NO148928B - PROCEDURE FOR POLYMERIZATION OF VINYL CHLORIDE IN Aqueous DISPERSION, AND THE REACTOR OF THE PROCEDURE - Google Patents

Description

The present invention relates to a method for polymerization of vinyl chloride monomers in aqueous dispersion, as well as a reaction vessel - reactor - for carrying out the method.

When vinyl halide monomers, especially vinyl chloride, are polymerized in aqueous dispersion in a reactor, it is well known that a problem arises in that surfaces inside the reactor become coated with sticky, adherent polymeric material, which is known as build-up. Polymerization in an aqueous dispersion means polymerization in an aqueous emulsion or aqueous suspension (including aqueous microsuspension). The formation of sticky, clinging build-up is undesirable with a view to achieving efficient heat transfer for cooling and heating the reactor contents, efficient utilization of monomers, effective regulation and monitoring of the polymerization reaction and acceptable polymer quality (with a view to contamination with detached particles of the build-up).

Due to the problems of heat transfer, control of polymerization and polymer quality, it is necessary to clean the reactor between each polymerization cycle, whereby the deposited material is removed as completely as possible, e.g.

by scraping or chopping by hand, solvent cleaning or pressure washing. This is wrong when you think about expenses for . equipment and "manpower" necessary to carry out such cleaning and also when one considers the loss of productivity for a given reactor that occurs due to the time it takes to carry out the cleaning. Furthermore, manual cleaning is undesirable because this can pose a health hazard in view of the deleterious properties of certain monomers, especially vinyl chloride.In reality, opening the reactor between polymerization cycles is in itself undesirable

since this leads the remaining monomer in the reactor into the surrounding atmosphere.

It is proposed in British Patent No. 1,444,360

to coat the inner surfaces of a reactor used in the polymerization of vinyl chloride with polyethyleneimine to prevent or reduce the formation of build-up therein. British patent document No. 1 439,339 is aimed at the same purpose, but according to this, polyethyleneimine which has been cross-linked with an aldehyde, such as formaldehyde, is used, among other things. We have now found that these techniques, although effective, are not completely satisfactory in factory-scale polymer production due to the fact that some build-up is still formed, especially above the liquid level of the polymerization medium, and this necessitates a quite frequent cleaning of the reactor.

We have now discovered an improved technique by which vinyl chloride can be polymerized in aqueous dispersion without any or greatly reduced formation of build-up.

The method according to the invention therefore relates to a method for the polymerization of vinyl chloride, alone or together with other vinyl halides or other comonomers that are copolymerizable with vinyl chloride, in an aqueous dispersion, and the method is characterized by the polymerization being carried out in a reaction vessel which on its inside surface has an adhesively deposited coating of a coating product obtained by reacting a mixture of at least polyethyleneimine and one or more representatives of the group hydroquinone, p-benzoquinone, catechol and o-benzoquinone at a temperature of 15-150°C.

The reaction vessel according to the invention is characterized in that it has adhesively deposited on its inner surface a coating of a coating product obtained by reacting a mixture of at least polyethyleneimine and one or more representatives of the group hydroquinone, p-benzoquinone, catechol and o- benzoquinone at a temperature of 15-150°C.

Production of the coating product used in connection with the invention is carried out in a temperature range varying from low-temperature production at temperatures in the range of 15-100°C to production at higher temperatures, in the range of 100-150°C. Typical temperature ranges for manufacturing are 15-100°C and 50-150°C.

The production of the coating product is preferably carried out in the presence of oxygen. This is conveniently added by exposing the ingredients from which the product originates to the ambient air, and this can be done during or after mixing. Oxygen can also be supplied by oxygen injection or from an added chemical agent which is a suitable oxidizing agent, and p-benzoquinone or o-benzoquinone can sometimes itself serve as an oxidizing agent.

The molar ratio between the repeating polyethyleneimine unit (-CH-^CJ^NH-) and the other component(s) (selected from one or more of hydroquinone, p-benzoquinone, catechone and o-benzoquinone) is not critical, although the polyethyleneimine (repeat unit) is preferably present in molar excess. For products derived from polyethyleneimine and hydroquinone, the preferred molar ratio of polyethyleneimine (repeat unit) hydroquinone is 6/0.5 to 1/1, typically 4/1 to 1/1 and especially 2.5/1 to 1/1.

The production of the coating product should preferably be carried out under alkaline conditions, e.g. with a pH>7 in the medium in which the mixture takes place. When a molar excess of polyethyleneimine (an amino compound) is preferably used for the production of the coating product, this condition is thereby provided, but it is of course assumed that the alkalinity due to the polyethyleneimine is not weakened by the presence of an added acidic component. Generally speaking, however, it is advantageous to use an added inorganic alkali, such as a metal or ammonium hydroxide (which may be added before, during or after mixing) to ensure that the medium is alkaline, and the inorganic alkali is preferably a caustic alkali such as sodium hydroxide or potassium hydroxide.

In carrying out the invention, the coating product preferably originates from a mixture of hydroquinone and polyethyleneimine under alkaline conditions (pH > 7), although p-benzoquinone can be used instead of or in addition to the hydroquinone in this embodiment.

Other organic oxygen-containing compounds may be incorporated into the mixture from which the coating product is derived, in particular polyhydric phenols of the formula where R^, R2, R^ and R^, which may be the same or different, are selected from H, halogen (fluorine, chlorine, bromine or iodo), hydroxyl, alkoxy, aryl (including substituted aryl), nitro, alkyl (including substituted alkyl) - preferably lower alkyl, alkenyl (including substituted alkenyl) - preferably lower alkenyl, esterified carboxyl and acyl, provided and the above formula excludes hydroquinone and catechol. The polyhydric phenol preferably contains no more than 3 core hydroxyl groups and preferably has at least two of R^, R^, R^ and R^ as H. It should be understood that none of the substituents should affect the formation of the coating product or the usefulness of the resulting coating product to suppress build-up. Examples of such phenols include resorcinol, chlororesorcinol, the isomeric dihydroxytoluenes and xylenes, the isomeric ethyl, propyl, butyl and pentyl dihydroxybenzenes, progallol, hydroxyquinol, phloroglucinol, the isomeric trihydroxytoluenes and xylenes and the isomeric ethyl, propyl, butyl and pentyl trihydroxybenzenes.

A particularly preferred coating product for use in the invention is one derived from mixing polyethyleneimine, hydroquinone and a small amount of pyrogallol, and the amount of pyrogallol used is typically <0.3 mol, preferably 0.1 mol, in relation to 1 mol hydroquinone.

The mixing of the ingredients for the coating product can be carried out on internal surfaces of the reactor or by a separate operation which is not carried out on the internal surfaces, to form a product which is then applied to the internal surfaces. In both methods, the coating product is applied to the surfaces as a dispersion or solution in a liquid carrier medium which can be allowed or caused (e.g. by heating and/or evacuating or blowing air) to evaporate so that it remains an adhesive coating.

When the mixing is carried out on internal surfaces of the reactor, this mixing is preferably carried out at a low temperature, e.g. 15-100°C, in the presence of oxygen. This mixing method is particularly applicable to the formation of a coating product derived from polyethyleneimine and hydroquinone, and it can conveniently be carried out by applying separate solutions or dispersions of the polyethyleneimine and hydroquinone successively or simultaneously to the surface or surfaces to be coated (before adding of the ingredients for the vinyl chloride polymerization reaction) after which a reaction quickly takes place to form a coating product which is carried in a liquid medium, especially when the components of the applied solutions or dispersions are exposed to the ambient oxygen in the air.

When the mixing is carried out by a separate operation before the application of the coating product to an internal surface, a solution or dispersion of the product is prepared in a carrier medium and this solution or dispersion is applied to the reactor surface e.g. by spraying, painting, dipping or over-flowing. In this embodiment, the temperature during mixing is not critical, e.g. both the low-temperature and high-temperature variants mentioned above are effective, and the temperature is preferably in the range 15-150°C. Sometimes the admixture is advantageously carried out in the presence of a small amount of an acidic catalyst, such as hydrochloric acid or aluminum chloride, although the use of an acidic catalyst is not essential.

When mixing polyethyleneimine and hydroquinone in a separate pre-mixing operation, these components are soluble in water so that the mixing can be carried out in water as a solvent, the water being preferably removed by distillation as part of the mixing operation to form the coating product. In such a case, the reaction temperature is conveniently the boiling point of water at atmospheric pressure (i.e. about 100°C), and the mixing can alternatively be carried out at subatmospheric pressure so that a lower mixing (and distillation) temperature can be used, e.g. a temperature of 50-100°C can be used, as the reduced pressure greatly facilitates the removal of water.

In another interesting system, the coating product is formed by pre-mixing hydroquinone, p-benzoquinone and polyethyleneimine (or equivalent catechol, o-benzoquinone and polyethyleneimine) under aqueous alkaline conditions, the alkalinity of the medium being ensured by the addition of a metal hydroxide, such as sodium hydroxide or potassium hydroxide. The order of mixing of the components of the aqueous alkaline mixture is not critical. For example, hydroquinone, p-benzoquinone and polyethyleneimine can first be mixed together in water, the hydroquinone and p-berisoquinone are for example added to an agitated aqueous polyethyleneimine solution, and to this mixture a caustic alkali such as sodium or potassium hydroxide, possibly mixing it further). Alternatively, a mixture of polyethyleneimine and a caustic alkali can be mixed together in water, and hydroquinone and p-benzoquinone are added to the agitated mixture. In a further method, a mixture of polyethyleneimine, caustic alkali, hydroquinone and p-benzoquinone can be mixed together in water in one step. The relative quantity ratio between hydroquinone and p-benzoquinone in the mixture is not believed to be critical, however good results have been achieved when the molar ratio hydroquinone/p-benzoquinone is essentially 1:1.

The product obtained from the premixing operation can vary from a very viscous substance to a glassy substance,

and usually makes the medium in which the mixing takes place too viscous to be applied directly to the internal surfaces of a reactor, even in cases where the medium has not been removed (eg, by distillation). Accordingly, the product resulting from the admixture (whether the admixture medium is still present or not) should usually be diluted with a solvent or dispersant which will then act as a liquid carrier for application to internal surfaces of a reactor. The coating products dissolve in very few liquids, however, ethanol (and to a lesser extent methanol) has been found to be a suitable solvent. The coating products will also dissolve in aqueous alkaline solutions (of e.g. NaOH and KOH), which can therefore also be used as solvents. A suitable non-solubilizing dispersant is non-alkaline water, although it is sometimes necessary to ensure that the product is uniformly dispersed in the water.

The chemical nature of the coating product has not been properly understood in any way. However, since the product is invariably deeply colored (e.g. red, brown or black), it is expected that the product may at least to some extent include aminoquinoid structures containing groups of the following type:

(and/or the corresponding ortho-structures) as the nitrogen atoms originate from the polyethyleneimine chain. It has been thought that this type of structure may be somewhat more prominent when the mixing takes place at a low temperature, e.g. 15-100°C.

It is also thought that the coating product at least to a certain extent consists of a condensation reaction product formed as a result of a condensation between the amino groups in the polyethyleneimine and the hydroxy groups in the hydroquinone (and/or catechol).

It is also thought that the coating product at least to a certain extent consists of a stabilized form of the anion radical which structurally originates from p-benzoquinone, i.e. the anion radical with the formula

(and/or the corresponding radical which structurally originates from o-benzoquinone) as the stabilization is effected by diffusion of the anion radical in the polyethyleneimine basic structure. A strong electron spin resonance (esr) signal characteristic of this radical has in fact been demonstrated from coating products of the invention which have been tested for this purpose. It is not critical what amount of coating product is used. Generally speaking, however, it is sufficient for many sizes and shapes of reactors to have an amount of 5 to 200 ppm, preferably 10 to 50 ppm, (based on the weight of the monomer to be added), coated uniformly over the inner surfaces of the reactor. Of course, the ratio between surface area and volume in the reactors will vary considerably according to the sizes of the reactors.

The coating can be formed on any inside of the reactor that is exposed to the formation of build-up thereon. For example, it can be applied to the inner surfaces of the main body of the reactor, and to the inner surfaces of the roof of the reactor, which is often above the liquid level of the polymerization medium and on which there is often a sticky build-up. If a condenser is installed in a part of the reactor which is in contact with the gas phase during polymerisation, or if it is installed outside the reactor and connected to it by conduit, the condenser and conduit can be coated in a similar manner. It should be understood that in order to obtain the best results, a surface to be coated should be as clean and smooth as possible to begin with. If the surface has a somewhat questionable quality in this area, it may be advisable to coat it with two or more successive layers of the coating mixture.

The coating can be formed on a surface in combination with one or more other materials, e.g. materials which also have a suppressive effect on polymerization build-up.

A reactor which has coated inner sur-

surfaces according to the invention can be used for polymerization of vinyl chloride, and the formation of build-up will then be eliminated or very strongly limited. The polymerization reaction is preferably carried out in the presence of a basic substance, such as NaHCO-j, or a suitable buffer system, in order to ensure a sufficiently high pH in the reaction medium (e.g. pH>4) since such an agent can also increase the build-limiting effect of the coating product.

By "polymerization" is meant both

homopolymerization of vinyl chloride and copolymerization with other comonomers that are copolymerizable thereby. Examples of the latter include vinyl esters such as vinyl acetate, acrylic esters such as methyl methacrylate and butyl methacrylate, acrylonitriles such as acrylonitrile and methacrylonitrile, unsaturated diesters such as diethyl maleate, allyl esters such as allyl acetate, α-olefins such as ethylene and propylene, vinyl ethers and styrene compounds.

The present invention can in particular be used in any polymerization technique where a monomer or monomers are dispersed in the form of droplets in a liquid aqueous phase. It can for example be used for polymerization in aqueous emulsion, and in this case any suitable emulsifier can be used, and in particular an ionic emulsifier such as sodium lauryl sulphonate or sodium dodecylbenzene sulphonate, and non-ionic emulsifiers. It is also possible to use any water-soluble free-radical polymerization initiator and in particular a persulfate.

The invention is also very applicable to polymerization in aqueous suspension and microsuspension.

Any suitable dispersing agent can be used for polymerization in aqueous suspension, and in particular finely dispersed solids, gelatin, polyvinyl acetates with varying degrees of hydrolysis, water-soluble cellulose esters and polyvinyl pyrrolidones. These dispersants can be used together with other surfactants, if desired. The amount used can vary greatly, and is usually between 0.05 and 1.5% by weight, calculated on the water used.

Any suitable free radical polymerization initiator which is monomer soluble can be used in aqueous suspension polymerization. Examples of these include peroxy compounds such as di-tert-butyl peroxide, lauroyl peroxide and acetylcyclohexyl sulfonyl peroxide, azo compounds such as azo-bis-isobutyronitrile and 2,2'-azo-bis-2,4-dimethylvaleronitrile and boron alkyls . Monomer-soluble free radical polymerization initiators which are particularly suitable for use in a polymerization process according to the invention are those dialkyl peroxydicarbonates whose alkyl radicals contain up to 20 carbon atoms, such as diethyl peroxydicarbonate, diisopropyl peroxydicarbonate and dicetyl peroxydicarbonate, dicycloalkyl peroxydicarbonates such as bis(4 -tert.butylcyclohexyl)peroxydicarbonate, and azo compounds such as 2,2'-azo-bis-2,4-dimethylvaleronitrile and azo-bis-isobutyronitrile. These initiators can be used in conventional amounts - generally speaking from 0.01 to 1% by weight, calculated on monomer.

Homogenized aqueous dispersion polymerization, sometimes referred to as microsuspension polymerization, involves mechanically homogenizing an aqueous dispersion of the monomer or monomers in the presence of a surfactant (for example, by subjecting it to high shear in a colloid mill), and polymerizing of the homogenized dispersion in the presence of an initiator which is monomer soluble.

Conventional emulsifiers and monomer-soluble initiators can be used in microsuspension polymerization, such as, for example, a cationic emulsifier such as sodium dodecylbenzenesulfonate, 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 which are sometimes used in conventional methods for polymerization in aqueous dispersion. Examples of such additives include particle size regulators, molecular weight regulators, stabilizers, plasticizers, dyes, strengthening agents and processing aids.

The operating conditions for polymerization according to the present invention can be such as are usually used.

When, for example, it concerns the polymerization of vinyl chloride, the polymerization temperature is usually between 40 and 75°C and the pressure is usually below 15 kg/cm 2 .

The present invention will now be illustrated with the following examples. If not stated otherwise, all parts and percentages are by weight. Where it was necessary to remove the dark color of coating compound on a surface, this was done by scouring with a damp non-abrasive mesh of soft copper wool.

EXAMPLE 1 (Comparison)

A stainless steel reactor (capacity 160 litres) was used which was fitted with a paddle stirrer. The interior of the reactor was carefully cleaned by hydrodynamic pressure washing.

In the reactor, a conventional homopolymerization of a vinyl chloride suspension was carried out at 57°C using 100 parts vinyl chloride, 160 parts water, 0.13% partially hydroxylated polyvinyl acetate (based on vinyl chloride) as suspending agent and 0.038% diethyl peroxydicarbonate (based on vinyl chloride ) as initiator. The polymerization was continued until well into the pressure drop area, and then the polymerization was terminated by venting the monomer.

Examination of the interior of the reactor, after removal of the polymer slurry, showed that severe build-up had formed on the roof of the autoclave, and there was also a chalky white film on the side walls of the reactor.

EXAMPLE 2

The reactor was carefully hydrodynamically cleaned, and the internal surfaces were sprayed first with 10 ppm (based on vinyl chloride) polyethyleneimine (as a 1% aqueous solution) and then with 10 ppm (based on vinyl chloride) hydroquinone (as a 1% aqueous solution -ning) . The coating dried quickly at the ambient temperature (approx. 20°C), no heat was added, and a reddish tinge appeared on the reactor surfaces. v

Polymerization was then carried out using the method of Example 1. Examination of the interior of the reactor after removal of the polymer slurry showed that the internal reactor surfaces (wall and ceiling) were completely clean and shiny.

EXAMPLE 3

The reactor was not cleaned after execution of example 2, but was coated again using the method from example 2. Polymerization was carried out in the reactor using the method from example 1.

The roof of the reactor was completely clean and shiny although a chalky white film had formed over a small area of the wall.

EXAMPLE 4

The reactor was not cleaned after execution of example 3, but it was again coated using the method from example 2. Polymerization was carried out in the reactor at an- . reversal of the procedure from example 1.

The roof of the reactor was completely clean and shiny although a thin white skin had formed over a small area of the wall.

EXAMPLE 5

The reactor, which contained no traces of coating product according to the invention and which had also been hydrodynamically cleaned, was sprayed inside first with 10 ppm (based on vinyl chloride) polyethyleneimine (as a 1% aqueous solution) and then with 10 ppm (based on vinyl chloride) p-benzoquinone (as a 1% ethanolic solution) . The coating dried quickly at the ambient temperature (approx. 20°C), no heat was added, and this gave a reddish tinge to the reactor surface.

It was then polymerized using the method of Example 1. Examination of the interior of the reactor after removal of the polymer slurry showed that the walls and roof were completely clean and shiny.

EXAMPLE 6

The internal surfaces of the reactor used in the example

1, which did not contain any traces of coating product according to the invention and which had been hydrodynamically cleaned, was coated using the method from example 2.

It was polymerized in the reactor using the method from Example 1, except that 100 was added

ppm NaHCO^ to the aqueous medium before the polymerization was started.

The internal surfaces of the reactor (roof and walls) were found to be completely clean and shiny after the polymer slurry was removed.

EXAMPLE 7

The inner surfaces of the reactor, which contained no traces of coating product according to the invention and which had been hydrodynamically cleaned, were coated using the method of Example 2, except that the amount of polyethyleneimine used was 20 ppm and the amount of hydroquinone used was 20 ppm.

It was polymerized using the method from Example 6. After removing the polymer slurry, it was observed that the interior of the reactor (roof and walls) was completely clean and shiny.

EXAMPLE 8

After removing the polymer slurry from Example

7, the reactor was not hydrodynamically cleaned, but was coated using the method of Example 2, except that 50 ppm polyethyleneimine and 50 ppm hydroquinone were used.

It was polymerized using the method of Example 6. After removal of the polymer slurry, it was observed that the interior of the av reactor (roof and walls) was completely clean and shiny. However, it was noted that parts of the ceiling had developed brown stains, probably due to an excess of coating product.

EXAMPLE 9

After removal of the polymer slurry from Example 8, the roof of the reactor was scrubbed appropriately to remove the brown spots, but was not hydrodynamically cleaned. The reactor was then coated using the method of Example 2, except that 25 ppm polyethyleneimine and 15 parts hydroquinone were used.

It was polymerized using the method from Example 6. After removing the polymer slurry, it was observed that the interior of the reactor (roof and walls) was completely clean and shiny.

EXAMPLE 10 (Comparison)

The reactor, which did not contain any traces of coating product according to the invention and which had been hydrodynamically cleaned, was used in the polymerization of vinyl chloride using the method from example 1, except that 0.061% (based on vinyl chloride) bis( 4-tert-butylcyclohexyl)peroxydicarbonate.

A buildup formed on the ceiling, and a chalky white film formed on parts of the walls of the autoclave.

EXAMPLE 11

The hydrodynamically cleaned reactor, which contained no trace of coating product, was coated using the method from example 2. It was polymerized in the reactor using the method from example 10.

The roof and walls of the reactor were completely clean and shiny after polymerization.

EXAMPLE 12

The hydrodynamically cleaned reactor, which contained no trace of coating product, was coated using the procedure of Example 2, except that 20 ppm polyethyleneimine and 10 ppm hydroquinone were used.

It was polymerized in the reactor using the method of Example 6. The roof and walls of the reactor were found to be completely clean and shiny.

EXAMPLE 13

After removing the slurry from Example 12, and without cleaning the reactor, the polymerization from Example 6 was

again carried out in the reactor. After polymerization, the walls and roof of the reactor were still completely clean and shiny.

EXAMPLE 14

The hydrodynamically cleaned reactor, which contained no trace of coating product, was coated using the procedure of Example 2, except that 15 ppm polyethyleneimine and 7.5 ppm hydroquinone were used.

It was polymerized using the procedure of Example 6. The roof and walls of the reactor were found to be completely clean and shiny.

EXAMPLE 15 (Comparison)

The reactor, which did not contain any traces of coating product according to the invention and which had also been hydrodynamically cleaned, was not coated according to the invention but used directly in a vinyl chloride polymerization. The procedure for the polymerization was as in example 6 (i.e. 100 ppm NaHCO^

was added to the aqueous medium before the polymerization was started).

Considerable build-up was observed in the roof of the reactor, which shows that the effect with build-up inhibition is not only due to the action of NaHCO^.

EXAMPLE 16

A mixture of polyethyleneimine (129 ml of a 20% aqueous solution), hydroquinone (16.5 g) and, conc. HCl (3.75 ml) was prepared and the mixture corresponds to a molar ratio of 4 (polyethyleneimine repeat units) /l (hydroquinone). The mixture was heated to reflux temperature (100°C) and hydroquinone dissolved at 60-70°C so that a clear solution was obtained. Water was distilled from the mixture until most of it was removed (about 1 hour).

Small amounts of starting materials were removed with the distillate. The remaining water was removed with nitrogen.

The product obtained was a gummy, dark reddish-brown material which was soluble in ethanol but not in dimethylformamide, acetone, methylene chloride, chloroform and various other common

organic solvents.

EXAMPLE 17

The procedure of Example 16 was repeated, except that the original reaction mixture also contained pyrogallol (1.65 g) - the mixture corresponding to a molar ratio of 4 (polyethyleneimine repeat units)/l (hydroquinone)/0.1 (pyrogallol). The distillation lasted approx. 1 hour.

The product was a brown-black material that was extremely viscous (almost a solid), indicating that it has a high degree of cross-linking. Like the product of Example 16, it was insoluble in various common organic solvents, but was soluble in ethanol.

EXAMPLES 18-24 (Ex. 18 is for comparison)

In these examples, conventional suspension homopolymerization of vinyl chloride was carried out in a stainless steel reactor (capacity 5 liters) equipped with a paddle stirrer. Unless otherwise stated, the inner surfaces of the reactor were carefully cleaned before each polymerization. . The polymerizations were carried out at 57°C using 100 parts of vinyl chloride, 222 parts of water, 0.22% of partially hydrolyzed polyvinyl acetate (based on added vinyl chloride) as suspending agent and bis(4-tert-butylcyclohexyl)peroxydicarbonate as initiator (amounts as shown in Table 1). The polymerization was continued until well into the pressure drop area, and then the polymerization was terminated by venting the monomer. In Examples 19-24, the inner surfaces of the reactor were painted with 10 ml of ethanol in which a certain amount of the product from either Example 16 or Example 17 had been dissolved (ppm based on added vinyl chloride, as indicated in Table 1), and the coatings were allowed to to dry before the polymerization ingredients were added.

The polymerizations in examples 20, 21 and 22 were carried out successively in the reactor, and before the polymerizations in the examples. 21 and 22, the pre-cleaning of the reactor main part and roof was omitted. The polymerizations in examples 23 and 24 were carried out successively in the reactor and pre-cleaning of the reactor main part and roof was omitted before the polymerization in example 24.

Observations of the formation of polymer build-up are in each case (after removal of the polymer slurry and washing out of all loose adhering soft wet cake) shown in table 1. It can be seen that the use of a coating product according to the invention had a marked suppressive effect on build-up.

EXAMPLES 25-30 (Ex. 25 is for comparison)

In these examples, conventional suspension homopolymerization of vinyl chloride in aqueous suspension was carried out in a stainless steel reactor (capacity 160 liters) equipped with a paddle stirrer. Unless otherwise stated, the inner surfaces of the reactor were carefully cleaned before each polymerization. The polymerizations were carried out at 57°C using 100 parts vinyl chloride, 156 parts water, 0.13% partially hydrolyzed polyvinyl acetate (based on added vinyl chloride) as suspending agent and bis(4-tert-butylcyclohexyl)peroxydicarbonate as initiator (amounts as shown) in table 2).. The polymerizations continued well into the pressure drop area and were then terminated by venting the monomer. In Examples 26-30, the inner surfaces of the reactor were sprayed with 50 ml of ethanol in which a certain amount of the product from either Example 16 or Example 17 had been dissolved (ppm based on added vinyl chloride as indicated in Table 2), and the coatings were allowed to to dry before the addition of the polymerization ingredients.

The polymerizations in examples 26, 27 and 28 were carried out successively in the reactor, and before the polymerizations in examples 27 and 28 the pre-cleaning of the reactor main part and the reactor roof was omitted.

The observations of formation of build-up are given in Table 2 for each case (after removal of the polymer slurry and washing off all loose adhering soft wet cake). It can be seen that application of a coating product according to the invention had a marked suppressive effect on the formation of build-up.

EXAMPLES 31-33 (Ex. 31 is for comparison) The polymerization procedure from Examples 25-30 was used, except that diethyl peroxydicarbonate was used as initiator (amounts as indicated in Table 3). In Examples 32 and 33, the inner surfaces of the reactor were sprayed with 50 ml of ethanol in which a certain amount of the product from either Example 16 or 17 had been dissolved (ppm based on added vinyl chloride as indicated in Table 3), and the coatings were allowed to drought. The polymerizations in examples 32 and 33 were carried out successively in the reactor and pre-cleaning of the reactor main body and roof was omitted before the polymerization in example 33.

The observations of the formation of polymer build-up are for each case indicated in table 3 (after removal of the polymer slurry and washing off all loose adhering soft wet cake). It can be seen that application of a coating product according to the invention had a marked suppressive effect on the formation of build-up.

EXAMPLE 34

A mixture of polyethyleneimine solution (145 ml of a

20% aqueous solution), potassium hydroxide solution (57 g of a 50% w/v aqueous solution), hydroquinone (12 g) and p-benzoquinone (12 g) were mixed in a commercially available mixer at ambient temperature (approx. 20°C), the hydroquinone and p-benzoquinone being added to the polyethyleneimine solution and the potassium hydroxide solution during operation of the machine. The resulting product was a viscous, dark red gel. The gel was diluted with 450 ml of water.

EXAMPLE 35

A mixture of polyethyleneimine solution (145 ml of a

20% aqueous solution), water (100 ml), hydroquinone (12 g) and p-benzoquinone (12 g) were mixed in a commercially available mixer at ambient temperature (about 20°C), the hydroquinone and p-benzoquinone was added to the polyethyleneimine solution and the water while operating the mixer. It was necessary to add an additional 100 ml of water during mixing because the mixture product became very viscous. Sodium hydroxide solution (8.72 g dissolved in 100 ml water) was added and the resulting product was a black-red gel containing some precipitated material. This gel was diluted with 350 ml of water, and the precipitate was separated by decantation as completely as possible.

EXAMPLES 36-39 (Ex. 36 is for comparison)

In these examples, conventional suspension homopolymerizations of vinyl chloride were carried out in a stainless steel reactor (capacity 160 liters) equipped with a paddle stirrer. Unless otherwise stated, the inner surfaces of the reactor were carefully cleaned before each polymerization. The polymerizations were carried out at 57°C using 100 parts vinyl chloride, 154 parts water, partially hydrolyzed polyvinyl acetate (0.13% based on added vinyl chloride) as suspending agent and bis(4-tert-butylcyclohexyl) peroxydicarbonate as initiator (0.065% based on added vinyl chloride) . The polymerization was continued until well into the pressure drop area, and then the polymerization was terminated by venting the monomer. In Examples 37 and 38, the internal surfaces of the reactor were painted with the aqueous alkaline mixture from Example 34, while in Example 39 the internal surfaces were painted with the aqueous alkaline mixture from Example 38, and in each case the amount applied was such that estimated solids content was 30 ppm based on added vinyl chloride. The coatings were allowed to dry before the addition of the polymerization ingredients.

The polymerizations in Examples 37 and 38 were carried out successively in the reactor without purification between batches.

The observations of the formation of polymer build-up are for each case shown in table 4 (after removal of the polymer slurry and washing out of all loose adhering soft wet cake). It can be seen that application of a coating product according to the invention had a marked suppressive effect on the formation of build-up.

EXAMPLE 40

The procedure from Example 16 was repeated, except that the initial reaction mixture consisted of polyethyleneimine (21.5 ml of a 20% aqueous solution), catechol (2.75 g) and conc. HCl (0.5 mL). The distillation lasted approx. 1 hour.

The product was a gummy, dark reddish-brown material which, like the products of Examples 1 and 2, was dissolved in ethanol.

EXAMPLES 41 and 42

In these examples, the procedure from Examples 18-24 was repeated, except that the inner surfaces of the reactor were coated with the product from Example 40, as indicated in Table 5.

The polymerizations in examples 41 and 42 were carried out successively in the reactor, and before the polymerization in example 42 the pre-cleaning of the reactor main part and roof was omitted.

The observations of build-up formation are for each case indicated in table 5 (after removal of the polymer slurry and washing out of all loose adhering soft wet cake). It can be seen that the use of a coating product according to the invention has a marked suppressive effect on the formation of build-up.

EXAMPLE 43 (Comparison)

A reactor made of stainless steel (capacity 160 liters) and with carefully cleaned internal surfaces, was internally sprayed first with 32 ppm (based on subsequently added vinyl chloride) of 4,7-diazadecane-1,10-diamine (formula NH 2 (CH 2 ) 3NH(CH2)3~ NH2) as a 1% aqueous solution and then with 10 ppm (based on subsequently added vinyl chloride) with hydroquinone as a 20% aqueous solution, the approximate molar ratio between diamine and hydroquinone being 2/ 1. The coating quickly changed to an almost black color at the ambient temperature (approx. 20°C) and was then given the opportunity to dry without the addition of heat.

A conventional vinyl chloride polymerization was carried out at 57°C in a reactor using 100 parts vinyl chloride, 154 parts water, 0.13% partially hydrolyzed polyvinyl acetate (based on vinyl chloride) as suspending agent and 0.038% (based on vinyl chloride) diethyl peroxydicarbonate as an initiator. The polymerization was continued until well into the pressure drop area, and then the polymerization was stopped by venting the monomer.

Inspection of the reactor contents, after removal of the polymer slurry, showed that a chalky white build-up had formed on the side walls of the reactor, and chalky white build-up plus a thin skin of build-up and a few hard lumps had also formed on the roof of the reactor.

EXAMPLE 44 (Comparison)

A mixture of fine ethylenediamine (6 g), solid hydroquinone (11 g) and conc. HCl (0.5 ml) was prepared at ambient temperature (ca. 20°C), and the mixture corresponded to a molar ratio of ethylenediamine to hydroquinone of ca. 1/1. An exothermic reaction quickly took place, and 10 ml of water was added to improve the dispersion of the product. The mixture was then heated to 100°C after which the product became viscous and acquired a deep red colour. The heating was removed and the product solidified on cooling. , The product was found to be soluble in ethanol.

The product (30 ppm based on later added vinyl chloride) was sprayed as an approximately 10% ethanolic solution on the inner surfaces of a clean stainless steel reactor (capacity 160 litres), and the ethanol was allowed to evaporate without heat being added . A conventional vinyl chloride polymerization was carried out in the reactor at 57°C using 100 parts vinyl chloride, 154 parts water, 0.13% partially hydrolyzed polyvinyl acetate (based on vinyl chloride) as suspending agent and 0.078% (based on vinyl chloride)' bis( 4-tert-butylcyclohexyl)peroxydicarbonate as initiator. The polymerization was carried out until well into the pressure drop area and the polymerization was then stopped by venting the monomer.

Inspection of the interior of the reactor, after removal of the polymer slurry, showed that the roof of the reactor had significant deposits of build-up, although the side walls of the reactor were clean.

Claims (2)

1. Process for the polymerization of vinyl chloride, alone or together with other vinyl halides or other comonomers that are copolymerizable with vinyl chloride, in an aqueous dispersion, characterized in that the polymerization is carried out in a reaction vessel that has an adhesively deposited coating of a coating product that is obtained by reacting a mixture of at least polyethyleneimine and one or more representatives of the group hydroquinone, p-benzoquinone, catechol and o-benzoquinone at a temperature of 15-150°C. 2. Reaction vessel for carrying out the method according to claim 1, characterized in that it has adhesively deposited on its inner surface a coating of a coating product obtained by reacting a mixture of at least polyethyleneimine and one or more representatives of the hydroquinone group, p -benzoquinone, catechol and o-benzoquinone at a temperature of 15-150°C.