Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymerizing in tubular or loop reactor
Reexamination Certificate
2002-07-11
2003-08-05
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymerizing in tubular or loop reactor
C526S089000, C526S217000, C526S227000, C526S319000, C526S330000, C526S352000
Reexamination Certificate
active
06602966
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method of producing nanocomposite materials by incorporating nanoclays during high pressure polymerizations. More specifically, the invention relates to a process wherein ethylene homopolymer or copolymer nanocomposites are produced by polymerizing the monomer(s) at high pressure in the presence of an organic peroxide initiator and an organically modified clay.
BACKGROUND OF THE INVENTION
Ethylene polymers and copolymers are widely used because of their desirable physical properties; however, the applications for these polymers could be extended if certain properties, such as melt strength and stress crack resistance, could be improved. While conventional fillers can be employed to improve certain physical properties, it is often at the expense of other properties.
In recent years, nanoclays, i.e., organically modified clays, have been extensively used to enhance the performance of olefin polymers and overcome the problems heretofore observed when conventional fillers such as talc and calcium carbonate. The nanoclays have improved dispersibility in the polymer matrix due to their plate-like structure. As a result, the size of the filler particle, when dispersed, is on a nanoscale so that property enhancement is achieved at much lower filler levels compared to traditional fillers. Separation of the clay platelettes occurs in two steps. The first step is to separate the platelettes just enough to allow the polymer to locate between the plates and to maintain the spacing. This is known as intercalation. The second step is to delaminate or separate the platelettes further, which typically is achieved by melt mixing in an extruder or the like. This is called exfoliation. The extent of property improvement is typically related to the extent of exfoliation.
Various processes to produce in-reactor-filled polyolefin composite materials are known. U.S. Pat. Nos. 5,412,001; 5,412,025 and 5,422,386 describe processes for reactor-filling polyolefins by polymerizing &agr;-olefins in the presence of conventional fillers, such as Kaolin, mica or talc, which have been pretreated with catalytic amounts of organometallic compounds such as transition metal ester compounds.
U.S. Pat. Nos. 5,830,820; 5,906,955; 5,925,587; 6,034,187 and 6,110,858 disclose 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 containing low levels of filler material.
U.S. Pat. No. 4,473,672 describes a process for making polyolefin compositions with a variety of fillers such as graphite, carbon black, 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. 6,252,020 discloses clay-filled compositions produced by bulk and suspension polymerization of vinyl monomers, such as styrene, in the presence of clay and catalysts such as peroxides. The polymerization of olefins such as ethylene or propylene is not described or suggested.
There is a need for improved methods of dispersing clay fillers into ethylene homopolymers and copolymers utilizing in-reactor-filling procedures.
SUMMARY OF THE INVENTION
The present invention relates to a high pressure process for producing ethylene homopolymers and copolymers having organically modified clays incorporated and intimately dispersed therein. The process involves producing ethylene (co)polymer nanocomposites by (co)polymerizing ethylene under high pressure polymerization conditions in the presence of an organic peroxide initiator and organically modified smectite clay. Intercalation and exfoliation of the clay is effected in this manner. For the process the organically modified clay can be added to the high pressure polymerization reactor by one of several methods which can include the use of polar solvents, polar monomers or incorporation of the organic peroxide initiator on the clay. The latter procedure involves pretreating the organically modified clay with the organic peroxide. Polymerization can be accomplished utilizing autoclave or tubular reactors operated at pressures from about 10000 to 50000 psi and temperatures from about 250 to 650° F.
Organically modified clays preferably used for the process are montmorillonite clays that have been ion exchanged and intercalated with a quaternary ammonium ion corresponding to the formula
(R)(R
1
)(R
2
)(R
3
)N
+
where R represents a C
18
alkyl substituent or mixture of alkyl substituents wherein the C
18
alkyl moieties constitute 50% or more of the mixture and R
1
, R
2
and R
3
are independently selected from the group consisting of R, H and C
1-22
hydrocarbon groups.
For the production of ethylene copolymers the comonomers are preferably olefinically unsaturated comonomers selected from the group consisting of C
3-8
&agr;-olefins, vinyl C
2-4
carboxylate and C
1-4
alkyl (meth)acrylates.
DETAILED DESCRIPTION OF THE INVENTION
Clays useful for the invention are smectite clays which 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 50-100 meq/100 g-clay.
Smectite clays can be synthesized from magnesium silicates or, more commonly, they are obtained 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.
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. If the cation is an organic cation, such as an ammonium cation, then the clay becomes more organophilic. These latter types of organically modified clays 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. Organically modified clays of the above types, also referred to herein as organoclays or nanoclays, are employed for the process of the present invention.
For the process of the invention, smectite clays of the above types, and particularly montmorillonite clays, reacted with ammonium compounds having one or more C
18
alkyl substituents are most advantageously employed. Montmorillonite clays that have been ion exchanged and intercalated with quaternary ammonium ions corresponding to the formula
(R)(R
1
)(R
2
)(R
3
)N
+
where R represents a C
18
alkyl substituent or mixture of alkyl substituents wherein the C
18
alkyl moieties constitute 50% or more of the mixture and R
1
, R
2
and R
3
are independently selected from the group consisting of R, H or a C
1-22
hydrocarbon group are particularly useful. Mixed alkyl substituents of the above types are typically obtained utilizing amines derived from natural sources such as beef tallow or mutton tallow. R moieties obtained from such natural products correspond to the constituent fatty acids and typically are mixtures of aliphatic radicals comprised of predominantly C
14-18
carbon atoms. The carbon number range and distribution within the carbon number range, i.e., percentage of each component, can vary depending on factors such as the tallow source, treatment and age of the tallow. Typical constituent fatty acid values have, however, been generated and are as follows:
Constituent Fatty Acid
Beef Tallow
Mutton Tallow
Myris
Chandrashekar Venki
Lynch Michael W.
Ruda Michael J.
Vargas Edward S.
Baracka Gerald A.
Cheung William
Equistar Chemicals LP
Heidrich William A.
Wu David W.
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