Expandable styrene polymer containing polymeric brominated flame retardants

Abstract

An expandable styrene polymer containing a polymeric brominated flame retardant, wherein the polymeric brominated flame retardant contains at least one brominated polybutadiene block having a degree of bromination of 33% to 75% based on the double bonds of the polybutadiene block before bromination; a method for preparing the expandable styrene polymer by suspension polymerization and a microcellular foam molded article made therefrom.

Description

[0001] The present invention relates to an expandable styrene polymer containing a polymeric brominated flame retardant, a method for preparing the expandable styrene polymer by suspension polymerization, and a particulate foam molded article made therefrom. Background Art

[0002] WO 2007 / 058736 discloses thermally stable brominated styrene / butadiene copolymers and their use as flame retardant additives in foamed and non-foamed polymer compositions, which contain a flame-retardant amount of brominated butadiene copolymer to replace hexabromocyclododecane (HBCD). However, this flame retardant has a strong nucleating effect in suspension-polymerized expandable polystyrene, and as a result, the polystyrene foam has a very small pore size and poor insulation performance.

[0003] US2012 / 0253914 A1 discloses flame-retardant expandable styrene polymers and foams, which contain 1 to 10% by weight of an infrared absorber and at least one halogenated polymer as a flame retardant.

[0004] WO 2015 / 065393 discloses that in the case where a foam body (foamed styrene polymer) is made by a melt extrusion method using a brominated styrene-butadiene block copolymer as a flame retardant, the inclusion of a small amount of non-brominated vinyl aromatic / butadiene block copolymer can improve the pore size uniformity of the foamed styrene polymer and reduce its density.

[0005] WO 2018 / 210961 and WO 2018 / 210965 propose to improve the miscibility of brominated block copolymers and polystyrene matrices to increase the pore size in polystyrene foams. The miscibility is improved by using a mixture of different brominated block copolymers or by adjusting the molecular weights of styrene and butadiene blocks before bromination. The method of metering or preparing brominated block copolymers is laborious.

[0006] In view of the above prior art, an object of the present invention is to provide a flame-retardant expandable styrene polymer, which can be prepared by a suspension polymerization method and can be converted into foam particles with an increased pore size and a flame-retardant particulate foam molded article with a low thermal conductivity and good insulation performance.

[0007] To solve these problems, the present invention provides an expandable styrene polymer containing a polymeric brominated flame retardant, wherein the polymeric brominated flame retardant contains at least one brominated polybutadiene block having a bromination degree of 33% to 75%, based on the double bonds of the polybutadiene block before bromination.

[0008] The bromination degree refers to the percentage of non-aromatic double bonds in the polybutadiene block that has been brominated. The bromination degree can be determined by 1H-NMR spectroscopy. For this purpose, the ratio of the integral areas of the signals related to the protons of the residual double bonds and the signals related to the protons in the brominated polybutadiene is determined.

[0009] Alternatively, the degree of bromination (BrD) can be calculated from the total bromine content (Br%), the number of non-aromatic double bonds (NDB), or the molecular weight of the polymer before bromination (MP) and the percentage of butadiene (BD%) according to the following equations:

[0010] Br% = (BrD * NDB * 160) / ((BrD * NDB * 160) + MP)

[0011] where

[0012] NDB = (MP * BD%) / 54

[0013] or

[0014] BrD = 3375 * Br% / (BD% (100% - Br%))

[0015] Preferably, the polymerized brominated flame retardant has a total bromine content in the range of 40% to 60% by weight, more preferably 50% to 55% by weight. The total bromine content of the polymerized brominated flame retardant can be determined by elemental analysis, i.e., by combustion and argentometric analysis.

[0016] Suitable polymerized brominated flame retardants are brominated vinyl aromatic-diene block copolymers (Br-SBCs) that contain at least one vinyl aromatic block S (especially a polystyrene block) and at least one brominated diene polymer block BB.

[0017] The following vinyl aromatic monomers can be used as block S: styrene, α-methylstyrene, p-methylstyrene, ethylstyrene, tert-butylstyrene, vinyltoluene, or a mixture thereof. Styrene is preferably used.

[0018] Preferred dienes used as block BB are as follows: butadiene, isoprene, 2,3-dimethylbutadiene, 1,3-pentadiene, or 1,3-hexadiene, or a mixture thereof. 1,3-Butadiene is particularly preferably used.

[0019] Preferably, the vinyl aromatic-diene block copolymer (SBC) contains 20 to 50% by weight of polymerized vinyl aromatic monomer units, especially styrene monomer units, and 50 to 80% by weight of polymerized diene units, especially butadiene units, before bromination. Most preferably, the vinyl aromatic-diene block copolymer (SBC) contains 25 to 45% by weight of polymerized vinyl aromatic monomer units, especially styrene monomer units, and 55 to 75% by weight of polymerized diene units, especially butadiene units, before bromination.

[0020] Vinyl aromatic-diene block copolymers (SBCs) can have a linear or symmetric or asymmetric star-shaped structure. Blends of vinyl aromatic-diene block copolymers (SBCs) can be used before or after bromination.

[0021] Preferably, the polymeric brominated flame retardant is selected from brominated styrene-butadiene-styrene triblock copolymers.

[0022] Preferably, the polymeric brominated flame retardant comprises 50 to 85% by weight of a brominated polybutadiene block.

[0023] Preferably, the polymeric brominated flame retardant has a weight-average molecular weight M w of 80,000 to 180,000 g / mol as measured before bromination.

[0024] The polymeric brominated flame retardant is most preferably selected from brominated styrene-butadiene-styrene triblock copolymers S 1 -B-S 2 wherein the S 1 -B-S 2 has a total styrene block content of 20 to 50% by weight (in particular 25 to 45% by weight), and the difference in weight-average molecular weight M 1 between S 2 and S w is less than 10,000 g / mol.

[0025] The weight-average molecular weight M w is measured by gel permeation chromatography (GPC) in accordance with ISO 16014-3:2012 in tetrahydrofuran at 25 °C relative to polystyrene standards before bromination.

[0026] Preferably, the vinyl content of the at least one brominated polybutadiene block is 50 to 95%, based on the double bonds of the polybutadiene block before bromination. The vinyl content refers to the relative proportion of 1,2-bonded diene units in the Br-SBC block copolymer before bromination, based on all 1,2-, 1,4-cis and 1,4-trans bonded diene units.

[0027] Bromination of the vinyl aromatic-diene block copolymer (SBC) can be carried out as described in WO

[0028] 2007 / 058736. Preferably, the brominated butadiene copolymer of the present invention is prepared by selective bromination, in particular under mild conditions. Bromination is preferably carried out ionically.

[0029] Once the desired degree of bromination is reached, especially when using tribromides (such as tetraalkylammonium tribromide or pyridinium tribromide) as brominating agents, by-products such as tetraalkylammonium monobromide or pyridinium hydrobromide can be removed from the reaction solution by washing, decanting, or filtering.

[0030] The advantage of controlling the degree of bromination is that various polybutadiene block copolymers can be used as precursors for preparing polymeric brominated flame retardants having the following properties, namely, the polymeric brominated flame retardants have sufficient miscibility with the polystyrene matrix and can increase the pore size in the polystyrene foam.

[0031] Another subject of the present invention is a method for preparing expandable styrene polymers.

[0032] A preferred method for preparing expandable styrene polymers comprises polymerizing a vinyl aromatic monomer in an aqueous suspension in the presence of a polymeric brominated flame retardant, wherein the polymeric brominated flame retardant comprises at least one brominated polybutadiene block having a degree of bromination of 33% to 75%, based on the double bonds of the polybutadiene block before bromination.

[0033] For aqueous suspension polymerization, the following can be used as vinyl aromatic monomers: styrene, α-methylstyrene, p-methylstyrene, ethylstyrene, tert-butylstyrene, vinyltoluene, or mixtures thereof. Styrene monomer is preferably used.

[0034] Aqueous suspension polymerization can be carried out using inorganic salts of phosphorus-containing acids as Pickering stabilizers. Preferably, tricalcium phosphate and / or magnesium pyrophosphate are used. The polymerization can also be carried out in the presence of additional organic suspending agents, such as hydroxyethyl cellulose, polyvinylpyrrolidone, or polyvinyl alcohol.

[0035] Most preferably, the polymerization is carried out in the presence of 0.5 to 10% by weight of athermanic particles (such as carbon black, coke, calcined coke, graphitized coke, natural and / or synthetic graphite, or mixtures thereof), preferably in the presence of graphite, based on the vinyl aromatic monomer. Before adding these athermanic particles to the polymer matrix, they can also be added to an inorganic polymer (such as a mineral polymer).

[0036] The amount of the polymeric brominated flame retardant is preferably 0.25 to 5% by weight, based on the vinyl aromatic monomer. Most preferably, the amount of the polymeric brominated flame retardant is 0.5 to 2% by weight.

[0037] Preferably, a synergist for polymer bromination is added. The synergist is a component having a half-life of one hour at a temperature of 120 to 270 °C (measured in monochlorobenzene). Preferably, the synergist is selected from dicumyl peroxide, di(tert-butylperoxyisopropyl)benzene, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, 2,3-dimethyl-2,3-diphenylbutane, and mixtures thereof.

[0038] During aqueous suspension polymerization, the blowing agent is preferably added after the vinyl aromatic monomer conversion rate reaches at least 20%. The blowing agent is selected from aliphatic hydrocarbons or cycloaliphatic hydrocarbons having 3 to 6 carbon atoms, such as n-pentane, isopentane, cyclopentane, and mixtures thereof.

[0039] Another subject of the present invention is a styrene polymer foam molded article, which can be obtained by pre-foaming and bonding the above-expandable styrene polymer. Preferably, the average pore size of the styrene polymer foam molded article is 120 to 250 microns.

[0040] The average pore size can be determined by microscopic measurement. The average value is obtained by the following method: Under the condition of 60-fold magnification of a transmission light microscope, at least 25 pores on a line of a section of the foam molded article are counted, and then the length of the line is divided by the number of pores. Examples

[0041] Hereinafter, the present invention will be described in more detail and specifically with reference to examples, but these are not intended to limit the present invention.

[0042] Brominated styrene-butadiene-styrene triblock copolymer Br-SBS

[0043] According to WO 2007 / 058736, a styrene-butadiene-styrene triblock copolymer SBS containing 33% by weight of polymerized styrene units and 67% by weight of polymerized butadiene units (wherein 78% by weight are 1,2-units and 22% by weight are 1,4-units) and having a total weight-average molecular weight M w of 130,000 g / mol (measured by GPC relative to a polystyrene standard at 25 °C in tetrahydrofuran before bromination according to ISO 16014-3:2012) was brominated with different molar ratios of tetraethylammonium tribromide to obtain brominated SBS block copolymers, and their characteristics are shown in Table 1.

[0044] The total bromine content in the Br-SBS triblock copolymer was determined by combustion and argentometric analysis.

[0045] The degree of bromination of non-aromatic double bonds was determined by 1Determined by H-NMR spectroscopy and comparing the integral areas of the signals of the residual double bond protons and the protons of the brominated polybutadiene.

[0046] Weight-average molecular molar mass M w By gel permeation chromatography (GPC), according to ISO

[0047] 16014-3:2012, using a Mixed B type polystyrene gel column from Polymer Labs, at room temperature of 20 °C with monodisperse polystyrene standards and tetrahydrofuran as the eluent.

[0048] Table 1: Br-SBS triblock copolymer:

[0049]

[0050] Examples 1 and 2 and Comparative Examples C1-C3

[0051] Preparation of expandable polystyrene (white EPS)

[0052] 15 g of benzoyl peroxide (Perkadox L-W75 from Nouryon), 115 g of dicumyl peroxide ( BC-FF from Nouryon) and the amounts of Br-SBS triblock copolymer shown in Table 2 were dissolved in 22.8 kg of styrene. The organic phase was poured into 17.5 kg of demineralized water in a 55-liter stirred vessel. Also included in this liquid phase was 36 g of magnesium pyrophosphate (prepared from sodium pyrophosphate and magnesium sulfate). The mixture was heated to 104 °C in 110 minutes with stirring and then to 134 °C in 255 minutes. After 105 minutes at 80 °C, 73 g of a 2 wt% solution of emulsifier E30 ( H40 from Lanxess) was metered in. After another 46 minutes, 1.21 kg of pentane ( pentanes 80 from ExxonMobil) was metered in. Then stirring was continued for one hour at the final temperature of 134 °C to complete the polymerization. The obtained expandable polystyrene was decanted and dried.

[0053] Then the beads were coated with 0.3% (w / w) of a mixture consisting of 60% (w / w) glyceryl tristearate ( 3168 from IOI Oleo), 30% (w / w) glyceryl monostearate ( 3995 from IOI Oleo) and 10% (w / w) zinc stearate ( 5 from Baerlocher).

[0054] Examples 3 and 4 and Comparative Examples C4-C6

[0055] Preparation of Expandable Polystyrene Containing Graphite (Gray EPS)

[0056] 22.4 g of dihexadecyl peroxydicarbonate (from Nouryon) 24-FL), 11.3 g tert-butyl ethylhexanoate (from Nouryon 21S), 100g dicumyl peroxide (from Nouryon BCFF), 825 g of graphite (UF 99.5 from Graphit Kropfmühl) and the amount of Br-SBS triblock copolymer indicated in Table 2 are dissolved in 16.5 kg of styrene. The organic phase is poured into 20.8 kg of demineralized water in a 55 liter stirred vessel. This liquid phase also contains 50 g of magnesium pyrophosphate (prepared from sodium pyrophosphate and magnesium sulfate). The mixture is heated to 94° C. within 90 minutes and then to 135° C. within 254 minutes while stirring. 95 minutes after reaching 80° C., 73 g of a 2% by weight solution of emulsifier E30 (from Lanxess) are metered in. H40). After 110 minutes, 1.25 kg of pentane (from ExxonMobil) was added. Then, stirring was continued for one hour at a final temperature of 135° C. to complete the polymerization. The expandable polystyrene obtained was decanted and dried.

[0057] The beads were then coated with 0.3% (w / w) of a 60% (w / w) tristearate glyceryl (from IOIOleo Corporation). 3168), 30% (w / w) glyceryl monostearate (from IOI Oleo 3995) and 10% (w / w) zinc stearate (from Baerlocher 5) A mixture of the composition.

[0058] Table 2: Amount of Br-SBS triblock polymer in Examples 1 to 4 and Comparative Examples C1 to C6

[0059]

[0060]

[0061] Production of particle foam moldings

[0062] In flowing steam, the beads prepared in Examples 1 to 4 and Comparative Examples C1 to C6 containing a blowing agent were pre-expanded. After storage for 12 hours, the pre-expanded particles were bonded in a closed mold with steam, and the resulting particulate foam molded articles had white EPS with a density of about 15 kg / m 3 and gray EPS with a density of about 20 kg / m 3 . The results are summarized in Table 3.

[0063] The determination of the combustion behavior for samples with a thickness of 20 mm was carried out according to EN 13238 under the conditioning of edge burning for 15 seconds according to EN 11925-2.

[0064] The determination of the thermal conductivity of the samples was carried out according to EN 12667 using a guarded hot plate apparatus and samples with a thickness of 50 mm at an average test temperature of 10 °C.

[0065] The average pore size was determined by microscopic measurement.

[0066] Compared with Examples 1 and 2, Comparative Examples C1 to C3 (which contain a Br-SBC block copolymer with a bromination degree of at least 78% as a flame retardant) showed lower pore sizes and higher thermal conductivities. When comparing Comparative Examples C4 to C6 with Examples 3 and 4, the same effect was also shown for the foam products made of EPS containing graphite.

[0067] Table 3: Analysis results of particulate foam molded articles

[0068]

[0069]

Claims

1. An expandable styrene polymer comprising a polymeric brominated flame retardant selected from brominated styrene-butadiene-styrene triblock copolymers and comprising at least one brominated polybutadiene block having a degree of bromination of 59% to 75%, based on the double bonds of the polybutadiene block before bromination, wherein the total bromine content of the polymeric brominated flame retardant is in the range of 40 to 60% by weight.

2. The expandable styrene polymer according to claim 1, wherein the total bromine content of the polymeric brominated flame retardant is in the range of 50 to 55% by weight.

3. The expandable styrene polymer according to claim 1 or 2, wherein the amount of the polymeric brominated flame retardant is 0.25 to 5% by weight.

4. The expandable styrene polymer according to claim 1 or 2, wherein the polymeric brominated flame retardant comprises 50 to 85% of brominated polybutadiene blocks.

5. The expandable styrene polymer according to claim 1 or 2, wherein the weight-average molecular weight M of the polymerized brominated flame retardant w is from 80,000 to 180,000 g / mol and is determined by gel permeation chromatography according to ISO 16014-3:2012 before bromination.

6. The expandable styrene polymer according to claim 1 or 2, wherein the polymerized brominated flame retardant is selected from brominated styrene-butadiene-styrene triblock copolymer S 1 -B-S 2 , said S 1 -B-S 2 having a total styrene block content of 20 to 50% by weight, and the difference in weight average molecular weight M 1 of block S 2 and S w is less than 10,000 g / mol, determined by gel permeation chromatography according to ISO 16014-3:2012 before bromination.

7. The expandable styrene polymer according to claim 1 or 2, wherein at least one brominated polybutadiene block has a 1,2-vinyl content of 50 to 95%, based on the double bonds of the polybutadiene block before bromination.

8. A method for preparing the expandable styrene polymer according to any one of claims 1 to 7, which is carried out by polymerizing a vinyl aromatic monomer in an aqueous suspension in the presence of a polymeric brominated flame retardant, wherein the polymeric brominated flame retardant comprises at least one brominated polybutadiene block having a degree of bromination of 59% to 75%, based on the double bonds of the polybutadiene block before bromination.

9. The method according to claim 8, wherein the polymerization is carried out in the presence of 0.5 to 10% by weight of heat-free particles, based on the vinyl aromatic monomer.

10. The method according to claim 8 or 9, wherein the amount of the polymeric brominated flame retardant is 0.25 to 5% by weight, based on the vinyl aromatic monomer.

11. A styrene polymer foam molded article obtainable by pre-foaming and bonding the expandable styrene polymer according to any one of claims 1 to 7.

12. The styrene polymer foam molded article according to claim 11, wherein the average pore diameter is 120 to 250 μm, determined by microscopic measurement.

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