid and resorcinol. Preferred (C) compounds are pyrogallol and hydroquinone.

We have found particularly good results may be obtained when the coating composition is derived from a minor amount of a compound from group (A) with at least two compounds chosen from each of groups (B) and (C), for example the combination of p-aminoazobenzene with p-phenylenediamine, tetraethylene-pentamine, pyrogallol, and hydroquinone.

The weight ratios of the amounts of compound from each of the groups (A), (B) and (C) to the total weight of the coating composition formed therefrom, are preferably in the range from 1:20 to 3:4. More preferably the ratios are in the range from 1:10 to 1:2.

The formation of the coating composition from the selected compounds of groups (A), (B) and (C) can be carried out simply by mixing the compounds together in solution. Aqueous solution can be conveniently employed. The mixing is usually accompanied by heat evolution and a rapid change in colour of the solution as the reaction products form. Depending on the particular compounds selected the colour may be light or dark red.

In some cases, where the product is only slightly soluble in water, a precipitate forms.

This precipitate can be readily dissolved by adding an organic solvent. The preferred solvents are those miscible with water such as alcohols and aldehydes.

There is also provided according to the invention a polymerisation reactor having internal surfaces which have been coated with a com position as herein defined.

The method of applying the coating composition of our invention is not narrowly critical.

The coating composition may be applied to any surface inside the reactor which is liable to suffer the formation of build-up. For example, it may be applied to the interior surface of the main body of the reactor, the interior surface of the roof of the reactor (which is often above the liquid level) of the polymerisation and usually suffers tenacious build-up), the surfaces of the stirrer system (stirrer shaft, paddle) and the surfaces of projections or protuberances inside the reactor such as baffles and thermocouple pocket covers. It may be pointed out that the coating compositions used according to the invention are exceptionally effective in preventing build-up above the liquid level of the polymerisation medium in the reactor.

If a condenser is installed in a part of the polymerisation vessel that is in contact with the gaseous phase or if it is installed outside the vessel and connected to the polymerization vessel, the condenser as well as the conduit pipe connecting the condenser and the polymerization vessel had best be similarly treated.

The composition is preferably deposited onto the surfaces very thinly. It can be deposited as is, or dissolved in some solvent or diluted with a diluent. What is recommended is that it be deposited at a rate of at least 0.1 g/m2. If the amount of the coating deposited is less than 0.001 g/m2, the effect of the treatment will not last long, but there is no upper limit to the thickness of the coating, so long as it has no adverse effect on the properties of the polyvinyl halide prepared. Therefore the composition may be deposited at a rate of for instance, 1 g/m2 or more.

In order to fix certain compositions of our invention onto the surface of the vessel walls, various fixing agents may be added to them.

Such fixing agents are exemplified by natural and synthetic polymers such as glue, gelatin, cellulose derivatives, polyvinyl alcohol and polyacrylic acid, polystyrene; thermosetting substances such as shellac resins, phenol resins, alkyd resins, epoxy resins, urethane resins, and tung oil; alcohols such as methanol, isopropyl alcohol and cetyl alcohol; organic acids such as acetic acid, p-toluenesulfonic acid and rosin; ketones such as acetone; aromatic hydrocarbons such as toluene, benzene, and xylene; esters such as ethyl acetate, butyl acetate and dioctyl phthalate; and water. Any one or more kinds of them may be employed.

Any other expedient known in the art to enhance the effect of the previously known single active component coating compositions may be used to enhance the effect of the coating composition of our invention.

The coating composition of our invention may be applied and any solvents in the composition allowed to evaporate before the reactor is charged or in some cases the reactor may be charged before the solvents evaporate. In a preferred embodiment of our process heat is applied to the coating composition. Typically the coating composition may be subjected to a baking treatment at moderate temperatures, say from 80-110"C.

It is a feature of our invention that a major proportion of the coating composition remains on the internal surfaces and walls of the reactor and prevents or inhibits the development of build-up. Thus the compositions can provide a coating efficient for a series of polymerisations without the need to recoat such surfaces prior to each polymerisation. Furthermore, since the coating compositions are not significantly soluble in the aqueous emulsions or suspensions in the reactor and, in cbntrast to the individual compounds from which the coating compositions are formed, the said compositions do not retard or inhibit the polymerisation reactions.

Although the invention has been described with reference hereinbefore to the polymerisation of vinyl chloride, it is also applicable to vinyl halide monomers in general By "vinyl halide monomers is meant those monomers polymerisable by free-radical polymerisation which are olefinically unsaturated in the alpha position and substituted by at least one halogen atom. These monomers are preferably selected from substituted derivatives of ethylene and contain only two carbon atoms.

Examples of such monomers include vinyl chloride, vinyl bromide, vinyl fluoride, vinlidene chloride, vinylidene fluoride, chlorotrifluoroethylene and tetrafluoroethylene. The invention is preferably applied to the polymerisation of fluorine or chlorine-containing vinyl monomers, especially vinyl chloride.

By "polymerisation" is meant both the homopolymerisation of the vinyl halide monomers and the copolymerisation with each other or with other comonomers copolymerisable therewith. Examples of the latter include vinyl esters such as vinyl acetate, acrylic esters such as methyl acrylate and butyl methacrylate, acrylic nitriles such as acrylonitrile and methacrylonitrile, unsaturated diesters such as diethyl maleate, allyl esters such as allyl acetate, a-olefines such as ethylene and propylene, vinyl ethers and styrene compounds.

However, we prefer to apply the invention to the preduction of polymers containing at least 50% molar, and more particularly at least 80% molar, of units derived from vinyl halide monomers, particularly vinyl chloride.

The process according to the invention may be employed in any polymerisation technique where the monomer(s) is dispersed in the form of droplets in a liquid aqueous phase. For example it may be used for polymerisation in aqueous emulsion in which case any suitable emulsifying agent can be used, and in particular where an ionic emulsifying agent such as sodium lauryl sulphonate or sodium dodecyl benzene sulphonate and non-ionic emulsifying agents is used.

The process of the invention is also most applicable to polymerisation in aqueous suspension and microsuspension.

Any suitable dispersing agent may be used for polymerisation in aqueous suspension, and particularly finely dispersed solids, gelatin, polyvinyl acetates of various degrees of hydrolysis, water-soluble cellulosic ethers and polyvinyl pyrrolidones. These dispersing agents can be used together with surface-active agents if desired. The amount employed may vary widely and is generally between 0.05 and 1.5% by weight calculated on the amount of water used.

Any suitable free-radical polymerisation initiator that is monomer-soluble may be used for polymerisation in aqueous suspension.

Examples of these include peroxy compounds such as di-tertiary-butyl peroxide, lauroyl peroxide and acetyl cyclohexyl sulphonyl peroxide, azo compounds such as azo-bisisobutyronitrile and 2,2'-azo-bis, 2,4,-dimethylvaleronitrile and boron alkyls. Monomersoluble free-radical polymerisation initiators that are particularly suitable for use in the process according to the invention are the dialkyl peroxydicarbonates whose alkyl radicals contain up to 20 carbon atoms, such as diethyl peroxydicarb onate, diisopropyl peroxydicarbonate and di(tertiarbutyl-cyclohexyl)peroxydicarbonate, and 2,2'-azo-bis, 2,4-dimethylvaleronitrile and azo-bis-isobutyron trile. These initiators may be used in conventional quantities - generally speaking from 0.01 to 1% by weight calculated on monomer.

Polymerisation in homogenised aqueous dispersion, sometimes known as polymerisation in microsuspension, comprises mechanically homogenising an aqueous dispersion of the monomer or monomers in the presence of a surface-active agent (for example by subjecting it to a violent shearing action), and polymerising the homogenised dispersion in the presence of an initiator that is monomer soluble.

Conventional emulsifying agents and monomer-soluble initiators can be used for polymerisation in microsuspension such as for example an ionic emulsifying agent like sodium dodecylbenzenesulphonate, and peroxide initiators of the dialkanoyl peroxide type, e.g.

lauroyl peroxide.

In addition to the emulsifying or dispersing agents and initiators, the aqueous dispersions (i.e. suspensions, microsuspensions and emulsions) may contain one or more additives that are normally employed in conventional processes for polymerisation in aqueous dispersion. Examples of such additives include particle size regulators, molecular weight regulators, stabilisers, plasticisers, colouring agents. reinforcing agents and processing aids.

The polymerisation medium may also contain one or more substances which themselves inhibit polymerisation buildup.

The operating conditions for polymerisation according to the process of the present invention may be those customarily used. For example, in the case of vinyl chloride polymerisation, the temperature is generally between 40 and 75"C and the pressure generally below 15 kg/cm2.

Our invention is illustrated by, but by no means limited to, the following examples. Unless otherwise specified all parts and percentages are by weight.

EXAMPLE 1 This comparative example describes a conventional process used as a control to compare with the improved process of the invention. A reactor in the form of a stainless steel pressure reactor of 7 litres nominal capacity equipped with heating and cooling means was charged with 3500 ml of demineralized water, 2.4 g of a peroxydicarbonate catalyst and 1.75 g polyvinyl alcohol (partially hydrolysed polyvinyl) acetate). The contents of the reactor were stirred and air was removed by evacuation.

3000 g of vinyl chloride monomer was added to the evacuated reactor and the contents were heated to 560C. The temperature was maintained until pressure drop indicated the end of the reaction of polymerization.

The residual gas was vented off, the slurry of polyvinyl chloride in water was dropped down through a bottom valve. The lid was opened and the remaining loose polymer was rinsed with water and the firm deposition of the polymer inside the reactor was examined.

There was a deposit of polymer firmly attached to the wall, to the stirrer shaft and to the thermometer well. The build-up was particularly prominent at the liquid-gas boundary.

To remove the deposit use of a scraper was necessary. The deposit on the stirrer shaft and on the stirrer blades was particularly hard to dislodge and it was necessary to use a chisel with a gentle blow of a hammer to chip off particularly hard portions of the build-up.

The total weight of the deposit constituted 0.6% of the vinyl chloride monomer charged to the pressure vessel.

EXAMPLE 2 This comparative example illustrates the result of carrying out a polymerisation reaction with the interior surfaces of the reactor coated with a composition comprising a compound selected from only one of the groups used in the process of our invention.

The pressure reactor of Example 1 was thoroughly cleaned free from all deposit, washed and dried. The internal surface of the reactor including stirrer and the lid was coated by a solution of aminoazobenzene (1 part) in an ethanol: water mix (20 parts). The solvent was allowed to evaporate by heating the reactor walls to 70 for approximately 30 min; this was followed by a quick rinse (1 min) of all surfaces with cold water to remove any loosely adhering suppressant.

The general polymerisation procedure of Example 1 was repeated in the coated reactor.

While the reactor walls were virtually free from film build-up, apart from patches near the liquid-gas boundary, there was considerable hard build-up on the lid, on the paddle, and around the shaft. The latter build-up was difficult to remove. The overall amount of hard build-up was ca. 0.03% of the total monomer charge.

EXAMPLE 3 This comparative example was carried out by the procedure of Example 2, except that the solution of aminoazobenzene was replaced by a solution of aminoazobenzene (1 part) and hydroquinone (1 part) in ethanol (50 parts).

While there was no significant build-up on the interior walls of the reactor, there was a hard lumpy deposit around the shaft and lid, and most of the lid was covered by a skin of deposit. The total build-up was 0.02% of the monomer charge.

EXAMPLE 4 The pressure reactor of Example 1 was thoroughly cleaned free from all deposit, washed and dried.

A solution of aminoazobenze (1 part), hydroquinone (1 part), p-aminobenzoic acid (1 part), and pyrogallol (1 part) in ethanol: water (80 parts) was prepared by mixing the components. After mixing a deep red colour was quickly developed and some precipitation was observed within 30 minutes. The solution was then used to coat the internal surfaces of the reactor including stirrer and the lid. The solvent was allowed to evaporate by heating the reactor walls to 700 for approxmately 30 mins and this was followed by a quick rinse (1 min) of all surfaces with cold water.

The general procedure of Example 1 was repeated in the coated reactor after the solvent in the coating had vaporised completely.

The first batch was free of the hard build-up and the accumulation of comparatively loose polymer was washed out with water.

A second polymerisation reaction was carried out in the same reactor without any cleaning of the internal surfaces of the reactor, and without any further application of the coating composition. After this reaction was completed a small amount of build-up formed but was very much lower than that of the control batch of Example 1. This build-up was loosely attached and easily removed by rinsing the reactor with water. The total build-up from these two consecutive polymerisation reactions was 0.1% of the initial monomer charge.

EXAMPLE5 The pressure reactor of Example 1 was thoroughly cleaned free from all deposit washed with water and dried. The internal surfaces of the reactor were heated to 70-800C and coated with a solution of aminoazobenzene (1 part), p-toluidine (1 part), p-aminobenzoic acid (1 part), pyrogallol (1 part), hydroquinone (1 part) and lessaminie (lissamine) yellow in an ethanol: water solvent (90:10 parts). (The word "LISSAMINE" is a registered trade mark).

The general polymerisation procedure of Example 1 was repeated in the coated vessel after the solvent in the coating had vaporised completely. All reactor surfaces were shiny and clean. A very small amount of build-up was found around the shaft, and this was easily removed by rinsing with water.

EXAMPLE 6 This Example illustrates the use of the coating composition without the baking step referred to hereinbefore.

The pressure reactor of Example 1 thoroughly cleaned free from all deposit, washed and dried.

The internal surfaces of the reactor were coated at room temperature with the solution described in Example 4. The solvent was allowed to evaporate at ambient temperature (ca. 30 min). This was followed by a 1 min rinse of all surfaces with cold water to remove any unreacted components of a coating composition and loosely adhering suppressant.

The general polymerisation procedure of Example 1 was then repeated in the coated reactor. After the reaction the walls were clean, although not shiny, and with a few patches of film build-up. Some heavy and firmly attached build-up was found on shaft, paddle and bottom of gland. The lid was almost covered by very thin film of polymer deposit.

While the amount of build-up was much less than that formed in the control procedure of Example 1, it was slightly more than that of Example 4 where the coated surfaces of the reactor were baked prior to the polymerisation reaction.

EXAMPLE 7 This is a comparative example to illustrate the effect of adding the coating composition of our invention to the polymerisation medium instead of applying the composition to the walls.

The pressure reactor of Example 1 was thoroughly cleaned free from all deposit, washed and dried. After charging all reactants the coating composition solution of Example 4 (.03% based on vinyl chloride) was heated to about 30"C and injected into the reactor. The reactor contents were then heated to 560C and the polymerisation procedure of Example 1 repeated.

The build-up was only marginally less than that of the control Example 1, with heavy deposit on all protrusions, shaft, paddle and lid. The reactor walls were completely covered by very thin film. The amount of firmly attached build-up was .06% of the vinyl chloride monomer charged.

EXAMPLE 8 This is a further comparative example to show the effect of adding the coating composition to the suspension medium of the polymerisation reaction instead of to the internal surfaces of the reactor.

The procedure of Example 7 was repeated except that the suppressant composition was added to the water charge before injecting the monomer. No significant improvement in buildup was found compared to the results of Example 7.

EXAMPLE 9 The pressure reactor of Example 1 was thoroughly cleaned free from all deposit, washed and dried. All internal surfaces of the reactor were heated to 700C and coated with a solution of hydroquinone (4.5 parts), tetraethylenepentamine (2.5 parts), salicyl aldehyde (2.5 parts), p-phenylenediamine (2 parts), pyrogallol (1 part), p-aminobenzoic acid (1 part) and durazol orange (1 part) in ethanol: water solvent (50:30 parts).

The general polymerisation procedure of Example 1 was repeated in the coated reactor.

The formation of build-up was negligible.

EXAMPLE 10 The pressure reactor of Example 1 was thoroughly cleaned free from all deposit, washed and dried. The internal surfaces of the reactor were heated to 800 and painted with a solution of hydroquinone (4.5 parts), salicylaldehyde (2.5 parts), p-cresol (2.5 parts), p-aminobenzoic acid (1 part), diphenylamine (3.5 parts), tetraethylenepentamine (2.5 parts) and metanyl yellow (0.5 part) in ethanol: water solvent (50: 30 parts). (Metanyl yellow is the sodium salt of 4-anilinoazolbenzene-3'-sulphonic acid; it is linked in the Colour Index as No. 13065 and designated Acid Yellow 36.) This solution had been kept for 48 hours at room temperature prior to application. When the solution was first prepared some precipitation occurred, and the mixture was light red in colour. Over the 48 hours the colour changed through dark red to an almost black colour.

The polymerisation procedure of Example 1 was repeated in the coated reactor. Only a few patchy areas of firmly attached build-up were found on walls, lid, shaft and paddle. The total amount of build-up was .04% of the original monomer charge.

EXAMPLE 11 The pressure reactor of Example 1 was thoroughly cleaned free from all brnld-up, washed and dried. The intemal surfaces of the reactor were heated to 800C and coated by a solution of hydroquinone (4 parts), tetraethylene pentamine (2 parts), salicylaldehyde (3 parts), p-phenylenediamine (2 parts), cresol (1 part), pyrogallol (1 part), p-aminobenzoic acid (1 part) and aminoazobenzene (1 part) in ethanol (50 parts) and water (30 parts).

The general polymerisation procedure of Example 1 was then repeated in the coated reactor. Formation of buildup was negligible.

WHAT WE CLAIM IS: 1. A process for the polymerisation of vinyl halide monomers (as hereinbefore defined) in aqueous dispersion wherein the polymerisation is carried out in a reactor, said reactor havirig deposited on the interior surfaces thereof a coating composition, said coating composition being prepared by reacting together at least one compound (A) selected from the group consisting of azo compounds; with at least one compound (B) selected from the group consisting of aliphatic and aromatic amines; and with at least one compound (C) selected from the group consisting of oxy-group substituted aromatic compounds and quinones.

2. A process according to claim 1 wherein the said vinyl halide monomer is vinyl chloride.

3. A process according to claim 1 or to claim 2 wherein the said compound (A) is selected from the group consisting of p-aminoazobenzene, p-hydroxyazobenzene, phenylazo-2napthol, and diazoaminobenzene.

4. A process according to any one of claims 1 to 3 inclusive wherein the said compound (B) is selected from the group consisting of paminobenzoic acid, phenothiazine, diphenylamine, p-phenylenediamine, triethanolamine, tributylamine, and tetraethylenepentamine.

5. A process according to any one of claims 1 to 4 inclusive wherein the said compound (C) is selected from the group consisting of hydroquinone, benzoquinone, pyrogallol, cresols, p-tertiarybutyl-catechol, resorcinol, and picric acid.

6. A process according to any one of claims 1 to 5 inclusive wherein the weight ratios of each of the said compounds (A), (B) and (C) to the total weight of the coating composition prepared therefrom are in a range from 1:20 to 3:4.

7. A process according to claim 6 wherein the said ratios are in a range from 1:10 to 1:2.

8. A process according to any one of claims 1 to 7 inclusive wherein the compounds selected for preparing the coating composition are p-aminoazobenzene, p-phenylenediamine, tetraethylenepenetamine, pyrogallol and hydroquinone.

9. A composition of matter which is a reaction product derived from reacting together at least one compound (A) selected from the group consisting of azo compounds; with at least one compound (B) selected from the group consisting of aliphatic and aromatic amines; and with at least one compound

Claims (22)

**WARNING** start of CLMS field may overlap end of DESC **. The pressure reactor of Example 1 was thoroughly cleaned free from all brnld-up, washed and dried. The intemal surfaces of the reactor were heated to 800C and coated by a solution of hydroquinone (4 parts), tetraethylene pentamine (2 parts), salicylaldehyde (3 parts), p-phenylenediamine (2 parts), cresol (1 part), pyrogallol (1 part), p-aminobenzoic acid (1 part) and aminoazobenzene (1 part) in ethanol (50 parts) and water (30 parts). The general polymerisation procedure of Example 1 was then repeated in the coated reactor. Formation of buildup was negligible. WHAT WE CLAIM IS:

1. A process for the polymerisation of vinyl halide monomers (as hereinbefore defined) in aqueous dispersion wherein the polymerisation is carried out in a reactor, said reactor havirig deposited on the interior surfaces thereof a coating composition, said coating composition being prepared by reacting together at least one compound (A) selected from the group consisting of azo compounds; with at least one compound (B) selected from the group consisting of aliphatic and aromatic amines; and with at least one compound (C) selected from the group consisting of oxy-group substituted aromatic compounds and quinones.

2. A process according to claim 1 wherein the said vinyl halide monomer is vinyl chloride.

3. A process according to claim 1 or to claim 2 wherein the said compound (A) is selected from the group consisting of p-aminoazobenzene, p-hydroxyazobenzene, phenylazo-2napthol, and diazoaminobenzene.

4. A process according to any one of claims 1 to 3 inclusive wherein the said compound (B) is selected from the group consisting of paminobenzoic acid, phenothiazine, diphenylamine, p-phenylenediamine, triethanolamine, tributylamine, and tetraethylenepentamine.

5. A process according to any one of claims 1 to 4 inclusive wherein the said compound (C) is selected from the group consisting of hydroquinone, benzoquinone, pyrogallol, cresols, p-tertiarybutyl-catechol, resorcinol, and picric acid.

6. A process according to any one of claims 1 to 5 inclusive wherein the weight ratios of each of the said compounds (A), (B) and (C) to the total weight of the coating composition prepared therefrom are in a range from 1:20 to 3:4.

7. A process according to claim 6 wherein the said ratios are in a range from 1:10 to 1:2.

8. A process according to any one of claims 1 to 7 inclusive wherein the compounds selected for preparing the coating composition are p-aminoazobenzene, p-phenylenediamine, tetraethylenepenetamine, pyrogallol and hydroquinone.

9. A composition of matter which is a reaction product derived from reacting together at least one compound (A) selected from the group consisting of azo compounds; with at least one compound (B) selected from the group consisting of aliphatic and aromatic amines; and with at least one compound (C) selected from the group consisting of oxy-group substituted aromatic compounds and quinones.

10. A composition of matter according to claim 9 wherein the said compound (A) is selected from the group consisting of paminoazobenzene, p-hydroxyazobenzene, phenylazo-2-napthol, and diazoaminobenzene.

11. A composition of matter according to claim 9 or claim 10 wherein the said compound (B) is selected from the group consisting of paminobenzoic acid, phenothiazine, diphenylamine, p-phenylenediamine, triethanolamine, tributylamine, and tet raethylenepentamine.

12. A composition of matter according to any one of claims 9 to 11 inclusive wherein the said compound (C) is selected from the group consisting of hydroquinone, benzoquinone, pyrogallol, cresols, p-tertiarybutyl-catechol, resorcinol, and picric acid.

13. A composition of matter according to any one of claims 9 to 12 inclusive wherein the compounds selected for preparing the coating composition are p-aminoazobenzene, p-phenylenediamine, tetraethylenepentamine, pyrogallol and hydroqinone.

14. A composition of matter according to any one of claims 9 to 13 inclusive wherein the weight ratios of each of the said compounds (A), (B) and (C) to the total weight of the coating composition prepared therefrom are in a range from 1:20 to 3:4.

15. A composition of matter according to claim 14 wherein the said ratios are in a range from 1:10 to 1:2.

16. A polymerisation reactor wherein the interior surfaces of said reactor are coated with a composition of matter according to any one of claims 9 to 15 inclusive.

17. A process according to any one of claims 1 to 8 inclusive wherein the said coating composition is dissolved in a solvent before applying to the said interior surfaces of said reactor.

18. A process according to claim 17 wherein the said solvent comprises an aqueous medium.

19. A process according to claim 18 wherein said aqueous medium comprises an aldehyde or alcohol.

20. A process according to claim 1 and substantially as described with reference to any one of the Examples 4 to 6, and 9 to 11.

21. A composition of matter according to claim 9 and substantially as described with reference to any one of the Examples 4 to 6, and9to 11.

22. A polymerisation reactor according to claim 16 and substantially as described with reference to any one of the Examples 4 to 6, and9to 11.