Method for producing peroxydicarbonates and their use in the radical polymerization of monomers

Peroxydicarbonates are of great use as initiators generating free radicals in polymerization processes, and in particular in the polymerization of ethylenically unsaturated monomers such as vinyl chloride. Typically, peroxydicarbonates are produced in large batches and sold pure or as pure or dilute products. Polymer manufacturers now store large amounts of peroxydicarbonates for use in their polymerization processes. Precautions should be taken when storing and handling these materials as they are unstable and sensitive to both thermal shock and shock and may detonate under certain conditions. Adhering to all these safety requirements for handling these materials makes the use of peroxydicarbonates very expensive in the manufacture of polymers.

So far, various solutions to this problem have been proposed. US Patent 4,359,427 proposes a process for the continuous production and purification of peroxydicarbonates at the polymerization site and for their storage in dilute phase prior to use. Another approach suggests the production of peroxydicarbonates in a large polymerization vessel prior to the addition of the polymerizable monomer. The production of peroxydicarbonates in a large reactor presented polymer quality problems for several reasons. One such reason is that there is insufficient mixing of low abundance reactants in the large reactor. Without proper agitation, the peroxydicarbonate formation reaction is ineffective and the yield of the peroxydicarbonate formed varies, so the polymerization reaction time using the peroxydicarbonate initiator (s) also changes. In order to obtain larger volumes, diluents such as solvents and water are often used. The use of these diluents leads to less conversion of the reactants and as a result produces large amounts of undesirable by-products forming and remaining in the large reactor, fouling the polymer ultimately formed in the reactor. The use of the solvent necessitates its recovery and this contaminates the recovery system by recovering unreacted monomer. In addition, the production of the peroxydicarbonate in the large polymerization reactor results in a decrease in yield as the polymerization vessel is occupied by the peroxydicarbonate synthesis process prior to each polymer batch preparation.

GB Patent Application 1484675-A proposes to solve these problems by producing peroxydicarbonates outside the polymerization reactor in the presence of a solvent, which leads to a proper mixing of the reactants. This is not a desirable process since the solvent must be removed, or it is also a contaminant in the polymerization process and contaminates the monomer recovery system in the polymerization process.

WO 97/27229 proposes to solve the problem by producing peroxydicarbonates outside the polymerization reactor in a two-step process and adding a water-insoluble liquid dialkyl alkanedicarboxylate. The dialkyl alkanedicarboxylate is a plasticizer for the resulting polymer and is undesirable for "rigid polymer" applications. Moreover, the two-step process is cumbersome and requires excessive equipment.

Each of US Patent Application 4359427-A, GB Patent Application 1484675-A and Patent Application WO97 / 27229 disclose that peroxydicarbonates can be prepared by reacting a chloroformate with an alkali metal peroxide.

In US patent application A-4359427 and J. Am. Chem. Soc, 1950, 72, 1254-1263 discloses methods for producing peroxydicarbonates by reacting an alkali metal peroxide with a chloroformate.

In one aspect of the invention, there is provided a method for producing a peroxydicarbonate comprising the steps of:

(a) reacting at least one inorganic peroxide with at least one alkali metal hydroxide in a first vessel to form at least one alkali metal peroxide; (b) introducing at least one haloformate, at least one dispersant, and water into a second vessel provided with homogenizing and cooling equipment, (c) mixing the contents in the second vessel and (d) dispensing the at least one alkali metal peroxide produced in the first vessel into the second vessel while homogenizing the contents in the second vessel;

Until substantially all of the alkali metal peroxide has reacted with the haloformate to form the carbonate peroxydivate.

Preferably, the peroxydicarbonate is described by the formula:

ROCOOCO-Rl ₁ where R and R¹ represent different or identical organic radicals containing from 2 to 16 carbon atoms.

₁

Conveniently, R and R.¹ in peroxydicarbonate are identical organic radicals containing from 2 to 8 carbon atoms.

Preferably, R and R.¹ the peroxydicarbonates are selected from the group consisting of ethyl, n-propyl and secondary butyl.

₁

Preferably, R and R.¹ peroxydicarbonate are ethyl groups.

Suitably, the peroxydicarbonate is diethyl peroxydicarbonate.

Preferably, the haloformate is a chloroformate.

Preferably, the alkali metal hydroxide is sodium hydroxide.

Suitably, the inorganic peroxide is hydrogen peroxide.

Preferably, the dispersant is selected from the group consisting of hydrolyzed polyvinyl acetate, methylcellulose, hydroxypropylmethylcellulose, gelatin, polyvinylpyrrolidone, polyoxyethylene sorbitan monolaurate and polyacrylic acid.

Preferably, said dispersant is polyvinyl acetate, hydrolyzed to a degree from about 70% to about 90%.

Conveniently, the contents in the second vessel are kept at a temperature below 40 ° C. Preferably, the contents in the second vessel are kept at a temperature below 22 ° C. Preferably, the contents in the second vessel are kept at a temperature of from about 0 ° C to about

10 ° C.

Conveniently, the alkali metal peroxide is dosed into the second vessel over a period of from about 2 minutes to about 20 minutes.

Preferably, one mole of the alkali metal peroxide is dosed into the second vessel for every two moles of the haloformate present in the second vessel.

Preferably, the second vessel is provided with mixing devices and the peroxydicarbonate is mixed.

Conveniently, the alkali metal peroxide is cooled to a temperature from about 0 ° C to about

10 ° C, before dispensing into the second vessel.

Preferably, the peroxydicarbonate is substantially free of organic solvents and plasticizers for the polymers.

The contents of the second vessel may be partially homogenized prior to dispensing any alkali metal peroxide into the second vessel.

According to another aspect of the invention, there is provided a method of polymerizing at least one ethylenically unsaturated monomer comprising:

(a) preparing at least one peroxydicarbonate by the method described above, (b) adding to the polymerization reactor at least one ethylenically unsaturated monomer, water, dispersant and a peroxydicarbonate produced according to (a);

(c) performing a polymerization reaction to achieve the desired degree of conversion of the ethylenically unsaturated monomer to form a polymer;

(d) discharging the polymer from the polymerization reactor;

(e) stripping the ethylenically unsaturated monomer from the polymer; and (f) dehydrating and drying the polymer to a compression form;

the first vessel and the second vessel are located outside the polymerization reactor.

Preferably, the entire contents of the second vessel are fed to the polymerization reactor. Suitably the ethylenically unsaturated monomer is vinyl chloride monomer.

Preferably, the peroxydicarbonate is substantially free of organic solvents and plasticizers for the polymer.

PL 202 098 B1

In the preferred methods of the invention, the alkali metal hydroxide is sodium hydroxide, the inorganic peroxide is hydrogen peroxide, and the dispersant is polyvinyl acetate hydrolyzed to a degree from about 70% to about 90%. It is preferred to maintain the contents of the second vessel at a temperature of from about 0 ° C to about 10 ° C and to cool the alkali metal peroxide to a temperature of from about 0 ° C to about 10 ° C prior to dispensing into the second vessel.

According to another aspect of the invention, there is provided a method of producing two or more different peroxydicarbonates in the same vessel, comprising: producing the first peroxydicarbonate in the above-described process wherein the haloformate is a chloroformate, and after the first peroxydicarbonate is formed, the process then comprises the step (e) of discharging a second chloroformate into a second vessel and dispensing additional alkali metal peroxide to the second vessel to form a second peroxydicarbonate. while homogenizing the contents in the second vessel until the second chloroformate has substantially reacted with the alkali metal peroxide to form the second peroxydicarbonate, and (f) repeating step (e) for each additional batch of peroxydicarbonate desired.

According to a further aspect of the invention, there is provided a process for polymerizing at least one ethylenically unsaturated monomer comprising producing a peroxydicarbonate by a method as described above, comprising:

(a) injecting at least one haloformate, at least one dispersant and water into a line provided with cooling devices and a homogenizer (in-line), this line is connected to the polymerization reactor, (b) dosing at least one alkali metal peroxide to this line. line, (c) homogenizing the mixture in this line to form the peroxydicarbonate, (d) injecting peroxydicarbonate from this line into a polymerization reactor containing ethylenically unsaturated monomer, dispersant and water, (e) carrying out the polymerization to the desired degree of monomer to polymer conversion in the polymerization reactor, (f) discharging the polymer from the polymerization reactor, (g ) stripping the remaining monomer from the polymer, dehydrating and drying the polymer to a powder with high compression plasticity.

Preferably, the ethylenically unsaturated monomer is vinyl chloride monomer.

Conveniently, the di (2-ethylhexyl) peroxy dicarbonate is selected from the group consisting of diethyl peroxy dicarbonate, di-n-propyl peroxydicarbonate, di-iso-propyl peroxydicarbonate, di (2-ethylhexyl) peroxydicarbonate, and butyl peroxydicarbonate peroxydicarbonate.

Preferably, the polymerization is carried out at a temperature of from about 40 ° C to about 70 ° C.

Suitably, the peroxydicarbonate is diethyl peroxydicarbonate, the alkali metal peroxide is sodium peroxide, and the peroxydicarbonate is homogenized sufficiently to form droplets of 1 to 10 microns in size.

It should be noted that it has surprisingly been found that the peroxydicarbonate initiator can be prepared at the polymerization site outside the polymerization reactor, which when used for polymerization of ethylenically unsaturated monomers produces polymers of high quality. The process for producing a peroxydicarbonate of the invention requires first mixing an alkali metal hydroxide with a peroxide to produce an alkali metal peroxide. The alkali metal peroxide is added to a mixture of the haloformate, dispersant and water to form the desired peroxydicarbonate. The reaction mixture is homogenized during the reaction to form small droplets of peroxydicarbonate. The peroxydicarbonates obtained do not need to be diluted with solvents or plasticizer, nor do they need to be purified. The peroxydicarbonates are prepared immediately prior to the polymerization reaction and introduced into the polymerization reactor, followed by the polymerization reaction to obtain a high quality polymer from the ethylenically unsaturated monomer.

The invention will now be described with reference to an example.

The peroxydicarbonates produced according to the invention have the general formula:

RO-C-OO-C-O-Rl

PL 202 098 B1 wherein R and R¹ represent different or identical organic radicals having from 2 to 16 carbon atoms, preferably 2 to 10 carbon atoms, and more preferably 2 to 6 carbon atoms. The most preferred peroxydicarbonates have R i as identical radicals. Specific examples of R and R¹ are alkyl radicals such as ethyl, n-propyl, isopropyl, n-butyl, isobutyl, secondary butyl, amyl, hexyl or 2-ethylhexyl, alkenyl, aryl, alkylaryl, aralkyl or cycloakyl or radicals derived from compounds in heterocycles, especially such such as: benzyl, cyclohexyl, cinnamyl, tetrahydrofuryl, as well as their substituted derivatives.

The most preferred peroxydicarbonates are diethyl peroxydicarbonate, di-npropyl peroxydicarbonate, di-isopropyl peroxydicarbonate, di-n-butyl peroxydicarbonate, di (secondary butyl) peroxydicarbonate and 2-ethylhexylhexyl peroxydicarbonate.

The haloformates used to make the peroxydicarbonates have the general formula:

ο

R2 — Ο — ϋ — r3 where R² represents an organic radical containing from 2 to 16 carbon atoms and R³ is 2 1 3 halogen. R² represents the same organic radical as described above for R and R¹. R³ means ₃ halogen such as chlorine, fluorine, iodine or bromine. Preferably, R.³ is chlorine. One or more haloformates may be used to make the peroxydicarbonate.

At least one dispersant is used in the synthesis of peroxydicarbonate, such as hydrolyzed polyvinyl acetates, alkyl and hydroxyalkyl cellulose ethers such as methyl cellulose, hydroxypropyl methyl cellulose, gelatin, polyvinylpyrrolidone, polyoxyethylene sorbitan monolaurate, and the like polyacrylate monolaurate compounds. Preferably, the selected dispersant is similar to that used in the polymerization of the ethylenically unsaturated monomer. In the polymerization of vinyl chloride monomer, the preferred dispersant is polyvinyl acetate hydrolyzed to a degree in the range of about 70% to about 90%. The dispersant is preferably added in the form of an aqueous solution. The amount of dispersant used should be sufficient to form an aqueous emulsion of the haloformate. It is typically from about 0.05 to 0.2 grams of dispersant per gram of haloformate, preferably from about 0.075 to about 0.1 grams of dispersant per gram of haloformate. The dispersant is added as an aqueous solution. The solution comprises from about 1% to about 10% by weight of the dispersant in water, preferably from about 3% to about 8% by weight of the dispersant in water. Once the peroxydicarbonate formation reaction is complete, some more dispersant may be added to stabilize the emulsion. Stabilization of the emulsion is particularly important when the peroxydicarbonate is not used immediately after preparation.

Water is also used in the synthesis of the peroxydicarbonates of the invention. Water is necessary to disperse the dispersant and the other reaction components. Water also participates in removing the heat generated in the exothermic reaction. It is preferable to use demineralized water. The amount of water used is not critical except that the amount necessary to disperse the dispersant and dissolve the alkali metal hydroxide and peroxide must be used. The alkali metal hydroxide and peroxide are used in the form of aqueous solutions and thus some of the required water is already provided. Preferably, a minimum amount of water is used to achieve the required cooling. Avoid excess water during the reaction, relative to the amount required to disperse the reactants and provide cooling, thereby providing a more direct contact of the reactants. Once the reaction is complete, more water may be added. Normally the amount of water used in the reaction is from about 5 grams to about 20 grams of water per gram of haloformate, preferably from about 7 grams to about 12 grams of water per gram of haloformate. Most of the water is added as a result of adding the ingredients as an aqueous solution.

In the synthesis of the carbonate peroxide according to the invention, at least one alkali metal peroxide is used. A preferred alkali metal peroxide is sodium peroxide. Alkaline peroxide is formed by reacting an inorganic peroxide such as hydrogen peroxide with an alkali metal hydroxide such as sodium hydroxide, potassium hydroxide, ammonium hydroxide, lithium hydroxide, calcium hydroxide, magnesium hydroxide, and alkali metal phosphates. The preferred sodium peroxide is formed by the reaction of sodium hydroxide with hydrogen peroxide. Two moles of alkali metal hydroxide are used per mole of inorganic peroxide. An excess of one of the reagents may be used, but this is not preferred.

PL 202 098 B1

One method for producing the peroxydicarbonates of the invention is to use two reaction vessels. The reaction vessels may be of any shape and material, but both the shape and material of construction should be conductive to cool. Metal utensils such as boilers and stainless steel pipes are satisfactory. In one vessel, alkali metal peroxide is produced by mixing an alkali metal hydroxide with an inorganic peroxide. The mixture of alkali metal hydroxide and inorganic peroxide is mixed thoroughly by conventional mechanical agitation to form the alkali metal peroxide. In the preparation of the preferred alkali metal peroxide, sodium hydroxide is mixed with hydrogen peroxide to produce sodium peroxide. The preferred sodium hydroxide is an aqueous sodium hydroxide solution. The concentration of sodium hydroxide is not critical, but is preferably 5% to 35% by weight of sodium hydroxide in water, and preferably 5% to 15% by weight of sodium hydroxide. The hydrogen peroxide is used in the range of 5% to 35% by weight of the solution of hydrogen peroxide in water and preferably in the range of 25% to 35% of the solution of hydrogen peroxide in water.

The mixture used to make the alkali metal peroxide contains two moles of alkali metal hydroxide and one mole of inorganic peroxide. The reversible reaction for beneficial components can be expressed by the equation:

2NaOH + H.₂ABOUT₂ »Na₂ABOUT₂ + 2H₂ABOUT

The reaction temperature should be below the decomposition temperature of the alkali metal peroxide. In addition, the mixture should be cooled so as not to add heat when later used to produce the peroxydicarbonate. The preferred alkali metal peroxide is cooled to a temperature below 28 ° C and more preferably to a temperature of 0 ° C to 10 ° C.

The haloformate, dispersant and water are initially mixed in the second vessel, which is a homogenizer or homogenization system and refrigeration equipment. The resulting mixture of haloformate, dispersant and water is cooled and homogenized while adding alkali metal peroxide from the first vessel. It is preferable to initiate homogenization before adding the alkali metal peroxide and continue until all the alkali metal peroxide has been added. The temperature of the mixture in the second vessel should be kept below the decomposition temperature of the peroxydicarbonate formed. For the preferred reactants, the temperature should be kept below 40 ° C, preferably below 22 ° C, and more preferably from 0 ° C to 10 ° C. As water is present, the mixture should not be cooled so as to freeze the water, although the freezing point of the water in the mixture is below 0 ° C due to the presence of by-products (salts). If the temperature is above the decomposition temperature of the peroxydicarbonate formed, the efficiency is reduced due to the decomposition of the peroxydicarbonate. Decomposition can be observed by foaming due to the release of carbon dioxide as the peroxydicarbonate decomposes. The alkali metal peroxide may be added to the second vessel at a rate determined by the ability of the second vessel to cool so as not to exceed the decomposition temperature of the peroxydicarbonate formed. The reaction of the alkali metal peroxide and the haloformate is almost instantaneous but very exothermic. Due to the highly exothermic course of the reaction, it is preferable to dose the alkali metal peroxide from the first vessel into the second vessel containing the haloformate over a period of about 2 to about 20 minutes. The rate of addition of the alkali metal peroxide depends only on the ability to cool the reaction mixture so as to keep the reaction temperature below the decomposition temperature of the peroxydicarbonate formed.

The haloformate, dispersant and the aqueous mixture from the second vessel may be added to the first vessel containing the alkali metal peroxide, but this method is less effective as the peroxydicarbonate yields are lower.

The reactants in the second vessel are used in an amount of one mole of alkali metal peroxide for two moles of haloformate. The reaction for the preferred reactants can be represented by the equation:

<img file="PL202098B1_D0001.tif" />

in which R.² is ethyl, in the most preferred embodiment of the present invention.

PL 202 098 B1

The homogenization of the ingredients in the second vessel is very important and is an essential feature of the invention as it provides direct contact between the reactants and therefore results in the use of fewer reactants. The use of fewer reagents eliminates the need to dilute the reaction mixture with a solvent or plasticizer, resulting in fewer by-products that are detrimental to the polymerization of the ethylenically unsaturated monomer. The homogenization further produces peroxydicarbonate droplets with a diameter less than 10 microns, preferably less than 5 microns, and more preferably 1 to 4 microns. The small droplet size of the peroxydicarbonate is advantageous in the preparation of polymers with low gels.

The Arde Barinko homogenizer has been found to be a preferred type of homogenizer suitable for the larger scale reaction of this invention. This type of homogenizer has a shaft extending to the reactants of the second vessel. The shaft end has narrow slots (teeth) in a fixed stator with a rotating disk having shifting teeth so that the reactants are led in and repeatedly returned through the narrow slots in the stator. For small scale laboratory reactions, a Fisher Schientic Tissue Disruptor No. 15-338-51 may be used.

An alternative method of obtaining the peroxydicarbonates of the invention for use in a polymerization process to make a polymer from an ethylenically unsaturated monomer is to use an in-line homogenizer. When using an in-line homogenizer, the haloformate, dispersant, and water are injected into the line, which is a tube. The tube is connected to a homogenizer. The alkali metal peroxide can be introduced into the line upstream of the homogenizer, or preferably by in-line recirculation between the homogenization steps. This method ensures that the haloformate is homogenized before adding the alkali metal peroxide and homogenized after all ingredients have been combined. Suitable homogenizers for use in the line are sold under the name Manton Gaulin. The homogenized ingredients can be passed through the homogenizer repeatedly until the desired homogenization is obtained. To produce the peroxydicarbonates of the invention, homogenization should result in the production of peroxydicarbonate droplets having a size of from about 1 to 10 microns, preferably from about 1 to about 4 microns. The peroxydicarbonate line is connected to the polymerization reactor and dosing to the reactor takes place at the desired time. The line is flushed with clean water after the peroxydicarbonate has been introduced into the polymerization reactor.

If it is desired to make more than one peroxydicarbonate for use in the polymerization, then the reaction to form the first peroxydicarbonate should be completed prior to the addition of the second haloformate and the corresponding alkali metal peroxide. If two different haloformates are mixed and alkali metal peroxide added, three different types of peroxydicarbonate are formed. The two types are symmetrical with the same end groups on each side, while the third type has a different end group on each side. While this type of peroxydicarbonate mixture can function as an initiator in the polymerization, it is not the most desirable mixture. The specific amounts of each of the three different types of peroxydicarbonate formed cannot be well controlled and the amount can vary widely. For this reason, it is preferable to complete the first peroxydicarbonate reaction before starting the second peroxydicarbonate reaction. When a third or subsequent peroxydicarbonate is desired, the reaction to the second peroxydicarbonate must be completed before adding the haloformate to produce the third peroxydicarbonate, etc. for any additional peroxydicarbonate needed.

The reaction in the second vessel to produce the peroxydicarbonate should preferably be completed just before it is needed for the polymerization cycle. When an unplanned delay occurs with the use of the peroxydicarbonate, the aqueous mixture should be stirred in the second vessel containing the peroxydicarbonate. It is therefore preferred that the second vessel has a mixing system as well as a homogenization system. Stirring is necessary because the peroxydicarbonate needed is heavier than the aqueous salt mixture in which it is suspended and will settle to the bottom over time if there is no agitation. The stability of peroxydicarbonates other than diethyl peroxydicarbonate is higher due to their lower density, but mixing is still preferred as it allows delay in the use of the peroxydicarbonate. Simple mixing is preferred rather than continuous homogenizer movement which applies heat to the aqueous peroxydicarbonate dispersion, which is undesirable. Any type of mixing system is acceptable, such as a paddle shaft or the introduction of inert gas bubbles into the vessel, as long as it does not cause the peroxydicarbonate to settle to the bottom of the vessel.

PL 202 098 B1

Various peroxydicarbonates can be prepared by the process of the invention. The nature or structure of the initiator produced will depend on the use of the particular haloformate in the reaction. The peroxydicarbonates can be used for the suspension polymerization of ethylenically unsaturated monomers. As examples of ethylenically unsaturated monomers, vinyl halides such as vinyl chloride, vinyl bromide and the like, vinylidene halides such as vinylidene chloride and the like, acrylic acid; acrylic acid esters such as methyl acrylate, ethyl acrylate, butyl acrylate, octyl acrylate, cyanoethyl acrylate and the like; methacrylic acid; methacrylic acid esters such as methyl methacrylate, butyl methacrylate and the like; vinyl acetate; acrylonitrile; styrene and styrene derivatives, including alpha-methylstyrene, vinyltoluene, chlorostyrene, vinylnaphthalene, and other monomers having at least one CH2 = C &lt;end group; mixtures of any of these types of monomers and other types of ethylenically unsaturated monomers known to those skilled in the art.

According to the present invention, the peroxydicarbonates are particularly suitable for the suspension polymerization of vinyl chloride to produce polyvinyl chloride (PVC). The present invention is further described with respect to the polymerization of vinyl chloride in an aqueous slurry.

When producing PVC from a vinyl chloride monomer in an aqueous slurry, the polymerization process is generally carried out in a temperature range from about 0 ° C to 100 ° C. However, it is preferable to maintain the temperature in the range of about 40 ° C to about 70 ° C as this temperature produces the polymers with the most advantageous properties. The polymerization reaction time will vary from about 2 to about 15 hours, and is preferably from 3 to 6 hours. For the production of PVC in the aqueous slurry process, in addition to the vinyl chloride monomer, water, dispersants, free radical initiator are used, and other ingredients such as buffers, retention agents, etc. may optionally be added. The aqueous slurry process to produce PVC is a batch process. and once the reactants have left the reactor, the process becomes continuous. A continuous process step requires stripping the residual vinyl chloride monomer from the PVC polymer and recovering the monomer for further use in later polymerizations. In addition, the polymer particles are dehydrated and dried to a compression free powder as is well known in the art.

Once the PVC polymerization reaction has reached the desired degree of conversion, which is typically from about 80% to 94% monomer to polymer conversion, the reaction is stopped and the reactor contents pumped out to empty the reactor. The empty reactor is then prepared for the next polymerization cycle by rinsing with water and coating the wall which prevents build-up of polymer. The rinse and coating cycle requires about 10 to 20 minutes, i.e. a time sufficient for the reaction to proceed to form the peroxydicarbonate which will be used in the next polymerization cycle.

The peroxydicarbonate obtained according to the invention, along with the by-products of the peroxydicarbonate reaction, are fed to the PVC reactor in the time required to start the polymerization of the vinyl chloride monomer. The order in which the ingredients are introduced into the PVC reactor is not critical, but it is preferable to charge the reactor with peroxydicarbonate when its contents have reached the desired polymerization temperature. If the peroxydicarbonate is added before the desired polymerization temperature is reached, some of it will be used at a lower temperature, which will consequently reduce the amount of initiator in the polymerization. This can be compensated for by adding the peroxydicarbonate in excess, but is less advantageous due to the increased cost.

The process for producing the peroxydicarbonate of the present invention has yields from about 90% to about 97%. A convenient method of determining the yield of the PVC reaction is to measure the cycle time with a given amount of peroxydicarbonate and compare the reaction time with the theoretical time as is well known in the art. The PVC reaction cycle times indicate that the peroxydicarbonate yields achieved according to the invention are very reproducible, at least 90%. A convenient method is to load the PVC reactor with about 10% excess over the theoretical required amount of peroxydicarbonate produced according to this invention. This is to compensate for an efficiency of less than 100%.

The amount and selection of a given type of peroxydicarbonate to be used in the PVC polymerization reaction will vary depending upon the desired reaction temperature and the overall reaction cycle time desired. The total cycle time desired is typically determined by the rate at which heat can be removed from the PVC reaction system. The rate of heat removal depends on several factors such as the surface area of ​​the reactor available for cooling, the cooling medium, and the heat transfer coefficient. PVC reactors can be equipped with reflux condensers to increase the cooling rate, and chilled water can be used in the reactor jacket as well as internally cooled surfaces such as baffles.

PL 202 098 B1

The peroxydicarbonate when the peroxydicarbonate is diethyl peroxydicarbonate is typically used in an amount in the range of 0.20 to 1 part by weight per 100 parts by weight of vinyl chloride monomer, preferably from 0.030 to 0.060 parts by weight per 100 parts by weight of vinyl chloride monomer. Different peroxydicarbonates are used in different amounts depending on their rate of decomposition to form free radicals at a given reaction temperature and their molecular weight, all well known to those skilled in the art. Conventional peroxydicarbonates or other initiators may be used in conjunction with the peroxydicarbonates of the invention to achieve specific reaction kinetic parameters, although this is not necessary since multiple batches of peroxydicarbonate can be obtained in the same vessel by the process of the invention.

One of the important advantages of the invention is that the entire contents of the peroxydicarbonate forming vessel can be fed into the PVC polymerization reactor. There is no need to purify the peroxydicarbonate or dilute with solvents or plasticizers, as has been demonstrated in the methods used so far.

The peroxydicarbonates are preferably custom-made in the amount required at the time. This eliminates the need for peroxydicarbonate storage. Of course, the peroxydicarbonates can be prepared by the process of the invention and stored for later use, but this is less desirable.

The following examples are provided to demonstrate the method of producing peroxydicarbonate and its subsequent use to produce high quality PVC polymers.

Example 1

This example describes the preparation of diethyl peroxydicarbonate by the process of the invention. The production of the peroxydicarbonate is carried out under the fume hood. An Arde Barinko homogenizer is used. The 15 liter beaker is placed in an acetone-dry ice cooling bath kept at approximately -10 ° C. In addition, an ethylene glycol cooling coil is placed in the beaker. The temperatures of both the reaction mixture and the external cooling bath are monitored continuously using glass thermometers attached to the site. The cooling coil works at a temperature of 4 ° C to 10 ° C. 1200 ml of water was placed in a 15 liter steel beaker, then 1000 ml of 5% by weight 72.5% hydrolyzed polyvinyl acetate dispersant in water and 541 ml (596 g) of ethyl chloroformate were added. This mixture was homogenized with an Arde Barinko homogenizer for approximately 1 minute to facilitate the formation of an emulsion of ethyl chloroformate.

In a separate glass beaker placed in an ice bath, 4154 ml (4391 g) of 5% by weight sodium hydroxide in water was mixed with 280 ml (311 g) of 30% by weight hydrogen peroxide in water. The glass beaker was mechanically agitated. The mixture was mechanically stirred for approximately 5 minutes to facilitate the dusting of sodium peroxide (which is formed by equilibrium from sodium hydroxide and hydrogen peroxide) as represented by the equation:

2NaOH + H.₂ABOUT₂ »Na₂ABOUT₂ + 2H₂ABOUT

This sodium peroxide mixture was then placed in a glass dropping funnel which was securely mounted above in a 15 liter stainless steel beaker containing ethyl chloroformate. The temperature in the steel beaker was 0 ° C. The homogenizer was operated during the peroxydicarbonate formation reaction.

Sodium peroxide was added dropwise from a glass dropping funnel at such a manually controlled rate that the temperature of the reaction mixture did not exceed 10 ° C. The reaction of sodium peroxide with ethyl chloroformate can be expressed by the equation:

0 0

2-C₂H.₅-Oi! -Cl + Na₂0 -► Ο₂Η₅-Ο-ϋ-Ο-Ο-ϋ-Ο-Ο₂Η₅ + 2 NaCl

At the end of the 10-15 minute addition of sodium peroxide, the reaction mixture was homogenized for a further 5 minutes while adding 3500 ml of 5 wt% polyvinyl acetate, 72.5% hydrolyzed in water, to stabilize the diethyl peroxydicarbonate emulsion. .

Relative to 100% yield, 489 g of diethyl peroxydicarbonate would be obtained.

PL 202 098 B1

The mixture at this stage contains all the diethyl peroxydicarbonate and 72.5% hydrolyzed polyvinyl acetate needed to feed the dispersed initiator to the reactor (4.2 m³) for the polymerization of vinyl chloride.

When it is desired to produce peroxydicarbonates other than diethyl peroxydicarbonate, different amounts of chloroformate are needed in the above-described procedure to achieve the same activity in terms of active oxygen, according to the following table:

Table 1

<td></td><td></td><td colspan="2">The amount of chloroformate used</td>

<td>Peroxydicarbonate used</td><td>Chloroformate used</td><td>grams</td><td>ml</td>

<td>Diethyl peroxydicarbonate</td><td>Ethyl chloroformate</td><td> 596</td><td> 541</td>

<td>N-Propyl peroxydicarbonate</td><td>N-Propyl chloroformate</td><td> 673</td><td> 617</td>

<td>Iso-propyl peroxydicarbonate</td><td>Iso-propyl chloroformate</td><td> 673</td><td> 624</td>

<td>N-Butyl peroxydicarbonate</td><td>N-Butyl chloroformate</td><td> 750</td><td> 698</td>

<td>S-Butyl peroxydicarbonate</td><td>S-Butyl chloroformate</td><td> 750</td><td> 714</td>

<td>2-ethylhexyl peroxydicarbonate</td><td>2-Ethylhexyl chloroformate</td><td> 1058</td><td> 1080</td>

The amounts of the other ingredients (other than the chloroformate) and the procedure may be the same as described above for the preparation of ethyl dichloroformate.

Example 2

This example is given to demonstrate vinyl chloride slurry polymerization using diethyl peroxydicarbonate prepared in Example 1.

₂

To clean 4.2 m² In a polymerization reactor equipped with mixing and cooling devices, 1479.86 kg of vinyl chloride monomer, 2013.278 kg of hot demineralized water, 3.9173 kg of methylcellulose as dispersant, 2.5243 kg of polyvinyl acetate hydrolyzed in with a degree of 88% as a dispersant and an aqueous emulsion of diethyl peroxydicarbonate prepared according to Example 1. The reaction started at 56.5 ° C and was held at this temperature for 45 minutes. After 45 minutes, the reaction temperature was reduced by 0.038 ° C per minute over 185 minutes until the reaction temperature was 49.5 ° C. The reaction temperature was held at 49.5 ° C until pressure drop occurred. Pressure drop occurred 312 minutes after the addition of the initiator and 591.9 g of a stopping agent was added to terminate the reaction. The PVC slurry was stripped of residual monomer and dried. Examination of the inner metal surface of the polymerization reactor showed that an accumulation of polymer unexpectedly occurred, which is very advantageous.

This example demonstrates that diethyl peroxydicarbonate prepared according to example 1 is very effective in polymerizing vinyl chloride monomer.

Example 3

This example is given to demonstrate a standard vinyl chloride slurry polymerization control using commercially available sec-butyl peroxydicarbonate. The same polymerization reactor (4.2 m³) and the reaction components and methods as in Example 2 except that 669 g of sec-butyl peroxydicarbonate was used as the initiator. At 291 minutes after the addition of the initiator, a pressure drop occurred and a stopping agent was added. The PVC slurry was stripped of residual monomer and dried. Examination of the inner surface indicated that some polymer build-up had occurred, which is normal for this type of reaction. The polymer accumulation was greater in this reaction than in the reaction of Example 2 when the peroxydicarbonate produced according to this invention was used.

Example 4

This example, compared with Examples 5 and 6, is given to demonstrate the advantages of using diethyl peroxydicarbonate according to the invention over the methods of producing the peroxydicarbonate in a PVC reactor previously used. This example is a control for examples 5 and 6.

PL 202 098 B1

The vinyl chloride slurry reaction was carried out in a 55 liter polymerization reactor equipped with stirring and cooling devices. The following polymerization components were introduced into a clean 55 liter reactor:

demineralized water - 25,440 kg vinyl chloride monomer - 18,544 kg

PVA (72.5%) - 439.898 g methyl cellulose - 68.681 g

PVA (88%) - 35.210 g sec-butyl peroxydicarbonate - 8.396 g

First, water was added and mixing was started. VCM was added and the reactor contents were heated to 56 ° C. The dispersants were then added and agitation was continued while maintaining the temperature at 56 ° C for 10 minutes. At the end of this time, a commercially available initiator, secondary butyl peroxydicarbonate, was added and the reaction was started. The reaction temperature was held at 56 ° C for 49 minutes. The reaction temperature was gradually lowered as in Example 2 over 197 minutes until it reached 50 ° C. The temperature was held at 50 ° C until a pressure drop occurred. The pressure drop occurred 272 minutes after adding the initiator, by which time the reaction was terminated by adding 3.709 g of a stopping agent. The PVC resin slurry was stripped of residual monomer and dried.

Example 5

This example is given to show that the vinyl chloride slurry reaction using diethyl peroxydicarbonate produced by the process of the invention is superior to the method used in the art to produce diethyl peroxydicarbonate in a polymerization reactor (as shown in example 6).

The same 55 liter reaction vessel as in Example 4 was used and the same methods as well as the same reaction components except that instead of 8.396 g of commercial secondary butyl peroxydicarbonate, diethyl peroxydicarbonate was used from Example 1 using 8.56 g. ethyl chloroformate. The pressure drop occurred 274 minutes after the addition of the initiator and the reaction was terminated thereafter by adding a retention agent as in Example 4. The PVC resin slurry was stripped of residual monomer and dried.

Example 6

This example is given to demonstrate the suspension polymerization of vinyl chloride monomer using the prior art method for producing diethyl peroxydicarbonate in a polymerization reactor prior to polymerization.

The same 55 liter reactor as in Examples 4 and 5 and the same methods as well as the same reaction components were used, except that in this example diethyl peroxydicarbonate was produced in a reaction vessel and about a 35% excess of initiator components was used. to obtain an equivalent pressure drop time, due to the inability to produce peroxydicarbonate in the reactor.

To produce an initiator in the reactor, first 8.1 kg of water (about 32% of all water used) was introduced into the reactor and agitation was started. It was necessary to keep the water level above the agitator in the reactor to make the initiator. The dispersants (72.5% PVA, 88% PVC, and methylcellulose) were then charged to the reactor, followed by 10.50 g of ethyl chloroformate, 15.4276 g of sodium hydroxide, and 5.5628 g of hydrogen peroxide. The ingredients were mixed for 5 minutes before adding the remaining amount of water. Vinyl chloride monomer was charged and the temperature was raised to 56 ° C. The temperature profile was then kept the same as in Examples 4 and 5. The pressure drop occurred after 277 minutes and the reaction was stopped as in Examples 4 and 5. The resulting PVC resin was dehydrated and dried.

The PVC resins prepared according to Examples 4, 5 and 6 were tested for properties relevant to PVC resins and the results are shown in Table III below:

Table III

<td>Properties of the resin</td><td>Example 4 (checklist)</td><td>Example 5 (according to the invention)</td><td>Example 6 comparative)</td>

<td> 1</td><td> 2</td><td> 3</td><td> 4</td>

<td>Average particle size (microns)</td><td> 126</td><td> 131</td><td> 146</td>

PL 202 098 B1 cont. table III

<td> 1</td><td> 2</td><td> 3</td><td> 4</td>

<td>Particle size distribution</td><td> 23</td><td> 23</td><td> 27</td>

<td>% coarse grains</td><td> 0,10</td><td> 0</td><td> 0,10</td>

<td>% minor</td><td> 21,48</td><td> 19,40</td><td> 12,61</td>

<td>DOP porosity (ml / g)</td><td> 0,414</td><td> 0,394</td><td> 0,361</td>

<td>Apparent Bulk Density (g / ml)</td><td> 0,419</td><td> 0,424</td><td> 0,452</td>

<td>Funnel discharge rate (seconds)</td><td> 28,4</td><td> 27,0</td><td> 22</td>

<td>Yellowing indicator</td><td> 8,07</td><td> 11,63</td><td> 14,54</td>

<td>DTS - Yellow (minutes)</td><td> 14</td><td> 18</td><td> 10</td>

<td>DTS - Black (minutes)</td><td> 24</td><td> 29</td><td> 22</td>

From the above data, it can be seen that the thermal stability and the initial color (yellowing index) of the PVC resin made with the initiator produced in the reaction vessel (example 6) are inferior to that of the PVC resin made according to this invention (example 5). The resin produced according to the invention is significantly more advantageous compared to the control (Example 4) which uses the conventional commercially available secbutyl peroxydicarbonate as initiator. The yellowing index and stability (DTS) problems of the prior art methods are believed to be caused by the low peroxydicarbonate yield in the reactor, with the result that significant amounts of chloroformate are not converted to peroxydicarbonate due to hydrolysis to acid and the PVC resin is adversely affected by these impurities in the polymerization process.

The above examples and the description of the invention are not limited to the specific substances or methods mentioned. The invention is limited only by the following patent claims.

As used herein, the term "includes means" includes or consists of and "including" means "including or consisting of.

Features disclosed in the above description or the following claims or the accompanying drawings, expressed in their specific forms or in terms of means of carrying out the function disclosed, or the method or method of achieving the disclosed result as appropriate, may be, separately or in any combination of such features, used in carrying out the invention in its various forms.