Compositions – Oxidative bleachant – oxidant containing – or generative – Composition containing a stabilizer or a product in the form...
Reexamination Certificate
2002-11-27
2004-07-20
Anthony, Joseph D. (Department: 1714)
Compositions
Oxidative bleachant, oxidant containing, or generative
Composition containing a stabilizer or a product in the form...
C252S186420, C252S186200, C252S182130, C252S182290
Reexamination Certificate
active
06764612
ABSTRACT:
FIELD OF INVENTION
The present invention relates to supported peroxides and a method of forming supported peroxides.
BACKGROUND OF THE INVENTION
Peroxides are used in polymer chemistry for a variety of purposes including, for example, reducing the molecular weight of polymers and vulcanizing rubber. One of the problems associated with the use of peroxides is that in their pure form, peroxides have a tendency to be relatively unstable. Peroxides can break down and lose their activity while in storage. Furthermore, the decomposition and instability of peroxides can present storage and use hazards. For these reasons, peroxides are often diluted with at least one other substance, which improves the stability of the peroxide and facilitates handling. Peroxides that have been diluted with another substance are commonly referred to as “supported peroxides” in the industry.
Peroxides are commonly used to initiate polymerization and cross-link (vulcanize) polymers. In the vulcanizing process, the peroxide increases molecular weight either by causing the concatenation of monomers into polymer chains or by forming covalent bonds (cross-links) between established polymer chains. However, peroxides are not useful in cross-linking all polymers since some polymers tend to depolymerize when heated in the presence of peroxides, which leads to a reduction in molecular weight rather than an increase in molecular weight. Examples of polymers that depolymerize when heated in the presence of peroxides include polypropylene, polystyrene, and ethylene-propylene elastomers that have a high degree of blockiness of their propylene units.
Peroxides are still useful in processing this group of polymers. Since peroxides induce polymer cleavage in these applications, they can be used to enhance the melt flow properties, which can facilitate processes such as extrusion. This type of application is known as visbreaking (viscosity breaking) since the effect of the peroxide treatment is a reduction in the molecular weight and an increase in the melt flow index.
Two peroxides that are particularly useful in visbreaking are a,a′-bis(t-butylperoxy)diisopropylbenzene and 2,5-dimethyl-2,5-di(t-butylperoxy)hexane. The first is often added in the form of a 20% dispersion of the peroxide on polypropylene particles, while the latter is usually added as a liquid. One of the drawbacks of the dispersion of peroxide on polypropylene is that the dispersion must be heated to the melting point of the peroxide. Another disadvantage of the dispersion of peroxide on polypropylene is that it consists of a blend of polypropylene particles and peroxide crystals without adhesive bonding between the components. Although there is no conclusive data, it is believed that this formulation would be prone to a density stratification process in which, during transportation and storage, the more dense peroxide crystals will become more highly concentrated at the bottom of the container. Concentration variations within the container could lead to inconsistencies in processing.
Another drawback to the use of a dispersion of a peroxide on polypropylene is that the polypropylene support is prone to oxidation. It is known to persons skilled in the art that polypropylene slowly reacts with oxygen in the air to form hydroperoxides along the polymer chain. This leads to chain reactions that eventually cause the decomposition of the polypropylene. Therefore, anti-oxidants are an important component in all polypropylene formulations since they eliminate hydroperoxides as they form and scavenge polymer radicals before they are able to form hydroperoxides. In the past it has been observed that inadequate loading of anti-oxidant in the polypropylene support can lead to excessive hydroperoxide formation. The hydroperoxide level can reach sufficient levels to neutralize the anti-oxidant in the polymer being processed. This may lead to unexpected discoloration or brittleness in the final product.
A need exists for a supported peroxide product that can be easily handled, does not contain foreign contaminants such as inorganic supports or masterbatch elastomers, is available in a free-flowing powder form, is not prone to density stratification during storage, and can be manufactured and used at relatively low temperatures.
SUMMARY OF INVENTION
The present invention provides supported peroxides, and a method of forming supported peroxides. Supported peroxides according to the invention are solid particles that comprise an organic peroxide, a metallic soap, and a polymer. In accordance with the method of the invention, supported peroxides are preferably formed by dispersing a mixture comprising at least one peroxide and at least one C
4
to C
30
carboxylic acid into an aqueous solution containing a basic compound that is capable of reacting with the C
4
to C
30
carboxylic acid to form a water soluble soap. Dispersing the mixture into the aqueous solution results in the formation of an emulsion. Polymer particles are added to the emulsion, where the polymer particles become uniformly dispersed, forming a suspension. The addition of polymer is followed by the addition of a polyvalent metal compound that is capable of reacting with the water soluble soap to form a water insoluble metallic soap, which converts the water soluble soap into a water insoluble metallic soap that precipitates from the solution, along with the suspended polymer and the emulsified organic peroxide. The organic peroxide and the polymer are entrained or encapsulated within the precipitate of water insoluble metallic soap.
Supported peroxide products in accordance with the invention can comprise as much as 50% organic peroxide by weight. Supported peroxides according to the invention are in the form of easy-to-disperse powders like inorganic supported grades, but readily melt in polymers like wax-based supported grades. The powders show exceptional resistance to aggregation (clumping) even when exposed to temperatures in excess of the melting point of the peroxide. The metallic soap adds lubricity to polymer melts and thus can function as a processing aid. Supported peroxides according to the invention are formed at lower temperatures, and thus are not prone to thermal decomposition during manufacturing.
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 OF PREFERRED EMBODIMENTS
Supported peroxide compositions according to the present invention comprise solid particles comprising an organic peroxide, at least one metallic soap, and at least one polymer. Without being held to a particular theory, applicants believe that the solid particles comprise a core consisting essentially of the organic peroxide and the polymer, and a coating layer disposed on the core that comprises the metallic soap. Scanning electron micrographs of the particles show that the coating layer is not continuous, meaning that portions of the organic peroxide and polymer core are left exposed. Rather than forming a continuous coating, the metallic soap appears to form discrete “platelets” that adhere to and form a mottled cladding over a substantial portion of the surface of the organic peroxide and polymer core.
Virtually any organic peroxide can be used in the invention. Preferably, however, the organic peroxide will be a solid at standard temperatures and pressures (25° C., 1 ATM) that has a melting point less than about 95° C., and more preferably less than about 50° C. Particularly suitable organic peroxides for use in the invention include, for example, a,a′-bis(t-butyl peroxy)-diisopropyl benzene, and 2,5-dimethyl-2,5-di(tbutylperoxy)hexane. It will be appreciated a combination of these peroxides can be used, and combinations of two or more organic peroxides can also be used
Anthony Joseph D.
GEO Specialty Chemicals, Inc.
Rankin, Hill Porter & Clark LLP
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