KR100457184B1 - Manufacturing Method of Polymer Particles - Google Patents

Abstract

Prepolymerizing the vinylarene polymer (the prepolymerized mass further contains an emulsifier); Suspending the prepolymerized mass; A method for producing polymer particles containing a vinylarene polymer by polymerizing a vinylarene monomer in a suspended droplet. The invention also relates to polymer particles comprising a vinylarene polymer, water and an emulsifier and wherein the amount of water ranges from 8 to 15% by weight, based on the total weight of the polymer particles.

Description

Method for producing polymer particles

The present invention relates to a method for producing polymer particles containing a polymer of vinylarene monomer and a physical blowing agent, and to such polymer particles.

Particles containing such polymers and blowing agents are generally known as expandable polymer particles. A well known type of expandable polymer particles is expandable polystyrene. Expandable polystyrene is produced on a commercial scale by suspension polymerization. Blowing agents are usually low-boiling hydrocarbons, such as C ₃ -C ₈ hydrocarbons, especially pentane isomers. Expandable polystyrene is used to make foams produced by expanding polystyrene particles. In the expansion process, hydrocarbon blowing agents can be released and released into the environment. Such releases are considered undesirable and efforts are being made to avoid such releases. One way is to recover or burn the released hydrocarbons. Another approach is to reduce the amount of hydrocarbon blowing agent in the expandable polymer particles.

US-A-5,096,931 describes expandable polystyrenes containing polystyrene, small amounts of polar polymers, some water and reduced amounts of hydrocarbon blowing agents. Although the content of hydrocarbon blowing agents has been reduced, such formulations must still be present to achieve satisfactory expansion.

GB-A-1,106,143 discloses a process for preparing water-expandable polystyrene particles by mixing styrene monomer, water and emulsifier with free-radical initiator to obtain an emulsion containing water droplets by vigorous mechanical stirring. Doing. The emulsion is then suspended in the aqueous phase and the suspension obtained is subjected to polymerization. In order to achieve satisfactory expansion, an amount of organic blowing agent is included.

In experiments to demonstrate the advantages of the teachings of the GB patent, it was found that the microdisperse water droplets obtained in the first emulsion tended to agglomerate during polymerization to form larger droplets. Experiments in GB-A-1,106,143 have confirmed that droplets larger than 40 μm result in unsatisfactory foams after expansion. In this known method, vigorous stirring is clearly required to produce and maintain microdispersed drops. However, it is difficult to stir with such a high energy input in commercial operation.

Therefore, it would be desirable to be able to reduce the tendency of aggregation of droplets.

Surprisingly, it has been found that the propensity of growth of water droplets can be reduced by producing a viscous water emulsion before fully polymerizing the vinylarene monomer in suspension polymerization. This makes it possible to stir less vigorously when the water is emulsified in the (partially polymerized) vinylarene monomer. Agitation can be carried out with an energy input of up to 500 revolutions per minute for a reactor with a 70 liter capacity, or even with an energy input of up to 350 revolutions per minute for a reactor with a 70 liter capacity.

Accordingly, the present invention provides a process for preparing a prepolymerized mass containing vinylarene monomers which are non-polymerized at 20 to 70% conversion, based on vinylarene monomers and water emulsified therein, and further containing emulsifiers,

b) suspending the prepolymerized mass in an aqueous medium to obtain suspended droplets,

c) polymerizing the vinylene monomer in the suspended droplets to complete monomer conversion to obtain a suspended polymer particle, the method for producing a polymer particle containing the vinylarene polymer by suspension polymerization.

The prepolymerized mass differs from the mixture of polymerized vinylarene and vinylarene monomers, with the former having a monomodal molecular weight distribution, while the latter will generally have a bimodal distribution. Flies For many applications, the latter is disadvantageous in that the physical properties of the material will change over a wide range. In order to obtain a one-way distribution for the mixture of polymerized vinylarene and vinylarene monomers, the process conditions will have to be very tightly controlled. This is not attractive for commercial work.

The good results obtained by the process of the present invention are considered to be due to the production of a viscous prepolymerized mass in which the water is emulsified before the vinylarene is suspended in an aqueous medium for suspension polymerization. The emulsified droplets become less mobile and have little tendency for their aggregation or migration into the aqueous suspension medium.

The process can produce polymer particles having satisfactory expandability that do not contain organic blowing agents. Thus, the process is preferably carried out in the substantial absence of C ₃ -C ₆ hydrocarbon blowing agents. By substantial absence is meant an amount of up to 0.5% by weight, preferably up to 0.25% by weight, more preferably of complete foaming agent, based on the amount of vinylarene monomer.

In a further aspect of the invention, the obtained polymer particles are separated from the aqueous mixture and optionally expanded to give preexpanded particles which are optionally further processed to obtain foam.

The production of a viscous prepolymerized mass is preferably carried out by bulk polymerizing the vinylarene monomer to the desired degree. Emulsification in the starting monomers of water can be accomplished in a variety of ways. In one aspect, water, emulsifiers and vinylarene monomers are stirred to produce an emulsion which is subsequently added to the prepolymerization at the desired conversion to produce a prepolymerized mass. In another embodiment, the vinylene monomers are first introduced into the prepolymerization, followed by addition of water and emulsifier to the (partially) prepolymerized vinylene mixture and emulsification of the water. The third embodiment includes the prepolymerization of the vinylarene monomer in the presence of an emulsifier, and the addition of water to be emulsified later. As a fourth embodiment, the emulsifier is prepared in situ in the presence of water, followed by addition of the vinylene monomer to the obtained emulsifier.

The emulsifier is preferably compatible (soluble) with vinylarene. Emulsifiers can be selected from a wide variety of compounds. Preferably the emulsifier is of a type that produces a water-in-oil emulsion. Emulsifiers may be non-ionic, anionic or cationic surfactants.

Suitable emulsifiers include non-ionic surfactants such as sorbitan carboxylate, sorbitol or mannitol carboxylate, glycol or glycerol carboxylate, alkanol amides, alkyl phenols and dialkyl ethers. Such emulsifiers may contain polyalkoxy chains with 1 to 20 oxyalkylene groups, such as oxyethylene or oxypropylene moieties. Suitable anionic emulsifiers include salts of long chain (C ₈ -C ₃₀ ) carboxylic acids, long chain (C ₈ -C ₃₀ ) alkyl sulfonic acids, alkylarylsulfonic acids, sulfosuccinic acids. The cation of such emulsifiers may suitably be ammonium moieties, alkali or alkaline earth metal ions. Suitable cationic surfactants can be selected from high molecular weight fatty acid amines, ammonium or other nitrogen derivatives of long chain carboxylic acids. Anionic and cationic emulsifiers may contain polyoxyalkyl groups. When bis-alkyl sulfosuccinic carbonate, sorbitol -C ₈ - ₂₀ - carboxylate and / or C ₈ - ₂₀ - Using the alkyl xylene sulphonate and yielded good results. Metal salts of bis (2-ethylhexyl) sulfosuccinic acid are preferred.

The amount of emulsifier to be used depends to some extent on the amount of water to emulsify. Suitably, the amount of emulsifier is in the range of 0.01 to 5% by weight, based on the amount of vinylarene monomer in the emulsion. The preferred range is 0.1 to 3% by weight, more preferably 0.2 to 1.5% by weight.

To some extent the amount of water to be emulsified to determine the desired amount of emulsifier can be selected from a wide range. Suitably, the amount of water ranges from 1 to 20% by weight, based on the weight of the vinylarene monomer and water. Well expandable particles can be obtained when 3 to 15% by weight of water is emulsified. At up to 1% by weight, the expandability may be too low, while at very high water contents the particles may produce an expansion that may lead to the risk of collapse.

The electrolyte may be included in the water to be emulsified. Suitable electrolytes are alkali and alkaline earth salts, but other inorganic salts may equally be used as well. The electrolyte may result in a drop in droplet size, but may also enhance the water-in-oil properties of the ionic surfactant. Thus, especially when ionic emulsifiers are used, it may be advantageous to use an aqueous phase with 0.5 to 5% by weight of electrolyte, based on the amount of water. Preferred salts are alkali metal halides such as NaCl and KCl.

The prepolymerization step can be carried out by other known methods. Such methods include free radical polymerization and thermal radical polymerization. Thermal polymerization can be carried out by heating the emulsion to a temperature of 120 to 150 ° C. When the desired conversion is achieved, the temperature is reduced. If the prepolymerization step is carried out by thermal radical polymerization with water already present, the prepolymerization needs to be carried out at elevated pressure. If the prepolymerization step is carried out by thermal radical polymerization before water is added, the prepolymerized mass is generally cooled before the addition of water. This in most cases makes it desirable to prepolymerize by free radical polymerization with the aid of one or more free radical initiators. For the same reason, the polymerization step c) is preferably carried out by free radical polymerization. Prepolymerization by free radical polymerization can be carried out by adding the initiator to the vinylarene / water emulsion and heating to 40-140 ° C. to initiate the polymerization. The prepolymerization of step a) is preferably carried out by heating to 40 to 120 ° C. The polymerization of step c) is preferably carried out by heating to 60 to 140 ° C. The free radical polymerization is suitably carried out at 0.5 to 5 bar, preferably at 0.7 to 1.5 bar, more preferably at atmospheric pressure. Additional process conditions are well known to those skilled in the art. Most preferably, the final step of the polymerization of step c) is carried out at elevated pressure and at a temperature of 110 to 140 ° C. to further reduce the amount of monomers present in the final product.

The optimal conversion of the prepolymerized mass can vary for different monomers. Suitably, the conversion rate varies from 20 to 70% of the vinylarene monomer.

If the conversion is 70% or more, the viscosity of the prepolymerized mass is too high and handling problems may occur. This may complicate the suspension of the prepolymerized mass in the aqueous phase or the emulsification of water into the prepolymerized mass. If the prepolymerization rate is 20% or less, the suspended droplets tend to become unstable. In such a case, undesirably large amounts of large droplet size aqueous suspension medium will be incorporated. This will result in foam collapse during expansion. Preferably, the conversion rate varies from 30 to 60%.

In order to improve the expandability of the final polymer particles, it is desirable to have a crosslinking agent present during the polymerization. The crosslinking agent may be added in step a) and / or in step c). Preferably, the crosslinking agent is added in step a). Suitably, the crosslinking agent is selected from the group of compounds having at least two olefinic double bonds. Examples of such compounds include divinylbenzene, α, ω-alkadienes such as isoprene, and diesters of acrylic or methacrylic acid with diols such as butanediol, pentanediol or hexanediol. Divinylbenzene is preferable for compatibility with vinylarene.

In order to obtain a meaningful crosslinking effect, the amount of crosslinking agent should not be too low. On the other hand, when the amount of the crosslinking agent is too high, the expandability of the final particles is reduced. The suitable range is 0.01 to 5% by weight, preferably 0.01 to 1.5% by weight based on the amount of vinylarene monomer. Most preferably 0.01 to 0.5% by weight of crosslinking agent is used.

Moreover, it has been found advantageous to polymerize vinylarene monomers in the presence of polyphenylene ethers. The presence of polyphenylene ethers has been found to reduce the chance that the foam material collapses during cooling. Suitable polyphenylene ethers are described in EP-A-350137, EP-A-403023 and EP-A-391499. Polyphenylene ether may be added in step a) and / or step c). Preferably, the polyphenylene ether is added in step a). The polyphenylene ether compound is preferably present in an amount of 1 to 30% by weight, based on the amount of vinylarene.

Subsequent to the prepolymerization step, the prepolymerized mass is suspended in an aqueous medium. The volume ratio between the aqueous suspension medium and the prepolymerized mass can vary widely, as will be appreciated by those skilled in the art. Suitable volume ratios include from 1: 1 to 1:10 (prepolymerized mass: aqueous phase). The optimal cost is determined by considering the economic aspects.

Aqueous media are polyvinylalcohol, gelatin, polyethyleneglycol, hydroxyethylcellulose, carboxymethylcellulose, polyvinylpyrrolidone, polyacrylamide, but also poly (meth) acrylic acid, as will be appreciated by those skilled in the art. , One or more conventional stabilizers, such as salts such as phosphonic acid or (pyro) phosphoric acid, maleic acid, ethylene diamine tetraacetic acid, and the like. Suitable salts include the ammonium, alkali metal and alkaline earth metal salts. An advantageous example of such salts is tricalcium phosphate. Preferably, the stabilizer is based on acrylic acid and / or methacrylic acid, optionally in the form of a combination with acrylamide. The amount of stabilizer may suitably vary from 0.05 to 1, preferably 0.15 to 0.6 weight percent, based on the weight of the aqueous medium.

For the same reasons as applied in the prepolymerization stage a), the polymerization stage c) is advantageously carried out by free radical polymerization with one or more free radical initiators.

The polymerization can be further enhanced by increasing the stability of the suspension. This increase in stability can be achieved by incorporating the polar polymer into the prepolymerized mass in addition to the emulsifier already present. Examples of such polymers include polyvinylalcohol, gelatin, polyethyleneglycol, hydroxyethylcellulose, carboxymethylcellulose, polyvinylpyrrolidone, polyacrylamide, but also poly (meth) acrylic acid, phosphonic acid or (pyro) phosphoric acid, Maleic acid, salts of ethylene diamine tetraacetic acid. Suitable salts include ammonium, alkali metal and alkaline earth metal salts. Preferably, the stabilizing polar polymer is based on acrylic acid and / or methacrylic acid, optionally in combination with acryl amide. The incorporation step can be carried out by mixing the polar polymer with the prepolymerized mass, but can be incorporated in situ by mixing the corresponding polar monomer with vinylarene monomer and water and polymerizing the polar monomer to give the desired polar polymer. The polar polymer may then be suspended together with the other components of the prepolymerized mass. Another method of incorporating polar polymers is to add the corresponding polar monomers to the prepolymerized mass and subsequently polymerize the monomers to obtain polar polymers. The amount of polar polymer is suitably from 0.1 to 10% by weight, based on emulsified water.

The free radical initiator can be selected from conventional initiators for free radical styrene polymerization. These include in particular organic peroxy compounds such as peroxides, peroxycarbonates and peresters. Combinations of peroxy compounds can also be used. Typical examples of suitable peroxy initiators are C ₆ -C ₂₀ acyl peroxides, such as decanoyl peroxide, benzoyl peroxide, octanoyl peroxy, stearyl peroxide, 3,5,5-trimethyl hexanoyl peroxide, t C ₂ -C ₁₈ acids and C ₁ -C ₅ alkyl groups such as -butyl perbenzoate, t-butylperacetate, t-butyl-perpivalate, t-butylperisobutyrate and t-butyl-peroxylaurate Per-esters and hydroperoxides and dihydrocarbyl (C ₃ -C ₁₀ ) peroxides such as diisopropylbenzene hydroperoxide, di-t-butyl peroxide, dicumyl peroxide or combinations thereof.

Radical initiators different from peroxy compounds are not excluded. Suitable examples of such compounds are α, α'-azobisisobutyronitrile. The amount of radical initiator is suitably 0.01 to 1% by weight based on the weight of the vinylarene monomer. The process is suitably initiated by heating the reaction mixture to an elevated temperature, for example in the range from 40 to 140 ° C.

The polymerization process can be suitably carried out in the presence of a chain transfer agent. Those skilled in the art will appreciate that such chain transfer agents may be used in combination with mercaptans such as C ₂ -C ₁₅ -alkyl mercaptans, for example n-dodecyl mercaptan, t-dodecyl mercaptan, n-butyl mercaptan or t-butyl It will be appreciated that it may be selected from mercaptans. Preference is given to aromatic compounds such as pentaphenyl ethane, in particular dimers of α-methyl styrene.

The present invention enables those skilled in the art to produce water-foamable particles containing water as blowing agent. Accordingly, the present invention provides polymer particles comprising a vinylarene polymer, water and an emulsifier, wherein the amount of water ranges from 8 to 15% by weight, based on the total weight of the polymer particles. The polymer particles do not need to contain a C ₃ -C ₆ hydrocarbon blowing agent. This fact means that the hydrocarbon blowing agent can be present in an amount of up to 0.5% by weight, preferably up to 0.25% by weight, more preferably in the absence of such blowing agent, based on the total amount of polymer particles.

The polymer particles may also contain an effective amount of several additives or coatings. Such additives include dyes, fillers, stabilizers, flame retardants, nucleating agents, antistatic agents and lubricants. Of particular interest are coating compositions containing glycerol- or metal carboxylates. These compounds reduce the agglomeration tendency of the particles. Suitable carboxylates are glycerol mono-, di- and / or tristearate and zinc stearate. Examples of such additive compositions are disclosed in GB-A-1,409,285. The coating composition is deposited on the particles via known methods, for example, through a dry coating in a ribbon blender or through a slurry or solution in a liquid that easily evaporates.

The particles advantageously have an average diameter of 0.1 to 6 mm, preferably 0.4 to 3 mm.

The expandable particles may be prefoamed with hot air or with (superheated) steam to produce expanded or preexpanded particles. Such particles have a reduced density, for example 800 to 30 kg / m 3. It will be appreciated that in order to evaporate the water contained in the particles for performing the foaming, the temperature must be higher than that used for the C ₃ -C ₆ hydrocarbon blowing agent having a lower boiling point than water. Foaming can also be accomplished by heating in oil or by microwaves.

The invention is illustrated in more detail by the following examples.

Example 1

In a 2-liter autoclave, a predetermined amount of styrene was added at 0.4 rpm by weight of dibenzoyl peroxide and 0.15 wt% of tert-butyl peroxybenzoate based on styrene at a stirring speed of 300 rpm under nitrogen, And mixed with sodium bis (2-ethylhexyl) sulfosuccinate (commercially available under the trademark "AOT"). The mixture is then polymerized by heating to 90 ° C. for 100 minutes. The conversion of styrene is about 55%. Water containing 0.9% by weight of sodium chloride is slowly added to the prepolymerized mass with stirring at 800 rpm. Stirring is continued for 5 minutes. In a 6.4 liter autoclave, the obtained emulsion is suspended in water containing 0.4% by weight of hydroxyethyl cellulose sold under the trademark "NATROSOL 250G" by the Dutch company "AQUALON". The weight ratio of water to prepolymerized mass is about 3: 1. The polymerization is continued at 90 ° C. for 5 hours. The nitrogen pressure is increased by 4 bars and the temperature is increased to 125 ° C. The suspension is maintained at this condition for an additional 5 hours to complete the polymerization. The polymer beads are separated from the water phase and washed with water. The water content of these beads is determined by TGA (thermogravimetric analysis) based on the amount of polystyrene, water and emulsifier. Beads are expanded with the aid of a hot air gun in hot air at 130 ° C. in a 500 ml glass container. The results are shown in Table 1. Expandability is expressed as the ratio of expanded volume of beads to bead volume before expansion.

Comparative Example

In a 2-liter autoclave, 900 g of styrene at a stirring speed of 300 rpm under nitrogen at 0.4 wt% dibenzoyl peroxide and 0.15 wt% tert-butyl peroxybenzoate based on styrene, And 10 g of sodium bis (2-ethylhexyl) sulfosuccinate (commercially available under the trademark "AOT"). 100 g of water containing 0.9% by weight of sodium chloride are added slowly with stirring at 800 rpm. Agitation is continued for 5 minutes. In a 6.4 liter autoclave, the resulting mixture is suspended in 3 liters of water containing 0.4% by weight of hydroxyethyl cellulose sold under the trademark "NATROSOL 250G". The weight ratio of water to styrene-containing mass is about 3: 1. It is observed that no discrete droplets can be found. This is probably due to the fact that oil-in-water emulsions have formed. The polymerization is continued at 90 ° C. After about 2 hours, the stirrer of the reactor is stopped. When the reactor was opened, it was found that the emulsion turned to a solid white mass and water.

Example 2

In a six-liter vessel, 3600 g of styrene was added at 0.4 rpm by weight of dibenzoyl peroxide based on styrene and 0.15% by weight of tert-butyl peroxybenzoate based on styrene at a stirring speed of 300 rpm under nitrogen, and Mix with 40 g of sodium bis (2-ethylhexyl) sulfosuccinate (commercially available under the trademark "AOT"). The mixture is then polymerized by heating to 90 ° C. for 100 minutes. The conversion of styrene is about 55%. 400 g of water containing 0.9% by weight of sodium chloride are added slowly with stirring at 800 rpm. Stirring is continued for 5 minutes. In a 10 liter autoclave, the obtained emulsion is suspended in 4 liters of water containing 0.4% by weight of hydroxyethyl cellulose sold under the trademark "NATROSOL 250G". Suspension: The weight ratio of the prepolymerized mass is about 1: 1. The polymerization was continued at 90 ° C. for 5 hours with stirring at 350 rpm. The nitrogen pressure is increased by 4 bars and the temperature is increased to 125 ° C. The suspension is maintained at this condition for an additional 5 hours to complete the polymerization. The polymer beads are separated from the water phase and washed with water. The water content of these beads is measured by TGA based on the amount of polystyrene, water and emulsifier. Beads are inflated with the help of a hot air gun in hot air in a 500 ml glass container. The results are shown in Table 2.

Example 3

In a 2-liter autoclave, 900 g of styrene at a stirring speed of 300 rpm under nitrogen at 0.4 wt% dibenzoyl peroxide and 0.15 wt% tert-butyl peroxybenzoate based on styrene, And 10.0 g of sorbitan tristearate (available under the trademark "SPAN 65"). The mixture is then polymerized by heating to 90 ° C. for 100 minutes. The conversion of styrene is about 55%. 100 g of water containing 0.9% by weight of sodium chloride are added slowly with stirring at 800 rpm. Stirring is continued for 5 minutes. In a 6.4 liter autoclave, the obtained emulsion is suspended in 3 liters of water containing 0.4% by weight of hydroxyethyl cellulose sold under the trademark "NATROSOL 250G". The weight ratio of water to prepolymerized mass is about 3: 1. The polymerization is continued at 90 ° C. for 5 hours. The nitrogen pressure is increased by 4 bars and the temperature is increased to 125 ° C. The suspension is maintained at this condition for an additional 5 hours to complete the polymerization. The polymer beads are separated from the water phase and washed with water. The water content of these beads is measured by TGA based on the amount of polystyrene, water and emulsifier. Beads are inflated with the help of a hot air gun in hot air in a 500 ml glass container. The results are shown in Table 2.

Example 4

In a 2-liter autoclave, 900 g of styrene at a stirring speed of 300 rpm under nitrogen at 0.4 wt% dibenzoyl peroxide and 0.15 wt% tert-butyl peroxybenzoate based on styrene, And 10.0 g of sorbitan monooleate (available under the trademark "SPAN 80"). The mixture is then polymerized by heating to 90 ° C. for 100 minutes. The conversion of styrene is about 55%. 100 g of water containing 0.9% by weight of sodium chloride are added slowly with stirring at 800 rpm. Agitation is continued for 5 minutes. In a 6.4 liter autoclave, the obtained emulsion is suspended in 3 liters of water containing 0.4% by weight of hydroxyethyl cellulose sold under the trademark "NATROSOL 250G". The weight ratio of water to prepolymerized mass is about 3: 1. The polymerization is continued at 90 ° C. for 5 hours. The nitrogen pressure is increased by 4 bars and the temperature is increased to 125 ° C. The suspension is maintained at this condition for an additional 5 hours to complete the polymerization. The polymer beads are separated from the water phase and washed with water. The water content of these beads is measured by TGA based on the amount of polystyrene, water and emulsifier. Beads are inflated with the help of a hot air gun in hot air in a 500 ml glass container. The results are shown in Table 2.

Example 5

In a two liter autoclave, 900 g of styrene is mixed with 10.0 g of sodium bis (2-ethylhexyl) sulfosuccinate (available under the trademark "AOT"). The mixture is heated to 60 ° C. 99 g of distilled water, 1 g of acrylic acid and 0.03 g of potassium persulfate are slowly added to the mixture with stirring at 800 rpm. Stirring is continued for 5 minutes. The resulting emulsion is heated to 60 ° C. for 3 hours to allow acrylic acid to polymerize under stirring at 800 rpm.

To this is added 0.4% by weight of dibenzoyl peroxide based on styrene and 0.15% by weight of tert-butyl peroxybenzoate based on styrene and the temperature is raised to 90 ° C. Hold this temperature for 100 minutes. The conversion of styrene is about 55%. In a 6.4 liter autoclave, the obtained emulsion is suspended in 3 liters of water containing 0.4% by weight of hydroxyethyl cellulose sold under the trademark "NATROSOL 250G".

Suspension: The volume ratio of the prepolymerized mass is about 3: 1. The polymerization is continued at 90 ° C. for 5 hours with stirring at 350 rpm. The nitrogen pressure is increased by 4 bars and the temperature is increased to 125 ° C. The suspension is maintained at this condition for an additional 5 hours to complete the polymerization. The polymer beads are separated from the water phase and washed with water. The water content of these beads is measured by TGA based on the amount of polystyrene, water and emulsifier. Beads are inflated with the help of a hot air gun in hot air in a 500 ml glass container. The results are shown in Table 2.

Example 6

In a 2-liter autoclave, 900 g of styrene was 0.45 g of divinylbenzene, 0.4% by weight of dibenzoyl peroxide based on styrene and 0.15% by weight of tert-butyl peroxybenzoate based on styrene, and sodium Mix with 10.0 g of bis (2-ethylhexyl) sulfosuccinate (commercially available under the trademark "AOT"). The mixture is heated to 90 ° C. for 100 minutes and stirred at 300 rpm. 100 g of distilled water containing 0.9% by weight of sodium chloride are slowly added with stirring at 800 rpm. Stirring is continued for 5 minutes. The conversion of styrene is about 55%. In a 6.4 liter autoclave, the obtained emulsion is suspended in 3 liters of water containing 0.4% by weight of hydroxyethyl cellulose sold under the trademark "NATROSOL 250G". The polymerization is continued at 90 ° C. for 5 hours with stirring at 350 rpm. The nitrogen pressure is increased by 4 bars and the temperature is increased to 125 ° C. The suspension is maintained at this condition for an additional 5 hours to complete the polymerization. The polymer beads are separated from the water phase and washed with water. The water content of these beads is measured by TGA based on the amount of polystyrene, water and emulsifier. Beads are inflated with the help of a hot air gun in hot air in a 500 ml glass container. The results are shown in Table 2.

Claims (12)

a) prepolymerizing the vinylene monomer at 20 to 70% conversion, based on the vinylene monomer (prepolymerization is carried out with water already present or before water is added), further containing emulsified water and emulsifier therein To obtain a prepolymerized mass, b) suspending the prepolymerized mass in an aqueous medium to obtain suspended droplets, c) polymerization of the vinylene monomer in the suspended droplets to complete monomer conversion to obtain suspended polymer particles. The process according to claim 1, wherein the obtained polymer particles are separated from the aqueous mixture and expanded to obtain pre-expanded particles. The method of claim 1 wherein the preexpanded particles are further treated to yield a foam. 4. Process according to any one of the preceding claims, wherein water, emulsifiers and vinylarene monomers are stirred to produce an emulsion which is then subjected to prepolymerization at the desired conversion to obtain a prepolymerized mass. 4. The process according to any one of claims 1 to 3, wherein the vinylene monomers are first introduced into the prepolymerization in the presence of an emulsifier, followed by the addition of water to the prepolymerized vinylene mixture. The method according to any one of claims to 3, wherein the emulsifier is pitching when carbonate, sorbitol -C ₈ alkyl sulfonic bis- method selected from alkyl xylene _{sulphonate-20-carboxylate,} and C ₈ - _20. The process according to any one of claims 1 to 3, wherein the amount of emulsifier is in the range of 0.01 to 5% by weight, based on the amount of vinylarene monomer. The process according to claim 1, wherein the amount of water to be used in step a) ranges from 1 to 20% by weight, based on the weight of the water and the vinylarene monomer. The process according to any one of claims 1 to 3, wherein the prepolymerization step a) and the polymerization step c) are carried out by free radical polymerization. The process according to claim 1, wherein the polar polymer is incorporated into the prepolymerized mass. The process according to any one of claims 1 to 3, wherein the crosslinking agent is present during the polymerization. A polymer particle comprising a polymer of vinylarene monomer, water in the form of droplets, and an emulsifier, wherein the amount of water ranges from 8.6 to 15% by weight, based on the total weight of the polymer particles.