BACKGROUND OF THE INVENTION [0002] Peroxides are used in polymer chemistry for a variety of purposes including, for example, reducing the molecular weight of polymers and vulcanizing rubber. 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.

[0003] One of the problems associated with the use of peroxides is that in their pure form, peroxides have a tendency to be relatively unstable. Under certain conditions, 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.

[0004] One known method of forming a supported peroxide product is to melt and spray one or more peroxides onto an inorganic support such as clay or calcium carbonate. The molten peroxide becomes absorbed or adsorbed on the inorganic support and solidifies. The resulting supported peroxide product will be a powder that is easier to handle and is less hazardous than a "pure"peroxide product. One of the drawbacks of inorganic supported grade peroxide products is that the peroxide concentration is generally limited to about 40% by weight, which is the maximum that can be absorbed or adsorbed onto the inorganic support.

[0005] Another known method of forming a supported peroxide product is to mill one or more peroxides into a rubber composition to form a master batch product. Master batch products of this type are typically sold as slabs or pellets, which are also easily handled and are substantially less hazardous than pure peroxides. Once again, however, the peroxide concentration for rubber supported grade peroxide products is generally limited to a maximum of about 40% by weight.

[0006] Yet another known method of forming a supported peroxide product is to blend one or more peroxides into a molten wax, which is then permitted to cool and solidify. The solidified wax can be granulated or pelletized. It is possible to form supported peroxide products in this manner than have peroxide concentrations of 40% to 70% by weight. One of the drawbacks with wax supported grade peroxide products is that the peroxide must be processed at a high enough temperature to melt the wax, typically above 100°C, which can cause the peroxides to decompose and create a hazardous processing environment. It is also difficult to incorporate other ingredients, such as co-agents and anti-scorch agents, into such compositions.

[0007] Yet another known method of forming a supported peroxide is to melt and/or spray a dispersion of one or more organic peroxides onto a polymeric particle. One of the drawbacks of this method is that in order to become flowable, the dispersion must be heated to a temperature above the melting point of the peroxide. Another disadvantage is that there is little or no adhesive bonding between the peroxide crystals and the polymeric support.

Although there is no conclusive data, it is believed that such supported peroxides formed by applying dispersions of organic peroxides onto polymeric particles tend to be prone to a density stratification process in which, during transportation and storage, the more dense peroxide crystals become more highly concentrated at the bottom of the container. Concentration variations within the container could lead to inconsistencies in processing.

[0008] Another drawback to the use of dispersions of peroxides on polymeric particles is that the polymeric support may undergo oxidation.

Some polymers, such as polypropylene for example, slowly react with oxygen in the air to form hydroperoxides along the polymer chain. This leads to chain reactions that eventually cause the decomposition of the polymer. 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.

[0009] 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 [0010] 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, optionally, 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 C4 to C3o carboxylic acid into an aqueous solution containing a basic compound that is capable of reacting with the C4 to C30 carboxylic acid to form a water soluble soap.

Dispersing the mixture into the aqueous solution results in the formation of an emulsion. Optionally, polymer particles can be added to the emulsion. When added, the polymer particles become uniformly dispersed in the emulsion and forming a suspension. A polyvalent metal compound that is capable of reacting with the water soluble soap to form a water insoluble metallic soap is added to the emulsion or suspension, which converts the water soluble soap into a water insoluble metallic soap that precipitates from the solution. The organic peroxide, as well as the polymer, if present, is entrained or encapsulated within the precipitate of water insoluble metallic soap.

[0011] Supported peroxide products in accordance with the invention can comprise as much as 90% 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.

[0012] 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 [0013] Supported peroxide compositions according to the present invention comprise solid particles comprising an organic peroxide, a metallic soap and, optionally, a polymer. Without being held to a particular theory, applicants believe that the solid particles comprise a core comprising of the organic peroxide (and the polymer, if present) 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 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 core.

[0014] 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, dicumyl peroxide, a, a'-bis (t-butylperoxy)-diisopropylbenzene, benzoyl peroxide and 2, 5-dimethyl-2, 5-di (t-butylperoxy) hexane. It will be appreciated a combination of two or more organic peroxides can also be used.

[0015] The metallic soap in the supported peroxide composition according to the invention comprises a salt of a polyvalent metal and at least one C4 to C30 carboxylic acid. Applicants have determined supported peroxide compositions comprising polyvalent salts of at least two different C4 to C30 carboxylic acids tend to exhibit superior handling properties (e. g. , anti- clumping properties) than supported peroxide compositions comprising a polyvalent salt of only one C4 to C3o carboxylic acid. This improvement is noted even when only very small amounts of a"secondary"metallic soap are present in the composition.

[0016] The presently most preferred carboxylic acids for use in the invention are stearic acid and/or palmitic acid. These"primary"carboxylic <BR> <BR> acids are preferably used in combination with smaller amounts (e. g. , about 0. 01% to about 5.0% by weight) of"secondary"carboxylic acids selected from the group consisting of phthalic acid, terephthalic acid, maleic acid, fumaric acid, benzoic acid, and combinations thereof. Preferred polyvalent metals are calcium, magnesium, and aluminum, with calcium being the presently most preferred polyvalent metal. Preferred metallic soaps include, for example, calcium stearate, magnesium stearate, aluminum stearate, calcium palmitate, magnesium palmitat, aluminum palmitat, calcium phthalate, magnesium phthalate, aluminum phthalate, calcium terephthalate, magnesium terephthalate, aluminum terephthalate, calcium maleat, magnesium maleat, aluminum maleat, calcium fumarate, magnesium fumarate, aluminum fumarate, calcium benzoate, magnesium benzoate, and aluminum benzoate.

It will be appreciated that combinations of two or more metallic soaps can also be used.

[0017] The supported peroxide compositions according to the invention comprise solid particles. The particles tend to have a relatively narrow size distribution (i. e., all of the particles tend to be of substantially uniform size), with the average size of the particles being dependent upon the processing conditions (e. g. , processing temperature, agitation, etc. ). When supported peroxide compositions according to the invention do not comprise the optional polymer, the particles will typically have an average particle size of from about 100 microns to about 400 microns. When supported peroxide compositions according to the invention do comprise the optional polymer, the particles will typically have an average particle size of about 500 microns. In such cases, the particle size will largely be determined by the size of the polymer particles suspended in the emulsion. Particles having an average particle size from about 100 microns to about 500 microns are easy to handle, and readily melt into and disperse in polymers.

[0018] The solid particles preferably comprise up to about 90% organic peroxide by weight. It will be appreciated that the concentration of organic peroxide in the particle will be determined according to the particular application or end use. For example, in high concentration applications, such as in the vulcanization of rubbers, the solid particles may comprise from about 40% by weight to about 90% by weight of one or more organic peroxides (e. g., dicumyl peroxide), with the balance of the weight comprising the metallic soap and any optional substances (e. g., calcium phthalate).

[0019] In lower concentration applications, such as in the visbreaking of polypropylene, the solid particles may comprise from about 10% by weight to about 20% by weight of one or more organic peroxides (e. g. , a, a'-bis (tert- butylperoxy)-diisopropylbenzene), from about 5% by weight to about 80% by <BR> <BR> weight of one or more polymers (e. g. , polypropylene), with the balance of the weight comprising the metallic soap and any optional substances.

[0020] Optionally, the solid particles according to the invention comprise from about 0. 1% to about 5% anti-oxidant by weight, most preferably from about 0. 1% to about 2% anti-oxidant by weight. The solid particles can further comprise up to a total of about 50% by weight of one or more optional substances such as, for example, co-agents, anti-scorch agents, anti- ozonants, and UV light stabilizers.

[0021] In accordance with the method of forming supported peroxides according to the invention, a mixture comprising an organic peroxide and a C4 to C30 carboxylic acid is formed. Suitable organic peroxides for use in the invention have previously been discussed above. It will be appreciated that the C4 to C30 carboxylic acids can be any form of carboxylic acids including, but not limited to fatty acids, dicarboxylic acids, branched-chain, and substituted carboxylic acids. Suitable C4 to C30 carboxylic acids include, for example: saturated carboxylic acids such as butyric, caproic, caprylic, capric, lauric, myristic, palmitic, stearic, arachic, behenic, lignoceric, and cerotic acids; unsaturated carboxylic acids such as butenoic, methacrylic, octenoic, caproleic, undecylenic, myristoleic, palmitoleic, oleic, erucic, linoleic, linolenic, arachodonic, and docosahexenoic acids; aromatic carboxylic acids such as benzoic and toluic acids; and dicarboxylic acids such as malonic, maleic, fumaric, succinic, adipic, phthalic, terephthalic, isophthalic, and itaconic acids.

It will be appreciated that combinations of two or more C4 to C30 carboxylic acids can be used. The mixture of organic peroxide and C4 to C30 carboxylic acid (s) is preferably heated to a temperature that is slightly above the melting point of the organic peroxide to facilitate good mixing and the formation of a uniform homogeneous mixture.

[0022] Particularly when the composition is to include a polymer, the mixture of organic peroxide and C4 to C30 carboxylic acids may also contain an anti-oxidant. The anti-oxidant greatly reduces or eliminates hydroperoxides that slowly form when polymers such as polypropylene are exposed to air. An anti-oxidant such as butylated hydroxytoluene may be added in an appropriate amount to prevent excessive hydroperoxide formation in the polymer-containing supported peroxide final product.

[0023] The heated mixture of organic peroxide and C4 to C30 carboxylic acid is dispersed in an aqueous solution that comprises a compound that is capable of reacting with the C4 to C30 carboxylic acid to form a water soluble soap. The compound that is capable of reacting with the C4 to C30 carboxylic acid to form a water soluble soap will preferably comprise a water soluble base such as sodium hydroxide, potassium hydroxide, or ammonium hydroxide. In a preferred embodiment of the invention, the aqueous solution further comprises the"secondary"C4 to C30 carboxylic acid.

[0024] Preferably, the heated mixture is added to the aqueous solution under constant stirring to promote the formation of an emulsion. To facilitate the formation of an emulsion, it is preferable for the aqueous solution to also be heated to a temperature slightly above the melting point of the organic peroxide. The aqueous solution will preferably only comprise the minimum amount of the compound that is capable of reacting with the C4 to C30 carboxylic acid to form a water soluble soap necessary to neutralize all of the C4 to C30 carboxylic acids (i. e. , primary and secondary) in the emulsion. If the ratio of base to total equivalents of C4 to C30 carboxylic acids is less than about 1, incomplete emulsification ("creaming") will likely occur. If the ratio of base to total equivalents of C4 to C30 carboxylic acids is greater than about 1.5, significant amounts of base will remain in the aqueous solution, which can present waste treatment problems. Accordingly, the preferred ratio of base to total equivalents of C4 to C30 carboxylic acids is from about 1.0 to about 1.2.

[0025] Optionally, after the heated mixture has been dispersed in the aqueous solution, a powdered polymer can be added to the emulsion.

Polymers suitable for this application include polymers that are cleaved by peroxides and halobutyl rubbers. Examples of such polymers include polypropylene, polystyrene, polyisobutylene, butyl rubber (copolymer of isobutylene and isoprene), chlorobutyl rubber, and bromobutyl rubber. The polymer is preferably in powder form. Upon addition of polymer to the emulsion, the emulsion and polymer are stirred to evenly distribute the polymer particles and form a polymer suspension.

[0026] The heated emulsion or polymer suspension is then preferably cooled to a temperature below the melting point of the organic peroxide.

Without being bound to a particular theory, applicants believe that the organic peroxide becomes trapped within the emulsion micelles. These micelles are formed when the water soluble soap coats at least a portion of the organic peroxide (and the optional polymer, if present) at the interface with the aqueous solution. When an optional polymer is present, the individual micelles contain organic peroxide that is adhered to a polymer particle, which later forms the core of the solid particles. As the emulsion or suspension cools to a temperature below the melting point of the organic peroxide, the organic peroxide solidifies (and perhaps crystallizes) within the micelles.

[0027] After the emulsion or polymer suspension has cooled to a temperature below the melting point of the organic peroxide, a polyvalent metal salt that is capable of reacting with a water soluble soap to form a water insoluble metallic soap is added. Preferred polyvalent metal cations that can be used for this purpose include : alkaline-earth metals such as beryllium, magnesium, calcium, strontium, and barium; transition metals such as titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, zirconium, molybdenum, palladium, cadmium, and mercury; and other metals such as aluminum, gallium, tin, lead, and lanthanoid metals. Calcium salts are preferred, with calcium chloride and/or calcium sulfate being presently most preferred. Combinations of two or more polyvalent metal compounds can be used, if desired.

[0028] Addition of the polyvalent metal compound causes the water soluble soap to convert to a water insoluble metallic soap, which precipitates from the aqueous solution. As used throughout the specification and in the appended claims, the term"water insoluble"means that the metallic soap has a solubility in water at 25°C of less than about 2.0%.

[0029] As noted above, without being held to a particular theory, applicants believe that each of the solid particles comprises a core comprising the organic peroxide (and the optional polymer, if present) 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 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 core. The precipitate can be separated from the aqueous solution by vacuum filtration or other conventional separation means. The resulting powder can but need not be washed and dried.

[0030] Supported peroxide products in accordance with the invention can comprise from about 5% by weight to about 90% by weight of organic peroxide. Supported peroxides according to the invention are more resistant to clumping due to the anti-blocking properties imparted by the metallic soap.

Supported peroxides according to the invention are in the form of easily handled and easy-to-disperse powders like inorganic supported grades, but readily melt in polymers like wax-based supported grades. 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 formation. When an optional polymer is used, the organic peroxide, the polymer and the metallic soap are co-precipitated as discrete particles in which these components are bonded together. This feature is believed to prevent concentration stratification during storage.

10031] In one preferred embodiment of the invention, the solid particles comprise from about 40% by weight to about 85% by weight of dicumyl peroxide, from about 15% by weight to about 60% by weight calcium stearate, and from about 0. 01% to about 5% by weight calcium phthalate. In another preferred embodiment of the invention, the solid particles comprise from about 65% to about 85% by weight of a, a'-bis (tert-butylperoxy)-diisopropylbenzene, from about 15% to about 35% by weight calcium stearate, and from about 0. 01% to about 5% by weight calcium phthalate.

[0032] 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. Solid particles according to the invention for use in such applications preferably comprise from about 10% to about 20% by weight of a, a'-bis (t-butylperoxy) diisopropylbenzene or 2, 5-dimethyl-2, 5-di (t- butylperoxy) hexane, from about 65% to about 90% by weight of polypropylene, from about 1% to about 10% by weight of calcium stearate, from about 0. 01% to about 5% by weight calcium phthalate, and from about 0.01 to about 1% by weight butylated hydroxytoluene.

[0033] The following examples are intended only to illustrate the invention and should not be construed as imposing any limitations upon the claims.

EXAMPLE 1 [0034] Supported Peroxide 1 was formed by mixing 5.0 grams of a, a'- bis (tert-butylperoxy)-diisopropylbenzene (available from GEO Specialty Chemicals of Cleveland, Ohio under the trade designation VUL-CUP3 R) and 1.2 grams of stearic acid together in a 4 ounce glass bottle. The mixture was heated in a water bath to 45°C and mixed until a homogeneous liquid phase was obtained. l0035] In a separate 400 mL beaker, 0.43 grams of solid sodium hydroxide (pellets) and 0.50 grams of phthalic acid were added to 100 mL of deionized water. The solution was heated on a hot plate to 45°C and mixed until all solids were completely dissolved.

[0036] The heated peroxide/stearic acid mixture was added into the heated aqueous solution under constant stirring. Stirring was continued for about 5 minutes until a uniform emulsion was formed. The emulsion was then allowed to cool to a temperature of less than about 30°C. The emulsion had a milky appearance.

[0037] After the emulsion had cooled to a temperature of less than about 30°C, 1.03 grams of solid calcium sulfate (dihydrate) was added to the emulsion under constant stirring. The calcium sulfate (dihydrate) caused the emulsion to break down and form a precipitate. After approximately 10 minutes, the precipitate was recovered from the solution by vacuum filtration.

The precipitate was then dried.

[0038] The precipitate consisted of about 75% by weight a, a'-bis (tert- butylperoxy)-diisopropylbenzene, about 24.8% calcium stearate, and about 0.2% calcium phthalate. The precipitate comprised a solid powder comprising a narrow distribution of particles having an average particle size of about 200 microns. Analysis of scanning electron micrographs taken of the particles suggest that the particles comprise a core consisting essentially of a, a'-bis (tert-butylperoxy)-diisopropylbenzene coated with a scaly coating comprising calcium stearate and calcium phthalate.

EXAMPLE 2 [0039] EPDM rubber compositions A, B, and C were formulated in accordance with conventional methods using the amounts of the components shown in Table 1 below : Table 1 Component C KELTANqD 512X50 100 phr 100 phr 100 phr HAF Black N330 50 phr 50 phr 50 phr KADOXe 911 5. 0 phr 5.0 phr 5.0 phr AGERtTE Resin D 1.0 phr 1.0 phr 1.0 phr VUL-KE 4. 0 phr---- VUL-CUP" 40C--4. 0 phr-- Supported Peroxide 1----2. 13 phr [0040] KELTANs 512X50 is an ethylene propylene diene monomer (EPDM) synthetic rubber available from DSM Elastomers of Addis, Louisiana. HAF Black N330 is a carbon black product available from Shinwoo Advanced Materials Co. , Ltd. of Seoul, Korea. KADOXe 911 is a zinc oxide product available from Zinc Corporation of America of Monaco, Pennsylvania.

AGERITEO Resin D is an anti-oxidant resin available from R. T. Vanderbilt Company, Inc. of Norwalk, Connecticut. VUL-CUPe 40KE and VUL-CUPe 40C are supported peroxide products available from GEO Specialty Chemicals of Cleveland, Ohio. VUL-CUPe 40KE comprises about 40% by weight of a, a'-bis (tert-butylperoxy)-diisopropylbenzene dispersed on Burgess KE clay. VUL-CUPe 40C comprises about 40% by weight of a, a'-bis (tert- butylperoxy)-diisopropylbenzene dispersed on calcium carbonate. Supported Peroxide 1 is the product formed in Example 1 above.

[0041] EPDM rubber compositions A, B, and C were subjected to oscillating disc rheometry (360°F, 3° Arc, 100 cpm, 24 minute motor), and the physical properties of vulcanized EPDM rubber compositions A, B, and C were tested for various physical properties, the results of which are reported in Table 2 below : Table 2 Oscillating Disc Rheometry Parameter Measured A B C Minimum Torque (in-Ibs) 13.75 13. 16 14.02 Maximum Torque (in-) bs) 44.39 44.43 45.40 Delta Torque (in-) bs) 30. 65 31.26 31.38 Ts2 (minutes) 1.33 1.25 1.25 T90 (minutes) 7.18 7.02 6.60 Physical Properties of Vulcanized Rubber Compound Parameter Measured A B C Modulus at 100% Elongation (psi) 170 160 160 Modulus at 200% Elongation (psi) 380 340 360 Modulus at 300% Elongation (psi) 780 720 790 Tensile Strength (psi) 2510 2620 2650 Elongation at Break (%) 600 630 590 Shore A Hardness 56 56 56 l0042] The results shown in Table 2 above demonstrate that lesser amounts, by weight, of a supported peroxide composition according to the invention are sufficient to provide equivalent vulcanization results as conventional supported peroxides.

EXAMPLE 3 [0043] Supported Peroxide 2 was formed by mixing 10.0 grams of a, a'- bis (tert-butylperoxy)-diisopropylbenzene (available from GEO Specialty Chemicals of Cleveland, Ohio under the trade designation VUL-CUPe R) and 1.5 grams of stearic acid together with 0.02 grams of butylated hydroxytoluene in a 4 ounce glass bottle. The mixture was heated in a water bath to 45°C and mixed until a homogeneous liquid phase was obtained.

[0044] In a separate 600 mL beaker, 0.67 grams of solid sodium hydroxide (pellets) and 0.40 grams of phthalic acid were added to 400 mL of deionized water. The solution was heated on a hot plate to 45°C and mixed until all solids were completely dissolved.

[0045] The heated peroxide/stearic acid mixture was added into the heated aqueous solution under constant stirring. Stirring was continued for about 5 minutes until a uniform emulsion was formed.

[0046] To the emulsion, 40.0 grams of polypropylene powder which had an average particle size in which more than 99% of the particles passed through a 60 mesh screen sieve but less than 1 % passed through a 140 mesh screen (Amoco 7200 Polypropylene) was added and the emulsion and polypropylene were stirred to form a suspension. The suspension was then allowed to cool to a temperature of less than about 30°C. The suspension had a milky appearance.

[0047] After the suspension had cooled to a temperature of less than about 30°C, 0.93 grams of solid calcium chloride (dihydrate), which had been dissolved in 100 mL of water, was added to the suspension under constant stirring. The calcium chloride (dihydrate) caused the suspension to break down and form a precipitate. After approximately 10 minutes, the precipitate was recovered from the solution by vacuum filtration. The precipitate was then dried.

[0048] The precipitate consisted of about 17.0 % by weight a, a'-bis (tert- butylperoxy)-diisopropylbenzene, about 3.0 % calcium stearate, about 0.2 % calcium phthalate, about 80 % polypropylene, and about 0.03 % butylated hydroxytoluene. The precipitate comprised a solid powder comprising a narrow distribution of particles having an average particle size which was comparable to the particle size of the polypropylene that was used.

[0049] Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and illustrative examples shown and described herein.

Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.