Abstract:
The present invention provides a new method for making an improved flame-retardant additive comprising a brominated syndiotactic styrenic polymer. The method includes the steps of providing a source of syndiotactic styrenic polymer; providing a source of inert reaction medium that is not capable of dissolving to any appreciable degree the syndiotactic styrenic polymer at ambient temperature and pressure; providing a source of brominating agent; providing a source of Lewis acid catalyst; mixing the syndiotactic styrenic polymer with the inert reaction medium and the Lewis acid catalyst; and reacting the syndiotactic styrenic polymer with the brominating agent to produce a brominated syndiotactic styrenic polymer.

Description:
FIELD OF INVENTION 
     The present invention concerns a method of making a material or additive for use as a flame retardant. More particularly, the present invention concerns a new method for making an improved flame-retardant additive comprising a brominated syndiotactic styrenic polymer. 
     BACKGROUND 
     Flame-retardant additives and methods of making and using the same are well-known in the prior art. Flame-retardant additives are added to many polymers during processing so as to render the finished product made with such polymers resistant to ignition. 
     One class of flame retardants that is used extensively in industry comprises halogenated polymers of styrenic monomers. This class of materials is utilized to impart flame-retardant properties to a broad range of polymeric resins such as, for example, polyamides, polyesters such as PET and PBT, polyolefins and styrenic polymers such as HIPS, ABS, SAN, etc. An example of a commercially successful product of this class is a brominated polystyrene flame-retardant additive sold by the Ferro Corporation of Cleveland, Ohio, under the trademark PYRO-CHEK® 68PB. 
     U.S. Pat. No. 4,352,909 which is owned by Ferro Corporation discloses a method for producing a brominated polystyrene flame-retardant additive such as PYRO-CHEK 68PB. Additional examples of references that disclose methods for producing brominated styrenic polymers are Naarmann et al. U.S. Pat. No. 4,143,221, Diebel et al., U.S. Pat. No. 4,200,703 and Lindenschmidt et al., U.S. Pat. No. 4,360,455. Prior art methods of brominating styrenic polymers to a useful degree, as taught in the above mentioned patents, all teach the step of putting the styrenic polymer into solution by use of a solvent during the bromination step. 
     One class of styrenic polymers that is beginning to attain some commercial interest is syndiotactic styrenic polymers. Nakano U.S. Pat. No. 5,200,454 concerns a flame-retardant resin composition wherein the host or base polymeric resin comprises syndiotactic styrenic polymer. Nakano &#39;454 also talks briefly of adding halogenated syndiotactic polystyrene to syndiotactic polystyrene polymeric resin. However Nakano &#39;454 does not provide any insight whatsoever into how to produce the halogenated syndiotactic polystyrene. 
     The present invention provides a novel method of producing brominated syndiotactic styrenic polymer additives that display unique and improved properties as compared to additives made using conventional methods. 
     SUMMARY OF THE INVENTION 
     The present invention provides a new method for making an improved flame-retardant additive comprising brominated syndiotactic styrenic polymers. The method of the present invention yields a flame-retardant additive that provides for better color and improved thermal stability as compared to conventionally produced brominated styrenic polymers. Quite unexpectedly, the method of the present invention does not include the step of dissolving the syndiotactic styrenic polymer. Prior art methods of brominating styrenic polymers such as polystyrene to a useful degree (i.e., over 15% by weight bromine) all teach the step of putting the styrenic polymer such as polystyrene into solution by use of a solvent before initiation of the bromination step. Contrary to the suggestions of the prior art, applicants have discovered that when brominating syndiotactic styrenic polymers it is not desirable to form a solution by use of a solvent prior to brominating. 
     Generally, the method of the present invention comprises the steps of providing a source of syndiotactic styrenic polymer, providing a source of reaction medium which does not dissolve the syndiotactic styrenic polymer to any appreciable degree at ambient temperature and pressure, providing a source of brominating agent, providing a Lewis acid catalyst, mixing the syndiotactic styrenic polymer with the reaction medium and the Lewis acid catalyst, and reacting the syndiotactic styrenic polymer with the brominating agent to produce a flame retardant comprising brominated syndiotactic styrenic polymer. 
     The foregoing and other features of the invention are hereinafter more fully described and particularly pointed out in the claims, the following description setting forth in detail certain illustrative embodiments of the invention, these being indicative, however, of but a few of the various ways in which the principles of the present invention may be employed. 
     DETAILED DESCRIPTION 
     In the preferred method of making brominated syndiotactic styrenic polymer in accordance with the present invention, syndiotactic styrenic polymer is suspended in an inert reaction medium and reacted with a brominating agent in the presence of a Lewis acid catalyst to produce brominated syndiotactic styrenic polymer. 
     As discussed further below, the selection of the reaction medium is critical. In the prior art, bromination of a styrenic polymer to a useful level of bromination (i.e., over 15% by weight bromine) was always conducted in a solution by use of a solvent. However, quite unexpectedly, applicants have found in respect to the present invention that the use of an inert reaction medium that does not dissolve the syndiotactic styrenic polymer during bromination results in a brominated syndiotactic styrenic polymer, such as, for example, brominated syndiotactic polystyrene, which is superior in properties to brominated styrenic polymers including brominated syndiotactic polystyrene obtained by use of the traditional in-solution process. 
     The syndiotactic styrenic polymer for use in the process according to the invention is a styrenic polymer having mainly the syndiotactic configuration. The styrenic polymer having mainly syndiotactic configuration means a styrenic polymer having a configuration that with respect to a main polymer chain comprising a carbon--carbon bond, and phenyl groups or substituted phenyl groups, has substituents that are positioned alternately on the opposite sides of the plane of the main polymer chain. 
     The styrenic polymer having mainly syndiotactic configuration to be used in the present invention includes polystyrene, poly(alkylstyrene) wherein the substituent is on the aromatic ring, poly(halogenated styrene), and poly(alkoxystyrene). Preferably, at least 60% by weight, and more preferably at least 75% by weight of the styrenic polymer resin displays a syndiotactic configuration. 
     Typical examples of the poly(alkylstyrene) are poly(methylstyrene) and poly(ethylstyrene). Typical examples of the poly(halogenated styrene) are poly(chlorostyrene), poly(bromostyrene), poly(fluorostyrene) and the like. Typical examples of the poly(alkoxystyrene) are poly(methoxystyrene), poly(ethoxystyrene) and the like. Particularly preferred examples of the syndiotactic styrenic polymers are polystyrene, poly-p-methylstyrene, poly-ortho-methylstyrene, poly-p-tert-butylstyrene, poly-p-chlorostyrene, poly-ortho-chlorostyrene and poly-p-fluorostyrene. 
     The styrenic polymer to be used in the present invention varies in molecular weight. The styrenic polymer to be used in the present invention is not critical in a distribution of molecular weight, and those having various distributions of molecular weight can be used. The weight average molecular weight of the syndiotactic styrenic polymer is usually from about 200,000 to about 550,000 although it is not limited thereto. 
     The styrenic polymer having mainly syndiotactic configuration can be prepared, for example, by polymerizing a styrenic monomer (corresponding to the above styrenic polymers) in the presence of a catalyst such as a catalyst comprising a titanium compound and an aluminum organo compound. Campbell, Jr. et al., U.S. Pat. No. 4,774,301, Schmidt et al., U.S. Pat. No. 4,808,680 and Seitz et al., U.S. Pat. No. 4,824,629 are incorporated herein by reference for their teachings of how to produce syndiotactic styrenic polymers. 
     Applicants believe that the present invention is best practiced using powdered, as compared to a conventional pelletized form. More particularly, the syndiotactic styrenic polymer utilized preferably has an average particle size of from about 0.1 to about 10 microns. 
     Lewis acid catalysts which are suitable for the process according to the invention and are used in amounts of from about 0.10% to 40% by weight, preferably from about 0.20% to 20% by weight, based on the weight of styrenic polymer used or charged, include, for example, iron-(III) chloride (FeCl 3 ), SbCl 3 , SbCl 5 , iron-(III) bromide (FeBr 3 ), aluminum-(III) chloride (AlCl 3 ), aluminum-(III) bromide (AlBr 3 ), boron-(III) bromide (BBr 3 ), boron-(III) chloride (BCl 3 ), copper-(II) bromide (CuBr 2 ), SbBr 3 , TiCl 4 , TiBr 4 , SnCl 2 , SnCl 4 , AlBr 3 , BeCl 2 , CdCl 2 , ZnCl 2 , BF 3 , BiCl 3 , ZrCl 4  and mixtures thereof. Care must be taken not to use a Lewis acid catalyst that crosslinks the syndiotactic styrenic polymer during the halogenation process when a halogen containing reaction medium is employed. Diebel et al., U.S. Pat. No. 4,200,703 is incorporated herein by reference for its teachings concerning the use of a Lewis base to prevent crosslinking during bromination. 
     The Lewis acid catalysts exhibit different levels of activity. Moisture, methanol and other materials that complex with the catalyst affect the level of activity of any given catalyst. For example, with respect to SbCl 3  less than 5% of the catalyst SbCl 3  can be used to achieve tribromination if the system is essentially dry. An &#34;essentially dry&#34; or &#34;substantially anhydrous&#34; system or reaction mixture is one in which all of the reaction medium employed has been azeotropically distilled to remove water. Typically this produces a moisture content of 0.002% or less based on the use of an ethylene dichloride reaction medium. Other components are purchased or made up to be as dry as feasible when employing a catalyst such as SbCl 3 . Comparable bromination results cannot be obtained if higher levels of moisture are present. 
     Bromine and bromine chloride may be used as the brominating agent. Bromine chloride is the preferred brominating agent for use in practicing the preferred mode of the invention when SbCl 3  or a catalyst of similar activity is utilized. As compared to the use of bromine per se, bromine chloride is generally preferred. 
     The reaction medium that is employed in the process is critical. The reaction medium must not dissolve the syndiotactic styrenic polymer to any appreciable degree at standard bromination temperatures and ambient pressures (i.e., 70° F. and 1 atmosphere). During the bromination process the suitable reaction medium is one in which the order of the syndiotactic styrenic polymer is not substantially altered at standard bromination conditions. 
     Examples of reaction media that are suitable for use in the present invention when syndiotactic polystyrene is utilized include, for example, 1,2-dichloroethane, chloroform, carbon tetrachloride, methylene bromide, 1,2-dibromoethane, 1,1,2-trichloroethane, and ethylene dichloride (EDC) and mixtures of such media. Materials that are not preferred for use with the present invention when syndiotactic polystyrene is utilized include, for example, 1,1,2,2-tetrachloroethane for it will dissolve the syndiotactic polystyrene and produce a solution. 
     To carry out the process according to the invention, the syndiotactic styrenic polymer and a suitable reaction medium are first introduced into a reaction vessel apparatus, which may, for example, be a stirred vessel or other mechanically agitated vessel or container. One of the conventional bromination catalysts is then added. The mixture is stirred or mixed and the desired amount of brominating agent is run in at from about -30° C. to about 50° C., preferably from about -20° C. to about 45° C. After completion of the reaction, excess brominating agent is neutralized by a reducing agent such as sodium bisulfite. The product may be isolated utilizing any one of several conventional isolation techniques such as, for example, flashing of the reaction medium by the addition of the reaction mixture to hot water. The product is then isolated from the water by conventional filtration and then dried. 
     The product obtained by the process according to the invention may be used for flame retarding thermoplastics. The high heat stability and good resultant color of the additive obtained by the process according to the present invention deserve particular mention. Suitable thermoplastics for such flame retarding include, for example, polyamides such as Nylon 6, Nylon 6,6, Nylon 4,6 and Nylon 6,12; polyesters such as PET, PCT and PBT; polyolefins, and styrenic polymers such as polystyrene (both atactic and syndiotactic), HIPS, SAN, ABS, etc. 
     The incorporation, into thermoplastics, of the brominated syndiotactic styrenic polymer additive and of synergistic agents which may or may not be used, as well as the incorporation of further additives which may be employed, can be carried out by suitable conventional mixing processes, for example in extruders, Banbury mixers, two roll mills or other plastic processing equipment. Self-extinguishing moldings and profiles can be produced, by injection-molding or extrusion, from the mixtures with thermoplastics prepared using the additive product or blended product resulting from the process according to the invention. 
     Brominated syndiotactic polystyrene made in accordance with the present invention displays a melting temperature (i.e., the temperature at which at least a portion of the material melts) of over 325° C. and has less than 1500 ppm halogen located on the backbone of the polystyrene as measured in HBr equivalents. In comparison, brominated syndiotactic polystyrene made in-solution displays a softening point well below 300° C. and it has well over 3500 ppm (and typically over 6000 ppm) halogen located on the backbone of the polystyrene as measured in HBr equivalents. Halogen on the backbone of the polystyrene is very undesirable. The halogen is preferably located on the ring of the polystyrene. Backbone halogenation leads to numerous problems such as poor thermal stability for the end user. 
     Brominated syndiotactic polystyrene made in accordance with the present invention also displays a thermal stability of less than about 1500 ppm HBr by the GE thermal stability test as compared to in-solution made brominated syndiotactic polystyrene which displays a thermal stability of over about 6000 ppm HBr by the GE thermal stability test. Further, it has been noted that brominated syndiotactic polystyrene made in accordance with the present invention displays a melting point and it is non-amorphous and thus it displays at ambient conditions a noncrystalline order. To the contrary, brominated syndiotactic polystyrene made in-solution is amorphous in nature and it does not display a melting point. A noncrystalline order is well documented and discussed beginning at Volume 4, page 449, of the Encyclopedia of Polymer Science and Technology© 1966. An additive having noncrystalline order that displays various beneficial properties can only be obtained by using the process of this invention. 
    
    
     In order to further illustrate the invention, the following Examples are provided. Unless otherwise indicated, in the following Examples as well as throughout the entire specification and in the appended claims, all parts and percentages are by weight and all temperatures are in degree Centigrade. 
     EXAMPLE I 
     Into a 5 L resin flask equipped with a mechanical stirrer, thermometer, spiral condenser, and a 500 mL jacketed pressure equalized addition funnel was placed 300.6 g (2.886 mole based upon molecular weight of a styrene repeating unit) powdered syndiotactic polystyrene having a weight average molecular weight of 450,000 and 2100 mL of 1,2 dichloroethane (EDC). To the stirred mixture was added 15 g (0.06576 mole) antimony trichloride (added as a solution in EDC--0.4 g/mL) and the mixture was cooled to 15° C. Bromine chloride 1125.0 g (9.75 mole) (added as a solution in EDC--50% w/w) was added to the flask at a rate of 3.25 moles/hr BrCl while keeping the bromination temperature at approximately 20° C.±2° C. After the addition of the BrCl was completed, the reaction mass was held at 20°-25° C. for an additional three hours (total contact time is six hours). Aqueous sodium bisulfite (620 g of 20% NaHSO 3 ) was added at such a rate as to not exceed 35° C. A weight of deionized water, equal to the weight of the aqueous sodium bisulfite used, was added to the mixture. The entire mass was stirred for an additional ten minutes, and then filtered to yield a white solid. 
     The white solid was washed three times by slurrying each time with 2500 mL of fresh deionized water for two hours, and filtering. During the second and third washes, the product exhibited a creamy/shaving cream like texture. After the third wash, the solid was charged along with six liters of deionized water to an appropriately sized resin flask equipped with a mechanical stirrer, distillation head, condenser, receiver, and heating mantle. The resulting slurry was heated gradually whereupon the EDC/water azeotrope was removed from the system. Ultimately the slurry was heated to 100° C. and was held at that temperature for two additional hours. During this time, the pH of the slurry was adjusted from 4 to 8 by the incremental addition of 10% aqueous NaOH. Propanol was added to the slurry to serve as a wetting aid and the slurry was then stirred at 80° C. for four hours. 
     The product was collected by filtration, washed on a filter with 4 L of hot deionized water and then 2 L of cold deionized water. The product was vacuum dried at 100° C. at 5-10 torr for 48 hours. The total yield of brominated syndiotactic polystyrene product was approximately 930 grams. 
     EXAMPLE II 
     Eighty-six grams of syndiotactic polystyrene was mixed in an extruder with 10 grams of the brominated syndiotactic polystyrene of Example I and 4 grams of Sb 2  O 3 . The flame-retarded composition displayed a flame retardance of V-O at  1/8 inch UL94. 
     EXAMPLE III 
     Utilizing the brominated syndiotactic polystyrene (BrSPS) of Example I, the following flame-retarded blends were produced using a twin screw extruder. 
     
         __________________________________________________________________________                      Oxygen Index For       Parts By Weight                      Host Polymer With                                 Oxygen Index WithHost Polymer       Formulation    No Flame Retardant                                 Flame Retardant                                           UL94- 1/8&#34;__________________________________________________________________________HIPS-Huntsman 840       81HIPS/4Sb.sub.2 O.sub.3 /15BrSPS                      18.10      23.91     V-OABS-GE Cycolac L1000       74ABS/6Sb.sub.2 O.sub.3 /20BrSPS                      17.77      25.98     V-OPET-DuPont Rynite 530       83PET/4Sb.sub.2 O.sub.3 /13BrSPS                      20.10      30.60     V-OPBT-Celanex 2002-2       77PBT/6Sb.sub.2 O.sub.3 /16BrSPS                      21.80      26.60     V-ONylon 6,6-DuPont       72Nylon/7Sb.sub.2 O.sub.3 /21BrSPS                      26.25      27.13     V-OZytel 101PPO-GE      84PP/4Sb.sub.2 O.sub.3 /12BrSPS                      23.17      31.08     V-ONoryl 731LDPE Mobil LMA 003       60LDPE/10Sb.sub.2 O.sub.3 /30BrSPS                      18.46      24.59     V-O__________________________________________________________________________ 
    
     EXAMPLE IV 
     Into a dried 100 gallon glass-lined reactor equipped with three-bladed retreating blade agitator, dip tube, H-style finger baffle with thermowell, condenser, receiver and scrubber are charged with stirring 421.0 pounds dry 1,2-dichloroethane (EDC), 47.5 pounds (0.4561 pounds-moles based on styrene repeating units) powdered syndiotactic polystyrene and 2,399 pounds (0.01052 pounds-mole) antimony trichloride dissolved in 0.75 gallon dry 1,2-dichloroethane. The mixture is stirred and cooled to 16° C. Bromine chloride, 180.0 pounds (1,560 pounds-mole), is added to the mixture at a rate of 1 lb/min, while keeping the reaction temperature between 20°-25° C. Approximately 2.75 hours into the bromine chloride addition, the mixture thickened into a pasty, but stirrable, mass. After the three-hour bromine chloride feed, the mixture is stirred for another 9 hours, maintaining the temperature at 20°-25 ° C. Aqueous sodium bisulfite, 400 pounds of 10% w/w, is then pumped in to neutralize the unreacted bromine chloride, followed by pH adjustment of the reaction mixture to pH 7 with 310 pounds 10% w/w aqueous sodium hydroxide. The crude product was then collected via centrifuge. 
     The solid was washed three times by slurrying each time in the reactor with 500 lb fresh water and centrifuging. After the third wash, the solid was charged back to the reactor, 500 pounds fresh water added and the mixture was heated with stirring to about 77° C., whereupon the EDC/water azeotrope was removed from the system. The resulting slurry was then gradually heated to 100° C. and held there for 2 hours. The slurry was then cooled and centrifuged to collect the solid product wet cake. 
     The wet cake was dried in a rotary vacuum drier at 110° C./25-26&#34; Hg vacuum for 48 hours, giving an off-white powder. The process yielded about 141 pounds of material. 
     While the invention has been explained in relation to its preferred embodiments, it is to be understood that various modifications thereof will become apparent to those skilled in the art upon reading this specification. Therefore, it is to be understood that the invention disclosed herein is intended to cover such modifications as fall within the scope of the appended claims.