GB1583364A

GB1583364A - Manufacture of styrene suspension polymers

Info

Publication number: GB1583364A
Application number: GB3769977A
Authority: GB
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 1976-09-11
Filing date: 1977-09-09
Publication date: 1981-01-28
Also published as: NL7709946A; JPS5335785A; FR2364229B3; FR2364229A1; DE2640999A1

Description

(54) MANUFACTURE OF STYRENE SUSPENSION POLYMERS (71) We, BASF AKTIENGESELLSCHAFT, a German Joint Stock Company of 6700 Ludwigshafen, Federal Republic of Germany, do hereby declare the invention, for which we pray that a Patent may be granted to us, and the method by which it is to performed, to be particularly described in and by the following statement: The present invention relates to a process for the manufacture of styrene bead polymers by suspension polymerization.

A suitable process for the manufacture of styrene bead polymers is suspension polymerization, in which the monomers are suspended, in the form of fine droplets, in water, and are polymerized at at elevated temperature in the presence of initiators. In carrrying out this process industrially, it is necessary to use suspension stabilizers in order to prevent coalescence of the polymerizing monomer droplets. The suspension stabilizers should provide reliable stabilization and be of broad applicability.

The suspension stabilizers used in practice are mostly macromolecular organic compounds which are water-soluble or water-dispersible. Examples of such compounds are homopolymers or copolymers of vinylpyrrolidone, polymers of acrylic acid, polyvinyl alcohols and cellulose ethers. The use of Pickering dispersing agents has also been disclosed. These are water-insoluble inorganic compounds, the use of which is described, for example, in Houben-Weyl, Volume XIV/1 (1961). pages 420 et seq. Examples of such inorganic compounds are sparingly soluble alkaline earth metal phosphates, carbonates, sulfates and silicates. Calcium phosphates are used most commonly. The inorganic compounds are as a rule employed in combination with small amounts of true emulsifiers or surfactants (Houben-Weyl. volume XIV/1, page 425). Examples of suitable emulsifiers are sodium dodecylsulfonate, sodium octyl-sulfate, sodium dioctylsulfosuccinate, alkali metal laurylsulfates and alkali metal salts of fatty acids.

Compared to organic suspension stabilizers, these systems are of limited use, since reproducible operation. and trouble-free suspension polymerization, is only possible within a relatively narrow range of conditions. On this subject. Houben-Weyl. page 420, states: "It is hardly possible to specify conditions under which a pulverulent dispersing agent would be of broader applicability." When using the combination of inorganic compounds with surfactants. the optimum amounts must be adhered to precisely, since either to little or too much of the surfactant could result in coagulation of the batch.

It is also to be noted that the working up of such batches at times presents difficulties. since the addition of surfactants results in more or less pronounced foaming of the aqueous phase.

The surfactants employed in these systems are also referred to as extenders, which together with the sparingly soluble inorganic compounds produce a stable suspension of the polymerizing monomer droplets in the aqueous phase. The use of small amounts of watersoluble persulfates as extenders has similarly been disclosed (US Patent Specification 2,652,393). However. the use of water-soluble per-compounds is critical inasmuch as these result in the formation of substantial amounts of emulsion polymer in the aqueous phase. For example. emulsionpolymers are conventionally manufactured with water-soluble persulfates as initiators.

German Laid-Open Application DOS 1.770.411 discloses the use of sodium bisulfite as an extender. in conjunction with calcium phosphate. in the suspension polymerization of styrene. However. the addition of sodium bisulfite increases the inner content of water of the polymer beads. and in fact as low an inner water content as possible is desirable since.

especially in the case of expandable polystyrenes, a severe drying treatment interferes with the cell structure. A further disadvantage of the use of sodium bisulfite is irregularities in control of the bead size distribution, coupled with the hazard of coagulation.

The present invention seeks to provide a process which permits reliable and reproducible operation when using sparingly soluble inorganic compounds in the suspension polymeriza tion of styrene, and which at the same time does not have an undesirable effect of the kproperties of the resulting bead polymer.

We have found that good results may be achieved by the use of special suspension stabilizers.

The present invention provides a process for the manufacture of a homopolymer or copolymer of styrene which contains at least 50% by weigh of styrene by polymerizing the monomer(s) in aqueous suspension the presence of a suspension stabilizer, wherein there is used as suspension stabilizer from 0.05 to 1% by weight, based on the suspension, of as at most sparingly water-soluble inorganic compound, and from 0.001 to 0.1, preferably from 0.005 to 0.05%, by weight, based on the suspension, of a water-soluble reducing organic compound. In addition, up to 50%by weight, based on the reducing organic compound, of an activating iron-II compound may be employed.

Particularly suitable water-soluble reducing organic compounds are acids and hydroxy compounds, ascorbic acid, tartaric acid and glucose being preferred. The presence of up to 50% by weight,based on the reducing organic compound, of an activating iron-II compound, e.g. iron-II sulfate or iron-II phosphate, is advantageous but not absolutely essential.

The reducing organic compound may be added to the polymerization batch either at the start of the suspension polymerization, the compound being suitably added to the aqueous phase as is the at most sparingly water-soluble inorganic compound, or during the suspension polymerization, suitably when the monomer conversion is from 5 to 40%. It is also possible to add the reducing compound as a mixture with the at most sparingly water-soluble inorganic compound during the bead polymerization, suitably when the monomer conversion-is 5 to 40%.

The term "at most sparingly water-soluble" means that the inorganic compounds used as suspension stabilizers are not more than sparingly water-soluble and includes those of negligible solubility. Examples include phosphates of calcium. barium, strontium, mag nesium, aluminum. zinc, iron, cobalt and the like. Sparingly or negligibly water-soluble hydroxides. oxides. carbonates, silicates or sulfates, e.g. aluminum hydroxide. barium sulfate or barium carbonate. may also be used. as may mixtures of different sparingly or negligibly water-soluble inorganic compounds.

Sparingly or negligibly soluble phosphates of divalent metals. especially calcium phosphates. are preferred. Amongst these, salts with 3 or more base equivalents, or mixtures of products with more than 3 base equivalents and products with less than 3 base equivalents are preferred. Examples of preferred phosphate compounds are tricalcium phosphate. hydroxylapatite or other phosphates having an apatite lattice.

Sparingly or negligibly water-soluble metal phosphate compounds are obtained when phosphate ions are reacted with suitable metal salts in aqueous solution. For example.

sparingly water-soluble calcium phosphates are manufactured by combining a sodium phosphate solution and a calcium chloride solution whilst stirring. The sparingly water-soluble metal phosphate compounds can. however. also be manufactured by reacting the corresponding metal oxides or metal hydroxides with ortho-phosphoric acid.

The particle sizes of the at most sparingly water-soluble metal compounds can vary within wide limits, from ().01 to 10(),am depending on their process of manufacture and on their shape; in the case of hydroxy-apatite the preferred particle size is in the main from 0.01 to 0.1,am.

The at most sparingly water-soluble inorganic compound is preferably manufactured. and employed. as a fine aqueous dispersion. However. it is also possible to isolate and dry these particles and obtain the appropriate particle size distribution by milling.

The process according to the invention is distinguished by great flexibility and thus offers a corresponding choice in respect of its optimum use in the field of suspension polymerization.

The process may be used for the manufacture of styrene homopolymers and for the copolymerization of monomer mixtures which contain not less than 50% by weight of styrene. Suitable monomers are acrylonitrile. esters of acrylic acid or methacrylic acid with alcohols of I to 8 carbon atoms. N-vinyl compounds. e.g. vinylcarbazole. and also small amounts of compounds which contain two double bonds. e.g. butadiene. divinylbeozene or butanediol diacrylate.

In the process of the invention. the polymers are obtained in the form of fine beads. If the suspension polymerization is carried out in the presence of a blowing agent, expandable bead polymers are obtained. Expendable polystyrenes are of particular importance in this context.

Expandable polymer beads arc obtained if a blowing agent is added to the suspension before.

during or after the polymerization. Suitable blowing agents are normally gaseous or liquid hydrocarbons which do not dissolve the styrene polymer, and which have boiling points below the softening point of the polymer.

Examples of suitable blowing agents are propane, butane, pentane, cyclopentane, hexane, cyclohexane and halohydrocarbons, e.g. methyl chloride, dichlorodifluoromethane or trifluorochloromethane, and mixtures thereof. In most cases, the blowing agents are used in amounts of from 3 to 12% be weight, based on the monomers.

The polymerization is started with organic polymerization initiators which decompose under the action of heat to give free radicals which initiate polymerization. Conventional initiators are peroxides, e.g. benzoyl peroxide, lauroyl peroxide, tert.-butyl perbenzoate, tert.-butyl peroctoate, tert.-butyl perpivalate and unstable azo compounds, e.g.

azodiisobutyronitrile. In general, the initiators are employed in amounts of from 0.01 to I % by weight, based on the monomers. The nature of the initiator to be used depends on the envisaged polymerization temperature. It is particularly advantageous to use mixtures of initiators, in which case the polymerization temperature can be matched to the corresponding half-life of the initiator. As a rule, the polymerization temperature is from 60 to 150"C, preferably from 80 to 120 C.

In the case of expandable polystyrene beads, in particular, the processing characteristics depend greatly on the cell structure. By the use of cell-regulating substances, the cell structure, which may, for example, be characterized in terms of the number of cells per mm@.

can be controlled.

To manufacture flame-retardant styrene polymers, it is necessary to use flameproofing agents, which are frequently added at the stage of the suspension polymerization reaction mixture. Organic halogen compounds, preferably brominated organic compounds, are particularly suitable for this purpose, examples being hexa-bromocyclododecane or tris (dibromopropyl) phosphate. Further components which may be present in the polymerization batch are organic or inorganic fillers, antistatic agents or plasticizers.

EXAMPLE I 100 parts of water are introduced into a stirred vessel and 0.92 part of Na3PO4.12H2O is dissolved therein. To form 0.4 part of a calcium phosphate precipitate. 0.6 part of CaCI2.2H2O disolved in 6 parts of water is added, whilst stirring, 100 parts of styrene, 0.15 part of dibenzoyl peroxide and 0.30 part of t-butyl perbenzoate are then added. This mixture is polymerized by stirring for 6 hours at 90"C and then for 3 hours at 105 70 minutes after reaching 90"C. at a conversion of 22%, an aqueous solution of 0.0125 part of ascorbic acid and 0.003 part of FeSO4.7H20 in 2 parts of water is added. 3 hours after reaching 90 C, 7 parts of n-pentane are added.

The bead polymer had the following size distribution: : 2.5 2.0 1.6 1.25 1.0 0.8 0.63 0.4 < 0.4 % : - 1.0 3.0 5.0 19.0 43.0 22.0 6.0 1.0 EXAMPLE 7 The procedure followed is as in Example 1. except that 95 parts of styrene and 5 parts of acrylonitrile are used. The bead polymer had the following size distribution: : 7.5 2.0 1.6 1.25 1.0 0.8 0.63 0.4 < 0.4 - 7.0 10.0 18.0 30.0 27.5 10.0 2.0 05 EXAMPLE 3 The procedure followed is an in Example I, but on reaching 9()0C. at a converison of 6%.

0,0063 part of ascorbic acid and 0.003 15 part of iron-Il sulfate are added as an aqueous solution. The bead polymer had the following size distribution: 2.5 2.0 1.6 1.25 1.0 0.8 0.63 0.4 < 0.4 - - 3.5 5.0 22.0 33.0 23.5 12.5 0.5 EXAMPLE 4 The procedure followed is as in Example I . but no iron-lI sulfate is used. The ascorbic acid solution is added 4() minutes after reaching 9() C at a conversion of 13%. The bead polymer had the following size distribution: 2.5 2.() 1.6 1.'5 1.0 ().8 0.63 ().4 < 0.4 % - 4.() 16.() 22.0 26.0 19.5 8.0 3.5 1.() EXAMPLE 5 The procedure followed is as in Example 4, but the calcium phosphate compound (0.24 part) is prepared from 0.55 part of Na3PO4. 12H2O and 0.354 part of CaCl 2.2H20. Instead of the ascorbic acid, 0.0125 part of tartaric acid, in the form of a 2% strength aqueous solution, is added 15 minutes after reaching 90 C, at a conversion of 9%. The bead polymer had the following size distribution: # : 2.5 2.0 1.6 1.25 1.0 0.8 0.63 0.4 < 0.4 % - - 3.0 7.0 14,0 34.0 29.0 12.0 1.0 EXAMPLE 6 The procedure followed is as in Example 4, except that 0.26 part of magnesium phosphate obtained from 0.7 part of Na3PO4.12H2O and 0.64 part of MgCl 2.6H20 is used. An aqueous solution of 0.0125 part of tartaric acid is added 60 minutes after reaching 90 C, at a conversion of 19%.

The bead polymer had the following size distribution: 2.5 : 2.5 2.0 1.6 1.25 1.0 0.8 0.63 0.4 < 0.4 % : - 0.5 2.5 15.0 30.0 31.5 14.0 5.0 1.5 EXAMPLE 7 The batch for the bead polymerization is as for Example 1, but the activators are added in the form of a mixture with a calcium phosphate suspension during the bead polymerization.

The calcium phosphate suspension employed is prepared beforehand from Na3PO4.12H2O and CaC12.2H2O (molar ratio 1:1.62) as follows: A solution of 147 g of CaCI2.2H2O dissolved in 500 ml of water is added uniformly in the course of 10 minutes to a solution of 228 g of Na2PO4.12H2O and 1,000 ml of water whilst stirring at room temperature.

7.7 parts of this suspension. containing 0.415 part of calcium phosphate and mixed with 0.0125 part of ascorbic acid and 0.003 part of FeSO4.7H2O, are added in each case 50 minutes after reaching 90 C. at a conversion of 16%.

The bead polymer had the following size distribution: 2.5 2.0 1.6 1.25 1.0 0.8 0.63 0.4 < 0.4 % - - 2.0 9.0 22.5 33.0 21.5 10.0 1.0 EXAMPLE 8 The procedure followed is as described in Example 7, except that 0.0125 part of tartaric acid mixed with 7.7 parts of the calcium phosphate suspension from Example 7 is added 30 minutes after reaching 90 C. at a conversion of 11%. The bead polymer had the following size distribution: 2.5 7.0 1.6 1.25 1.0 0.8 0.63 0.4 < 0.4 /c - - 8.0 13.0 35.5 30.5 7.5 5.0 0.5 EXAMPLE 9 The procedure followed is as described in Example I except that 0.6 ml of a 4% strength glucose solution (manufactured as described in Houben-Weyl. "Methoden der organischen Chemie", volume XIV, I. page 719, except that no emulsifier is added) and 0.003 part of ferrous phosphate (manufactured as described in Houben-Weyl. Methoden der organischen Chemise, volume XIV,' 1. page 722. from equal parts of FeSO4.7H2O and K4P207 as an 0.1 96, strength suspension) are added to the aqueous phase at a conversion of 6%. 'The bead polymer had the following size distribution: P) 2.() 1.6 1.25 1.0 0.8 ().63 ().4 < 0.4 C, - - 4.5 12.5 20.0 '5.5 23.0 9.5 1.5 WHAT WE CLAIM IS: 1. A process for the manufacture of a hompolymer or copolymer of styrene which contains at least 5()c,6 by weight of styrene by polymerizing the monomer(s) in aqueous suspension in the presence of a suspension stabilizer. wherein there is used as suspension stabilizer from ().()5 to 1% be weight. based on the suspension. of an at most sparingly water-soluble' inorganic compound and from 0.001 to 0.1% by weight. based on the suspension. of a water-soluble reducing organic compound. with from 0 to 50% by weight of an activating iron-ll compound. based on the reducing compound.

2. A process as claimed in claim 1, in which the at most sparingly water-soluble inorganic

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

EXAMPLE 5 The procedure followed is as in Example 4, but the calcium phosphate compound (0.24 part) is prepared from 0.55 part of Na3PO4. 12H2O and 0.354 part of CaCl 2.2H20. Instead of the ascorbic acid, 0.0125 part of tartaric acid, in the form of a 2% strength aqueous solution, is added 15 minutes after reaching 90 C, at a conversion of 9%. The bead polymer had the following size distribution: # :

2.5 2.0 1.6 1.25 1.0 0.8 0.63 0.4 < 0.4 % - - 3.0 7.0 14,0 34.0 29.0 12.0 1.0 EXAMPLE 6 The procedure followed is as in Example 4, except that 0.26 part of magnesium phosphate obtained from 0.7 part of Na3PO4.12H2O and 0.64 part of MgCl 2.6H20 is used. An aqueous solution of 0.0125 part of tartaric acid is added 60 minutes after reaching 90 C, at a conversion of 19%.

The bead polymer had the following size distribution: 2.5 : 2.5 2.0 1.6 1.25 1.0 0.8 0.63 0.4 < 0.4 % : - 0.5 2.5 15.0 30.0 31.5 14.0 5.0 1.5 EXAMPLE 7 The batch for the bead polymerization is as for Example 1, but the activators are added in the form of a mixture with a calcium phosphate suspension during the bead polymerization.

The calcium phosphate suspension employed is prepared beforehand from Na3PO4.12H2O and CaC12.2H2O (molar ratio 1:1.62) as follows: A solution of 147 g of CaCI2.2H2O dissolved in 500 ml of water is added uniformly in the course of 10 minutes to a solution of 228 g of Na2PO4.12H2O and 1,000 ml of water whilst stirring at room temperature.

7.7 parts of this suspension. containing 0.415 part of calcium phosphate and mixed with 0.0125 part of ascorbic acid and 0.003 part of FeSO4.7H2O, are added in each case 50 minutes after reaching 90 C. at a conversion of 16%.

The bead polymer had the following size distribution: 2.5 2.0 1.6 1.25 1.0 0.8 0.63 0.4 < 0.4 % - - 2.0 9.0 22.5 33.0 21.5 10.0 1.0 EXAMPLE 8 The procedure followed is as described in Example 7, except that 0.0125 part of tartaric acid mixed with 7.7 parts of the calcium phosphate suspension from Example 7 is added 30 minutes after reaching 90 C. at a conversion of 11%. The bead polymer had the following size distribution: 2.5 7.0 1.6 1.25 1.0 0.8 0.63 0.4 < 0.4 /c - - 8.0 13.0 35.5 30.5 7.5 5.0 0.5 EXAMPLE 9 The procedure followed is as described in Example I except that 0.6 ml of a 4% strength glucose solution (manufactured as described in Houben-Weyl. "Methoden der organischen Chemie", volume XIV, I. page 719, except that no emulsifier is added) and 0.003 part of ferrous phosphate (manufactured as described in Houben-Weyl. Methoden der organischen Chemise, volume XIV,' 1. page 722. from equal parts of FeSO4.7H2O and K4P207 as an 0.1 96, strength suspension) are added to the aqueous phase at a conversion of 6%. 'The bead polymer had the following size distribution: P) 2.() 1.6 1.25 1.0 0.8 ().63 ().4 < 0.4 C, - - 4.5 12.5 20.0 '5.5 23.0 9.5 1.5 WHAT WE CLAIM IS: 1. A process for the manufacture of a hompolymer or copolymer of styrene which contains at least 5()c,6 by weight of styrene by polymerizing the monomer(s) in aqueous suspension in the presence of a suspension stabilizer. wherein there is used as suspension stabilizer from ().()5 to 1% be weight. based on the suspension. of an at most sparingly water-soluble' inorganic compound and from 0.001 to 0.1% by weight. based on the suspension. of a water-soluble reducing organic compound. with from 0 to 50% by weight of an activating iron-ll compound. based on the reducing compound.
2. A process as claimed in claim 1, in which the at most sparingly water-soluble inorganic

compound is introduced into the aqueous phase of the suspension before starting the polymerization and the reducing compound is added to the suspension in the course of the polymerization.
3. A process as claimed in claim 2, in which the reducing compound is added at a monomer conversion of from 5 to 40%.
4. A process as claimed in claim I, in which the at most sparingly water-soluble inorganic compound and the reducing compound are premixed and the mixture is added to the suspension before or during the polymerization.
5. A process as claimed in claim 4, in which the mixture is added at a monomer conversion of from 5 to 40%.
6. A process as claimed in any of claims 1 to 5, in which the at most sparingly watersoluble inorganic compound is a phosphate of a divalent metal.
7. A process as claimed in claim 6, in which the phosphate is a calcium phosphate.
8. A process as claimed in any of claims 1 to 7, in which the reducing organic compound is an acid or a hydroxy compound.
9. A process as claimed in claim 8, in which the reducing organic compound is ascorbic acid.
10. A process as claimed in claim 8, in which the reducing organic compound is tartaric acid.
II. A process as claimed in any of claims 1 to 10, in which a blowing agent is added to the suspension before, during or after the polymerization.
12. A process as claimed in any of claims 1 to 11, wherein a flameproofing agent, filler, antistatic agent or plasticizer is present during the polymerization.
1 3. A process for the manufacture of a homopolymer or copolymer of styrene carried out substantially as described in any of the foregoing Examples.
14. Polystyrene and styrene copolymers containing at least 506As by weight of polymerized styrene units when manufactured by a process as claimed in any of claims 1 to 13.