Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2002-01-23
2003-11-11
Choi, Ling-Siu (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S090000, C526S158000, C526S348000, C526S128000, C526S156000
Reexamination Certificate
active
06646072
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method of exfoliating clay into polyolefins. In particular, the invention relates to treating smectite clay with a Ziegler-Natta catalyst and polymerizing an olefin in the presence of an organoaluminum cocatalyst and the treated clay.
BACKGROUND OF THE INVENTION
Polyolefins are widely used because of their properties. Nevertheless, the applications for polyolefins could be extended if certain properties such as stiffness, strength and heat resistance were improved. While fillers can improve these properties, their use is limited because there does not exist a good method for dispersing the fillers and achieving the desired properties without concomitant loss of toughness. This is presumably due to the high levels of fillers needed and concomitant problems with dispersing the fillers in the polyolefin matrix. There is a need for an improved method to disperse clay filler into a polyolefin matrix.
U.S. Pat. Nos. 5,830,820; 5,906,955; 5,925,587; 6,034,187 and 6,110,858 provide supported catalysts for the polymerization of olefins. Low levels of these supported catalysts are then used to catalyze the polymerization of olefins and provide polyolefins with only low levels of the support material.
U.S. Pat. No. 6,252,020 provides for clay-filled compositions by bulk and suspension polymerization of vinyl monomers such as styrene in the presence of clay and catalysts such as peroxides. Neither the polymerization of olefins such as ethylene or propylene nor the use of transition metals as catalysts is described or suggested.
U.S. Pat. No. 4,473,672 describes a process for making polyolefin compositions with a variety of fillers such as graphite, carbon black, an aluminosilicate clay, mica, talc, vermiculite or glass fibers by pretreating the filler with an organic magnesium compound and then adding the resultant composition to a transition metal and subsequently initiating the polymerization with an organoaluminum compound.
U.S. Pat. No. 4,564,647 teaches a process for producing a filled polyethylene composition with a variety of fillers. The process is general with regard to fillers. Specifically mentioned are metals, metal oxides, metal carbonates, titanium dioxide, mica, glass beads, glass fibers, silica, alumina, silica aluminate and organic pigments among many others. The filler may take various forms, such as powder, granule, flake, foil, fiber and whisker. The catalyst component is a transition metal treated with either a magnesium or manganese compound or is a Group 4 cyclopentadienyl compound. Despite a very broad disclosure, there is no mention of clay and no indication of a method of exfoliating clay.
PCT Int. Appl. WO 01/30864 discloses a method for producing a nanocomposite polymer by use of an acid-treated, cation-exchanging layered silicate material. The reference teaches that the silicate material is acidified by contacting it with a Bronsted acid such as a mineral acid or an amine hydrochloride. This requires an extra step, which increases the cost and complexity of the process. We found that the acid can also a have deleterious effect on the yield of the polymerization process, particularly when a Ziegler-Natta catalyst is used instead of a metallocene complex.
It has been observed that the synthesis of polyolefin-silicate nanocomposites remains a synthetic challenge (Bergman et al.,
Chem. Commun
. (1999) 2179). These workers attributed the difficulty to the sensitivity of the vast majority of olefin polymerization catalysts to Lewis bases and water. Therefore, they used late transition metal catalysts to attempt to polymerize ethylene in the presence of a synthetic fluorohectorite. The product formed was described as a rubbery polymer that was highly branched. Such a polymer is unsuitable for many applications because of difficulties in processing.
There is a need for a simple process for providing clay-filled compositions and, in particular, for polyolefin compositions containing exfoliated clay.
SUMMARY OF THE INVENTION
The invention is a process for incorporating clay into polyolefins. The process involves treating smectite clay with a hydrocarbon solution of a Ziegler-Natta catalyst and polymerizing the olefin in the presence of the treated clay and an organoaluminum cocatalyst.
This invention provides for a simple method to prepare polyolefin compositions that contain exfoliated clay platelets. The invention also includes clay-filled polyolefin compositions prepared by this method.
DETAILED DESCRIPTION OF THE INVENTION
The clays useful in the invention are non-acid-treated smectite clays. Smectite clays are well described in the literature (see Izumi, Y. et al.,
Zeolite, Clay and Heteropoly Acid in Organic Reactions
, VCH Publishers Inc. (1992)). They are layered materials with exchangeable cations between the layers to compensate for the negative charge of the layers. Clays are classified according to their layer charge. Smectite clay minerals have cation exchange capacity in the range of 60-100 meq/100 g-clay.
Smectite clays can be synthesized from magnesium silicates. Synthetic smectite clays are available from ZEN-NOH UNICO America Corporation. More commonly, they are available from naturally occurring bentonite ore. Two common types of smectite clay are montmorillonite and hectorite. Montmorillonite is classified as magnesium aluminum silicate and hectorite as magnesium silicate. Montmorillonite is more available due to the vast naturally occurring deposits.
By “non-acid-treated,” we mean that the clay has not been treated with a Bronsted acid to exchange the cations with a proton. Bronsted acids are acids that can donate a proton. Examples include HCl, H
2
SO
4
, triethylammoniumchloride and N,N-diethylanilinium chloride.
The cations on the clay surface affect the organophilicity of the clay. If the cation is a metallic cation such as sodium or calcium, the clay is not very organophilic and will not dissolve in organic solvents such as toluene. These clays are useful in the invention. However, optionally, it may be preferred to use a more organophilic clay. If the cation is an organic cation such as an ammonium cation, then the clay becomes more organophilic. These are readily prepared by cation exchange of the sodium clay with an organic cation. Suitable organic cations include ammonium cations where the nitrogen has four non-hydrogen substituents, such as hexadecyloctadecyldimethyl ammonium, dimethyldioctadecyl ammonium, benzyl triethyl ammonium, methyltrioctylammonium and poly(oxypropylene)methyldiethyl ammonium. This increases the solubility and ease of dispersion in organic solvents. Dependent upon the amount of cation exchange and the particular organic cation used, the clay may be soluble in organic solvents such as toluene.
Optionally, the clay can be surface treated to react hydroxyl groups on the clay and to increase the organophilicity of the clay. By reacting the hydroxyl groups on the clay, the catalyst performance and hydrogen response is often improved. By “hydrogen response,” we mean the ability to incorporate hydrogen as a means of controlling polyolefin molecular weight. The surface treatment can be done with a silicon compound or with a monoalkyl metal compound. Preferably, the surface treatment is done with a silicon compound and preferably the silicon compound is an alkyl disilazane. Suitable alkyl disilazanes include hexaalkyl disilazanes having the formula R
1
3
SiNHSiR
1
3
where R
1
is a C
1
-C
20
hydrocarbyl. In particular, hexamethyldisilazane is preferred. Preferred monoalkyl metal compounds contain a single C
1
to C
8
alkyl group, as in ethyl aluminum dichloride, isobutyl aluminum dichloride or methyl magnesium chloride.
Optionally, the clay is dried. When the clay has an organic cation or has been treated with an organosilicon compound, it is less hydrophilic and has a tendency to retain less water. For these clays, the drying step is less important. When the clay has a metal cation, it is more hydrophilic and therefore it is preferable to dry the clay. If the clay has a
Klendworth Douglas D.
Reinking Mark K.
Choi Ling-Siu
Equistar Chemicals LP
Schuchardt Jonathan L.
Tyrell John
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