MXPA99000227A - Procedure for the preparation of polime particles - Google Patents

Abstract

A process for the preparation of polymer particles containing a vinylarene polymer, said process comprising the reaction of a vinylarene monomer together with a copolymerizable compound containing a polar half and a vinyl half up to a conversion degree of 20 to 70 %, the suspension of the prepolymerized mass, and the polymerization of the vinylarene monomer in the suspended droplets

Description

PROCEDURE FOR THE PREPARATION OF POLYMER PARTICLES FIELD OF THE INVENTION The present invention relates to a process for the preparation of polymer particles containing a polymer of a vinylarene monomer and a physical foaming agent, and to said polymer particles and honeycomb articles.

BACKGROUND OF THE INVENTION The particles containing said polymer and foaming agent 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. The foaming agent is generally a low boiling hydrocarbon, such as a C3-C8 hydrocarbon, in particular pentane isomers. Expandable polystyrene is used to make alveolar articles that are produced by the expansion of polystyrene particles. At REF .: 29147 Expansion procedure The foam forming hydrocarbon agent is released and can be emitted into the environment. Such emissions are not considered desirable and "ways to avoid them are sought." One way is to recover or burn the hydrocarbon emitted.Another way is to reduce the amount of foaming hydrocarbon agent in expandable polymer particles. -5, 096, 931 describes the expandable polystyrene containing polystyrene, a small amount of a polar polymer, a certain amount of water and a reduced amount of a foaming hydrocarbon agent.While the content of the foaming hydrocarbon agent has been reduced, said agent must still be present to achieve a satisfactory expansion GB-A-1, 106,143 discloses a process for preparing expandable polystyrene particles in water by mixing, by means of vigorous mechanical stirring, a styrene monomer , water and an emulsifier with a free radical initiator in order to obtain an emulsion containing small water droplets. The emulsion is suspended in an aqueous phase and the suspension obtained is subjected to polymerization. In order to achieve satisfactory expansion, certain amounts of organic foaming agents are included. In the experiments to verify the merits of the teaching of the above-mentioned British patent, it was found that finely dispersed water droplets which are obtained in the first emulsion tend to combine and form larger droplets during the polymerization. In an experiment in GB-A-1, 106, 143 it is confirmed that droplets greater than 40 μm cause unsatisfactory alveolar articles after expansion. Vigorous agitation is apparently necessary in this known procedure for the purpose of creating and maintaining finely dispersed water droplets. However, it is inconvenient to stir up said high energy input in the commercial operation. Therefore, it would be desirable if the tendency of the water droplets to be combined could be reduced. Surprisingly, it was found that the tendency of the water droplets to grow could be reduced by creating a viscous emulsion with water content before completely polymerizing the vinylarene monomer in a suspension polymerization. This makes it possible to shake less vigorously.

DESCRIPTION OF THE INVENTION Accordingly, the present invention relates to a process in which a viscous emulsion with water content of vinylarene monomer is pre-polymerized before being suspended in an aqueous medium. The present invention relates to a process in which the emulsifier is prepared in-situ. The case of the patent claiming the priority of European application No. 96201904.8 relates to a process in which emulsifier is added. The present invention provides a process for the preparation of polymer particles containing a vinylarene polymer by suspension polymerization., said process comprises: a) the preparation of a pre-polymerized mass by the reaction of a vinylarene monomer together with a copolymerizable compound containing a polar portion and a vinyl portion, so that the vinylarene monomer is pre-polymerized until a degree of conversion of 20 to 70%, based on the vinylarene monomer, to the copolymerizable compound and to water emulsified therein; b) suspending the prepolymerized mass in an aqueous medium to produce suspended droplets; and c) polymerizing the vinylarene monomer in the suspended droplets to complete the conversion of the monomer to produce suspended polymer particles. The present invention has the advantage that it has been found that the emulsifier prepared in-situ is very effective. This makes a substantial amount of water can be incorporated into the pearls. The present process is capable of producing polymer particles with satisfactory expansion properties that do not contain an organic foaming agent. Accordingly, the process is preferably carried out in the substantial absence of C3-C6 hydrocarbon foaming agent. In the substantial absence it means in an amount of less than 0.5% by weight based on the amount of vinylarene monomer, preferably less than 0.25% by weight, more preferably in the complete absence of said foam-forming agents. In a further embodiment of the invention, the polymer particles that are obtained are separated from the aqueous mixture and, optionally, expanded to produce pre-expanded particles which are optionally further treated to produce honeycomb articles. The present invention also relates to polymer particles and honeycomb articles obtainable by said method.

The present invention further relates to expandable polymeric particles which additionally contain 1-20% by weight based on the weight of the vinylarene monomer, of water emulsified therein. The present invention also relates to foam forming articles based on a polymer of a vinylarene monomer and 0.001 to 5% by weight, based on the amount of viT-iiafcene monomer of a copolymerizable compound containing a polar portion. and a vinyl portion. The creation of the viscous, pre-polymerized mass is preferably carried out by the volumetric polymerization of the ihylrene mohomer to the desired degree. The emulsifier can be prepared in-situ in several ways. Preferably, the vinylarene copolymerizable compound and water are mixed together and subsequently subjected to prepolymerization. The copolymerizable compound can be selected from any compound that combines the two functionalities: a polar portion and a vinyl portion. Suitable compounds are styrene compounds with a polar moiety. The polar half is preferably derived from an acidic moiety, more particularly an inorganic aeid moiety. Suitable examples include acrylic acid or the salts thereof. Other preferred examples are polar styrene derivatives such as styrene sulfonic acid or a salt thereof. For the purpose of preparing the emulsifier, the mixture of copolysable compound and vinylarene compound preferably contains a phase transfer catalyst that allows copolymerization. The phase transfer catalyst can be selected from a wide variety of known compounds. For anionic polar moieties, suitable phase transfer catalysts are quaternary ammonium and / or phosphonium compounds. Preferred compounds include ammonium halides or tetraalkyl phosphonium (eg with 1 to 15 carbon atoms), such as tetrabutylammonium bromide, tetramethylammonium chloride or trioctylmethylammonium chloride. The emulsification can be easily achieved by stirring the water and the other components of the emulsification mixture. The suitable agitation is then carried out at an energy input equivalent to or less than 500 revolutions per minute for a 70 1 reactor, even at an energy input equivalent to or less than 350 revolutions per minute for a 70 1 reactor. The amount of copolymerizable compound that should be used depends to a certain extent on the amount of water to be emulsified. Conveniently, the amount of copolymerizable compound ranges from 0.001 to 5% by weight, based on the amount of the monomer of the isomer. Preferred scales are between 0.05 and 3, more preferably between 0.1 and 1.5% by weight. The amount of water to be emulsified which determines to a certain extent the desired amount of copolymerizable compound can be chosen from broad scales. Conveniently, the amount of water ranges from 1 to 20% by weight, based on the weight of the vinylarene monomer. The particles that can expand well can be obtained when emulsifying between 3 and 15% by weight of water. Below 1% by weight, the expansion capacity may be too low, while at very high water contents the particles produce expanded articles which may run the risk of breaking. An electrolyte can be included in the water to be emulsified. Suitable electrolytes are alkali metal or alkaline earth salts, although other inorganic salts can also be used equally well. The electrolyte can lead to a decrease in the size of the droplets and can increase the water-in-oil character of the ionic surfactants. Therefore, it may be convenient to use a water phase with between 0.5 and 5% by weight of electrolyte, based on the amount of water, especially when an ionic emulsifier is used. Preferred salts are alkali metal halides, such as NaCl and KCl. The prepolymerization step can be carried out in any known manner. This includes polymerization of free radicals and thermal polymerization of radicals. The thermal polymerization can be effected by heating the emulsion to a temperature of 120 to 50 ° C. When the desired convon has been achieved, the temperature is reduced. If the prepolymerization step is carried out by thermal radical polymerization in the presence of water, the prepolymerization needs to be carried out at elevated pressure. This means that in most cases, it is preferred to prepolymerize by polymerization of free radicals with the aid of one or more free radical initiators. For the same reasons, the polymerization step c) is preferably carried out by polymerization of free radicals. The prepolymerization by free radical polymerization can be carried out by adding an initiator to the vinylarene / water emulsion and starting the polymerization by heating at 40-140 ° C. The prepolymerization of step a) is preferably carried out by heating at 40-120 ° C. The polymerization of step c) is preferably carried out by heating to 60-140 ° C. The polymerization of free radicals is conveniently carried out at a pressure of 0.5 to 5 bar, preferably 0.7 to 1.5 bar and, more preferably, at atmospheric pressure. The additional process conditions are well known to the experienced pn. More preferably, the final step of the polymerization of step c) is carried out at elevated pressure and at a temperature of 110-140 ° C in order to further reduce the amount of monomer present in the final product. The optimum convon rates of the prepolymerized mass can vary for different monom Conveniently, the convon varies between 20 and 70% of the vinylarene monomer. If the convon is greater than 70%, the viscosity of the prepolymerized mass can be so high that maneuverability problems can occur. This can complicate the suspension of the prepolymerized mass in the aqueous phase or the emulsion of the water in the prepolymerized mass. If the degree of prepolymerization is less than 20%, the suspended droplets will tend to be unstable. In such a case, large unwanted quantities of the aqueous suspension medium of large droplet size will be incorporated. This will lead to the sinking of the foam during expansion. Preferably, the convon varies between 30 and 60%. In order to improve the expansion properties of the possible polymer particles, it is preferred to have the crosslinking agent present during the polymerization. The crosslinking agent can be added in step a) and / or in step c). Preferably, the crosslinking agent is added in step a). Conveniently, the crosslinking agent is selected from the group of compounds possessing at least two double olefinic bonds. Examples of such compounds include divinylbenzene, α, α-alkadienes, e.g. ex. isoprene, and the diester of acrylic acid or methacrylic acid with a diol, such as butanediol, pentanediol or hexanediol. Preferred for its compatibility with vinylarene is divinylbenzene. In order to obtain a significant crosslinking effect, the amount of the crosslinking agent should not be too low. On the other hand, if the amount of crosslinking agent was too high, the expansion capacity of the eventual particles would deteriorate. A suitable scale is between 0.01 and 5% by weight, preferably between 0.01 and 1.5% by weight, based on the amount of vinylarene monomer. More preferably, 0.01 and 0.5% by weight of crosslinking agent is used. LikewiseIt has been discovered that it is advantageous to polymerize the vinylarene monomer in the presence of a polyphenylene ether. It has been found that the presence of polyphenylene ether reduces the opportunity for the alveolar material to be crushed during cooling. Suitable polyphenylene ethers have been described in EP-A-350137, EP-A-403023 and EP-A391499. The polyphenylene ether may be added in step a) and / or in step c). Preferably, the polyphenylene ether is added in step a). The polyphenylene ether compound is preferably present in an amount comprised between 1 and 30% by weight, based on the amount of vinylarene. Subsequent to the pre-polymerization step, the polymerized mass is suspended in an aqueous medium to produce suspended droplets. The volume ratio between the aqueous suspension medium and the pre-polymerized mass can vary between broad scales as a person skilled in the art will appreciate. Suitable volume ratios include 1: 1 to 1:10 (prepolymerized mass: aqueous phase). The optimal ratio is determined by economic considerations. The suspension polymerization can be improved by increasing the stability of the water-in-oil emulsion. This can be achieved by the use of an aqueous medium containing one or more conventional stabilizing agents, such as polyvinylalcohol, gelatin, polyethylene glycol, hydroxyethylcellulose, carboxymethylcellulose, polyvinylpyrrolidine, polyacrylamide, but also the salts of poly (meth) acrylic acid, acid phosphonic or acid (pyro) phosphoric, maleic acid, tetraethylenic acid of ethylenediamine, and the like, as the person skilled in the art will appreciate. Suitable salts include the ammonium, alkali metal and alkaline earth metal salts. A convenient example of said salt is tricalcium phosphate. Preferably, the stabilizing agent is based on acrylic acid and / or methacrylic acid, optionally in combination with acrylic amide. The amount of the stabilizing agents can conveniently vary between 0.05 and 1, preferably between 0.15 and 0.6% by weight, based on the weight of the aqueous medium.

The free radical initiator can be selected from conventional initiators for the polymerization of styrene free radicals. They 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 C6-C2o acyl peroxides such as decanoyl peroxide, benzoyl peroxide, peroxy octanoyl, stearyl peroxide, 3, 5, 5-trimethylhexanoyl peroxide, C2-C18 acid peresters. and C1-C5 alkyl groups, such as t-butylperbenzoate, t-butylperacetate, t-butylperpivalate, t-butylperisobutyrate and t-butyl peroxylarate, and hydroperoxides and dihydrocarbyl peroxides (C3-C10), such as hydroperoxide diisopropylbenzene, di-t-butyl peroxide, dicumyl peroxide or combinations thereof. Radical initiators other than peroxy compounds are not excluded. A suitable example of said compound is a, α'-azobisisobutyronitrile. The amount of radical initiator is suitably comprised between 0.01 and 1% by weight, based on the weight of the vinylarene monomer. The process is conveniently initiated by heating the reaction mixture to an elevated temperature, e.g. ex. on the scale between 40 and 140 ° C. The polymerization process can be conveniently carried out in the presence of a chain transfer agent. The person skilled in the art will appreciate that these chain transfer agents can be selected from mercaptans, such as C2-Ci5-alkyl mercaptans, e.g. ex. n-dodecyl mercaptan, t-dodecyl mercaptan, n-butyl mercaptan or t-butyl mercaptan. The aromatic compounds such as pentaphenylethane and, in particular, the dimer of α-methyl styrene are mentioned. The polymerization can be further improved by increasing the stability of the suspension. Said increase in stability can be carried out by incorporating a polar polymer into the prepolymerized mass in addition to the emulsifying agent already present. Examples of such polymers are polyvinylalcohol, gelatin, polyethylene glycol, hydroxyethylcellulose, carboxymethylcellulose, polyvinylpyrrolidone, polyacrylamide, but also the salts of poly (meth) acrylic acid, phosphonic acid or (pyro) phosphoric acid, maleic acid and tetraacetic acid of ethylenediamine. Suitable salts include the ammonium, alkali metal and alkaline earth metal salts. Preferably, the polar stabilization polymer is based on acrylic acid and / or methacrylic acid, optionally in combination with acrylic amide. Generally, the polar polymer will be incorporated by the addition of the polymer in step a) of the process. The incorporation can be effected by mixing the polar polymer with the prepolymerized mass, but it can also be incorporated in-situ by mixing the corresponding polar monomer with the vinylarene monomer and water and polymerizing the polar monomer to produce the desired polar polymer. . Subsequently, the polar polymer can be suspended together with the other components of the prepolymerized mass. Another way of incorporating the polar polymer is to add the corresponding polar monomer to the pre-polymerized mass and subsequently polymerize the monomers to produce the polar polymer. The amount of polar polymer is suitably comprised between 0.1 and 10% by weight, based on the emulsified water. The present invention has allowed the skilled person to prepare particles capable of producing foam in water, which do not contain an organic foaming agent. The polymer particles may also contain various additives or coatings in effective amounts. These additives include dyes, fillers, stabilizers, combustion retardant compounds, nucleating agents, antistatic compounds and lubricants. Of particular interest are coating compositions containing glycerol carboxylates or metal. Said compounds reduce the tendency of the particles to agglomerate. Suitable carboxylates are mono-, di- and / or glycerol tristearate and zinc stearate. Examples of said additive compositions are disclosed in GB-A-1, 409, 285. The coating compositions are deposited on the particles through known methods, e.g. ex. through dry coating in a ribbon mixer or by an aqueous mixture or solution in a readily vaporizable liquid. The particles conveniently have an average diameter of between 0.1 and 6 mm, preferably between 0.4 and 3 mm. The expandable particles can be pre-heated by hot air or by using steam (superheated), to produce particles that can be reduced in size, eg. between 800 and 30 g / m3. It will be appreciated that, in order to vaporize the water included in the particles to effect foaming, the temperature must be higher than that used for the C3-C6 hydrocarbon frothing agents which have a lower boiling point than Water. Foaming can also be carried out by heating in hot air, in oil or by means of icicles. The invention will also be illustrated by means of the following example. EXAMPLE In a 2 liter container, 900 grams of styrene containing 0.4% by weight of dibenzoyl peroxide and 0.15% by weight of terbutyl perbenzoate, both based on the amount of styrene, 100 ml of distilled water, 10 g . of sodium styrene sulfonate as a copolymerizable compound and 2.0 g. of trioctylmethylammonium chloride as a phase transfer catalyst, were mixed and polymerized at 90 ° C for 2.5 hours while stirring at 800 rpm. The degree of conversion of the pre-polymerized mass was approximately 55%. Subsequently, the pre-polymerized mass was suspended in 3 liters of distilled water containing 12 grams of a suspension stabilizer based on acrylic amide and acrylic acid. The polymerization was continued for 5 hours at 90 ° C and, subsequently, for 5 hours at 125 ° C under a nitrogen pressure of 4 bar. Finally, the system was cooled to room temperature and the solid polymer beads were separated. The water content of the obtained pearls was measured with the help of thermogravimetric analysis. The pearls had a water content of 13.0% by weight of water, based on the amount of polystyrene, copolymerized compound and water. The beads were expanded in 135 ° C hot air in a 500 ml glass container. with the help of a hot air injector. The pearls could be expanded up to 24 times their original volume.

It is noted that in relation to this date, the best known method for carrying out the aforementioned invention, is that which is clear from the present description of the invention. Having described the invention as above, the contents of the invention are claimed as property. the following

Claims (13)

1. CLAIMS A process for the preparation of polymer particles containing a vinylarene polymer by suspension polymerization; said process is characterized in that it comprises: a) the preparation of a prepolymerized mass based on a vinylarene monomer, a copolymerizable compound containing a polar portion and a vinyl portion, and water emulsified therein, by reaction of the vinylarene monomer together with the copolymerizable compound such that the vinylarene monomer is prepolymerized to a degree of conversion of 20 to 70%, b) the suspension of the prepolymerized mass in an aqueous medium to produce suspended droplets, and c) the polymerization of the vinylarene monomer in the droplets suspended to complete the conversion of the monomer in order to produce suspended polymer particles.
2. 2. A process according to claim 1, characterized in that the copolymerizable compound is reacted with the vinylarene compound in the presence of a phase transfer catalyst.
3. 3. A process according to claim 1 6 2, characterized in that the suspended polymer particles are separated from the aqueous mixture and expanded to produce pre-expanded particles.
4. 4. A process according to claim 3, characterized in that the pre-expanded particles are further treated to obtain honeycomb articles.
5. 5. A process according to any of claims 1 to 4, characterized in that the vinylarene monomer is polymerized in the presence of a polyphenylene ether.
6. 6. A process according to any of claims 1 to 5, characterized in that the vinylarene, the copolymerizable compound and water are mixed together, and subsequently subjected to prepolymerization.
7. 7. A process according to any of claims 1 to 6, characterized in that the amount of copolymerizable compound ranges from 0.001 to 5% by weight, based on the amount of vinylarene monomer.
8. 8. A process according to any of claims 1 to 7, characterized in that the copolymerizable compound is a styrene compound with a polar portion.
9. 9. A process according to claim 8, characterized in that the copolymerizable compound is styrene sulfonic acid or a salt thereof.
10. 10. A process according to any of claims 1 to 9, characterized in that the polar polymers are incorporated in the prepolymerized mass.
11. 11. A process according to any of claims 1 to 10, characterized in that the crosslinking agent is present during the polymerization.
12. 12. The expandable polymer particles based on a vihilarene monomer and 0.001 to 5% by weight, based on the amount of vinylarene monomer, of a copolymerizable compound containing a polar portion and a vinyl portion, characterized in that such polymer particles they also contain 1-20% by weight, based on the weight of vinylarene monomer, of water emulsified therein.
13. 13. The alveolar articles characterized because they are based on a polymer of a vinylarene monomer and

    0. 001 to 5% by weight, based on the amount of vinylarene monomer, of a copolymerizable compound containing a polar portion and a vinyl portion.