Patent Publication Number: US-2023146413-A1

Title: Expandable styrene polymers comprising polymeric brominated flame-retardant

Description:
The present invention relates to expandable styrene polymers comprising polymeric brominated flame-retardants, a process for producing such expandable styrene polymers by suspension polymerization and particulate foam moldings made therefrom. 
     RELEVANT PRIOR ART 
     WO 2007/058736 discloses thermally stable brominated styrene/butadiene copolymers and their use as a flame-retardant additive for polymeric compositions, both foamed, and non-foamed, that incorporate a flame-retarding amount of brominated butadiene copolymer as alter-native to hexabromocyclododecane (H BCD). This flame retardant, however, shows a strong nucleating effect in suspension-polymerized expandable polystyrene, which results in polystyrene foams with very small cell sizes and poor insulation properties. 
     US 2012/0253914 A1 discloses flame retardant expandable styrene polymers and foams comprising 1 to 10 wt.-% of an infrared absorber and at least one halogenated polymer as flame retardant. 
     WO 2015/065393 discloses that the inclusion of a small amount of unbrominated vinyl aro-matic/butadiene block copolymer improves cell size homogeneity and reduces density in foamed styrene polymers, when the foam is made in a melt extrusion process using brominated styrene-butadiene block copolymers as flame retardant. 
     WO 2018/210961 and WO 2018/210965 suggest improving miscibility of the brominated block copolymer with the polystyrene matrix to enlarge cell size in the polystyrene foams. Miscibility is improved by using mixtures of different brominated block copolymers or by adjusting the molecular weights of the styrene and butadiene blocks before brominating. Dosing or manufacturing process of the brominated block copolymers is effortful. 
     The present invention was made in view of the prior art described above, and the object of the present invention is to provide flame-retardant expandable styrene polymers, which can be pro-duced by a suspension-polymerization process and which can be converted to foam particles with enlarged cell size and flame-retardant particle foam moldings with low thermal conductivity and good insulation properties. 
     To solve the problem, the present invention provides expandable styrene polymers comprising polymeric brominated flame-retardants, wherein the polymeric brominated flame-retardant comprises at least one brominated polybutadiene block having a bromination degree between 33 and 75%, based on the double bonds in the polybutadiene block before bromination. 
     The bromination degree is the percentage of the non-aromatic double bonds in the polybutadiene block, which have been brominated. The bromination degree may be determined by  1 H-NMR spectroscopy. For this purpose, the ratio of the integrated areas of signals relating to residual double bond protons and signals relating to protons for brominated polybutadiene are determined. 
     Alternatively, the bromination degree (BrD) can be calculated from the total bromine content (Br %), number of non-aromatic double bonds (NDB) or molecular weight of the polymer (MP) before bromination and percentage of butadiene (BD %) according to the following equations: 
       Br %=(BrD*NDB*160)/((BrD*NDB*160)+MP) 
     with 
       NDB=(MP*BD %)/54 
     or 
       BrD=3375*Br %/(BD %(100%-Br %)) 
     Preferred embodiments are described in claims  2  to  7 . 
     Preferably, the polymeric brominated flame retardant has a total bromine content in the range from 40 to 60 wt.-%, more preferably in the range from 50 to 55 wt.-%. The total bromine content of the polymeric brominated flame retardant may be determined by elemental analysis, i.e through combustion and argentometric analysis. 
     Suitable polymeric brominated flame-retardants are brominated vinylaromatic-diene block copolymers (Br—SBC) comprising at least one vinylaromatic polymer block S, in particular polystyrene block, and at least one brominated diene polymer block BB. 
     The following can be used as vinylaromatic monomers for the block S: styrene, alpha-methylstyrene, p-methylstyrene, ethylstyrene, tert-butylstyrene, vinyltoluene or a mixture thereof. It is preferable to use styrene. 
     The following are preferably used as dienes for the block BB: butadiene, isoprene, 2,3-dime-thylbutadiene, 1,3-pentadiene or 1,3-hexadiene or a mixture thereof. It is particularly preferable to use 1,3-butadiene. 
     Preferably, the vinylaromatic-diene block copolymers (SBC) comprises before bromination 20 to 50 wt.-% of polymerized vinylaromatic monomer units, in particular styrene monomer units, and from 50 to 80 wt.-% of polymerized diene units, preferably butadiene units. Most preferably, the vinylaromatic-diene block copolymers (SBC) comprises before bromination 25 to 45 wt.-% of polymerized vinylaromatic monomer units, in particular styrene monomer units, and from 55 to 75 wt.-% of polymerized diene units, preferably butadiene units. 
     The vinylaromatic-diene block copolymers (SBC) may have a linear or a symmetrical or asym-metrical star-shaped structure. Blends of vinylaromatic-diene block copolymers (SBC) may be used before or after bromination. 
     Preferably, the polymeric brominated flame retardant is selected from a brominated styrene-butadiene-styrene triblockcopolymer. 
     Preferably, the polymeric brominated flame retardant comprises 50 to 85 wt.-% of brominated polybutadiene blocks. 
     Preferably, the weight average molecular weight M w  of the polymeric brominated flame-retardant is in the range from 80.000 to 180.000 g/mol, determined before bromination. 
     The polymeric brominated flame retardant is most preferably selected from a brominated sty-rene-butadiene-styrene triblock copolymer S 1 —B—S 2  with a total styrene block content of 20 to 50 wt.-%, in particular 25 to 45 wt.-% and a difference in the weight average molecular weight M w  between block S 1  and S 2  is less than 10.000 g/mol. 
     The weight average molecular weight M w  is determined prior prior to the bromination by Gel Permeation Chromatography (GPC) according to ISO 16014-3: 2012 relative to polystyrene standards in 25° C. in THF 
     Preferably, the at least one brominated polybutadiene-block has a vinyl content between 50 and 95%, based on the double bonds in the polybutadiene block before bromination. Vinyl content means the relative proportion of 1,2 linkages of the diene units of the Br—SBC block copolymer before bromination, based on the entirety of the 1,2,1,4-cis and 1,4-trans linkages. 
     Bromination of vinylaromatic-diene block copolymers (SBC) may be carried out as described in WO 2007/058736. It is preferable to produce the brominated butadiene copolymers of the present invention by selective bromination, particularly by selective bromination under mild condi-tions. The bromination is preferably carried out ionically. 
     Once a desired degree of bromination has been achieved, in particular when a tribromide is used as brominating agent, for example tetraalkylammonium tribromide or pyridinium tribromide, byproducts such as tetraalkylammonium monobromide or pyridinium hydrobromide can be re-moved from the reaction solution by washing, decanting or filtration. 
     Control of the bromination degree has the advantage, that a wide variety of polybutadiene block copolymers can be used as precursor for preparing a polymeric brominated flame retardant with sufficient miscibility with the polystyrene matrix and enlarged cell size in polystyrene foams. 
     A further subject of the present invention is a process for manufacturing the expandable styrene polymers. Preferred processes are described in claims  8 - 10 . 
     A preferred process for producing expandable styrene polymers includes polymerization of vinylaromatic monomers in 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 bromination degree between 33 and 75%, based on the double bonds in the polybutadiene block before bromination. 
     The following can be used as vinylaromatic monomers for the aqueous suspension polymerisation: styrene, alpha-methylstyrene, p-methylstyrene, ethylstyrene, tert-butylstyrene, vinyltoluene or a mixture thereof. It is preferable to use styrene monomer. 
     The aqueous suspension polymerisation may be performed using inorganic salts of an acid containing phosphorous serving as a Pickering stabilizer. Preferably, tricalcium phosphate and/or magnesium pyrophosphate are used. The polymerization can also be performed in the presence of further organic suspending agents like hydroxyethylcellulose, polyvinylpyrrolidone or polyvinyl alcohol. 
     Most preferably the polymerisation is carried out in the presence of 0.5 to 10% by weight of athermanic particles (e.g. carbon black, coke, calcined coke, graphitized coke, natural and/or synthetic graphite or a mixture thereof), preferably graphite, based on the vinylaromatic monomers. These athermanic particles can also be incorporated into inorganic polymers (e.g. geo-polymers), before incorporating them into the polymer matrix. 
     The amount of polymeric brominated flame retardant is preferably in the range from 0.25 to 5% by weight, based on the vinylaromatic monomers. Most preferably the amount of polymeric brominated flame retardant is in the range from 0.5 to 2% by weight. 
     Preferably, a synergist for the polymeric brominated is added. This synergist is a component with a half-life time of 1 hour at temperatures between 120 and 270° C. (determined in monochlo-robenzene). Preferably, the synergist is chosen 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. 
     During the aqueous suspension polymerisation, the blowing agents are preferably added after a conversion of the vinylaromatic monomer of at least 20%. The blowing agents are chosen from aliphatic or cycloaliphatic hydrocarbons containing from 3 to 6 carbon atoms such as n-pentane, isopentane, cyclopentane and mixtures thereof. 
     A further subject of the present invention are styrene polymer foam moldings, obtainable by prefoaming and welding of the expandable styrene polymers described above. Preferably the styrene polymer foam moldings have an average cell size is in the range from 120 to 250 μm. 
     The average cell size may be determined by microscopic measurement. An average is built by counting at least 25 cells in a line of a sliced piece of a foam molding under a through-light mi-croscope at 60-fold magnification and dividing the length of the line by the number of cells. 
    
    
     EXAMPLES 
     Hereinafter, the present invention is described in more detail and specifically with reference to the Examples, which however are not intended to limit the present invention. 
     Brominated Styrene-Butadiene-Styrene triblock copolymers Br—SBS 
     Styrene-Butadiene-Styrene triblock copolymers SBS with 33 wt.-% polymerized styrene units and 67 wt.-% of polymerized butadiene units (thereof 78% wt. 1,2-units and 22 wt.-% 1,4-units) and a total molecular weight M w  of 130.000 g/mol (determined by GPC according to ISO 16014-3: 2012 relative to polystyrene standards in 25° C. in THF prior to the bromination) were brominated according to WO 2007/058736 with different molar ratios of tetraethylammonium tribromide to obtain the brominated SBS block copolymers with the characteristics shown in Table 1. 
     Total bromine content in the Br—SBS triblock copolymer was determined by combustion and argentometric analysis. 
     The degree of bromination of the non-aromatic double bonds was determined by  1 H-NMR spectroscopy by comparing integrated areas of signals due to residual double bond protons and protons for brominated polybutadiene. 
     The weight-average molar masses M w  were determined by Gel permeation chromatography methods (GPC) according to ISO 16014-3: 2012 on polystyrene-Gel columns from company Polymer Labs of the type Mixed B, with monodisperse polystyrene standards and tetrahydrofu-ran as eluent at room temperature with 20° C. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Br-SBS triblock copolymers: 
               
            
           
           
               
               
               
               
            
               
                   
                 Br-SBS triblock 
                 Bromine content in Br-SBS 
                 Degree of 
               
               
                   
                 copolymer 
                 [wt.-%] 
                 bromination 
               
               
                   
                   
               
               
                   
                 FR 59 
                 54% 
                 59% 
               
               
                   
                 FR 62 
                 55% 
                 62% 
               
               
                   
                 FR 78 
                 61% 
                 78% 
               
               
                   
                 FR 96 
                 65% 
                 96% 
               
               
                   
                 FR 100 
                 66% 
                 100%  
               
               
                   
                   
               
            
           
         
       
     
     Examples 1 and 2 and Comparative Examples C1-C3 
     Preparation of Expandable Polystyrene (White EPS) 
     15 g of benzoyl peroxide (Perkadox L-W75 from Nouryon), 115 g of dicumyl peroxide (Perkadox® BC—FF from Nouryon) and the amount of Br—SBS triblock copolymer indicated in table 2 were dissolved in 22.8 kg of styrene. This organic phase was entered in 17.5 kg of demineralized water in a 55 l stirred vessel. The aqueous phase contained in addition 36 g of magnesium pyrophosphate (prepared from sodium pyrophosphate and magnesium sulfate). The mixture was heated under stirring to 104° C. within 110 minutes and then heated to 134° C. within 255 minutes. 105 minutes after reaching 80° C., 73 g of a 2 wt.-%-solution of emulsifier E30 (Mersolat® H40 from the company Lanxess) were metered in. After further 46 minutes, 1.21 kg of pentane (Exxsol® pentanes 80 from the company ExxonMobil) were metered in. Stirring is then continued for 1 h hour at the final temperature of 134° C. to complete polymerization. The expandable polystyrene obtained is decanted off and dried. 
     Then the beads were coated with 0.3% (w/w) of a mixture of 60% (w/w) glycerol tristearate (Soft enol® 3168 from the company 101 Oleo) 30% (w/w) glycerol monostearate (Softenol® 3995 from the company 101 Oleo) and 10% (w/w) zinc stearate (Zincum® 5 from Baerlocher). 
     Examples 3 and 4 and Comparative Examples C4-C6 
     Preparation of Graphite-Containing Expandable Polystyrene (Grey EPS) 22.4 g dicetylperoxodicarbonate (Perkadox® 24-FL from Nouryon), 11.3 g tert.-butylethylhexanoat (Trigonox® 21S from Nouryon), 100 g of dicumyl peroxide (Perkadox® BC—FF from Nouryon), 825 g graphite (UF 99.5 from Graphit Kropfmuhl) and the amount of Br—SBS triblock copolymer indicated in table 2 were dissolved in 16.5 kg of styrene. This organic phase was entered in 20.8 kg of demineralized water in a 551 stirred vessel. The aqueous phase contained in addition 50 g of magnesium pyrophosphate (prepared from sodium pyrophosphate and magnesium sulfate). The mixture was heated under stirring to 94° C. within 90 minutes and then heated to 135° C. within 254 minutes. 95 minutes after reaching 80° C., 73 g of a 2 wt.-%-solution of emulsifier E30 (Mersolat® H40 from the company Lanxess) were metered in. After further 110 minutes, 1.25 kg of pentane (Exxsol® Pentane 80 from the company ExxonMobil) were metered in. Stirring is then continued for 1 h hour at the final temperature of 135° C. to complete polymerization. The expandable polystyrene obtained is decanted off and dried. 
     Then the beads were coated with 0.3% (w/w) of a mixture of 60% (w/w) glycerol tristearate (Softenol® 3168 from the company 101 Oleo) 30% (w/w) glycerol monostearate (Softenol® 3995 from the company 101 Oleo) and 10% (w/w) zinc stearate (Zincum® 5 from Baerlocher). 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Amount of Br-SBS triblock copolymer used in Examples 
               
               
                 1 to 4 and Comparative Examples C1 to C6 
               
            
           
           
               
               
               
               
            
               
                   
                 Example 
                 BR-SBS 
                 Amount [g] 
               
               
                   
                   
               
               
                   
                 1 
                 FR 59 
                 235 g 
               
               
                   
                 2 
                 FR 62 
                 235 g 
               
               
                   
                 C1 
                 FR 78 
                 213 g 
               
               
                   
                 C2 
                 FR 96 
                 199 g 
               
               
                   
                 C3 
                 FR 100 
                 195 g 
               
               
                   
                 3 
                 FR 59 
                 277 g 
               
               
                   
                 4 
                 FR 62 
                 277 g 
               
               
                   
                 C4 
                 FR 78 
                 251 g 
               
               
                   
                 C5 
                 FR 96 
                 235 g 
               
               
                   
                 C6 
                 FR 100 
                 230 g 
               
               
                   
                   
               
            
           
         
       
     
     The Production of Particle Foam Molding 
     The blowing agent-containing beads from Examples 1 to 4 and Comparative Examples C1 to C6 were pre-foamed in flowing steam. After 12 h of storage the prefoamed particles were weld-ed in a closed mold with steam to give particle foam moldings having a density of about 15 kg/m 3  for white EPS and about 20 kg/m 3  for grey EPS. The results are summarized in table 3. 
     The determination of the fire behavior according to EN 13238 on 20 mm thick samples was carried out after conditioning according to EN 11925-2 with 15 s edge inflammation. 
     The thermal conductivity of the samples was determined according to EN 12667 with a guarded hot plate apparaturs with 50 mm thick samples at a mean test temperature of 10° C. 
     The average cell size was determined by microscopic measurement. 
     Comparative Examples C1 to C3, which comprise Br—SBC block copolymers with a degree of bromination of at least 78% as flame retardant show a lower cell size and higher thermal conductivity compared with Examples 1 and 2. The same effect is demonstrated for foam moldings made from graphite-containing EPS, when comparing Comparative Examples C4 to C6 with Examples 3 and 4. 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Results of the analysis of the particle foam moldings 
               
            
           
           
               
               
               
               
               
            
               
                   
                   
                 Fire class 
                 Thermal 
                 Average 
               
               
                   
                 Density 
                 according 
                 conductivity 
                 cell size 
               
               
                 Example 
                 [kg/m 3 ] 
                 to EN 13501-1 
                 [mW/(m*K)] 
                 [μm] 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 20.1 
                 E 
                 34.4 
                 192 
               
               
                 2 
                 20.2 
                 E 
                 34.6 
                 150 
               
               
                 C1 
                 19.6 
                 E 
                 36.4 
                 105 
               
               
                 C2 
                 21.2 
                 E 
                 36.0 
                 84 
               
               
                 C3 
                 19.7 
                 E 
                 36.8 
                 88 
               
               
                 3 
                 16.9 
                 E 
                 30.6 
                 157 
               
               
                 4 
                 15.5 
                 E 
                 30.9 
                 149 
               
               
                 C4 
                 16.1 
                 E 
                 31.8 
                 108 
               
               
                 C5 
                 15.0 
                 E 
                 32.3 
                 108 
               
               
                 C6 
                 14.6 
                 E 
                 32.1 
                 110