Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
1999-04-13
2001-03-27
Lipman, Bernard (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S333400, C525S357000
Reexamination Certificate
active
06207765
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to the discovery of a highly beneficial solvent for use in the bromination of a styrenic polymer.
Brominated styrenic polymers, e.g., brominated polystyrene, are well recognized flame retardants for use in engineering thermoplastics, e.g., nylon, polyethylene terephthalate, polybutylene terephthalate, etc. These flame retardants are prepared by reacting a brominating agent, e.g., bromine or bromine chloride, with a polystyrene in the presence of a Lewis acid catalyst. Since the styrenic polymer is usually very viscous or a solid, it has been deemed necessary to provide it to the reaction as a solute in a lower viscosity solution. The art generally describes the solvent as being a halogenated hydrocarbon, and, more specifically, a chlorinated hydrocarbon. Methylene chloride and dichloroethane are universally considered to be the solvents of choice. Despite their apparent attractiveness, these two solvents are not without disadvantage.
Methylene chloride is favored as it is relatively inert in the process. However, it is disadvantaged because it has a low boiling point and is challenged as being potentially depletive of the global ozone layer.
In distinction, dichloroethane has an acceptable boiling point and, in use, is more environmentally desirable than methylene chloride. It is not, however, a panacea as it reacts in the process to a significant extent and its use is not associated with an exceptionably low color brominated polystyrene product.
It is, therefore, an object of this invention to provide a solvent for use in the bromination of styrenic polymers which is environmentally beneficial, has a boiling point in the range of 80-95° C., is relatively inert in the bromination process, and is associated with a near-white brominated styrenic polymer product.
THE INVENTION
This invention relates to a process for brominating styrenic polymers, which process comprises: brominating styrenic polymer in the presence of Lewis acid catalyst and solvent quantities of bromochloromethane.
The bromination of the styrenic polymer is preferably effected by either (1) adding a brominating agent to a reactor containing styrenic polymer, bromochloromethane and a Lewis acid catalyst; (2) adding, to a Lewis acid catalyst, (i) a styrenic polymer stream which is comprised of a solution of styrenic polymer and bromochloromethane and (ii) a brominating agent stream, the streams being added separately but substantially concurrently; or (3) adding a mixture which includes a brominating agent, styrenic polymer and bromochloromethane to a Lewis acid catalyst. Besides these preferred modes of addition, it is contemplated that any addition mode which effects reactive contact between the brominating agent, catalyst and styrenic polymer will be benefitted by the use of bromochloromethane as the process solvent. The first-described addition mode is conventional and is illustrated in U.S. Pat. No. 4,200,703 and U.S. Pat. No. 4,352,909. Both of these patents are incorporated herein by reference for all of their teachings except for that teaching which refers to the identity of the process solvent. (Thus, in the '703 patent, column 3, lines 3-16, the Examples and the claims are excluded, while in the '909 patent, the paragraph bridging columns 7 and 8, the Examples and the claims are also excluded.) The second-described addition mode is illustrated by U.S. Pat. No. 4,975,496 which is also incorporated herein by reference for all of its teachings except for that teaching which refers to the process solvent.
For addition mode (2), it is a feature that there be a dispersion of at least a portion of the brominating agent substantially throughout the catalyst before there is any substantial complexing (cross-linking) of the styrenic polymer. When the brominating catalyst is AlCl
3
, there is generally a need to pre-add a portion of the bromine to the catalyst prior to introduction of the styrenic polymer. In such cases, at least 5 mole percent of the brominating agent is pre-added. See incorporated U.S. Pat. No. 4,975,496 for further details concerning the pre-addition of the brominating agent.
For mode (3), it is preferred that the mixture be formed via mixing of the components in a device which is outside or inside of the reactor and feeding the resultant mix to the reactor. In addition, a stream from the reactor can also be fed to the mixing device to contribute to the total resultant mix being sent back to the reactor. Also, for addition mode (3), it is preferred that the bromochloromethane, styrenic polymer and the brominating agent be substantially free of brominating catalyst at least prior to their being mixed. 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, little or no catalyzed bromination or cross-linking should occur. Generally, such amounts will be less than 500 ppm (weight basis) of styrenic polymer present.
The amount of bromochloromethane solvent used is that amount which can dissolve the styrenic polymer and any of the brominated styrenic polymer species produced. Also, it is preferred that the amount of bromochloromethane used will result in an easily-stirred reaction mass. Generally, the total solvent used will be that amount which is needed to dissolve the styrenic polymer to yield an easy-flowing solution and that amount which may be initially present in the reactor and associated with reaction components other than styrenic polymer. In most cases, the amount of bromochloromethane used to form the styrenic polymer solution will provide a solution which contains 3 to 30 wt % styrenic polymer, based upon the total weight of the solution.
The presence or absence of water in the bromochloromethane will be in accordance with the water requirements of the particular process chosen. For example, anhydrous processes, such as that described in U.S. Pat. No. 4,352,909, will be sensitive to the solvent water content. Other processes, such as that disclosed in U.S. Pat. No. 4,200,702, require a certain level of water and, thus, are not as sensitive to the solvent water content. Still other processes, which are substantially independent of water content, can be somewhat indifferent about the solvent water content. Unless the solvent is being used as a major contributor of water to the process, most practitioners will choose bromochloromethane having less than about 100 ppm (weight basis) water.
PREFERRED EMBODIMENTS
Styrenic polymers which are brominated in accordance with the present invention are homopolymers and copolymers of vinyl aromatic monomers, that is, monomers having an unsaturated moiety and an aromatic moiety. The preferred vinyl aromatic monomers have the formula:
H
2
C═CR—Ar
wherein R is hydrogen or an alkyl group having from 1 to 4 carbon atoms and Ar is an aromatic radical (including various alkyl and halo-ring-substituted aromatic units) of from 6 to 10 carbon atoms. Examples of such vinyl aromatic monomers are styrene, alpha-methylstyrene, ortho-methylstyrene, meta-methylstyrene, para-methylstyrene, para-ethylstyrene, isopropenyltoluene, isopropenylnaphthalene, vinyl toluene, vinyl naphthalene, vinyl biphenyl, vinyl anthracene, the dimethylstyrenes, t-butylstyrene, the several chlorostyrenes (such as the mono- and dichloro-variants), the several bromostyrenes (such as the mono-, dibromo- and tribromo-variants). Polystyrene is the currently preferred styrenic polymer and, when the styrenic polymer being brominated is 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.
The styrenic polymers, which are brominated in accordance with the present invention, are readily prepared by bulk or mass, solution, suspension or emulsion polymerization techniques comparable to those employed in the polymerization of styrene. Polymerization can be effected in the presence of
Ao Meng-Sheng
Balhoff Donald E.
Brackenridge David R.
Brockman Thorsten W.
Dadgar Billie B.
Albemarle Corporation
Lipman Bernard
Spielman, Jr. E. E.
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