IMPROVED BROMINATED POLYSTYRENIC RESINS, AND THEIR USE

Abstract: Novel brominated styrenic polymers have an ionic bromine content of 2000 ppm or less, and one or more of the following additional characteristics: (a) a TGA temperature for 1 % weight loss which is 340 DEG C or higher, and a chlorine content, if any, of less than about 700 ppm C1; (b) an actual Mw which is within about 20 % of the calculated theoritical Mw, the theoretical Mw being based upon the actual bromine content of the brominated styrenic polymer and the Mw of the styrenic polymer reactant used to produce the brominated styrenic polymer; and (c) essentially no content of impurities selected from the group consisting of ethylene dichloride, bromodichloroethane, dibromochloroethane, dibromodichloroethane, and tribromochloroethane. Such flame retardant polymers exhibit superior performance qualities during use, especially in thermoplastics such as glass-filled polyesters and glass-filled nylons.

Description: IMPROVED BROMINATED POLYSTYRENIC RESINS, AND THEIR USE BACKGROUND OF THE INVENTION Brominated polystyrenes are well established flame retardants for thermoplastics. Generally, brominated polystyrenes are produced by reaction between polystyrene and a brominating agent (e.g. , bromine or bromine chloride) in the presence of a solvent (e.g. , dichloroethane) and a Lewis acid catalyst. Heretofore the art has proffered many processes which are claimed to produce a superior brominated polystyrene. See U.S. Pat. Nos. 4,200,703; 4,352,909; 4,975,496 and 5,532,322. Previously-known brominated polystyrene flame retardants remain deficient in certain properties which translate into deficient performance of thermoplastic polymer blends in which they are used when the blends are subjected to polymer processing conditions. For example, prior art brominated polystyrene polymers evaluated for thermal stability have exhibited a 1 % weight loss at temperatures less than 336 °C when submitted to Thermo- gravimetric Analysis (TGA) and most have exhibited a 1 % weight loss at temperatures around 300 °C. Such low thermal stabilities are undesirable, especially under the high temperatures to which flame retarded thermoplastics formulated with brominated polystyrene polymers are exposed during processing. Corrosion of metal processing equipment such as melt blenders, extruders, and molding machines, attributable to the release of hydrogen halide under thermal processing conditions is another deficiency of flame retarded thermoplastic polymer blends made using prior brominated polystyrene flame retardants. In the presence of moisture, HC1 and HBr released from the brominated polystyrene in the blend at processing temperatures can result in acid formation and consequent metal corrosion. The bromine content of a brominated polystyrene is the sum of (1) bromine substituted on the aromatic portions of the polymer, (2) bromine substituted on aliphatic portions of the polymer, e.g. , the polymer backbone or alkyl substituents resulting from alkylation of the aromatic portion of the polymer, and (3) any ionic bromine present, e.g. , NaBr. Alkylation of aromatic rings in brominated polystyrene is catalyzed by the Lewis acid catalyst used in producing the brominated styrenic polymer, with the reaction solvent (usually a 1-3 carbon atom dihaloalkane) serving as the alkylating agent. The bromine for (1) is referred to herein as aromatic bromide, while the bromine for (2) is referred to as aliphatic bromide. Even though ionic bromine can contribute to the total bromine content, its contribution to the total bromine content is small. Nevertheless, as pointed out in U.S. Pat. No. 5,328,983, ionic impurities in brominated polystyrene may degrade polymer formulations in respect to their ultimate electrical properties, and also may result in corrosion of processing equipment or in the corrosion of metallic parts in their end-use applications. The chlorine content of brominated polystyrenes, like the bromine content, is chiefly part of the polymer structure as aromatic and/or aliphatic chloride substituents. Use of bromine chloride as the brominating agent is the largest contributor to the chlorine content. However, chlorinated solvents and/or chlorine-containing catalysts used in the production of the brominated polystyrene may also contribute to its chlorine content. The aliphatic halide content of the brominated polystyrene is not desirable as aliphatic halide is not as thermally stable as aromatic halide and, thus, aliphatic halide can be easily converted to hydrogen halide, e.g. , HBr or HC1, under normal end-use processing conditions. Aliphatic bromide and chloride are generally referred to by the art and quantified, respectively, as hydrolyzable bromide and hydrolyzable chloride since such halides are easily hydrolyzed as compared to aromatic halides. To evaluate brominated styrenic polymers for their tendencies to release hydrogen halide under thermal processing conditions, use is made of the method described in U.S. Pat. No. 5,726,252 and referred to therein as the Thermal Stability Test Procedure. In essence, this method indicates the content of halogen atoms in the brominated polystyrene that is not bonded directly to the aromatic rings and thus is more readily released from the polymer when at elevated temperature. The Thermal Stability Test is described in greater detail hereinafter. Apart from whether the halide is present as an aromatic or aliphatic halide, it is also desirable to minimize total chlorine content of the brominated polystyrene as chlorine is not as efficacious or as stable a flame retardant constituent as is bromine. Additionally, it has been demonstrated that prior art processes for manufacturing brominated polystyrene give rise to significant cleavage of the polymer chain. This cleavage results in the produced brominated polystyrene having an M w , as measured by Gel Permeation Chromatography, which is significantly lower than the calculated theoretical M w of the brominated polystyrene. The calculation is based upon the bromine content (wt%) of the brominated polystyrene product and the M w of the polystyrene reactant at reaction initiation. It is advantageous if the theoretical M w and the actual M w of the produced brominated polystyrene are close to each other, given the ± margins of error for GPC, since such closeness evidences a paucity of polymer cleavage. The degree of cleavage should be minimized since cleavage results in an increase of alkyl end groups in the brominated polystyrene, which alkyl end groups provide loci for the facile formation of the undesirable hydrolyzable halides discussed above. Conversely, if cross-linking occurs, the molecular weight of the brominated polystyrene is increased, and if not controlled, such cross-linking can result in formation of insoluble residues and/ or gelation of the reaction mixture. In addition, viscosity specifications related to end product usage can be disrupted by such undesirable increases in molecular weight. Total halogen content, especially total bromine content, of the brominated polystyrene is another important consideration. Pyro-Chek 68PB brominated polystyrene flame retardant (Ferro Corporation) is reported to have a total halogen content of about 67 wt% . U.S. Pat. Nos. 5,637,650 and 5,726,252 of Ferro Corporation report that Pyro-Chek® 68PB flame retardant has 3000 to 6000 ppm of backbone halogen, 5000-6000 ppm being typical. And when Pyro-Chek 68PB flame retardant was subjected to the Thermal Stability Test in our laboratories, it evolved 1960 ppm HBr. In order to provide a brominated polystyrene that melt blends more easily and efficiently than Pyro-Chek 68PB flame retardant, Ferro Corporation developed another product with a lower total halogen content, namely, Pyro-Chek (8) 60PB brominated polystyrene flame retardant. This product, which has a total bromine content of about 61 wt%, is reported to melt at a lower temperature and to flow more easily during compounding and processing operations than Pyro-Chek 68PB flame retardant. However, these improvements in melt flow are achieved with a reported concomitant reduction in aromatic bromine content of 10% . Thus, if anything, the 10% reduction in aromatic bromine content portends at best no improvement in thermal stability and at worst a reduction in thermal stability as compared to Pyro-Chek (B) 68PB flame retardant. It would be especially desirable if most if not all of the above-mentioned disadvantages of brominated polystyrenes could be avoided or at least minimized. For example, it would be of considerable advantage, especially for achieving better electrical properties, if a more thermally stable brominated styrenic polymer, e.g. , brominated polystyrene, could be provided that also has a suitably low ionic bromine content. Another welcome contribution to the art would be a brominated polystyrene styrene polymer in which the theoretical M w and the actual M w of the produced brominated polystyrene are close to each other and in which the content of ionic bromine is sufficiently low for inclusion in polymers used in electrical applications, such as glass-filled nylon polymers. From another point of view, it would be desirable and advantageous, if a brominated styrenic polymer, e.g. , brominated polystyrene, could be provided that has both improved melt flow characteristics and improved thermal stability. It would also be of great advantage if improved melt flow and thermal stability could be achieved without material sacrifice of other important properties, and if possible with concomitant provision of other desirable properties such as low ionic bromide content, minimal (if any) chlorine content, and desirable color and odor properties. Also, a need exists for thermoplastics, especially engineering thermoplastics, and particularly nylon (a.k.a. polyamide) thermoplastics, flame retarded by a brominated polystyrene, having enhanced thermal stability and reduced metal corrosiveness. This invention is deemed to at least minimize, if not overcome, most, if not all, of the above-mentioned disadvantages of brominated polystyrenes. SUMMARY OF THE INVENTION In accordance with this invention, new, high quality brominated styrenic polymers having suitably low ionic bromine contents are provided. In addition, these new brominated styrenic polymers possess or exhibit other superior properties or characteristics enhancing their utility as flame retardants for thermoplastic polymers of various types, including glass-filled polyesters and glass-filled nylons. Thus pursuant to a first aspect of this invention there is provided a brominated styrenic polymer, preferably a brominated polystyrene, that has (i) a TGA temperature for 1 % weight loss which is 340°C or higher, preferably within the range of from 340°C to 380°C, and more preferably within the range of from 345°C to 380°C, and a chlorine content, if any, of less than about 700 ppm Cl, preferably less than 500 ppm Cl, and more preferably less than 100 ppm Cl, and (ii) an ionic bromine content of 2000 ppm or less, preferably 1500 ppm or less, more preferably 1000 ppm or less, and most preferably 500 ppm or less, all such ppm levels being based on the total weight of the brominated styrenic polymer. Also provided by the first aspect is a brominated styrenic polymer, preferably brominated polystyrene, that has an actual M w which is within about 20%, and preferably within about 10%, of its calculated theoretical M w , the theoretical M w being based upon the actual bromine content of the brominated styrenic polymer and the M w of the styrenic polymer reactant used to produce the brominated styrenic polymer, and that has an ionic bromine content of 2000 ppm or less, preferably 1500 ppm or less, more preferably 1000 ppm or less, and most preferably 500 ppm or less. Preferably, such brominated styrenic polymer is also characterized (i) by containing less than about 700 ppm Cl, preferably less than 500 ppm Cl, and more preferably less than 100 ppm Cl and/or (ii) by having a TGA temperature for 1 % weight loss which is 340 °C or higher, preferably within the range of from 340 °C to 380 °C, and more preferably within the range of from 345°C to 380°C. The first aspect also provides a brominated styrenic polymer, preferably brominated polystyrene, that is essentially free of impurities selected from the group consisting of (a) methylene chloride, (b) ethylene dichloride, and especially (c) bromodichloroethane, (d) dibromochloroethane, (e) dibromodichloroethane, (f) tribromochloroethane, and (g) any mixture of two or more of the foregoing, especially a mixture that contains at least one of (c) through (f), and that has an ionic bromine content of 2000 ppm or less, preferably 1500 ppm or less, more preferably 1000 ppm or less, and most preferably 500 ppm or less. In additional alternative preferred embodiments such brominated styrenic polymer is also characterized (i) by containing, if any, less than about 700 ppm Cl, preferably less than 500 ppm Cl, and more preferably less than 100 ppm Cl and/or (ii) by having a TGA temperature for 1 % weight loss which is 340 °C or higher, preferably within the range of from 340 °C to 380 °C, and more preferably within the range of from 345 °C to 380 °C, and/or (iii) by having a thermal stability in the Thermal Stability Test described hereinafter of 1500 ppm HBr or less, preferably 1000 ppm of HBr or less, and more preferably 500 ppm of HBr or less, and/or (iv) by having an actual M w which is within about 20%, and preferably within about 10%, of its calculated theoretical M w , the theoretical M w being based upon the actual bromine content of the brominated styrenic polymer and the M w of the styrenic polymer reactant used to produce the brominated styrenic polymer. In each of the above embodiments of the first aspect the brominated styrenic polymer, preferably a brominated polystyrene, additionally has a thermal stability in the Thermal Stability Test described hereinafter of 1500 ppm HBr or less, preferably 1000 ppm of HBr or less, more preferably 500 ppm of HBr or less, and most preferably 200 ppm of HBr or less (e.g. , as little as 100 ppm of HBr or less), all such ppm levels being based on the total weight of the brominated styrenic polymer. Each of the brominated polymer compositions of the first aspect of this invention described above preferably has a total bromine content of at least 50 wt%, more preferably at least 60 wt%, and most preferably at least about 67 wt% (e.g. , in the range of about 68-71 wt%). A second aspect of this invention provides brominated styrenic polymers, e.g. , brominated polystyrene, that possess both improved melt flow characteristics and improved thermal stability. In addition, this invention makes it possible to achieve these beneficial advantageous properties without material sacrifice of other important properties. Indeed, this aspect of the invention makes it possible to provide brominated styrenic polymers, e.g. , brominated polystyrene, that have other desirable properties such as low ionic bromide content, minimal (if any) chlorine content, and desirable color and odor properties. Accordingly, pursuant to the second aspect of this invention there is provided a brominated styrenic polymer, preferably a brominated polystyrene, that has a bromine content in the range of 60 to 66 wt% bromine; a total chlorine content, if any, of less than 700 ppm; a GPC weight average molecular weight in the range of 500,000 to 800,000; a DSC glass transition temperature (Tg) of less than 175 °C; and a thermal stability in the Thermal Stability Test of 250 ppm HBr or less. In preferred embodiments, the thermal stability in the Thermal Stability Test is 150 ppm HBr or less, and more preferably 100 ppm or less. Preferably, the Tg is 165°C or less, and most preferably 160°C or less. Preferably the bromine content is in the range of 60 to 65 wt%, and most preferably in the range of 60 to 64 wt% . Chlorine contents, if any, are preferably 500 ppm or less, more preferably 200 ppm or less, and most preferably 100 ppm or less. The GPC weight average molecular weight is preferably in the range of 500,000 to 700,000. In still other preferred embodiments of the second aspect, the brominated styrenic polymer, preferably brominated polystyrene, (i) has essentially no content of impurities selected from the group consisting of (a) methylene chloride, (b) ethylene dichloride, and especially (c) bromodichloroethane, (d) dibromochloroethane, (e) dibromodichloroethane, (f) tribromochloroethane, and (g) any mixture of two or more of the foregoing, especially a mixture that contains at least one of (c) through (f); and/or (ii) has a solution ΔE value (10 wt% in chlorobenzene) of less than 20, preferably within the range of from 2 to 18, and most preferably in the range of from 2 to 15; and/or a TGA temperature for a 1 % weight loss that is above about 315°C, and more preferably is about 325 °C or above. A third aspect of this invention provides a composition which comprises a thermoplastic polymer, preferably a thermoplastic engineering thermoplastic polymer, having blended therewith at least a flame retardant amount of brominated styrenic polymer having, prior to blending, (i) a total bromine content above about 50 wt% (preferably above about 60 wt%, and more preferably at least about 67 wt%), (ii) a TGA temperature for 1 % weight loss which is 340 °C or higher, preferably within the range of from 340°C to 380°C, and more preferably within the range of from 345 °C to 380°C, and (iii) a chlorine content, if any, of less than about 700 ppm Cl (more preferably, less than about 500 ppm Cl, and still more preferably less than about 100 ppm Cl). Another embodiment of the third aspect of this invention is a composition which comprises a thermoplastic polymer, preferably a thermoplastic engineering thermoplastic polymer, having blended therewith at least a flame retardant amount of brominated styrenic polymer having, prior to blending, (i) a total bromine content above about 50 wt% (preferably above about 60 wt%, and more preferably at least about 67 wt%), (ii) a chlorine content, if any, of less than about 700 ppm Cl (preferably less than about 500 ppm Cl, and more preferably less than about 100 ppm Cl), and (iii) in the Hydrolyzable Bromine Test described hereinafter, a hydrolyzable bromine content of 3600 ppm Br or less, and preferably a hydrolyzable bromine content of 2800 ppm Br or less. In another embodiment of this aspect there is provided a composition which comprises a thermoplastic polymer, preferably a thermoplastic engineering thermoplastic polymer, having blended therewith at least a flame retardant amount of brominated styrenic polymer having, prior to blending, (i) a total bromine content above about 50 wt% (preferably above about 60 wt%, and more preferably at least about 67 wt%), (ii) a TGA temperature for 1 % weight loss which is 340°C or higher, preferably within the range of from 340°C to 380°C, and more preferably within the range of from 345 °C to 380 °C, and (iii) in the Hydrolyzable Bromine Test described hereinafter, a hydrolyzable bromine content of 3600 ppm Br or less, and preferably a hydrolyzable bromine content of 2800 ppm Br or less. Particularly preferred for use in this embodiment is a brominated styrenic polymer which is further characterized in that it has, prior to blending, a chlorine content, if any, of less than about 700 ppm Cl (more preferably, less than about 500 ppm Cl, and still more preferably less than about 100 ppm Cl). A further embodiment of the third aspect of this invention is a composition which comprises a thermoplastic polymer, preferably a thermoplastic engineering thermoplastic polymer, having blended therewith at least a flame retardant amount of brominated styrenic polymer having, prior to blending, (i) a total bromine content above about 50 wt% (preferably above about 60 wt%, and more preferably at least about 67 wt%), and (ii) thermal stability in the Thermal Stability Test described hereinafter of 200 ppm HBr or less, preferably 150 ppm of HBr or less, and more preferably 100 ppm of HBr or less. Particularly preferred for use in this embodiment is a brominated styrenic polymer which is further characterized in that it has, prior to blending, a chlorine content, if any, of less than about 700 ppm Cl (more preferably, less than about 500 ppm Cl, and still more preferably less than about 100 ppm Cl). Still another embodiment is a composition which comprises a thermoplastic polymer, preferably a thermoplastic engineering thermoplastic polymer, having blended therewith at least a flame retardant amount of brominated styrenic polymer having, prior to blending, (i) a total bromine content above about 50 wt% (preferably above about 60 wt%, and more preferably at least about 67 wt%), (ii) a TGA temperature for 1 % weight loss which is 340 °C or higher, preferably within the range of from 340°C to 380°C, and more preferably within the range of from 345 °C to 380 °C, and (iii) thermal stability in the Thermal Stability Test described hereinafter of 200 ppm HBr or less, preferably 150 ppm of HBr or less, and more preferably 100 ppm of HBr or less. Particularly preferred for use in this embodiment is a brominated styrenic polymer which is further characterized in that it has, prior to blending, a chlorine content, if any, of less than about 700 ppm Cl (more preferably, less than about 500 ppm Cl, and still more preferably less than about 100 ppm Cl). A still further embodiment of the third aspect of this invention is a composition which comprises a thermoplastic polymer, preferably a thermoplastic engineering thermoplastic polymer, having blended therewith at least a flame retardant amount of brominated styrenic polymer having, prior to blending, (i) a total bromine content above about 50 wt% (preferably above about 60 wt%, and more preferably at least about 67 wt%), (ii) a TGA temperature for 1 % weight loss which is 340°C or higher, preferably within the range of from 340°C to 380°C, and more preferably within the range of from 345 °C to 380 °C, (iii) in the Hydrolyzable Bromine Test described hereinafter, a hydrolyzable bromine content of 3600 ppm Br or less, and preferably a hydrolyzable bromine content of 2800 ppm Br or less, and (iv) thermal stability in the Thermal Stability Test described hereinafter of 200 ppm HBr or less, preferably 150 ppm of HBr or less, and more preferably 100 ppm of HBr or less. Particularly preferred for use in this embodiment is a brominated styrenic polymer which is further characterized in that it has, prior to blending, a chlorine content, if any, of less than about 700 ppm Cl (more preferably, less than about 500 ppm Cl, and still more preferably less than about 100 ppm Cl). Yet another embodiment is a composition which comprises a thermoplastic polymer, preferably a thermoplastic engineering thermoplastic polymer, having blended therewith at least a flame retardant amount of brominated styrenic polymer having, prior to blending, (i) a total bromine content of about 67 wt% or more, and (ii) a TGA temperature for 1 % weight loss which is 340°C or higher, preferably within the range of from 340°C to 380°C, and more preferably within the range of from 345 °C to 380 °C. Preferably, the brominated styrenic polymer used in each of the above compositions of the third aspect of this invention is further characterized by: a) containing, prior to blending, no detectable quantity of Cl; and/or b) having, prior to blending, an actual M w which is within about 20% , and preferably within about 10%, of its calculated theoretical M w , the theoretical M w being based upon the actual bromine content of the brominated styrenic polymer and the M w of the styrenic polymer reactant used to produce the brominated styrenic polymer; and/or c) containing, prior to blending, no detectable quantity of any one or more of bromodichloroethane, dibromochloroethane, dibromodichloroethane, and tribromochloroethane . d) having, prior to blending, a ΔE color value that is less than 20 (preferably within the range of from 5 to 18, and most preferably within the range of from 3 to 15). Each of the compositions of the third aspect of this invention described above most preferably also further comprises a reinforcing amount of reinforcing filler or fiber, preferably glass fiber, and/or a flame retardant synergist dispersed therein. In each of the compositions of the third aspect of this invention described above, most preferably the thermoplastic polymer is a thermoplastic polyester or a thermoplastic polyamide. A feature of this third aspect is that it has now made it possible to provide flame retarded compositions that have increased thermal stabilities and reduced metal corrosiveness at elevated polymer processing temperatures vis-a-vis corresponding compositions made with prior art brominated polystyrenes. In addition it is now possible to provide flame retarded compositions that have other superior characteristics such as reduced odor when at elevated temperatures, and reduced color. All ppm levels referred to herein are based on the total weight of the brominated styrenic polymer. Other embodiments and features of this invention will be further apparent from the ensuing description and appended claims. BRIEF DESCRIPTION OF THE DRAWING Figure 1 is a schematic diagram depicting a process suitable for producing preferred brominated polystyrenes of each of the aspects of this invention. THE FIRST ASPECT OF THIS INVENTION - FURTHER DESCRIPTION Brominated Styrenic Polymers The brominated styrenic polymers of this aspect are brominated styrenic polymers, (preferably a brominated polystyrene) . These brominated styrenic polymers have a total bromine content of at least 50 wt%, preferably above 60 wt%, and more preferably at least 67 wt%; and an ionic bromine content of 2000 ppm or less, preferably 1500 ppm or less, more preferably 1000 ppm or less, and most preferably 500 ppm or less, all wt% and ppm levels herein being based on the total weight of the brominated styrenic polymer, unless otherwise stated. Moreover, the brominated styrenic polymers (preferably brominated polystyrenes) of this invention possess certain additional important properties or characteristics pertaining to such factors as TGA temperature for 1 % weight loss, total chlorine content (if any), thermal stability in the Thermal Stability Test described hereinafter, actual M w closely matching calculated theoretical M w , and freedom from specified impurity contents. The properties of other suitable brominated styrenic polymers of this invention will be apparent as the description proceeds. The high TGA temperatures which are characteristic of brominated styrenic polymers that possess the TGA characteristics specified above are not believed to be due to post reaction purification techniques. Rather, it is believed that such enhanced thermal stability is due to the chemical makeup of the brominated styrenic polymer itself. As to the brominated styrenic polymers that possess the M w properties specified above, a difference between the actual M w and the theoretical M w outside of the normal ± margin of error for GPC analysis, is evidence of either cross-linking (increases the M w ) or polymer chain cleavage (decreases the M w ). The 20% difference mentioned above for the brominated styrenic polymers that possess this characteristic includes the + margin of error. Preferred differences are those less than 20%, with differences of less than 10% being most preferred. Since GPC techniques can give different but similar values for the same polymer tested, the testing is best performed by taking the arithmetic average of five consecutive GPC determinations of the polymer to be tested. Other data averaging techniques are suitable, such as using the average of 10 consecutive GPC determinations with discard of the high and low values, the only requirement being that accurate and reproducible results are obtained. This invention also provides a novel thermally stable brominated polystyrene which is comprised of polymer units represented by Formula (I), as follows: wherein each X is independently -H or a halide atom, the identity of each X for each polymer unit being such that the brominated polystyrene contains less than 6000 ppm of X-type halide atoms, and wherein the value of n for each polymer unit is such that the brominated polystyrene contains at least 50 wt% bromine. From an economic and performance standpoint, it is preferred that the bromine content be within the range of from above 60 wt% to 70-71 wt% (n = 1.9 to 2.9-3.0), and especially within the range of from 68 wt% to 71 wt% (n = 2.7 to 3.0). With regard to the halide atoms, X, preferred brominated polystyrenes will be those in which X is bromide. Such polymers may contain some chlorine atoms, but the amount will be insignificant, usually less than 500 ppm, and where possible, less than 100 ppm. If chlorine is present, its source would probably be the Lewis acid catalyst or the solvent used in the preparation of the brominated polystyrene. Preferred brominated polystyrene polymers are those in which the chlorine content is less than 500 ppm in accordance with X-Ray Fluorescence analysis. It is beneficial, from the viewpoint of economy and performance, that the X-type bromide content be less than 4000 ppm, say within the range of from 1000 ppm to 3000 ppm. Most beneficial are those X-type bromide contents which are within the range of from 0 ppm to 1500 ppm. The brominated polystyrenes of this aspect of the invention are unique in that, from their very inception, the polymer has the very low X-type halide content discussed above. This is an important aspect as the polymers do not need further treatment to reduce the X-type halide content. Reduction of the X-type halide content, say by hydrolysis, is not desirable as it yields a polymer having hydroxyl, ether, and/or olefinic functionality in its structure which can alter polymer properties. It is preferred that the brominated polystyrenes of this invention contain little or no hydrolysis residues, say less than 500 ppm and preferably less than 100 ppm. The most preferred brominated polystyrene components of this aspect of the invention will be those which provide, at the lowest cost, the highest bromine content and the lowest X- type halide content which obtain the desired properties referred to above. The brominated styrenic polymers of this aspect preferably exhibit additional superior physical properties, e.g. , little or no color or odor. For flame retardants, color is an important property, with pure white being the ultimate goal. Due to the formation of various color bodies by all bromination processes, the industry has accepted near- white products as being acceptable. The color of prior art brominated polystyrene, expressed as a solution ΔE value, generally will fall within the range of 20 to 35. In distinction, the brominated polystyrenes used pursuant to this invention typically feature ΔE values (10 wt% in chlorobenzene) of less than 20 and preferably within the range of from 2 to 18. Most preferably, such ΔE value will be within the range of from 2 to 15. Another physical property of the preferred brominated styrenic polymers of this aspect is that they have essentially no odor, or very little odor, when heated to a temperature above 150 C. In comparison, Pyro-Chek 68PB brominated polystyrene flame retardant (Ferro Corporation) has a noticeable and strong odor at 150 °C. The strong odor is believed to be attributable to the presence of bromochloroethanes, e.g. , bromodichloroethane, dibromochloro- (§) ethane, dibromodichloroethane and tribromochloroethane, which are in the Pyro-Chek 68PB product. Such bromochloroethanes are not seen in detectable quantities in the brominated styrenic polymers of this invention. Styrenic Polymer Reactants Styrenic polymers which are brominated to form the brominated styrenic polymers of this aspect of the invention are homopolymers and copolymers of vinyl aromatic monomers. Preferred vinyl aromatic monomers have the formula: H 2 C = CR-Ar wherein R is a hydrogen atom or an alkyl group having from 1 to 4 carbon atoms and Ar is an aromatic group (including alkyl-ring substituted aromatic groups) of from 6 to 10 carbon atoms. Examples of such monomers are styrene, α//?/tα-methylstyrene, σrt/tø-methylstyrene, meta- methylstyrene, /?αrα-methylstyrene, pαrα-ethylstyrene, isopropenyltoluene, vinylnaphthalene, isopropenylnaphthalene, vinylbiphenyl, vinylanthracene, the dimethylstyrenes, tert-butylstyrene, the several bromostyrenes (such as the monobromo-, dibromo-, and tribromo- variants). Polystyrene is the preferred reactant. When the brominated styrenic polymer is made by bromination of a copolymer of two or more vinyl aromatic monomers, it is preferred that styrene be one of the monomers and that styrene comprise at least 50 weight percent of the copolymerizable vinyl aromatic monomers. If a bromo styrenic polymer is selected for bromination to make a brominated styrenic polymer, the initial bromostyrenic polymer must have a lower bromine content than the bromine content to be present in the brominated styrenic polymer of this invention. In this connection, the terms "brominated styrenic polymer" and "brominated polystyrene" as used in the specification and in the claims hereof refer to a brominated polymer produced by bromination of a pre-existing styrenic polymer such as polystyrene or a copolymer of styrene and at least one other vinyl aromatic monomer, as distinguished from an oligomer or polymer produced by oligomerization or polymerization of one or more brominated styrenic monomers, the properties of the latter oligomers or polymers being considerably different from brominated polystyrene in a number of respects. The polystyrene reactant used in the production of the brominated polystyrenes of this first aspect can be any of those which are commercially available. Generally, the polystyrene backbone will not have been hydrogenated and, thus, will have unsaturation. There is no need for the brominated polymers of this invention to be produced from anionically produced polystyrene as is taught in EPO 0 201 411; in fact, it is preferred that the polystyrene reactant not be an anionically produced polystyrene as such polystyrene polymers are expensive and not readily available. The aromatic pendant constituents of the polymer can be alkyl substituted, but in most cases, will not be so substituted. The polystyrene used to produce the brominated polystyrenes of this invention will have a M w within the range of from 500 to 500,000 and a polydispersity within the range of from above 1 to 4. For most purposes, the polystyrene reactant will have a M tt within the range of from 100,000 to 300,000 and will have a polydispersity within the range of from 1.25 to 2.5. The lower molecular weight polystyrene reactants will have a M w within the range of from 500 to 100,000 and a polydispersity less than about 10 and preferably within the range of from above 1 to 4. Higher molecular weight polymer reactants of this invention have a M w within the range of from 300,000 to 500,000 and a polydispersity within the range of from above 1 to 4. The M w and polydispersity values are both based on gel permeation chromatography (GPC) techniques which are hereinafter described. It has also been found preferable that the polystyrene used in the formation of the brominated polystyrenes flame retardant not contain any additives, such as zinc stearate, paraffins, mineral oils and the like. A highly preferred polystyrene is Styron 612 which is marketed by Dow Chemical Company. However, additive-containing polystyrene such as Styron 668, Styron 677, Styron 680 of Dow Chemical Company, as well as Piccolastic A5, Piccolastic A75, or Piccolastic D125 of Hercules Incorporated, and EA 3300, MB 3200, MC 3100, or EA 3000 of Chevron Chemical Company, or equivalent materials from other producers, can be used. Production of the Brominated Polystyrene For purposes of simplification, much of the description hereinafter refers to preparation of brominated polystyrene, the preferred flame retardant of this invention. The principles and procedures described are applicable to preparation of other brominated styrenic polymers. The brominated polystyrenes of this invention are not conventionally produced. Generally, a suitable process comprises feeding a mixture of bromine and a solution of bromochloromethane and polystyrene (2.5 to 5 moles of bromine per mole of polymerized styrene in the polystyrene) to a reactor containing a further amount of bromochloromethane and a catalytic amount of A1C1 3 . The mixture of polystyrene, bromochloromethane and bromine is substantially free of a bromination catalyst. The phrase, "substantially free of a bromination catalyst", is to be taken to mean less than a catalytically effective amount of catalyst. With such low amounts of catalyst, little or no catalyzed bromination or cross-linking should occur. Generally, such amounts will be less than 500 ppm based on the weight of polystyrene reactant present. The reaction temperature will be within the range of from -10°C to l5°C. Preferably, the reaction is conducted at one or more temperatures in the range of -10°C to 10°C as this provides product of the highest quality and, surprisingly, the reaction itself proceeds at a suitably rapid rate at these low temperatures such that the process meets commercial production requirements. After the reaction mass is formed, it is usually maintained at reaction temperature for a period in the range of 5 minutes to 2 hours, and preferably in the range of 5 minutes to 60 minutes. After this period, the reaction product is worked up by adding water and then settling to remove the acidic phase. Multiple water washes can be performed as desired. Next the reaction mass is treated with a base such as sodium hydroxide, sodium sulfite, and/or sodium borohydride, usually as an aqueous solution, to adjust the reaction pH to a suitable level of basicity and kill any remaining brominating agent. After these treatments, the reaction mass is settled to obtain a two-phase reaction mass containing an organic phase, which contains, as a solute, the brominated styrenic polymer product and an aqueous phase. The aqueous phase is decanted and the remaining organic phase is stripped of its solvent component. It is most convenient to accomplish this strip by pumping the organic phase into boiling water. As the solvent is flashed off, the brominated styrenic polymer product forms a precipitate. The precipitate can be recovered by any liquid-solid separation technique, e.g. , filtration, or centrifugation. The recovered precipitate is then dried. If desired, a thermal stabilizing amount of base can be incorporated in the finished brominated polystyrene composition. That is, the finished brominated polystyrene composition can be treated to contain an amount of alkali metal base such that if a sample of the finished composition is dissolved in bromochloromethane and the resultant solution is extracted with water, the aqueous extract has a pH of at least about 9.0, preferably a pH in the range of 9.5 to 11, and more preferably in the range of 10 to 10.5. Commonly-owned application Serial No. 09/066, 172, filed April 24, 1998, describes processes in which a suitable amount of aqueous base is employed to improve the thermal stability of the resultant brominated polystyrene. A preferred way is to suitably increase the amount of base used during the catalyst deactivation stage so that a suitable residual amount of the base remains within the finished brominated polystyrene. A preferred process can be used to ensure recovery of a purified brominated polystyrene polymer (or other brominated styrenic polymer) having a suitably low ionic halogen content (e.g. , ionic bromine or ionic chlorine content) from the reaction mass formed by brominating polystyrene with bromine in a halocarbon or halohydrocarbon solvent having a boiling point below 100°C and in the presence of a Lewis acid catalyst. Such preferred process comprises: a) quenching the reaction mass in water to form an aqueous phase and an organic phase, and recovering the organic phase; b) mixing the organic phase with water at a temperature in the range of 10 to 100° C in a ratio of from 0.02 to 0.6 part by volume of the aqueous phase per each 1 part by volume of organic phase to form an aqueous extraction phase and an extracted organic phase, and recovering the extracted organic phase; c) optionally but preferably, mixing inorganic alkali metal base and water with extracted organic phase from b) to form an alkaline mixture in which the pH of the aqueous phase in this mixture is in the range of 7 to 14, and preferably in the range of 10 to 14; d) mixing a bromine scavenger and water with alkaline mixture from c) to form a bromine scavenged mixture; e) precipitating brominated polystyrene by mixing bromine scavenged mixture from d) with a water solution of inorganic alkali metal base maintained at or above the boiling temperature of the halocarbon or halohydrocarbon solvent; and f) recovering brominated polystyrene formed as a precipitate in e) . Before proceeding to step c) above, step b) above can be repeated one or more times as may be necessary or appropriate in achieving the desired reduction in ionic halogen (e.g. , ionic bromine). Alternatively, step b) can be conducted on a continuous basis using liquid-liquid extraction apparatus such as a liquid-liquid extraction tower. Sodium sulfite and sodium borohydride are the preferred bromine scavengers for use in step d) above. However, other water-soluble inorganic sulfides can be used. And in step d) above, a coalescing filter can be employed, if desired, to remove additional aqueous phase from the organic phase, and thereby still further reduce the ionic halogen content of the finished product. In the production of brominated polystyrene, it is important that the iron content be kept to a minimum, say less than about 10 ppm iron. The introduction of iron into the product usually occurs due to iron equipment which is in contact with the reaction and product streams. Thus, it is preferred to use process equipment which does not act as a source of iron contamination. For example, the equipment can be glass-lined or corrosion resistant alloy. A more detailed process description with reference to the accompanying drawing is given below. Detailed Description of Bromination Process with Reference to the Drawing Preferred process technology for producing brominated polystyrenes is described herein. It will be appreciated that, unless otherwise indicated in the specification hereof or specified in any claim hereof, this invention is not limited to use of all of this preferred process technology. Polystyrenes useful for the production of the brominated polystyrenes by this preferred process are any of those which have been described above. Also, as mentioned previously, it is preferred that the polystyrene be additive-free. The catalyst used in the preferred process can be any of the aluminum based catalysts, e.g. , A1C1 3 , AlBr 3 and Al. Mixtures of aluminum catalysts can also be used. Once the catalyst has been added to the reaction system, it may undergo some reaction without significant loss of catalytic activity, e.g. , A1C1 3 may convert to some extent to AlBr 3 . A1C1 3 , because of its availability and price, is the catalyst of choice, and powder grade A1C1 3 is most preferred due to its ease of dispersibility. The catalyst is used in an amount which is sufficient to obtain the catalytic effect sought. These catalytic amounts will depend on the activity of the catalyst, but will generally fall within the range of from 0.2 to 10 weight percent and preferably within the range of from 0.5 to 5 weight percent, based on the weight of the styrenic polymer being brominated. The most active catalysts will be used in the lower amounts, while the less active catalysts will be used in the higher amounts. When AlCl 3 is the catalyst, amounts within the range of from 0.5 to 3 weight percent are preferred. The brominating agent is preferably bromine. Bromine can be obtained commercially in the diatomic form or can be generated by the oxidation of HBr. Br 2 can be supplied either as a liquid or a gas. The amount of brominating agent used in the process should provide an overall mole ratio of total brominating agent to total styrenic polymer fed which will provide from 1 to 3 bromine substitutions per styrenic monomer unit in the polymer. It is preferred that the brominated polystyrene contain at least about 60 wt% bromine, and desirably at least about 68 wt% bromine and most preferably within the range of from 69 to 71 wt% bromine. For any particular styrenic polymer, the amount of brominating agent used in the process will be determined by the bromine content desired considering the highest bromine content which is obtainable with the process parameters chosen. The higher bromine contents will require the most brominating agent. It is pointed out that as perbromination is approached, it becomes more difficult to substitute the last bromines. Adding ever larger amounts of a brominating agent does not always attenuate this difficulty. The stoichiometry is easily determined as it requires one mole of Br 2 per substitution sought. In practice, the practitioner will determine the bromine content sought on a weight basis and then will calculate, on an idealized basis, the number of moles of brominating agent needed to obtain the same. For example, if the styrenic polymer is polystyrene and the bromine content sought is 68 wt%, at least 2.7 moles of bromine per styrenic monomer unit will be required, not including any desired stoichiometric excess. All of the bromine can be added with the polystyrene-bromochloromethane solution or a portion of the bromine can be pre-added to the reactor with the remainder being added with the solution. If pre-addition is to be used then the pre-added portion will amount to 0.5 to 20% of the total bromine used in the process. Generally, the mixture which is to be fed is formed from 1 to 8 moles of brominating agent per mole of styrenic monomer units at any time during the feed period. During the feed, the quantitative relationship can be constant or can vary within the above-mentioned range. (It is possible to allow for some excursions outside of the range so long as such does not do significant harm to the process efficiency or to product quality.) A preferred range is from 2.5 to 5 moles of brominating agent per mole of styrenic monomer units to form the feed mixture. As can be appreciated, the use of an amount of brominating agent in the feed mixture which gives a mole ratio of brominating agent to styrenic monomer units which is less than or greater than the selected overall mole ratio of brominating agent to styrenic monomer units will result in exhaustion of either the brominating agent or the styrenic polymer as a mixture constituent before exhaustion of the other constituent. For example, to produce brominated polystyrene with a 70 wt% bromine content, an overall molar ratio of bromine to styrenic monomer units of 3.0: 1 would be suitable. But to form a feed mixture in which the molar ratio of bromine to styrenic monomer units is 1: 1, the amount of polystyrene to be fed will be completed before obtaining the needed overall amount of bromine. In this case, the practitioner first uses the 1: 1 mixture and then continues on with just a bromine feed after the polystyrene feed has been exhausted. If, on the other hand, the molar ratio in the feed mixture is chosen to be 5: 1, then the bromine will first become exhausted and the feed will have to be finished with the polystyrene alone. Generally, it is preferred to have the overall molar ratio and the feed mixture ratio at least somewhat similar. In all cases though, the initial feed should preferably contain at least a molar ratio of bromine to styrenic monomer units of 1: 1. It is preferred that the bromine used in the process be essentially anhydrous, i.e. , contain less than 100 ppm (weight basis) water and contain no more than 10 ppm impurities, e.g. , oil, grease, carbonyl containing hydrocarbons, or iron. Available, commercial grade bromine may have such purity. If, however, such is not available, the organic impurities and water content of the bromine can be conveniently reduced by mixing together a 3 to 1 volume ratio of bromine and concentrated (94-98 percent) sulfuric acid. A two-phase mix is formed which is stirred for 10-16 hours. After stirring and settling, the sulfuric acid phase, along with the impurities and water, is separated from the bromine phase. To further enhance the purity of the bromine, the recovered bromine phase can be subjected to distillation. The preferred organic solvent for the bromination, bromochloromethane, is preferably essentially anhydrous, containing less than 100 ppm (weight basis) water. It is most preferred that the solvent contain as little water as is practically obtainable, say between 0 to 30 ppm (weight basis). The process benefits from the reaction mass being in an anhydrous condition. Water tends to affect the catalytic activity of the aluminum catalyst, which effect may hinder the quick aromatic bromination of the styrene rings. If, for some reason, the practitioner has large amounts of water in the process and dewatering is not practical, then it may be possible to overcome the situation by simply increasing the amount of catalyst used. By forming a solution of bromochloromethane and styrenic polymer, the polymer becomes easy to handle and mix with bromine. These solutions preferably contain from 5 to 50 wt% polymer. More highly preferred are those which contain from 5 to 30 wt% polymer. It is preferred to have the bromination catalyst, to which the bromine/ styrenic polymer mixture is fed, to be in association with bromochloromethane so that the catalyst can be in a solution, slurry, dispersion or suspension. Such will enhance reaction mass mixing and mass transfer qualities. The mixture of bromochloromethane and catalyst is best described as a suspension. Generally, it is suitable to use from 95 to 99.9 wt% , preferably from 99 to 99.8 wt%, bromochloromethane, based on the total weight of bromochloromethane and catalyst. The styrenic polymer /brominating agent mixture feed should occur expeditiously, with consideration being given to the ability of the process equipment to handle the heat load from the exothermic process, the evolving HBr, and other process concerns. In short, the feed can occur over the shortest time period that will be allowed by the equipment without excursion outside of critical process parameters. Generally, it is anticipated that the feed period will be from 0.5 to 3 hours for a commercial-size plant. Shorter feed periods are expected for smaller scale processes. It is possible to conduct the bromination reaction at a temperature within the range of from -20 °C to 60 °C. Desirably, the bromination temperature is maintained within the range of from -10°C to 15°C. Most preferred temperatures are in the range of from -10°C to 0°C. This last-mentioned temperature range provides product of the highest quality and, surprisingly, the reaction itself proceeds at a suitably rapid rate at these low temperatures such that the process meets commercial production requirements. The pressure can be atmospheric, subatmospheric or superatmospheric. In carrying out the process, a bromination catalyst, preferably powdered A1C1 3 , is suspended in essentially anhydrous bromochloromethane, to give an easily stirrable suspension. The suspension is prepared in a glass-lined, stirred reactor and brought to a temperature within the range of from -10°C to -5°C. The mix is kept under an inert, dry atmosphere in the reactor. A solution of a styrenic polymer and bromochloromethane is prepared and intimately mixed with a bromine stream to yield a homogenous mixture. The mixture is fed into the stirred bromination catalyst suspension in the reactor. The intimate mixing of the styrenic polymer solution and bromine can be accomplished in a number of ways. For example, the solution and bromine can be fed to a mixing device, e.g. , a mixing nozzle, at the lower end of the diptube in the reactor which extends to a point below the suspension level. The mixing device is designed to obtain the intimate mixing of the solution and bromine. Also, the mixing device acts to impart mixing energy, at the point of feed, to the intimate mixture and catalyst suspension. Another technique for obtaining intimate mixing of the styrenic polymer solution and brominating agent, is to use an exterior reactor loop having an in-line mixer, such as an impingement mixer. Generally, the use of an exterior reactor loop includes first charging the reactor with a bromination catalyst slurry, or suspension, and then withdrawing from the reactor a stream which is then fed to a mixer external of the reactor. A mixture formed from at least bromine and styrenic polymer is also fed to the mixer to yield a second mixture which is formed from the two feeds to the mixer. The second mixture is subsequently fed back to the reactor. The stream withdrawn from the reactor will initially comprise the catalyst. After the second mixture is fed to the reactor and the process runs, the withdrawn stream will begin to comprise brominated polystyrene along with catalyst. Exemplifying the use of a reactor jet mixer, reference is made to Figure 1 wherein there is shown a reactor, generally designated by the numeral 10. Reactor 10 is a stirred reactor, and initially it contains a suspension comprising catalyst and bromochloromethane. Reactor discharge conduit 40 provides a recycle stream from reactor 10 which is fed to pump 50. Pump 50 pressurizes the stream so that it is fed with force via conduit 70 back to reactor 10. Bromine is fed via conduit 20 to pump P x while, at the same time, a solution of polystyrene and bromochloromethane is fed via conduit 22 to pump P 2 . Pumps P x and P 2 feed jet mixer 24 via lines 26 and 28, respectively, to thereby produce an intimate mixture of bromine, polystyrene, and solvent. This intimate mixture is fed into the reaction mass in proximity to agitator 30 to ensure thorough mixing of the reactor contents. The removal of contents from, and their recycle back to, reactor 10, and also the feed of fresh reactants to jet mixer 24 are continued until at least substantially all of the bromine and polystyrene/bromochloromethane solution have been fed into the reaction mass. As can be appreciated, the contents of reactor 10 change in composition during the bromine and bromochloromethane solution feeds. Initially, the contents of reactor 10 comprise catalyst and solvent. As the process runs, the reactor contents comprise and begin to become more rich in brominated polystyrene. Irrespective of whether or not a diptube mixer or an exterior impingement mixer is used, the bromination of styrenic polymer will yield HBr as a major by-product. The HBr formed in the process first saturates the solvent and from then on HBr escapes into the head space above the reactor contents. It is preferred that the HBr be removed and passed to a water scrubber or stored as dry HBr. A dry, inert gas, e.g. , nitrogen, can be used as a pad over the reactor contents to minimize the presence of water therein. The reactor, in all cases, is preferably kept at a low temperature, e.g. , from -10°C to 10 °C, during the feed of the styrenic polymer and/or brominating feed, as the case may be, and most preferably from -10°C to 5°C. Also, after the feed is accomplished, the reactor is maintained at reaction temperature (desirably in the range of -10°C to 15°C and preferably in the range of -10°C to 10°C) for a period of from 5 minutes to 2 hours and preferably from 5 to 60 minutes. Such additional period of time following completion of the feed serves to continue the bromination until the desired degree of bromination has been achieved. Such period will be longer if the reaction parameters provide for mild bromination conditions during the bromine-polystyrene feed than if the parameters chosen provide for more severe bromination conditions during the feed. Also, such period will be longer if a high degree of bromination (e.g. , above 69 wt% bromine in the brominated polystyrene) is sought. The reaction mass can be kept in the reactor during the additional period of time following completion of the feed. Also, the hold period can be used to strip more HBr from the reaction mass by using an inert gas sweep. When the desired degree of bromination has been achieved, the preferred process described above for recovery of a purified brominated polystyrene polymer having a suitably low ionic halogen content involving steps a) through f) can be used. Another similar method for working up the reaction mass is to treat the reaction mass with water to deactivate the catalyst. Then the reaction mass is settled to remove the aqueous HBr phase. Sodium sulfite or sodium borohydride, typically as an aqueous solution, can then be added (and preferably is added) to remove any remaining brominating agent, followed by sodium hydroxide, again typically as an aqueous solution, to adjust the pH of the reaction mass. Although sodium sulfite and sodium borohydride are the preferred bromine scavengers for use in removing any remaining brominating agent, other water-soluble inorganic sulfides such as lithium sulfite, potassium sulfite, magnesium sulfite, ammonium sulfite, or other water soluble borohydrides such as lithium borohydride, or potassium borohydride can be used, in as much as the scavenging function is performed by the sulfite or borohydride anion and/ or by whatever other species may form when the inorganic sulfite or borohydride is dissolved in water. Aqueous solutions of the sulfite or borohydride can contain any suitable concentration of the dissolved inorganic sulfite or borohydride, and the amount of water-soluble sulfite or borohydride salt used should be at least sufficient to react with (destroy) the amount of residual brominating agent present in the mixture being treated. It is not necessary or advisable to use a large excess of sulfite or borohydride, e.g. , more than about 2-3 mole % excess, as the excess represents wasted material serving no useful purpose. After scavenging the brominating agent, additional sodium hydroxide or other alkali metal base can be added, if desired, in a suitable amount and preferably in the form of an aqueous solution to act as a stabilizer for the brominated polystyrene. Whether or not such stabilizer is used, the reaction mass is settled to obtain a two-phase reaction mass containing an organic phase, which contains, as a solute, the brominated styrenic polymer product, and an aqueous phase. The aqueous phase is decanted and the remaining organic phase is stripped of its solvent component. It is most convenient to accomplish this strip by pumping the organic phase into boiling or near-boiling water. As the solvent is flashed off, particles of the brominated styrenic polymer product form in and separate from the residual liquid phase as a precipitate, and if desired, concurrently a suitable amount of the base can be incorporated into the particulate brominated polystyrene as it is being formed. If desired, a surfactant, such as dioctyl sulfosuccinate sodium salt, can be added to the hot water. The amount of dioctyl sulfosuccinate, if used, can be within the range of from 0.01 to 0.05 wt%, based upon the total weight of water and surfactant. The precipitate can be recovered by any liquid-solid separation technique, e.g. , filtration, or centrifugation. The recovered precipitate is then dried. Analytical Methods Since brominated styrenic polymers have good, or at least satisfactory, solubility in solvents such as tetrahydrofuran (THF), the determination of the total bromine content for the brominated styrenic polymers is easily accomplished by using conventional X-Ray Fluorescence techniques. The sample analyzed is a dilute sample, say 0.1 + 0.05 g brominated polystyrene in 60 mL THF. The XRF spectrometer can be a Phillips PW1480 Spectrometer. A standardized solution of bromobenzene in THF is used as the calibration standard. The total bromine values described herein and reported in the Examples are all based on the XRF analytical method. To determine the ionic bromine content of brominated styrenic polymers, the procedure used involves dissolving a sample of the polymer in a suitable organic solvent medium and titrating the solution with a standard solution of silver nitrate. In particular, a 2.0 gram sample of the brominated styrenic polymer weighed to the nearest 0.1 mg is placed in a 600 mL beaker, followed by 200 mL of tetrahydrofuran (THF), and a stir bar. The solids are stirred until completely dissolved. To this solution is added 50 mL of toluene, and the mixture is stirred. Immediately prior to conducting the titration, 50 mL of acetone, then 50 mL of isopropyl alcohol, and then 10 mL of glacial acetic acid are added to the sample mixture. The sample is then titrated immediately with standardized 0.0 IN AgNO 3 using an automatic potentiometric titrator such as a Metrohm 670, 716, or 736, or equivalent. Reagent grade (A.C.S.) THF, toluene, acetone, isopropyl alcohol, and acetic acid are used in the procedure. The analysis is conducted using duplicate samples, plus a determination on a blank sample conducted in identical fashion except using no polymer. If both ionic bromine and ionic chlorine are present, the bromide titrates first. The distance between the inflection points is the chloride titre. The average of the two sample determinations is reported. However, if duplicate samples do not agree within less than 10% of each other, an additional replicate sample is analyzed in the same way, and the average of the three analyses is reported to three significant digits. The calculation for ionic bromine or chlorine are as follows: Ionic bromine (ppm) = mL AgNO-, x normality of AgNO ^ x (7.99)xl0 4 sample weight in grams Ionic chlorine (ppm) = mL AgNO ^ x normality of AgNO? x (3.545)xl0 4 sample weight in grams mL AgNO 3 = mL required for sample - mL required for blank To determine the color attributes of the brominated polymers of this invention, use is again made of the ability to dissolve brominated styrenic polymers in easy-to-obtain solvents, such as chlorobenzene. The analytical method used is quite straight-forward. Weigh 5 g + 0.1 g of the brominated polystyrene into a 50 mL centrifuge tube. To the tube also add 45 g + 0.1 g chlorobenzene. Close the tube and shake for 1 hour on a wrist action shaker. After the 1 hour shaking period, examine the solution for undissolved solids. If a haze is present, centrifuge the solution for 10 minutes at 4000 rpm. If the solution is still not clear, centrifuge an additional 10 minutes. Should the solution remain hazy, then it should be discarded as being incapable of accurate measurement. If, however, and this is the case most of the time, a clear solution is obtained, it is submitted for testing in a HunterLab ColorQuest Sphere Spectrocolorimeter. A transmission cell having a 20-mm transmission length is used. The colorimeter is set to "Delta E-lab" to report color as ΔE and to give color values for "L", "a" and "b". DSC values were obtained with a TA Instruments DSC Model 2920. Samples were heated from 25 °C to 400 °C at 10°C/min under nitrogen. Thermogravimetric analysis (TGA) is used to test the thermal behavior of the brominated styrenic polymers of this invention. The TGA values are obtained by use of a TA Instruments Thermogravimetric Analyzer. Each sample is heated on a Pt pan from 25 °C to 600 °C at 10°C/min with a nitrogen flow of 50-60 mL/min. To determine thermal stability and estimate the corrosive potential of a sample, the following test procedure as described in U.S. Pat. No. 5,637,650 is used. Each sample is run in duplicate. A 2.00+0.01 g sample is placed into a new clean 20x150 mm test tube. With a neoprene stopper and Viton ® fluoroelastomer tubing, the test tube is connected to a nitrogen purge line with exit gas from the test tube being passed successively through subsurface gas dispersion frits in three 250-mL sidearm filter flasks each containing 200 mL of 0.1 N NaOH and 5 drops of phenolphthalein. With a constant nitrogen purge at 0.5 SCFH, the test tube is heated at 300°C in a molten salt bath (51.3 % KNO 3 /48.7% NaNO 3 ) for 15 minutes followed by 5 minutes at ambient temperature. The test tube containing the sample is then replaced with a clean dry test tube, and the apparatus is purged with nitrogen for an additional 10 minutes with the empty test tube in the 300°C salt bath. The test tube, tubing and gas dispersion tubes are all rinsed with deionized water, and the rinse is combined quantitatively with the solutions in the three collection flasks. The combined solution is acidified with 1: 1 HNO 3 and titrated with 0.01 N AgNO 3 using an automatic potentiometric titrator (Metrohm 670, 716, 736, or equivalent). Results are calculated as ppm HBr, ppm HC1, and ppm HBr equivalents as follows: ppm HBr = (EP l)(N)(80912)/(sample wt.) ppm HC1 = (EP 2 - EP l)(N)(36461)/(sample wt.) ppm HBr equivalents = (EP 2)(N)(80912)/(sample wt.) where EP(x) = mL of AgNO 3 used to reach end point x; and N = normality of AgNO 3 . The tubing is thoroughly dried with nitrogen before the next analysis. Each day before the first sample, three empty clean test tubes are run as blanks to assure there is no residual hydrogen halide in the system. The M w values were obtained by GPC using a Waters model 510 HPLC pump and, as detectors, a Waters Refractive Index Detector, Model 410 and a Precision Detector Light Scattering Detector, Model PD2000. The columns were Waters, μStyragel, 500A, 10,OOθA and 100,000 A. The autosampler was a Shimadzu, Model Sil 9A. A polystyrene standard (M w = 185,000) was routinely used to verify the accuracy of the light scattering data. The solvent used was tetrahydrofuran, HPLC grade. The test procedure used entailed dissolving 0.015-0.020 g of sample in 10 mL of THF. An aliquot of this solution is filtered and 50 μL is injected on the columns. The separation was analyzed using software provided by Precision Detectors for the PD 2000 Light Scattering Detector. The calculated theoretical M w values were obtained in accordance with the equation: Theoretical M w BrPS = M W PS + (M... PS)(Atom. wt. Br - Atom, wt. H)(Mol. wt. Stv.)(0.01)(wt% Br) (Atom. wt. Br )(Mol. wt Sty.) - (Atom. wt. Br - Atom. wt. H)(Mol. wt. Sty.)(0.01)(wt% Br) As used throughout this application, "PS" is used interchangeably with and meant to designate polystyrene, while "Sty" means styrene. The term "M w " means weight average molecular weight as determined by GPC (light scattering detector) described supra. Substrate Polymer, Other Components. Proportions Particular thermoplastics with which the foregoing brominated styrenic polymers can be blended pursuant to further embodiments of this invention include polyethylene terephthalate, polybutylene terephthalate, polycyclohexylene dimethylene terephthalate, polytrimethylene terephthalate, blends or mixtures of two or more of these, and analogous copolymeric thermoplastic polyesters, especially when filled or reinforced with a reinforcing filler such as glass fiber. Preferred thermoplastic polyesters are polyethylene terephthalate and polybutylene terephthalate. Poly amide thermoplastics, such as poly amide 6, poly amide 6,6, or poly amide 12, again preferably when glass filled, can also be effectively flame retarded in like manner. Conventional additives, such as flame retardant synergists, antioxidants, UV stabilizers, dyes, pigments, impact modifiers, fillers, acid scavengers, plasticizers, flow aids, blowing agents, and the like, can be included with the formulations as is appropriate. Preferred polymer blends of this invention do contain a flame retardant synergist or glass fiber filler or reinforcement, and most preferably both a synergist, and a reinforcing fiber and/or filler. The brominated styrenic polymer flame retardants of this invention are used in flame retardant amounts, which typically are within the range of from 5 to 20 wt%, the wt% being based on the total weight of the thermoplastic polymer formulation or blend. When used, the amount of reinforcing fillers such as glass fiber will typically be in the range of up to about 50 wt% based on the total weight of the finished composition. The amount of flame retardant synergist, when used, such as antimony trioxide, antimony pentoxide, sodium antimonate, potassium antimonate, iron oxide, zinc borate, or analogous synergist generally will be in the range of up to about 12 wt% based on the total weight of the finished composition. Masterbatch compositions wherein the components except for the substrate thermoplastic polymer are in suitable relative proportions but are blended in a smaller amount of the substrate polymer, are also within the scope of this invention. Thus this invention includes compositions which comprise at least one thermoplastic polymer such as a polyalkylene terephthalate or a nylon polymer with which has been blended a brominated styrenic polymer (preferably a brominated polystyrene) of this invention in a weight ratio (substrate polymer: brominated polystyrene) in the range of, say, 1:99 to 70:30. Such masterbatch blends need not, but may also contain filler or reinforcing fiber and/or at least one flame retardant synergist such as iron oxide, zinc borate, or preferably an antimony oxide synergist such as antimony trioxide, antimony pentoxide, sodium antimonate, or potassium antimonate. Typical examples of reinforcing agents or fillers that can be used include low-alkali E-glass, carbon fibers, potassium titanate fibers, glass spheres or microballoons, whiskers, talc, wollastonite, kaolin, chalk, calcined kaolin, and similar substances. Sizing agents can be used with such reinforcing agents or fillers, if desired. A number of suitable glass-filled polyalkylene terephthalates or nylon molding compositions are available on the open market, and these can be used in preparing the compositions of this invention. Also provided by this invention are additive blends composed of a brominated styrenic polymer of this invention and a synergist such as, for example, a blend of 75 parts by weight of a brominated polystyrene and 25 parts by weight of a synergist such as antimony trioxide, antimony pentoxide, sodium antimonate, potassium antimonate, iron oxide, zinc borate, or analogous synergist. Typically such blends will contain in the range of 70 to 98 parts by weight of the brominated polystyrene and 30 to 2 parts by weight of the synergist, with the total of the two components being 100 parts by weight. Suitable amounts of other suitable additive components can also be included in such additive blends. Various known procedures can be used to prepare the blends or formulations constituting such additional compositions of this invention. For example the polyalkylene terephthalate polymer or a nylon polymer and the brominated styrenic polymer such as brominated polystyrene and any other components or ingredients to be incorporated into the finished blend can be blended together in powder form and thereafter molded by extrusion, compression, or injection molding. Likewise the components can be mixed together in a Banbury mixer, a Brabender mixer, a roll mill, a kneader, or other similar mixing device, and then formed into the desired form or configuration such as by extrusion followed by comminution into granules or pellets, or by other known methods. The following Examples are presented for purposes of illustration and are not to be construed as imposing limitations on the scope of the invention. Examples 1-3 give preferred general procedures for producing brominated polystyrene of this invention. EXAMPLE 1 A mixture of 770.0 g bromochloromethane (BCM, 9 ppm water) and 2.775 g powdered A1C1 3 was prepared in a 5-L jacketed glass reactor equipped with a mechanical paddle stirrer, condenser, and thermowell. A jacketed glass mixing tee was mounted on an inlet port on the reactor to which bromine (533.35 g, 3.337 mole) and a solution of 134.00 g (1.287/n mole) polystyrene (Mitsubishi Kasei Polytex, M w = 270,000) in 1204 g BCM were pumped at average rates of 8.74 g/min and 20.27 g/min, respectively. The reactor and mixing tee were cooled with a circulating glycol bath to maintain a temperature of 0°C to 2°C throughout the 1 hour feed time and subsequent 1 hour cook. The reaction mixture was then washed with water and neutralized with a mixture of aqueous sodium gluconate, sodium sulfite, and sodium hydroxide. After diluting the organic phase with additional BCM (1450 g), the solution was added dropwise to 1.8 L hot (90°C-94°C) water containing 0.25 g dioctyl sulfosuccinate sodium salt (surfactant) to precipitate the product and distill the solvent. The slurry was filtered and the off-white solid was washed with water. Drying to constant weight at 150 °C gave 389.8 g. The product contained 69.5% total bromine and 1300 ppm hydrolyzable bromine. EXAMPLE 2 A 7.209 g (54.1 mmol) portion of powdered aluminum chloride was suspended (stirred at 250 rpm) in 1549.83 g of dry (10 ppm water) bromochloromethane (BCM) in a 5-L jacketed reaction flask cooled to 0°C by a circulating glycol bath. A 10.00 wt% solution of PS (360.96 g, 3.4657/n mol) in dry BCM (3250.44 g) was prepared in a second 5-L flask. The PS used was Dow Styron ® 612 which had a M w of 190,000. The PS solution was pumped from the bottom valve of this feed reservoir to a jacketed, glycol-cooled mixing tee mounted on the reaction flask. At the same time, bromine was pumped from a tared feed reservoir to the same mixing tee where it combined with the polystyrene solution before dropping into the stirred catalyst suspension in the reaction flask. Two Masterflex ® 7550-90 pumps were used. The PS feed system used an all-Teflon feed line with pump head 77390 operating at a constant speed of 60 rpm. This provided a constant feed rate of 21.02/n mmol PS/min (21.89 g/min) . The bromine feed system used a combination of Teflon and Viton tubing with pump head 7518-10 operating at a rate of 70.05 mmol/min for the first 18 min, 38.80 mmol/min for 18-23 min, and 56.75 mmol/min for 23-165 min. Both feeds ended at 165 min. The overall mole ratio of Br 2 /PS was 2.70. A rinse of 260.95 g of dry BCM was used for the PS solution feed system to assure complete transfer of the polymer to the reaction flask. The reaction temperature was maintained at 0°C to 4°C throughout the addition and subsequent 2.3 hour cook period (with nitrogen purge of the reactor overhead). The weight increase for the caustic exit gas scrubber was 665.4 g (87.8% of theory for HBr). The catalyst was deactivated by addition of 125.0 g of a 10 wt% aqueous solution of sodium gluconate. A 63.41 g portion of 10 wt% aqueous sodium sulfite was added, and the pH was adjusted to 14 by addition of 423.0 g of 10 wt% aqueous NaOH. After dilution with BCM (1334.6 g), the organic phase was separated and then washed with water (1011.8 g). The product was recovered from the organic phase by addition to vigorously stirred hot (90°C-94°C) water to which was added 1.23 g of the sodium salt of dioctyl sulfosuccinate. The solvent distilled from the hot water leaving a slurry of brominated polystyrene product in water. After suction filtering, the off-white solid was rinsed with water and dried to a constant weight of 1085.98 g (97.9% yield) in a vacuum oven (150°C/2 torr/5 hr). The ionic bromine content of the brominated polystyrene so produced was only 88 ppm by weight. EXAMPLE 3 The procedure of Example 2 was followed except that: a 2-L flask and 40 g of polystyrene were used; the A1C1 3 wt% (based on polystyrene) was 2.0 wt%; the feed mole ratio of bromine to polystyrene was 3.33; the total equivalents of bromine was 2.78; the temperature range was 0°C to 5°C; the feed times for the bromine/polystyrene was 32 min/38 min; and the cook time was 150 minutes. Example 4, wherein all parts are by volume unless otherwise specified, illustrates a preferred purification process for removing ionic bromine from brominated polystyrene during the course of preparing the polymer. EXAMPLE 4 A brominated polystyrene reaction mass (1500 parts), formed by reacting bromine with a 10 wt% solution of polystyrene in bromochloromethane (BCM) using aluminum chloride as catalyst, was quenched in 450 parts of water, and thoroughly mixed for 15 minutes. A sample of the quenched reaction mass (Sample A) was taken for use in the purification process described below. The aqueous and organic phases were allowed to settle and the aqueous phase was removed by decantation. The organic phase was then brought to pH 12 by the addition of 50 parts of fresh water and 25 parts of 25 wt% sodium hydroxide solution. This mixture was thoroughly mixed. Any residual bromine was scavenged by addition to the mixture of 1.7 parts of 6.9 wt% sodium borohydride in 23 wt% aqueous sodium hydroxide solution, followed by thorough mixing. A sample of the resultant organic phase (Sample B) was taken for recovery of the brominated polystyrene without use of the following purification process. Application of the purification process to Sample A was performed as follows: Sample A was poured into a 1000 mL glass separatory funnel. The aqueous and organic phases were allowed to separate for 5 minutes. The organic phase was removed from the bottom of the funnel (325.2 grams). The aqueous layer was recovered (71.0 grams). The organic phase was separated into two equal halves and placed into two 8-ounce jars. Fresh water was placed into each jar for a second water wash (46.1 grams). This water level is equivalent to a ratio of 850 parts of water to 1500 parts of reaction mass. Both jars were shaken for 30 minutes on a Burrell Wrist Action Shaker. The contents of both jars were poured into and combined in a 1000 mL separatory funnel and allowed to separate for 5 minutes. The organic phase was recovered from the bottom (319.5 grams), and 95.3 grams of aqueous phase remained in the funnel. Fresh water (12.8 grams) was added to the organic phase to assist in pH reading using strips of pH indicator paper. The pH of the organic phase was 5. The pH was raised to 14 by the addition of 25% by weight aqueous sodium hydroxide solution (2.4 grams). Excess bromine was scavenged by the addition of 6.9 wt% sodium borohydride in 23 wt% aqueous sodium hydroxide solution (0.5 gram) . The brominated styrene product from Sample A was recovered by precipitation into a mixture formed from 1500 grams of water and 12.6 grams of 25% by weight aqueous sodium hydroxide solution. In conducting this precipitation operation, the water-sodium hydroxide mixture was in a 3000 mL glass reactor, with baffles, and was heated to 100°C. The vessel was stirred by an agitator set on 500 rpm. The organic phase was fed into this reactor by a peristaltic pump, set on 42 rpm through 1/8" polypropylene tubing into the water. The feed point was approximately 1/2" underneath the water surface. The BCM was condensed and removed overhead. After the organic phase was fed, the water temperature was allowed to return to 100°C to remove any residual BCM and then cool. The brominated polystyrene product was vacuum filtered in a 2000 mL fritted glass filter. It was washed three times with approximately 1000 mL of warm water. The solids were dried in a vacuum oven at 140°C overnight. The ionic bromine level detected in the final brominated polystyrene product from Sample A was 222 ppm. The brominated polystyrene product from Sample B, without use of the above purification process, was recovered by use of the foregoing precipitation procedure. The precipitation used 1500 grams of water and 13.0 grams of 25% by weight sodium hydroxide aqueous solution followed by three washings with warm water. The ionic bromine level detected in the final brominated polystyrene product recovered from Sample B was 1810 ppm. In carrying out the purification process illustrated in Example 4, effective use can be made of coalescing filters and/or a liquid-liquid extraction column. The principles involved in the design and operation of such equipment is known and reported in the literature. Anyone interested in pursuing such information can refer, for example, to I. Bartik, Liquid/Liquid Separation Through The Use of Coalescence, a paper presented on February 8, 1977 at The Filtration Society, New England Chapter, Sturbridge, Massachusetts 01566; and McCabe and Smith, Unit Operations of Chemical Engineering, Third Edition, McGraw-Hill Book Company, pages 619-627; or other similar sources. In using a liquid-liquid extraction tower the water should be introduced into the column below the incoming countercurrent flow of the crude organic phase to the tower, so that the water extract is taken from the upper portion of the tower and the extracted organic phase is removed from the lower portion of the tower. Comparative Examples CE-1 and CE-2 describe the preparation of brominated polystyrene in accordance with the teachings of U.S. Pat. No. 5,532,322, which issued in 1996. COMPARATIVE EXAMPLE CE-1 A solution of 75.10 g (0.721/n mole) of polystyrene (Mitsubishi Kasei Polytex, M w = 270,000) in 750 g of 1 ,2-dichloroethane (EDC, containing 12 ppm water) was prepared in a 5-L jacketed glass reactor equipped with a mechanical paddle stirrer, condenser, and thermowell. The temperature of the reaction was controlled with an ethylene glycol circulating bath on the reactor jacket. After cooling to 15 °C, 11.03 g of antimony (III) oxide was added to the polystyrene solution. A previously prepared solution of 149.7 g (0.937 mole) bromine and 66.3 g (0.935 mole) chlorine in 505 g cold (-5 °C) EDC was added to the reactor under the liquid surface through a diptube attached to the cooled bromine chloride feed reservoir. The reaction temperature was slowly increased from 10 °C to 25 °C during the 2 hour addition. The mixture was then held at 30 °C until hydrogen halide evolution was complete (1.5 hr) as indicated by an end of the weight gain of the caustic scrubber on the exit gas line from the reactor. The reaction mixture was washed with water and neutralized with aqueous sodium sulfite and caustic. The organic phase was then added dropwise to 3.5 L methanol to precipitate the product. The slurry was filtered and the solid was washed with methanol. After vacuum drying at 150 °C, the light yellow solid (product 1) weighed 203.7 g. COMPARATIVE EXAMPLE CE-2 Comparative Example CE-1 was repeated using 230.8 g (2.00 mole) commercial bromine chloride with 80.20 g (0.770/n mole) polystyrene and 11.77 g Sb 2 O 3 . The water washed and neutralized organic phase was divided into two equal portions. One portion was added to 1.5 L of methanol as in Example CE-1 to obtain 101.6 g of light yellow solid (product A) after drying to constant weight at 150 °C. The other portion was added dropwise to 1.9 L of hot (89°C-94°C) water to precipitate the product and distill the solvent. The dry light yellow solid (product B) weighed 100.3 g. In Table 1 a compilation of the properties of the brominated polystyrene products produced in Examples 1-3 and CE-1 and CE-2 is given. In addition, the properties of Pyro-Chek 68PB flame retardant of Ferro Corporation are given. Pyro-Chek 68PB flame retardant is believed to be produced in accordance with the teachings of U.S. 4,352,909. TABLE 1 1 Determined by use of the method of U.S. Pat. No. 5,637,650 as described above. 2 Calculated Theoretical M w for Pyro-Chek 68PB could not be determined since the M w of the polystyrene reactant used in 68PB is not known. 3 Tg = glass transition temperature. Examples 5, 6, and 7 illustrate additional procedures by which brominated polystyrenes of this invention can be prepared. EXAMPLE 5 A 0.910 g (6.82 mmol) portion of powdered aluminum chloride was suspended (stirred at 250 rpm) in 190 g of dry (13 ppm water) bromochloromethane (BCM) in 1-L jacketed flask cooled to 0°C by circulating glycol bath. A 419.86 g portion of a 10.00 wt% solution of polystyrene (403.1/n mmol) in dry BCM was pumped at a constant rate of 8.46 g/min (8.13 mmol/min) to a jacketed, gly col-cooled mixing tee mounted on the reaction flask. At the same time, bromine was pumped at a constant rate of 6.09 g/min (38.1 mmol/min) to the same mixing tee where it combined with the polystyrene solution (feed mole ratio of Br 2 /PS is 4.69) before dropping into the stirred catalyst suspension in the reaction flask. The bromine feed was stopped after 30.0 min (1143.5 mmol) and the polystyrene solution feed was stopped after 49.6 minutes (overall mole ratio of Br 2 /PS is 2.84). A rinse of 160 g of dry BCM was used for the polystyrene solution feed system to assure complete transfer of the polymer to the reaction flask. The reaction temperatare was maintained at 0°C-5°C throughout the addition and subsequent 2 hr cook period. The catalyst was deactivated by addition of 16.4 g of 10 wt% aqueous solution of sodium gluconate, and pH was adjusted to 14 by addition of 60.7 g of 10 wt% aqueous NaOH. The reaction mixture was washed with 10 wt% aqueous sodium sulfite followed by a water wash. The product was recovered from the organic phase by addition to vigorously stirred hot (90°C) water containing 0.02 wt% dioctyl sulfosuccinate sodium salt surfactant. The solvent is distilled from the hot water leaving a slurry of the brominated polystyrene product in water. After filtering, the powdery solid was rinsed with water and dried to constant weight in a vacuum oven (150°C/2 torr/5 hr). The dry solid weighed 127.08 g (95% yield). The product contained 69.6 wt% total Br. In the thermal stability test referred to above, the product evolved 174 ppm of HBr in 15 minutes at 300 °C. The Hunter Lab solution color (10 wt% in chlorobenzene) values were L = 94.58, a = -2.79, b = 17.29, Delta E = 18.34. EXAMPLE 6 A Y-shaped mixing apparatus having a cooling jacket was equipped with 2 feed lines, each connected to a pump. One of the feed lines was for delivering bromine and the other was for delivering a PS and BCM solution. Bromine (93.3 g, 31.3 mL or 0.583 mole), delivered at a rate of 1 mL/min (19.4 mmol/min), and a PS/BCM solution (22.4 g PS, 0.215 mol and 97 mL or 194 g of anhydrous BCM), delivered at 4 mL/min (7.17 mmol/min), were fed simultaneously from their respective feed lines into the cooled (5°C) Y-mixing apparatus. The resultant intimate mixture from the mixing apparatus was then fed into a cooled (5 °C) suspension of 0.45 g (2 wt% based on PS) of powdered aluminum chloride in 49 mL (98 g) of anhydrous BCM. Evolved HBr was scrubbed by a caustic solution during the reaction. The feeds were complete in 35 minutes and the mixture was cooked for 2 hours at 5°C. After water and sodium sulfite washes, solid BrPS was isolated by precipitating from 500 mL of hot (90 °C) water as described above. A total of 66 g of BrPS (97% yield) was obtained. The product contained 68.4 wt% total Br. In the thermal stability test referred to above, the product evolved 71 ppm of HBr in 15 minutes at 300°C. The HunterLab solution color (10 wt% in chlorobenzene) values were L = 96.74, a = -1.90, b = 15.99, Delta E = 16.44. EXAMPLE 7 A 0.910 g (6.82 mmol) portion of powdered aluminum chloride is suspended (stirred at 250 rpm) in 190 g of dry (13 ppm water) bromochloromethane (BCM) in 1-L jacketed flask cooled to 0°C by circulating glycol bath. A 419.86 g portion of a 10.00 wt% solution of polystyrene (403.1/n mmol) in dry BCM is pumped at a constant rate of 8.46 g/min (8.13 mmol/min) to a jacketed, gly col-cooled mixing tee mounted on the reaction flask. At the same time, bromine is pumped at a constant rate of 6.09 g/min (38.1 mmol/min) to the same mixing tee where it is combined with the polystyrene solution (feed mole ratio of Br 2 /PS is 4.69) before dropping into the stirred catalyst suspension in the reaction flask. The bromine feed is stopped after 30.0 min (1143.5 mmol) and the polystyrene solution feed is stopped after 30 minutes (overall mole ratio of Br 2 /PS is 2.84). A rinse of 160 g of dry BCM is used for the polystyrene solution feed system to assure complete transfer of the polymer to the reaction flask. The reaction temperature is maintained at 0 °C-5 °C throughout the addition and subsequent 45 minute cook period. The catalyst is deactivated by addition of 16.4 g of water. The crude organic and aqueous phases are allowed to settle, and the aqueous acidic phase is removed. Then the pH is adjusted to 14 by the addition of 10 wt% aqueous NaOH, and sodium borohydride is added to scavenge any excess bromine. The product is then recovered from the organic phase by addition to vigorously stirred hot (90 °C) water. The solvent is distilled from the hot water leaving a slurry of the brominated polystyrene product in water. After filtering, the powdery solid is rinsed with water and dried to constant weight in a vacuum oven (150°C/2 torr/5 hr). Examples 8-21 illustrate additional preferred procedures for producing brominated polystyrenes of this invention. EXAMPLES 8-21 The following procedure was used in these Examples: A mixture of 1.44 g (10.8 mmol) of aluminum chloride (Aldrich, anhydrous) and 310 g of dry (10-60 ppm water after drying over (S) molecular sieves) bromochloromethane (BCM) was stirred at 350 rpm with a paddle of Teflon polymer in a 1-L three-necked jacketed round bottom flask. The flask contents were cooled to the desired temperature by circulating chilled ethylene glycol through the jacket. A 10 wt% solution of Dow Styron 612 polystyrene (72.2 g; 0.69 equivalents) in dry BCM (650g) was charged to a separate vessel (500 mL graduated addition funnel). The polystyrene solution was pumped from the bottom of this feed reservoir to a vacuum jacketed mixing tee mounted on the reaction flask. The tee was maintained at the same temperature as the reaction mixture by circulating the ethylene glycol exiting from the flask to the tee. As the polystyrene solution was pumped from the reservoir, bromine (295.5 g; 1.85 mol) was simultaneously pumped from a 125-mL graduated addition funnel to the same mixing tee where it combined with the polystyrene solution. The resulting red solution flowed through the jacketed, spiral column (approximately 12" in length) and exited above the surface of the stirred catalyst suspension. Two Masterflex pumps were used for the feed to the mixing tee. The polystyrene system used an all Teflon line with a Cole-Palmer 77390 pump head. The bromine feed system used a combination of Teflon and Viton tubing with the latter being used with a Masterflex 7518-10 pump head. Both feeds ended in approximately 32-35 minutes. Constant attention to feed rates was necessary in order to achieve complete addition simultaneously. The overall mole ratio of Br 2 /PS was 2.7. A rinse of 57 g of dry BCM was used for the polystyrene solution feed system to assure complete transfer of the polymer to the reaction flask. After the addition was complete, the reaction was stirred at temperature for 45 minutes while being swept with nitrogen and was then quenched by the addition of 13 g of a 10 wt% solution of sodium sulfite. During the quench the material was stirred at 450 rpm and was stirred at this rate for 5 minutes. The reaction color changed from red/brown to a cream (light tan) during the sulfite addition. The reaction was allowed to stand for 5 minutes and the phases were separated using a bottom valve on the reaction flask. After removing the aqueous phase from the reactor, the organic layer was returned to the reactor and the pH was adjusted to 14 with the use of 10 wt% aqueous NaOH (100-200 g). Additional BCM (267 g) was added, the mixture was transferred to a separatory funnel, and the phases were allowed to separate. Product was recovered from the organic phase by addition to hot water as follows. A 2-L three-necked creased flask equipped with a mechanical stirrer, 125 mL addition funnel, thermometer, and Dean-Stark trap with a condenser was charged with 700 mL of water and heated to 92-94 °C with a heating mantle. The addition funnel was filled with the contents from the bottom phase of the separatory funnel. The feed rate from the addition funnel was controlled so that the condenser on the Dean-Stark trap was not overloaded and so that the water temperature did not fall below 91 °C. BCM and some water were removed overhead while the product precipitated in the water as white to yellowish- white solids. The addition funnel was refilled as necessary to have a continuous flow of material to the flask. After the addition was complete, the slurry was stirred at temperature for about 10 minutes to ensure complete removal of BCM. The slurry was allowed to cool to about 65 °C and collected on a Buchner funnel using suction filtration through #2 filter paper. About 300 mL of hot water was used to rinse the flask and the filter cake. The solids were transferred to a 2-L beaker, thoroughly mixed with 400 mL of water and reisolated by suction filtration. The solids were air dried overnight and then dried at 150°C in a vacuum oven (l-5mm Hg) until a constant weight (180-200 g) was achieved. The product was powdered with a mortar and pestle prior to analysis (see Table 2). TABLE 2 Determined by use of the method of U.S. Pat. No. 5,637,650 as described above Determined by use of the method of U.S. Pat. No. 5,637,650 as described above The ionic bromine content of the brominated polystyrene formed in Example 14 was measured and found to be only 320 ppm by weight. Commonly-owned application Serial No. 09/066,172, filed April 24, 1998, describes processes in which a suitable amount of aqueous base is employed to improve the thermal stability of the resultant brominated polystyrene. It is to be noted that the use of such processes, while desirable, is not required pursuant to this invention, as the excellent results referred to hereinabove were achieved without using brominated polystyrene formed in this way. Thus the process procedures which are fully described in this commonly-owned copending application, constitute optional, but entirely suitable procedures for producing brominated polystyrenes of the present invention. Inclusion of the suitable amount of inorganic alkali metal base such as NaOH or KOH into the brominated polystyrenes of Examples 8-21 is preferably accomplished substantially in the manner described in Example 22, infra, by utilizing a suitable excess of aqueous NaOH (or KOH) when precipitating the brominated polystyrene from BCM, and either eliminating the final water wash step or substituting an aqueous NaOH (or KOH) solution as the final wash. Alternatively, and less preferably, brominated polystyrenes formed as described in Examples 8- 21 in finely-divided or powder form can be powder blended with suitable quantities of powdered alkali metal base such as sodium hydroxide, sodium acetate, or potassium hydroxide. EXAMPLE 22 The procedure of Example 1 is repeated and in the step wherein the reaction mixture is washed with water and neutralized with a mixture of aqueous sodium gluconate, sodium sulfite, and sodium hydroxide, the amount of the aqueous sodium hydroxide is such that a dried sample of the brominated polystyrene composition produced in the process, when subjected to the following pH determination procedure, gives an aqueous extract having a pH of 9.3. The procedure for determining pH of the brominated polystyrene composition is as follows: Place in a beaker 1 gram to 1.5 grams of a representative sample, weighed to the nearest 0.1 gram, and dissolve same in 50 mL of BCM. Then add 50 mL of water which has been boiled to remove carbon dioxide and has a pH of 7. Vigorously stir the resultant mixture with a magnetic stirrer such that the two liquid phases are intimately mixed for 2 to 5 minutes. Then reduce the stirrer speed such that the two phases separate in the beaker, and lower the pH electrode in the upper layer only. Measure the pH of the upper layer using a Hach EC- 10 pH meter (or equivalent) that has been calibrated the same day. THE SECOND ASPECT OF THIS INVENTION - FURTHER DESCRIPTION Except as otherwise described below, the materials, facilities, operating conditions, analytical methods, test conditions, substrate polymers, proportions, and all other details of the second aspect of the invention are as described above in connection with the first aspect of this invention. Brominated Styrenic Polymers The brominated styrenic polymers of this aspect (preferably a brominated polystyrene) have a total bromine content in the range of 60 to 66 wt%, more preferably from 60 to 65 wt% , and most preferably from 60 to 64 wt% . In addition, the brominated styrenic polymers, preferably brominated polystyrenes, of this invention have a specified minimal total chlorine content, if any; a specified GPC weight average molecular weight (M w ); a specified DSC glass transition temperature (Tg); and a specified thermal stability in the Thermal Stability Test, all as set forth above in the Summary of the Invention. With reference to Formula (I) above, the identity of each X for each polymer unit of the polymers of the second aspect is such that the brominated polystyrene contains substantially less than about 5000-6000 ppm of X-type halide atoms, and wherein the value of n for each polymer unit is such that the brominated polystyrene contains in the range of 60 to 66 wt% bromine (n = 1.9 to 2.5). From an economic and performance standpoint, it is preferred that the bromine content be within the range of from 60 wt% to 65 wt% (n = 1.9 to 2.4), and especially within the range of from 60 to 64 wt% (n = 1.9 to 2.3. Preferably the brominated polystyrene polymers are those in which the chlorine content is less than 500 ppm and most preferably less than 100 ppm in accordance with X-Ray Fluorescence analysis. The following Examples are presented for purposes of illustrating the second aspect of this invention, and are not to be construed as imposing limitations on the scope of the invention. In Examples 23 and 24 a co-feed procedure was employed whereas Examples 25-30 were conducted using a pre-mix procedure. See in this connection U.S. Pat. No.5, 767, 203. EXAMPLE 23 Aluminum chloride (4.804 g, 36.0 mmol, 1.2 wt% based on PS) was combined with anhydrous bromochloromethane (BCM, 1824.6 g) in a 5-L five-necked fully jacketed reaction flask. After cooling the stirred mixture to -2°C with a glycol circulating bath, a 42 mL (0.815 mol) portion of bromine (Aldrich, 99.5 %) was pumped into the flask from a 500-mL graduated addition funnel containing a total of 1273.92 g (7.972 mol) bromine. A solution of 415.2 g (3.986 mol based on styrene repeat unit) of polystyrene (Dow Styron ® 612, M w = 190,000) in 3735.6 g anhydrous BCM was pumped into the vigorously stirred reaction mixture in 192 minutes (average rate of 21.6 g/min), while at the same time, the remaining bromine (370 mL) in the addition funnel was pumped to the reaction flask as a separate stream (average rate of 5.97 g/min). The reaction mixture was held between -3°C and 0°C during the co-feed and subsequent 1 hr cook period. Water was then added to destroy the catalyst followed by 10 wt% aqueous Na 2 SO 3 and 10 wt% aqueous NaOH. The organic phase was separated and washed with water. Product was recovered from the organic phase by addition to hot (88-92°C) water which caused the solvent to distill leaving a slurry of solid brominated polystyrene in water. The slurry was suction filtered. The wet cake was rinsed with water and then dried to a constant weight in a vacuum oven (150°C/2 torr) to obtain 1017.9 g (97% yield) of white brominated polystyrene product. EXAMPLE 24 The bromination of PS was repeated substantially as described in Example 23 except that this reaction was performed in a 3-Liter reactor with appropriate adjustments in the amounts of materials fed into the reactor. EXAMPLE 25 A Y-shaped glass mixing apparatus having a jacket for circulating coolant was equipped with two feed lines, each connected to a pump. One of the feed lines was for delivering bromine, and the other was for delivering a solution of PS in BCM. Bromine (1253.2 g, 7.842 mol) and a PS/BCM solution (404.9 g Styron ® 612 PS in 3604.3 g anhydrous BCM) were pumped simultaneously into the cooled (0°C) Y-mixing apparatus that was mounted on a 5-L five-necked fully jacketed reaction flask. The intimate cooled mixture of bromine/PS/BCM that formed in the mixer dropped into the reaction flask where it combined with a stirred mixture of anhydrous A1C1 3 (4.91 g, 1.2 wt% based on PS) and anhydrous BCM (1675.0 g) that was held at -2°C to 0°C by a circulating cooler. Both feeds were completed in 120 minutes for an average feed rate of 10.44 g/min for bromine and 33.4 g/min for PS/BCM. After stirring for 5 minutes at 0°C, the catalyst was destroyed by addition of water. The mixture was treated with 10 wt% aqueous Na 2 SO 3 and neutralized with 10 wt% aqueous NaOH. The organic phase was separated and washed with water. The product was isolated by feeding the organic phase to hot (88-92°C) water to distill the solvent and form a slurry of solid brominated polystyrene in water. After suction filtration, the solid was rinsed with water and dried in a vacuum oven to obtain 991.1 g (96% yield) of white product. EXAMPLES 26-30 In each of these Examples the general procedure of Example 25 was utilized. In Examples 26-30 the amount of bromine used was increased from 1253.2 g (7.842 mol), to 1347.4 g (8.431 mol), 1500.2 g (9.388 mol), 1509.9 g (9.448 mol), 1653.3 g (10.346 mol), and 1659.6 g (10.385 mol), respectively. Also appropriate adjustments were made in the rate of bromine delivery (matching the PS/BCM delivery time in each run). Table 3 summarizes the bromination reaction conditions used in Examples 23-30, and Table 4 sets forth analytical data for the respective products of Examples 23-30. -» O J-» The excellent melt stability characteristics of brominated styrenic polymers of this second aspect of the invention are illustrated by capillary rheometry melt stability tests in which the melt viscosities of a blend of glass-filled nylon 6,6 and a brominated polystyrene of this invention were determined and compared to the melt flow characteristics of the same glass-filled nylon 6,6 devoid of the brominated polystyrene. The base nylon 6,6 mixture was composed of 70 wt% nylon 6,6 and 30 wt% glass fibers. The composition of this invention was made by blending 19.85 wt% of brominated polystyrene of this invention containing 61.5 wt% of bromine. The tests were performed on a Kayeness LCR 6000 Capillary Rheometer, operating at at 285 °C at a shear rate of 500 1/sec. The die on the capillary rheometer had a diameter of 1 mm and a length of 20 mm. Approximately 12 grams of extruded pellets were forced into the heated capillary. This material was allowed to preheat for 6 minutes. The packing force placed on the material was 991 N. At the end of the 6 minute preheat, the material was forced through the die form a ram starting position of 100 mm to a ram position of 120 mm. The ram was moving at a rate of 41 mm/min. This took approximately 30 sec. During this time, the Viscosity of the material, the Stress and Force were measured. After the 6 minutes, the material was forced through the die from a ram position of 120 mm to 140 mm (same rate each time). Again the Viscosity, Stress, and Force were measured. This cycle went on for a total of five measurements, which amounted to 32.4 minutes in the capillary. The data points were as follows: Glass-filled Nylon 6.6 Formulation: Ram Position = 120 mm, Time = 6.5 min. , Viscosity = 208.8 Pa-s Ram Position = 140 mm, Time = 13.0 min. , Viscosity = 203.2 Pa-s Ram Position = 160 mm, Time = 19.4 min. , Viscosity = 210.2 Pa-s Ram Position = 180 mm, Time = 25.9 min. , Viscosity = 207.8 Pa-s Ram Position = 200 mm, Time = 32.4 min. , Viscosity = 185.2 Pa-s Glass-filled Nylon 6.6 Formulation Containing Brominated Polystyrene Low Br Sample, 62% Br Ram Position = 120 mm, Time = 6.5 min. , Viscosity = 181.8 Pa-s Ram Position = 140 mm, Time = 13.0 min. , Viscosity = 174.1 Pa-s Ram Position = 160 mm, Time = 19.4 min. , Viscosity = 169.2 Pa-s Ram Position = 180 mm, Time = 25.9 min. , Viscosity = 153.4 Pa-s Ram Position = 200 mm, Time = 32.4 min. , Viscosity = 151.3 Pa-s It can be seen from the above data that in all instances the blend of this invention containing the brominated polystyrene had lower viscosity indicating better melt flow, and equivalent melt stability than the same formulation devoid of the brominated polystyrene. THE THIRD ASPECT OF THIS INVENTION - FURTHER DESCRIPTION Except as otherwise described below, the materials, facilities, operating conditions, analytical methods, test conditions, proportions, and all other details of the third aspect of the invention are as described above in connection with the first aspect of this invention. Thermoplastic Polymer Components Various thermoplastic polymers such as polyolefin polymers, styrenic polymers, ABS, and other similar thermoplastics can be flame retarded pursuant to this third aspect of the invention. Examples of polyolefin polymers that can be flame retarded include 1-olefin homopolymers such as polyethylene, polypropylene, polybutene, and copolymers of ethylene and/or propylene with one or more higher 1-olefins and/or diolefinic monomers. Polystyrene, whether rubber modified or not, and copolymers of two or more styrenic monomers such as styrene, alpha-methylstyrene, vinylnaphthalene, homopolymers of ring alkyl-substituted vinylaromatic monomers such as individual or mixed ar-methylstyrene isomers, individual or mixed ar-ethylstyrene isomers, individual or mixed ar-methyl isomers of alpha-methylstyrene, and copolymers of two or more such vinylaromatic monomers serve as examples of styrenic polymers that can be flame retarded pursuant to this aspect of the invention. Preferred compositions are those in which the substrate polymer being flame retarded is an engineering thermoplastic polymer, such as polyethylene terephthalate, polybutylene terephthalate, polycyclohexylene dimethylene terephthalate, nylon, and the like, especially when filled or reinforced with a reinforcing filler such as glass fiber. Pursuant to the most preferred embodiments of this invention, the engineering thermoplastic substrate is a nylon engineering thermoplastic (a.k.a. polyamide), such as polyamide 6, polyamide 6-6, polyamide 12, polyamide 4-6, and equivalent thermoplastic polyamides, including blends of two or more such thermoplastic polyamide resins. Suitable nylon engineering thermoplastics which can be used in the practice of this invention are available as articles of commerce. Components referred to by chemical name or formula anywhere in the specification or claims hereof, whether referred to in the singular or plural, are identified as they exist prior to coming into contact with another substance referred to by chemical name or chemical type (e.g. , another component or a solvent). It matters not what preliminary chemical changes, transformations and/or reactions, if any, take place in the resulting mixtare or solution as such changes, transformations, and/or reactions are the natural result of bringing the specified components together under the conditions called for pursuant to this disclosure. Thus the components are identified as ingredients to be brought together in connection with performing a desired operation or in forming a desired composition. Even though the claims hereinafter may refer to substances, components and/or ingredients in the present tense ("comprises" or "is"), the reference is to the substance, component or ingredient as it existed at the time just before it was first contacted, blended or mixed with one or more other substances, components and/ or ingredients in accordance with the present disclosure. The fact that a substance, component or ingredient may have lost its original identity through a chemical reaction or transformation during the course of contacting, blending or mixing operations, if conducted in accordance with this disclosure and with the application of common sense and the ordinary skill of a chemist, is thus wholly immaterial for an accurate understanding and appreciation of the true meaning and substance of this disclosure and the claims thereof. This invention is susceptible to considerable variation in its practice. Therefore the foregoing description is not intended to limit, and should not be construed as limiting, the invention to the particular exemplifications presented above. Rather, what is intended to be covered is as set forth in the ensuing claims.

Claims: THAT WHICH IS CLAIMED IS: 1. A brominated styrenic polymer that has: I) an ionic bromine content of 2000 ppm or less, and at least one of the following additional characteristics of a), b), and c): a) a TGA temperatare for 1 % weight loss which is 340 °C or higher and a chlorine content, if any, of less than about 700 ppm Cl; b) an actual M w which is within about 20% of its calculated theoretical M w , the theoretical M w being based upon the actual bromine content of the brominated styrenic polymer and the M w of the styrenic polymer reactant used to produce the brominated styrenic polymer; c) essentially no content of impurities selected from the group consisting of bromodichloroethane, dibromochloroethane, dibromodichloroethane, tribromochloroethane, and ethylene dichloride; or II) a bromine content in the range of 60 to 66 wt% bromine; a total chlorine content, if any, of less than 700 ppm; a GPC weight average molecular weight in the range of 500,000 to 800,000; a DSC glass transition temperature of less than 175°C; and a thermal stability in the Thermal Stability Test of 250 ppm HBr or less. 2. A brominated styrenic polymer of claim 1 that has an ionic bromine content of 2000 ppm or less, and at least one of said additional characteristics a), b), and c). 3. A brominated styrenic polymer of claim 2 wherein said ionic bromine content is 1500 ppm or less. 4. A brominated styrenic polymer of claim 2 wherein said ionic bromine content is 1000 ppm or less. 5. A brominated styrenic polymer of claim 2 wherein said polymer has at least two of said additional characteristics. 6. A brominated styrenic polymer of claim 2 wherein said polymer has all three of said additional characteristics. 7. A brominated styrenic polymer of claim 2 wherein said polymer has all three of said additional characteristics, and additionally has a thermal stability in the Thermal Stability Test of 1500 ppm HBr or less. 8. A brominated styrenic polymer of claim 2 wherein said polymer has a total bromine content of at least about 60 wt% . 9. A brominated styrenic polymer of claim 2 wherein said polymer has a total bromine content of at least about 67 wt%. 10. A brominated styrenic polymer of claim 2 wherein said polymer has at least the additional characteristics of a) with the proviso that the chlorine content, if any, is less than about 100 ppm Cl. 11. A brominated styrenic polymer of claim 10 wherein said ionic bromine content is 1000 ppm or less, and wherein said polymer has a thermal stability in the Thermal Stability Test of 1000 ppm HBr or less. 12. A brominated styrenic polymer of claim 10 wherein said ionic bromine content is 500 ppm or less, and wherein said polymer has a thermal stability in the Thermal Stability Test of 500 ppm HBr or less. 13. A brominated styrenic polymer of claim 2 wherein said polymer has at least additional characteristic b). 14. A brominated styrenic polymer of claim 13 wherein said ionic bromine content is 1000 ppm or less, and wherein said polymer has a thermal stability in the Thermal Stability Test of 1000 ppm HBr or less. 15. A brominated styrenic polymer of claim 13 wherein said ionic bromine content is 500 ppm or less, and wherein said polymer has a thermal stability in the Thermal Stability Test of 500 ppm HBr or less. 16. A brominated styrenic polymer of claim 2 wherein said polymer has at least additional characteristic c). 17. A brominated styrenic polymer of claim 16 wherein said ionic bromine content is 1000 ppm or less, and wherein said polymer has a thermal stability in the Thermal Stability Test of 1000 ppm HBr or less. 18. A brominated styrenic polymer of claim 16 wherein said ionic bromine content is 500 ppm or less, and wherein said polymer has a thermal stability in the Thermal Stability Test of 500 ppm HBr or less. 19. A brominated styrenic polymer of any of claims 10-18 wherein said polymer is a brominated polystyrene having a total bromine content of at least about 67 wt%. 20. A brominated styrenic polymer of claim 5 wherein said polymer has at least additional characteristics a) and b). 21. A brominated styrenic polymer of claim 5 wherein said polymer has at least additional characteristics a) and c). 22. A brominated styrenic polymer of claim 5 wherein said polymer has at least additional characteristics b) and c). 23. A brominated styrenic polymer of claim 2 wherein said polymer has at least additional characteristic c), and wherein the total chlorine content of said polymer, if any, is less than about 100 ppm Cl. 24. A brominated styrenic polymer of any of claims 20-23 wherein said polymer is a brominated polystyrene having a total bromine content of at least about 67 wt%, and wherein said ionic bromine content is 500 ppm or less. 25. A brominated polystyrene of claim 2 characterized in that it has: A) an ionic bromine content of 1000 ppm or less; B) a TGA temperature for 1 % weight loss which is 340 °C or higher; C) a chlorine content, if any, of less than about 100 ppm Cl; D) a thermal stability in the Thermal Stability Test of 1500 ppm HBr or less; E) an actual M w which is within about 20% of its calculated theoretical M w , the theoretical M w being based upon the actual bromine content of the brominated styrenic polymer and the M w of the styrenic polymer reactant used to produce the brominated styrenic polymer; and F) essentially no content of impurities selected from the group consisting of bromodichloroethane, dibromochloroethane, dibromodichloroethane, and tribromochloroethane . 26. A brominated polystyrene of claim 25 wherein said thermal stability in the Thermal Stability Test 1000 ppm HBr or less, wherein said actual M w is within about 10% of said calculated theoretical M w , and wherein said brominated polystyrene has a total bromine content of at least about 60 wt% . 27. A brominated polystyrene of claim 26 wherein said thermal stability in the Thermal Stability Test 500 ppm HBr or less. 28. A brominated polystyrene of claim 27 wherein said total bromine content is at least about 67 wt% . 29. A brominated styrenic polymer of claim 1 that has a bromine content in the range of 60 to 66 wt% bromine; a total chlorine content, if any, of less than 700 ppm; a GPC weight average molecular weight in the range of 500,000 to 800,000; a DSC glass transition temperature of less than 175 °C; and a thermal stability in the Thermal Stability Test of 250 ppm HBr or less. 30. A brominated styrenic polymer of claim 29 wherein said chlorine content, if any, is 500 ppm or less, and wherein said glass transition temperatare is 165°C or less. 31. A brominated styrenic polymer of claim 29 wherein said thermal stability is 150 ppm HBr or less. 32. A brominated styrenic polymer of claim 29 wherein said chlorine content, if any, is 500 ppm or less, wherein said glass transition temperatare is 165°C or less, and wherein said thermal stability is 150 ppm HBr or less. 33. A brominated styrenic polymer of claim 29 wherein said thermal stability is 100 ppm HBr or less. 34. A brominated styrenic polymer of claim 29 wherein said bromine content is in the range of 60 to 65 wt%, wherein said chlorine content, if any, is 500 ppm or less, and wherein said glass transition temperature is 160°C or less. 35. A brominated styrenic polymer of claim 29 wherein said bromine content is in the range of 60 to 65 wt%, wherein said glass transition temperatare is 160°C or less, and wherein said thermal stability is 100 ppm HBr or less. 36. A brominated styrenic polymer of claim 29 wherein said bromine content is in the range of 60 to 65 wt%, wherein said chlorine content, if any, is 500 ppm or less, wherein said glass transition temperatare is 160°C or less, and wherein said thermal stability is 100 ppm HBr or less. 37. A brominated styrenic polymer of claim 29 wherein said bromine content is in the range of 60 to 64 wt%, and wherein said GPC weight average molecular weight in the range of 500,000 to 700,000. 38. A brominated styrenic polymer of claim 37 wherein the chlorine content, if any, of said polymer is 500 ppm or less, and wherein the glass transition temperature of said polymer is 160°C or less. 39. A brominated styrenic polymer of claim 38 wherein the thermal stability of said polymer in the Thermal Stability Test is 100 ppm HBr or less. 40. A brominated styrenic polymer of claim 29 that has essentially no content of impurities selected from the group consisting of bromodichloroethane, dibromochloroethane, dibromodichloroethane, tribromochloroethane, methylene dichloride and ethylene dichloride. 41. A brominated styrenic polymer of any of claims 29, 32, 36, 38, or 40 wherein the content, if any, of ionic bromine in said polymer is 1000 ppm or less. 42. A brominated styrenic polymer of any of claims 29, 32, 36, 38, or 40 wherein the ΔE solution color value of said polymer if dissolved at the level of 10 wt% in chlorobenzene is in the range of from 2 to 15. 43. A brominated styrenic polymer of any of claims 29, 32, 36, 38, or 40 wherein said polymer has a TGA temperatare for a 1 % weight loss of at least about 320 °C, wherein the ΔE solution color value of said polymer if dissolved at the level of 10 wt% in chlorobenzene is in the range of from 2 to 15, and wherein the content, if any, of ionic bromine in said polymer is 1000 ppm or less. 44. A brominated styrenic polymer of claim 29 wherein said polymer is brominated polystyrene. 45. Brominated polystyrene of claim 44 wherein said chlorine content, if any, is 500 ppm or less, and wherein said glass transition temperature is 165°C or less. 46. Brominated polystyrene of claim 44 wherein said thermal stability is 150 ppm HBr or less. 47. Brominated polystyrene of claim 44 wherein said chlorine content, if any, is 500 ppm or less, wherein said glass transition temperatare is 165°C or less, and wherein said thermal stability is 150 ppm HBr or less. 48. Brominated polystyrene of claim 44 wherein said thermal stability is 100 ppm HBr or less. 49. Brominated polystyrene of claim 44 wherein said bromine content is in the range of 60 to 65 wt% , wherein said chlorine content, if any, is 500 ppm or less, and wherein said glass transition temperature is 160°C or less. 50. Brominated polystyrene of claim 44 wherein said bromine content is in the range of 60 to 65 wt% , wherein said glass transition temperature is 160°C or less, and wherein said thermal stability is 100 ppm HBr or less. 51. Brominated polystyrene of claim 44 wherein said bromine content is in the range of 60 to 65 wt%, wherein said chlorine content, if any, is 500 ppm or less, wherein said glass transition temperature is 160°C or less, and wherein said thermal stability is 100 ppm HBr or less. 52. Brominated polystyrene of claim 44 wherein said bromine content is in the range of 60 to 64 wt%, and wherein said GPC weight average molecular weight in the range of 500,000 to 700,000. 53. Brominated polystyrene of claim 52 wherein the chlorine content, if any, of said polymer is 500 ppm or less, and wherein the glass transition temperature of said polymer is 160°C or less. 54. Brominated polystyrene of claim 53 wherein the thermal stability of said polymer in the Thermal Stability Test is 100 ppm HBr or less. 55. Brominated polystyrene of claim 44 that has essentially no content of impurities selected from the group consisting of bromodichloroethane, dibromochloroethane, dibromodichloroethane, tribromochloroethane, methylene dichloride and ethylene dichloride. 56. Brominated polystyrene of any of claims 44, 47, 51, 53, or 55 wherein the content, if any, of ionic bromine in said polymer is 1000 ppm or less. 57. Brominated polystyrene of any of claims 44, 47, 51, 53, or 55 wherein the ΔE solution color value of said polymer if dissolved at the level of 10 wt% in chlorobenzene is in the range of from 2 to 15. 58. Brominated polystyrene of any of claims 44, 47, 51, 53, or 55 wherein said polymer has a TGA temperatare for a 1 % weight loss of at least about 320 °C, wherein the ΔE solution color value of said polymer if dissolved at the level of 10 wt% in chlorobenzene is in the range of from 2 to 15, and wherein the content, if any, of ionic bromine in said polymer is 1000 ppm or less. 59. A composition which comprises a thermoplastic polymer with which has been blended a flame retardant amount of a brominated styrenic polymer of claim 1. 60. A composition which comprises a thermoplastic polymer with which has been blended a flame retardant amount of a brominated styrenic polymer of claim 2. 61. A composition which comprises a thermoplastic polymer with which has been blended a flame retardant amount of a brominated styrenic polymer of claim 29. 62. A composition which comprises a thermoplastic polymer with which has been blended a flame retardant amount of a brominated polystyrene of claim 28 or 54. 63. A composition of claim 59 wherein said thermoplastic polymer is a glass-filled nylon polymer. 64. A composition of claim 62 wherein said thermoplastic polymer is a glass-filled nylon polymer. 65. A molded or extruded article or shape formed from a composition of claim 59. 66. A molded or extruded article or shape formed from a composition of claim 62. 67. A composition which comprises a thermoplastic polymer having blended therewith at least a flame retardant amount of brominated styrenic polymer having, prior to blending, a total bromine content of about 50 wt% or more, and at least two of (i), (ii), and (iii) where (i) is a TGA temperatare for 1 % weight loss which is 340 °C or higher, (ii) is a chlorine content, if any, of less than about 700 ppm, and (iii) is a hydrolyzable bromine content in the Hydrolyzable Bromine Test of 3600 ppm Br or less. 68. A composition of claim 67 wherein said brominated styrenic polymer has, prior to blending, at least (i) and (ii). 69. A composition of claim 68 wherein the brominated styrenic polymer has, prior to blending, a bromine content above about 60 wt%, and wherein the composition further comprises (A) a flame retardant synergist dispersed therein, or (B) a reinforcing amount of a reinforcing filler or fiber dispersed therein, or (C) both of (A) and (B). 70. A composition of claim 69 wherein the thermoplastic polymer is a thermoplastic polyamide, wherein said composition contains a flame retardant amount of the brominated styrenic polymer in the range of 5 to 20 wt% based on the total weight of the polymer blend. 71. A composition of claim 68 wherein the brominated styrenic polymer is a brominated polystyrene. 72. A composition of claim 71 wherein the brominated polystyrene has, prior to blending, a bromine content above about 60 wt% . 73. A composition of claim 72 wherein the thermoplastic polymer is a thermoplastic polyamide, wherein said composition contains a flame retardant amount of the brominated polystyrene in the range of 5 to 20 wt% based on the total weight of the polymer blend, and wherein the composition further comprises (A) a flame retardant synergist dispersed therein, or (B) a reinforcing amount of a reinforcing filler or fiber dispersed therein, or (C) both of (A) and (B). 74. A composition of claim 71 wherein the brominated polystyrene has, prior to blending, a bromine content at least in the range of 68-71 wt% . 75. A composition of claim 74 wherein the thermoplastic polymer is a thermoplastic polyamide, wherein said composition contains a flame retardant amount of the brominated polystyrene in the range of 5 to 20 wt% based on the total weight of the polymer blend, and wherein the composition further comprises (A) a flame retardant synergist dispersed therein, or (B) a reinforcing amount of a reinforcing filler or fiber dispersed therein, or (C) both of (A) and (B). 76. A composition of claim 67 wherein said brominated styrenic polymer has, prior to blending, at least (ii) and (iii). 77. A composition of claim 76 wherein said thermoplastic polymer is an engineering thermoplastic polymer, wherein said brominated styrenic polymer is a brominated polystyrene having, prior to blending, a total bromine content above about 60 wt% , and wherein said composition contains a flame retardant amount of the brominated polystyrene in the range of 5 to 20 wt% based on the total weight of the polymer blend. 78. A composition of claim 77 wherein said engineering thermoplastic polymer is a thermoplastic polyamide, and wherein said composition further comprises (A) a reinforcing amount of a reinforcing filler or fiber dispersed therein or (B) a flame retardant synergist dispersed therein, or (C) both of (A) and (B). 79. A composition of claim 76 wherein said total bromine content of is above about 67 wt%. 80. A composition of claim 79 wherein said thermoplastic polymer is an engineering thermoplastic polymer, wherein said brominated styrenic polymer is a brominated polystyrene, and wherein said composition contains a flame retardant amount of the brominated polystyrene in the range of 5 to 20 wt% based on the total weight of the polymer blend. 81. A composition of claim 80 wherein said engineering thermoplastic polymer is a thermoplastic polyamide, and wherein said composition further comprises (A) a reinforcing amount of a reinforcing filler or fiber dispersed therein, or (B) a flame retardant synergist dispersed therein, or (C) both of (A) and (B). 82. A composition of claim 81 wherein, prior to blending, the hydrolyzable bromine content of the brominated polystyrene is 2800 ppm Br or less, and wherein, prior to blending, the chlorine content, if any, of the brominated polystyrene is less than 500 ppm. 83. A composition of claim 67 wherein said brominated styrenic polymer has, prior to blending, at least (i) and (iii). 84. A composition of claim 83 wherein said brominated styrenic polymer is a brominated polystyrene, and wherein said total bromine content is at least about 60 wt%. 85. A composition of claim 84 wherein said total bromine content is about 67 wt% or more, and wherein the hydrolyzable bromine content of the brominated polystyrene is 2800 ppm Br or less. 86. A composition of claim 83 wherein said thermoplastic polymer is an engineering thermoplastic polymer, wherein said brominated styrenic polymer is a brominated polystyrene having, prior to blending, a total bromine content above about 60 wt%, and wherein said composition contains a flame retardant amount of the brominated polystyrene in the range of 5 to 20 wt% based on the total weight of the polymer blend. 87. A composition of claim 86 wherein said engineering thermoplastic polymer is a thermoplastic polyamide, and wherein said composition further comprises (A) a reinforcing amount of a reinforcing filler or fiber dispersed therein, or (B) a flame retardant synergist dispersed therein, or (C) both of (A) and (B). 88. A composition which comprises a thermoplastic polymer having blended therewith at least a flame retardant amount of brominated styrenic polymer having, prior to blending, a total bromine content above about 50 wt%, and a thermal stability in the Thermal Stability Test of 200 ppm HBr or less. 89. A composition of claim 88 wherein said thermal stability in the Thermal Stability Test is 150 ppm HBr or less. 90. A composition of claim 88 wherein said thermal stability in the Thermal Stability Test is 100 ppm HBr or less. 91. A composition of claim 88 wherein said total bromine content is above about 60 wt%. 92. A composition of claim 91 wherein said brominated styrenic polymer is a brominated polystyrene. 93. A composition of claim 92 wherein said thermal stability in the Thermal Stability Test is 200 ppm HBr or less. 94. A composition of claim 92 wherein said thermal stability in the Thermal Stability Test is 100 ppm HBr or less. 95. A composition of claim 88 wherein said total bromine content is at least about 67 wt%. 96. A composition of claim 88 wherein said thermoplastic polymer is an engineering thermoplastic polymer, wherein said brominated styrenic polymer is a brominated polystyrene having, prior to blending, a total bromine content above about 60 wt%, and wherein said composition contains a flame retardant amount of the brominated polystyrene in the range of 5 to 20 wt% based on the total weight of the polymer blend. 97. A composition of claim 96 wherein said engineering thermoplastic polymer is a thermoplastic polyamide. 98. A composition of claim 96 wherein said composition further comprises (A) a flame retardant synergist dispersed therein, or (B) a reinforcing amount of a reinforcing filler or fiber dispersed therein, or both of (A) and (B). 99. A composition of claim 96 wherein said engineering thermoplastic polymer is a thermoplastic polyamide, wherein said thermal stability in the Thermal Stability Test is 200 ppm HBr or less, and wherein said composition further comprises (A) a reinforcing amount of a reinforcing filler or fiber dispersed therein, or (B) a flame retardant synergist dispersed therein, or (C) both of (A) and (B). 100. A composition of claim 96 wherein said total bromine content is at least about 67 wt% . 101. A composition of claim 100 wherein said engineering thermoplastic polymer is a thermoplastic polyamide. 102. A composition of claim 101 wherein said composition further comprises (A) a flame retardant synergist dispersed therein, or (B) a reinforcing amount of a reinforcing filler or fiber dispersed therein, or (C) both of (A) and (B). 103. A composition of claim 88 wherein said brominated styrenic polymer has, prior to blending, a TGA temperature for 1 % weight loss which is 340 °C or higher. 104. A composition of claim 103 wherein said brominated styrenic polymer is a brominated polystyrene, and wherein said total bromine content is above about 60 wt% . 105. A composition of claim 104 wherein said thermoplastic polymer is an engineering thermoplastic polymer, and wherein said composition contains a flame retardant amount of the brominated polystyrene in the range of 5 to 20 wt% based on the total weight of the polymer blend. 106. A composition of claim 105 wherein said engineering thermoplastic polymer is a thermoplastic polyamide, and wherein said composition further comprises (A) a flame retardant synergist dispersed therein, or (B) a reinforcing amount of a reinforcing filler or fiber dispersed therein, or both of (A) and (B). 107. A composition of claim 105 wherein said total bromine content is at least about 67 wt%. 108. A composition of claim 107 wherein said engineering thermoplastic polymer is a thermoplastic polyamide. 109. A composition of claim 108 wherein said composition further comprises (A) a flame retardant synergist dispersed therein, or (B) a reinforcing amount of a reinforcing filler or fiber dispersed therein, or (C) both of (A) and (B). 110. A composition of claim 109 wherein said thermal stability in the Thermal Stability Test is 200 ppm HBr or less. 111. A composition of claim 109 wherein said thermal stability in the Thermal Stability Test is 100 ppm HBr or less. 112. A composition of claim 88 wherein said brominated styrenic polymer has, prior to blending, a total bromine content above about 60 wt%, and a hydrolyzable bromine content in the Hydrolyzable Bromine Test of 3600 ppm Br or less. 113. A composition of claim 112 wherein said brominated styrenic polymer is a brominated polystyrene, and wherein said brominated polystyrene has, prior to blending, a TGA temperatare for 1 % weight loss which is 340 °C or higher. 114. A composition of claim 113 wherein said thermoplastic polymer is an engineering thermoplastic polymer, and wherein said composition contains a flame retardant amount of the brominated polystyrene in the range of 5 to 20 wt% based on the total weight of the polymer blend. 115. A composition of claim 114 wherein said engineering thermoplastic polymer is a thermoplastic polyamide, and wherein said composition further comprises (A) a flame retardant synergist dispersed therein, or (B) a reinforcing amount of a reinforcing filler or fiber dispersed therein, or both of (A) and (B). 116. A composition of claim 115 wherein said thermal stability in the Thermal Stability Test is 200 ppm HBr or less, and wherein said hydrolyzable bromine content in the Hydrolyzable Bromine Test of 2800 ppm Br or less. 117. A composition of claim 115 wherein said thermal stability in the Thermal Stability Test is 100 ppm HBr or less, and wherein said hydrolyzable bromine content in the Hydrolyzable Bromine Test of 2800 ppm Br or less. 118. A composition of claim 117 wherein said brominated polystyrene has, prior to blending, a total bromine content of at least about 67 wt%. 119. A composition of any of claims 68, 83, 88, 91, 95, 103, or 112 wherein said brominated styrenic polymer is further characterized by (1) containing, prior to blending, less than about 700 ppm Cl, or (2) having, prior to blending, an actual M w which is within about 20% of its calculated theoretical M w , the theoretical M w being based upon the actual bromine content of the brominated styrenic polymer and the M w of the styrenic polymer reactant used to produce the brominated styrenic polymer, or (3) containing, prior to blending, no detectable quantity of any one or more of bromodichloroethane, dibromochloroethane, dibromodichloroethane, and tribromochloroethane, or (4) having, prior to blending, a ΔE color value that is less than 20, or (5) a combination of any two or more of (1) through (4). 120. A composition of any of claims 69, 70, 84, 85, 92, 96, 104, 111, 113, or 118 wherein said brominated polystyrene is further characterized by (1) containing, prior to blending, less than about 700 ppm Cl, or (2) having, prior to blending, an actaal M w which is within about 20% of its calculated theoretical M w , the theoretical M w being based upon the actaal bromine content of the brominated styrenic polymer and the M w of the styrenic polymer reactant used to produce the brominated styrenic polymer, or (3) containing, prior to blending, no detectable quantity of any one or more of bromodichloroethane, dibromochloroethane, dibromodichloroethane, and tribromochloroethane, or (4) having, prior to blending, a ΔE color value that is less than 20, or (5) a combination of any two or more of (1) through (4). 121. A composition according to claim 68 or 113 wherein said composition is a masterbatch. 122. A composition according to claim 68 or 96 wherein said composition is a melt or powder blend. 123. A composition according to claim 71 or 106 wherein said composition is in the form of a molded or extruded shape or article. 124. A method of forming a flame retarded thermoplastic polymer composition which comprises blending together a thermoplastic polymer and at least a flame retardant amount of a brominated styrenic polymer having, prior to blending, a total bromine content above about 60 wt% and in addition (i) a TGA temperature for 1 % weight loss which is 340 °C or higher and a chlorine content, if any, of less than about 700 ppm Cl, or (ii) a hydrolyzable bromine content of 2800 ppm Br or less using the Hydrolyzable Bromine Test and a chlorine content, if any, of less than about 700 ppm Cl, or (iii) a thermal stability of 200 ppm HBr or less using the Thermal Stability Test. 125. A method of claim 124 wherein said brominated styrenic polymer is a brominated polystyrene. 126. A method of claim 125 wherein said brominated polystyrene has at least both of (i) and (ii). 127. A method of claim 125 wherein said brominated polystyrene has at least both (i) and (iii).

Inventors: AO MENG-SHENG, BALHOFF DONALD E, DADGAR BILLIE B, KOLICH CHARLES H, LIN HOMER C, AO, MENG-SHENG, BALHOFF, DONALD, E., DADGAR, BILLIE, B., KOLICH, CHARLES, H., LIN, HOMER, C.
Applicants: ALBEMARLE CORP, ALBEMARLE CORPORATION
Application year: 1999
Main classification: C08F8
IPC codes: C08F8, C08J5, C08K7, C08L77, C08L101