Flame retardant compositions

Abstract: A novel flame-retardant material is prepared by copolymerizing pentabromobenzyl-acrylate with a metal salt of a compound of Formula I: wherein R₁ is H or lower alkyl, and R₂ is selected from H, lower alkyl and OH. The novel flame retardant has improved thermal stability and is useful in a variety of uses, e.g. as a flame retardant in engineering plastics and styrenic.

Description: The present invention relates to flame-retardant copolymers having thermal stability, to plastic materials containing them and to a method for imparting thermal stability of synthetic resins. More particularly, the invention refers to flame-retardant compositions containing copolymers of poly-pentabromobenzyl acrylate (PBB-PA). PBB-PA has been known for some time, and is a valuable flame-retardant material, useful in a number of synthetic resins. PBB-PA is prepared by the polymerization of pentabromobenzylester acrylate (PBB-MA), e.g., by the process described in DE-A-25 27 802. The PBB-PA polymeric flame-retardant material is incorporated into the synthetic resin to which it is desired to impart flame-retardant properties, by techniques known in the art. The use of this valuable flame-retardant material, however, has been somewhat limited so far because of its limited thermal stability. Thermal stability, as will be known to the skilled person, is an important property both in the lifetime of the synthetic resin which embodies the flame-retardant material, as well as during its preparation. The use of many flame-retardant materials is limited, because the compounding temperatures required in order to incorporate them into a given resin are too high, and the flame-retardant materials are not thermally stable enough to permit their compounding at such temperatures. Consequently, flame-retardant materials which would be efficient in certain resins are not used, because it is impossible to effect the compounding operation, without adversely affecting the flame-retardant material. Methyltetrahalobenzyl acrylates and methacrylates and polymers and plastics compositions based thereon are disclosed in GB-A-2018570. It has now been found, that it is possible to provide copolymers based on PBB-MA, which possess thermal stability, and which thus can be employed with a number of synthetic resins requiring high compounding temperatures. It has further been surprisingly found that it is possible, by relatively slight modifications, to obtain the advantages provided by the improved characteristics of the flame-retardant material, without causing the final compound which incorporates it substantially to depart from the behaviour of a final compound embodying substantially pure PBB-PA. This, as will be apparent to the skilled person, is very important, because it opens the door for a wide use of the product obtained according to this invention. Thus, the invention is primarily directed to a flame-retardant copolymer resulting from the copolymerization of pentabromobenzyl acrylate with a metal salt of a compound of Formula I: and wherein R 1 is H and R 2 is selected from H, and According to a preferred embodiment of the invention, the metal, generally indicated by M in this specification, is selected from Mg, Zn, Na and K. Still more preferably, the metal salt is selected from sodium acrylate, magnesium acrylate, zinc acrylate, potassium acrylate, bis-sodium-maleate, and their mixtures. The amount of metal salt contained should normally not exceed 50% by mole of the total content of the flame-retardant material. In a second aspect, the invention provides also a flame-retardant plastics composition comprising a polymer matrix, for example one selected from engineering plastics and styrenic materials, such as those selected from HIPS, ABS, PET, PBT, polyamides and blends thereof, and a copolymer as described immediately above. Preferably the polymer matrix is reinforced, more preferably glass fibre reinforced. The copolymer of the invention will be constituted of the repetitive units shown in Formula II wherein R 1 , R 2 and M have the meanings defined above, and the ratio x/n is equal or less than 1. It should be noted that the improvement in thermal stability properties has a maximum, and that the addition of too much salt may impair the properties of the resulting product. Thus, for instance, when sodium acrylate is employed, the amount of sodium acrylate employed is more preferably about 3 wt.%. The invention, as will be understood by the skilled chemist, also embraces a method for imparting thermal stability to a PBB-PA-based polymer, which method comprises copolymerizing PBB-MA with a compound of Formula I, as hereinbefore defined. Thus, any of the known polymerization processes which polymerize PBB-MA to obtain PBB-PA can be easily modified, according to the invention, by adding a compound of Formula I to the polymerization mixture, to obtain a copolymer as herein described. The compound of Formula I may be added in an amount of up to 9wt.%, preferably 1.5 to 5 wt.%. Flame-retarded synthetic articles which contain a flame-retardant material according to the invention, of course also form part of this invention. The process and advantages of the invention and of the resulting flame-retardant composition will now be further illustrated through the following examples, which are provided for the purpose of illustration. Example 1 Preparation in solution To a 50 ml, three-necked flask containing 0.72 g (0.01 mole) of acrylic acid there are added 0.95 g of NaHCO 3 which were previously slurried in about 1 ml of water. This addition results in the evolution of CO 2 gas, and when evolution is completed methylethyl ketone, 25 ml, is added, together with 22.4 g PBB-MA (0.04 mole). Nitrogen is bubbled through the solution for a few minutes. The flask, which is equipped with a stirrer and a condenser is put into a thermostatic bath preheated to 100-105°C. During the first minutes, the mixture is very viscous and is difficult to stir, but the materials then dissolve almost completely and stirring becomes easier. At this stage, the initiator, benzoyl peroxide (0.04 g in crystalline form), which has been previously dissolved in 1 ml methylethyl ketone is added. The mixture obtained is heated for about one half hour, during which time a heavy precipitate is formed. When this period has lapsed, the mixture is cooled to room temperature, diluted with methylene chloride and vacuum-filtered and washed again with methylene chloride. 22.5 g of a dry solid are obtained, with a yield in excess of 95%. The above process was carried out with 8 different PBB-MA/sodium acrylate ratios, and the resulting product was tested for thermal stability. Thermal stability was tested as follows: heating with a heating rate of 50°C per minute in a nitrogen atmosphere up to 290°C and then keeping the sample at 290°C for one half hour. Weight losses resulting from this procedure were recorded. The material tested in the thermal stability test was previously dried to constant weight. The result for 10 experiments, together with the exact compositions, are reported in Table I below. The results clearly indicate a substantial improvement of the thermal stability of the product, throughout the entire range of sodium acrylate concentrations. Optimal results were obtained with about 2 to about 8 wt.% sodium acrylate in PBB-MA. It should be noted that the weight loss for pure PBB-PA under the test conditions was between 40-75%, while optimum conditions brought this weight loss to values as low as 3%. Thermal Stability of Product Polymerized in Solution Experiment No. gr Na Acrylate 100 gr PBB-MA Mole Na Acrylate Mole PBB-MA Weight loss (%) 1 0 0 54 2 0 0 40-54 3 0 0 75 4 0.5 0.03 18 5 1.0 0.06 10 6 2.1 0.12 3 7 4.2 0.24 3 8 8.4 0.50 3 9 12.6 0.76 6 10 16.8 1.00 7 It should be noted that the results for pure PBB-PA are erratic, giving weight losses ranging from 40% to 75% when all conditions are kept substantially constant. This does not happen with the copolymers of the invention, in which only insignificant fluctuations of this value are noted. The copolymers according to the invention have been fully characterized as being of structure II, both by elemental and spectroscopic analyses. By way of illustration, the results for the material obtained according to Experiment No. 10, (16.8% Na-Acrylate) are reported below. % Na: theoretical: 4.11, found: 3.94. % Br: theoretical: 59.75, found: 59.33. FT-IR spectra of the product were prepared using KBr as a standard. One such spectrum is shown in Fig. 1, in which the characteristic peaks of the salt are seen at 1318 cm -1 and at 1564 cm -1 . The spectrum of pure PBB-PA (Experiment No. 2) is also shown in Fig. 2 for the purpose of comparison. Example 2 Thermal Polymerization in an Extruder A mixture of PBB-MA and sodium acrylate in the desired proportions, with and without a radical initiator, were polymerized in an extruder. The polymerization temperature was between 140-240°C. The residence time in the extruder was 1-10 minutes. The polymer obtained in this process was ground to a powder, before thermal stability was evaluated. Thermal stability was evaluated as in the previous experiment, and the results are shown in Table II below. It can be seen from the results of this table that no substantial difference was seen between the product polymerized in solution, and that heat-polymerized in an extruder. Thermal Stability of Product Polymerized by Extrusion Experiment No. Catalyst gr Na Acrylate 100 g PBB-MA Weight loss (%) 1 none 3 6 2 Luperox-D-1 0.1% 3 4 3 Luazo AD 0.05% 3 4 The product obtained in Experiment No. 1 was analyzed to give: % Na: Calcd: 0.73, found: 0.50. % Br: Calcd: 69.66, found: 69.31. Example 3 Copolymerization with Different Salts Example 1 was repeated, using a number of different salts, to show the effect of different compounds of Formula I on the thermal stability of the resulting product. The results are shown in Table III below, from which it can be appreciated that all salts tested give an appreciable improvement, as compared with the 40-75% weight loss of the product which does not contain any copolymerized salt. Small fluctuations in the thermal stability between different salts are not such as to substantially change this conclusion. Thermal Stability of Different Copolymers Co-Monomer gr Co-Monomer 100 gr PBB-MA Weight loss (%) Mg-Acrylate 2 8 Zn-Acrylate 2 9 Bis-Na-Maleate 3 13 K-Acrylate 2 5 It should be noted that, for the case of sodium acrylate which is believed to be the most convenient of the comonomers employed, when using up to 20 wt.% of sodium acrylate, a polymer is obtained which is a white flowable and homogeneous powder. Amounts higher than 20 wt.% result in two different products, a white powder and an amorphous product which has not been identified, but which is believed to be a polyacrylic acid or a salt thereof. These limiting amounts, therefore, are only related to the nature of the product obtained, and may vary when different salts or compounds of Formula I are employed. Example 4 Two different compositions based on high-impact polystyrene (HIPS) were prepared, to evaluate the effect of the thermally stabilized PBB-PA on the properties of the final product, as compared with conventional PBB-PA. The contents of the two compositions tested, containing also conventional additives, as well as the results of the tests, are shown in Table IV below. It can be seen that the Na-acrylate-containing copolymer, while remaining V-O rated, according to UL-94, also improves the results for the Notched Izod Impact and the HDT. Comparison of FR and Mechanical Properties with Compositions of the Art in HIPS Component/Parameter Comp. 1 % Comp. 2 % HIPS Vestyron 638 82.7 82.7 PBB-PA 12.9 - PBB-PA containing 3% NaAcrylate (Exp. 2, Example 2) - 12.9 Antimony Trioxide 3.3 3.3 Tinuvin P 0.2 0.2 Irganox PS 800 - 0.2 Irganox 245 0.2 0.2 AC 400 A (Allied) 0.5 0.5 UL 94 (3.2mm) Rate V-O V-O Notched Izod Impact (J/m) 57 69 HDT (°C) 58 62 Br % 9.3 9.0 Example 5 Two mixtures of pure PBB-PA, one with 5 wt% Na Acetate, and the other with 5 wt% Na Polyacrylate were prepared. The thermal stability of these mixtures was measured as described in Example 1, to show that non-copolymerized mixtures do not improve the thermal stability. The results are shown in Table V below: Thermal Stability of Mixtures Experiment No. Component 1 Component 2 Wt ratio Comp. 1 Comp. 2 Weight loss (%) 1 PBB-PA Na Acetate 95% 51 2 PBB-PA Na Polyacrylate 95% 33 As is seen from Table V, the weight losses of these mixtures are of the same order of magnitude as for pure PBB-PA. Example 6 In order to further illustrate the effect of the metal salt on the thermal stability of PBB-PA, a product obtained according to the procedure described in Example 2, Experiment No. 1, was treated to remove the metal ion, and the treated and untreated materials were compared for thermal stability. The treatment was effected by stirring 32.5 gr of the copolymer in 150 ml of aqueous HCl solution 1:5, for two days. After filtration the cake was washed with distilled water until neutral, and was then washed with methanol. After drying, 28.9 gr of the copolymer were recovered. The product was tested for weight loss by TGA, as described hereinbefore. TGA was run for 30 minutes, and the results are shown in Table VI below. Thermal Stability of Washed and Unwashed Products Copolymer Na Content Br (%) Weight Loss (TGA), % Unwashed 0.496 % 69.31 6.3 Washed 8.5 ppm 70.83 34.5 Example 7 The same PBB-PA/Na Acrylate copolymer of Example 4 was used to prepare flame-retarded glass fiber reinforced polyethylene terephthalate (GFR PET ex Allied Corp.). The properties of the resulting compositions are reported in Table VII. Properties of 30% GFR PET Component/Parameter % Flame retardant 9.8 GFR- PET (PETRA 130) 85.3 ANTIMONY TRIOXIDE 4.9 (ex CAMPINE) UL 94 (0.8 mm) Rate VO " Max Flame (sec.) 19.0 " Total Flame (sec.) 29.0 " Number Ignit. Cotton 0 Izod Notched Impact (J/m) 49.0 HDT (°C) 162 Br% 7.0 GFR PET means glas fibre reinforced polyethylene terephthalate Example 8 Example 7 was repeated, but using 30% GFR polybutylene terephthalate (GFR PBT - ex G.E.P.). The results are shown in Table VIII. Properties of 30% GFR PBT Component/Parameter % Flame retardant 11.4 ANTIMONY TRIOXIDE 5.7 FR- PBT (Valox 420) 82.8 UL 94 (0.8 mm) Rate VO " Max Flame (sec.) 2.0 " Total Flame (sec.) 10.0 " No. Ignit. Cotton 0 Izod Notched Impact (J/m) 92.0 HDT (°C) 202.4 Br % 8.0 GFR PBT means glass fibre reinforced polybutylene terephthalate Example 9 Example 7 was repeated, but using Nylon 6 (CAPRON 8200 HS, ex Allied Corp.). The results are shown in Table IX. Properties of Nylon 6 Component/Parameter % FR 15.7 ANTIMONY TRIOXIDE 5.2 CAPRON 8200 HS 77.5 Mg. Stearate 0.5 Hostaflon TF 3202 1.0 UL 94 (1.6 mm) Rate VO UL 94 (1.6 mm) Max Flame (sec.) 8.0 UL 94 (1.6 mm) Total Flame (sec.) 19.0 UL 94 (1.6 mm) No. Ignit. Cotton 0 Br % 11.0 Example 10 Example 7 was repeated, but using Acrylonitrile-butadiene-styrene terpolymer (ABS) ex Borg Warner, U.S.A.. The results are reported in Table X below. Properties of ABS Component/Parameter % FR 20.0 ANTIMONY TRIOXIDE 4.2 ABS 75.8 UL-94 (1.6mm) Rate VO " Max Flame (sec.) 1.0 " Total Flame (sec.) 2.0 " No. Ignit. Cotton 0 Izod Notched Impact (J/m) 98.0 HDT (°C) 90.0 Br% 14.0

Claims: A flame-retardant copolymer of pentabromobenzyl-acrylate with a metal salt of a compound cf Formula I: and wherein R 1 is H and B 2 is selected from H and A flame-retardant copolymer comprising the repetitive units of the formula: wherein M is a metal ion, R, is H R 2 is H or and the ratio x/n is equal or less than 1. A flame-retardant copolymer as claimed in claim 1 or 2, wherein the metal is selected from magnesium (Mg), zinc (Zn), sodium (Na), and potassium (K). A flame-retardant copolymer as claimed in claim 3, wherein the salt is selected from sodium acrylate, magnesium acrylate, zinc acrylate, potassium acrylate, bis-sodium-maleate, and their mixtures. A method for imparting thermal stability to a poly-pentabromobenzyl acrylate (PBB-PA) based polymer, comprising copolymerizing (PBB-MA) with a compound of Formula I as defined in claim 1. A method according to claim 5, wherein the compound of Formula I is added in an amount of up to 9 wt.%. A method according to claim 6, wherein the compound of Formula I is added in an amount of 1.5 to 5. wt.%. A flame-retarded plastics composition comprising a polymeric matrix and a copolymer of pentabromobenzyl-acrylate with a metal salt of a compound of Formula I: and wherein R 1 is H , and R 2 is selected from H and A flame-retarded composition according to claim 8, wherein the polymeric matrix is selected from engineering plastics and styrenic materials. A flame-retarded composition according to claim 9, wherein the polymeric matrix is selected from high impact polystyrene (HIPS), acrylonitrile-butadiene-styrene terpolymer (ABS), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyamides and blends thereof. A flame-retarded composition according to any one of claims 8 to 10, wherein the polymeric matrix is reinforced. A composition according to claim 11, wherein the polymeric matrix is glass fiber reinforced. Flame-retarded synthetic articles containing a flame-retardant material as claimed in any one of claims 1 to 4.

Inventors: KORNBERG NURIT, PELELD MICHAEL R, SCHEINERT JACOB, KORNBERG, NURIT, PELELD, MICHAEL R., SCHEINERT,JACOB
Applicants: BROMINE COMPOUNDS LTD, BROMINE COMPOUNDS LTD.
Application year: 1990
Main classification: C08F220
IPC codes: C08F220, C08L101, C08L33, C08F20, C08K5