DE1951775A1 - Process for the production of spheres or beads from a polymer of a vinyl compound - Google Patents

Description

SHELL INTERNATIONAL EESEAEOH MATSCHAPPIJ N, V. \ 50, Oarel van Bylandtlaan, The Hague / NETHERLANDS

concerning: .

" Process for the production of spheres or beads from a polymer of a vinyl compound"

The invention relates to a polymerization process of monomeric vinyl compounds including vinyl aliphatic and vinyl aromatic monomeric compounds by polymerization in aqueous suspension, with a poorly soluble phosphate as a suspension stabilizer is used. The invention also relates to the polymers produced in this way. ,,

It is known that a suspension stabilizer in the Polymerization in aqueous suspension is required, in order the polymerizing organic substances in the aqueous Hold phase during the polymerization. Difficult to dissolve Phosphates were used as suspension stabilizers according to British patents.-659 771 "and 690 877, According to British Patent 690 877 can-with advantage

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a water-soluble persulfate can be used in a calcium phosphate stabilized system. If such a sparingly soluble phosphate is used as a suspension stabilizer, you can select the optimal working conditions in the reactor with regard to the phosphate concentration, the stirring speed, the presence and concentration of other additives, such as surface-active agents, inorganic salts and chain transfer agents, which are advantageous in the polymerization system prove, and you can adjust the ratio of monomeric vinyl compound and water. Under properly selected operating conditions, such a process should produce spheres or beads of polymers of a vinyl compound which are useful for a limited number of uses but have disadvantages in general applicability because they are relatively small. If the beads or spheres To be brought into an expandable or foamable iOrm, as used in the manufacture of foam products, the size of the expandable beads or spheres is particularly important. The hard position .requires different size ranges of the balls depending on the type of. cellular foam product to be made therefrom and the type of devices used in the? Production of the foams are to be used. ,; ■■ - ■■; ...- / .-. -y. ;:.;:,. -. .-- - ■■ ■: /: '■ -. -,:

In general, the. Smaller balls that. a _v ,, size up to 0.7, have · according to the sieve analysis, without much difficulty ../? can be obtained by suspension polymerization, a phosphate being used as a suspension stabilizer according to Dor-British patent 690 877.

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However, this method has generally not been found to allow larger spheres such as one size in the range from 1.0 to 2.0 mm with an average "ball size of, for example, 1 to 1.2 mm will. ·

So far it has not been possible to polymerize in aqueous phase to adjust the polymerization conditions so that that a bead product was obtained with all of the beads within a certain desired size range fall. A product is obtained which includes a spectrum of ball sizes. Much effort has been made to find Vege, the sphere size distribution to keep closer and to influence the course of the polymerization in such a way that as many spheres as possible in a desired Size range fall. For example, according to British Patent 1,056,470, a suspension polymerization process is used described, a system made of bentonite and gelatin being used as the suspension stabilizer as well as other conditions are met, including advantages result in terms of the sphere size distribution. The polymerization in aqueous suspension is batchwise carried out. Here it is advantageous to use the balls provided Size * to be made in each polymerization batch. For example, if some of the approaches have a spherical size distribution with a larger proportion of smaller spheres Size results as required and can be expected from the working conditions used, a significant occurrence occurs Share of unusable product.

It has hitherto been considered desirable that the pH of the aqueous phase of the suspension is kept above 6.

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For example, British Patent 715,867 states that buffers should be used to keep the pH between 6 and 9 is held. It has now been found that a Phosphate stabilizer advantageous in aqueous suspension polymerization Can be used to make larger beads if the pH of the aqueous phase is at most 6 and kept constant within a range of one pH unit while the spheres are formed, by working in the presence of a buffer. Here the pH of the aqueous phase during the formation of the spheres is below that which has been proposed or carried out so far Polymerization suspensions in a phosphate stabilized Suspension held. In practicing the invention, the pH of the aqueous phase is determined by the Presence of a buffer during the controlled period of time is kept at a value which is higher than the value at the phosphate calibrates in a noticeable way * in the aqueous Phase resolves, but at a pH value of 6 or less.

Accordingly, the inventive method for the preparation of spheres or beads of a polymer of a vinyl compound by polymerization of the monomeric, poiymeri- ...... sierbaren vinyl compound in an aqueous, a sparingly soluble phosphate as a stabilizer containing suspension characterized in that the polymerization is in an aqueous phase durchfuhrt containing at least 75% of the total phosphate content in undissolved form and the pH of which is' most 6, being kept constant within a unit during at least part "of the polymerization, the pH-value by means of a buffer. ί μ

<Preferably, the pH of the aqueous phase is set to a,

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The value is set between 4 and 6, in particular 4.5 to 5.5, and in particular it is kept at 5 as practicable during the controlled period. This controlled period of time can be the period after the polymerization has reached a low monomer conversion, for example about 20 % conversion up to a monomer conversion of the order of 80%, for example the period between a conversion of about 40% and 60%. In general, however, it is advantageous and may indeed be desirable to maintain the aqueous phase within the desired pH range throughout the duration of the polymerization, with a suitable buffer being added to the aqueous phase before or very soon after the onset of polymerization. Investigations have shown ¹ that if the pH of the aqueous phase is maintained in the above manner in a phosphate stabilized system, a product of the desirable larger spherical size is obtained. Although the reasons why control of pH in this manner should be important are not entirely clear, it has been found that these selected conditions allow larger spheres to be formed with certainty. There may be other benefits as well. For example, one can obtain a considerably narrower sphere size distribution, which opens up the possibility of influencing the number of spheres more easily which are present within a desired fraction of the size spectrum of the end product. In general, working according to the invention with a given reactor and given Kihrgeschwindigkelt a control of the sphere size together with advantages with regard to the phase ratio of the monomeric vinyl compound, such as styrene, to water in the reaction mixture, the

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can be applied, and there will continue to be advantages with regard to the desired low water * the content of the balls produced according to the invention achieved. While it was previously possible, in a reactor operated under certain stirring conditions, either the Ball size distribution or the ratio of vinyl ■ However, to improve monomers and water or the water content of the pearls produced, the improvement went one size at the expense of the deterioration in the other sizes. The inventive control of the pH value can now all three sizes at the same time improved, representing an important technical advance in the manufacture of spheres and beads Means vinyl polymers.

The invention also includes the vinyl produced polymer in spherical or bead shape, including in particular Balls or beads formed by the incorporation of a blowing agent, for example one usually liquid vaporizable hydrocarbon such as pentane, either subsequently or preferably during; the production these beads or spheres have been made expandable.

The pH of the aqueous phase is preferably on the

desired S1 | and during essentially the entire j

Polymerization held by adding a gel i

Appropriate puffir is added. The buffers that do not have any- {

partial influence on education and maintenance

the desired suspension and the polymerization |

have yourself, j can be used *? The means to \

Buffering is used ₉ depending on the circumstances and the \

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desired, to be maintained pH ¥ ert of the aqueous phase can be selected during the polymerization. Examples of suitable buffers are sodium acetate / acetic acid, sodium hydroxide / acetic acid and sodium acetate / hydrochloric acid. The two last-mentioned mixtures of substances form the first-mentioned mixture in situ and are therefore preferred. The buffers required and close may depend on the used suspension polymerization, wherein the buffers are used soil ₁ and from the buffer itself. In general, very small amounts are used, though can be in pointed circumstances larger amounts needed so that an effective pH control or regulation the solubility of the phosphate is achieved. The minimum amount can be determined by tests or calculations in a manner known per se.

When performing the method according to the invention Any poorly soluble phosphate can be used, for example the phosphates of calcium, strontium and magnesium which are suitable as suspension stabilizers in the polymerization in aqueous suspension. Oalcium phoephate is preferably used and in particular that Calcium phosphate in which the ratio CaO / PpOc is at least 1.35 and that in the UK patent 659 771 is · The amount of phosphate used usually depends on factors such as charging speed and the construction of the reactor and / or drill. in general, the amount of phosphate can be between 0.08 and 0.60 % By weight, based on the total starting material used monomeric vinyl compound. To manufacture the larger balls using the preferred oalcium

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Phosphate stabilizer can vary the amount of phosphate between about 0.14 and 0.24 wt. # based on the monomers Vinyl compound. The use of a phosphate stabilizer in combination with a water soluble persulfate according to British Patent 690,877 advantageous when carrying out the process according to the invention, the addition of the persulfate in particular gradually, e.g. in three separate additions during the Main time the polymerization takes place. An amount of persulfate of e.g. about 5 to 75% by weight, based on the phosphate stabilizer, can be beneficial.

When carrying out the method according to the invention, other factors must be taken into account are known, e.g. the need for sufficient touching, the possibility of using a surfactant Means in the aqueous phase, the use of catalysts and the preference of using a phosphate an optimal particle size and / or chemical constitution. These factors are known in such methods and do not need to be explained in more detail. The polymerization conditions, in addition to the aforementioned control of the pH, such as the temperature and the polymerization time and the method for isolating and washing out the polymer are known per se and need them not to be explained in more detail.

The inventive method is for the production of Polymers and copolymers of all vinyl compounds can be used which can be polymerized by aqueous suspension polymerization, e.g. with the aid of peroxide catalysts, such as benzoyl peroxide or t-butyl perbenzoate or

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any catalyst combination. Examples of such monomeric vinyl compounds are styrene, oc-methylstyrene, the vinyl toluenes and the halostyrenes, acrylonitrile and its derivatives and the alkyl acrylic acid esters and methacrylic acid esters. However, the invention is particularly suitable for the polymerization of styrene and allows its manufacture of polystyrene balls, which are excellent for transferring into expandable spheres are suitable. The invention can can also be used in the manufacture of refractory, e.g. self-extinguishing, balls. Accordingly lies the presence of additives that impart such properties to the polymer and / or other additives in the. Reaction mixture within the scope of the invention.

The invention is further illustrated by the following examples explained.

Example 1 -

Styrene was polymerized in a steam-heated reactor of 450 liters with a stirrer with three propellers and three impact arms for stirring the contents of the heater in the usual manner in suspension polymerization of styrene. * The polymerization was carried out by adding 224 liters of demineralized water to the reactor and then 448 g (0.2% by weight, based on water) of Hätriümaeetät and 110 ml of concentrated salic acid were added to adjust the pH of the aqueous phase to 5. .The wäßiige "Phase \ was then stirred," wherein check a homogeneous solution VFM Hätriumä ^ e ^ at / Salzsäü2 | e \ formed as Ptiffer. McS dem tested diö pl values for the> aqueous phase at 20 C with eihei; pENiieigöiät wuMön 224 3 ^

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added distilled styrene. The temperature of the reactor contents was increased to 90 C with adequate drilling of the Reactor content increased. The volume ratio of styrene to water was 50:50. At this temperature, 620 g (0.3 % By weight, based on styrene) of benzoyl peroxide (dry weight) was added as a catalyst. It was further heated so that the The temperature of the reactor contents remained at 90 ° 0. After 15 min were 0.08 wt .-% calcium phosphate, based on the total content Water and styrene, added.

The polymerization was continued at 90 ° C. until the conversion of styrene to polystyrene was 90 % . Samples of the reactor contents were taken every 15 minutes and the sphere size was checked visually. When the styrene conversion reached 90 % , the reactor was closed and the polymerization was brought to an end by heating to 100 ° C. for 6 hours. The polystyrene beads obtained were separated off in a centrifuge, washed with water and dried ^{with air at 25 to 30 0 O.}

Eg 1 2

Styrene was polymerized in a reactor of 850 ml, which was heated in a water bath and equipped with a Üehrblattrührer and an inner baffle of 4 arms to the Reaktorinhält - to stir in customary for the Suspehsiönspöiymerisätiöh of styrene manner. There were 28? ml of demineralized water and then 106 ml of an Oi2ffl-EaliumdihydrögehpEophatlösung and y 32.23 ml of an Ö, 2m-sodium hydroxide solution added ^ to bring the pÖ host to the aqueous phase to 6§§>. The aqueous phase was then until a homo-

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Genen solution of the buffer stirred. After checking the pH of the aqueous phase at 2O Werta ⁰ O having a pH-value measuring device 425 "1 of distilled styrene were added. The temperature of the reactor contents was increased to 92 ° 0 with adequate agitation of the reactor contents. The volume ratio of styrene to water was 50:50. At this temperature, 1.96 g (0.58 % by weight, based on styrene) of benzoyl peroxide (dry weight) were added as a catalyst. Heating was continued to keep the reactor contents at 92 ° 0. After 15 minutes at this temperature, calcium phosphate was added in an amount of 0.105 % by weight , based on the total amount of water and styrene, together with 0.1 ml of a 2% by weight solution of potassium pereulfate. Another 0.1 ml quantity of xaluminum persulfate solution was added after 45 minutes. The polymerization was continued at 92 ⁰ O for 5 h . The suspension then collapsed.

Example 3

Styrene was polymerized according to Example 2, except that the following conditions were observed.

The reactor was charged with 222 ml of demineralized water and then with 96.7 ml of a 0.2 M sodium hydroxide solution and 106.2 ml of a 0.2 M potassium phthalate solution in order to bring the pH of the aqueous phase to 6.0 bring. The polymerization was continued at 92 ⁰ O up to a styrene conversion to polystyrene of 80 % . Samples were taken from the contents of the reactor every 15 minutes and the stability and ball size were visually checked. After 80 % tJmsatm 0.1 ml of the potassium persulfate solution was added. Diethylene temperature of the reactor was ER 95 ⁰ O

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increased and the polymerization allowed to proceed to completion. The polystyrene balls obtained were collected on a sieve, washed with water and dried ^{in the air at 25 to 30 0 O.}

Example 4

Styrene was polymerized according to Example 3, but with the following conditions have been met.

The reactor was charged with 425 ml of demineralized water and then with 0.78 g of sodium acetate and a sufficient amount of hydrochloric acid to bring the pH of the aqueous phase to 4.0. After 15 min at 92 0 0.105 wt were -. Oalciumphosphat%, based on the total content of water and · styrene, together with 0.4 ml of a 2% added wt .- solution of potassium persulfate. After a further 45 minutes, 0.4 ml of the potassium persulfate solution was added. After a styrene conversion of 80 % , 2 ml of the potassium persulfate solution were added. The polystyrene beads were collected on a sieve, washed with water and dried in air at 25 to 30 ⁰ O.

Example 5

Styrene was polymerized according to Example 4, but the following conditions were met.

The reactor was filled with 425 nil of demineralized water and then with 7-06 g of sodium acetate and sufficient concentrated hydrochloric acid to adjust the pH of the aqueous phase to bring to 2.3, charged. With a styrene conversion of

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80 % was added to 1.2 ml of the potassium persulfate solution. The polystyrene beads obtained were collected in a sieve, washed with water and dried ^{in the air at 25 to 30 0 O.}

The beads obtained according to Examples 1 to 5 were subjected to a sieve analysis, the sphere size distribution being was determined. The results are shown in Table I below.

TABE.LLE I

pH of the poly wt% beads retained on sieve merization-dependent mesh size

axuxi 1.4 mm 1.0 mm 0.699 mm over 6, 8th, 99 mm 6.5 approach after 3 Useless for hours 1 6.0 31.5 4-5.5 15.0 6, Q 5.0 ■ 17 68 14th O, 4.0 2.0 27.5 64.5 0 2.3 54 37.5 8.0 5,

PATENOI CLAIMS:

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Claims (11)

PATENT CLAIMS 1) Process for the production of spheres or beads from a polymer of a vinyl compound by polymerizing the monomeric, polymerizable vinyl compound in an aqueous suspension containing a sparingly soluble phosphate as a stabilizer, characterized in that the polymerization is carried out in an aqueous phase which is at least 75% of the total phosphate content in undissolved form and its pH value is at most 6, the pH value being kept constant within one unit by means of a buffer during at least part of the polymerization time. 2) Method according to claim 1, characterized in that the control of the pH value during the entire duration of the polymerization by adding the buffer to the aqueous phase before or very soon after the onset of polymerization is effected. 3) The method according to claim 1, characterized ge ke η η - is characterized in that the control of the pH value / is effected after the polymerization has reached a monomer conversion of 20 % and is maintained until at most 80 % of the monomers are converted. - 2 - 009819/1885 ^BAÜ 1A-36,932 4) Method according to claim 1, 2 or 3, characterized in that g e that the pH of the aqueous phase is adjusted to a value between 4 and 6. 5) Method according to claim 4, characterized in that g e k e η η draws that the pH is adjusted between 4.5 and 5 [beta]. 6) '"Method according to claim 1 to 51, thereby g e k e η η draws that calcium phosphate is used as the poorly soluble phosphate. 7) A method according to claim 6, characterized in _t that a phosphate amount of 0.08 to 0.60 wt .-%, based on the vinyl material used as the starting compound is used. 8) Method according to claim 71, characterized in "that one has an amount of phosphate 0.14 to 0.24% by weight, based on the monomeric vinyl compound, used. 9) Method according to claim 1 to 8, characterized in that g e that you also have a water-soluble in the aqueous polymerization suspension Persulfate used. 10) Method according to claim 9, characterized in that the persulfate is potassium persulfate used. 00 9819/1865 ORIGINAL BATHROOM 1A-36,932 11) Method according to claim "9 or 10, characterized in that the ferrous sulfate in added to a series of separate additions during the polymerization. IH) Method according to claim 1 to 11, characterized '; that one as a monomeric vinyl compound Styrene used. 009819/1865 ^BATH ORIGINAL