Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Adhesive outermost layer
Reexamination Certificate
1996-06-20
2002-04-09
Wu, David W. (Department: 1713)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Adhesive outermost layer
C428S402000, C428S3550EN, C526S161000, C526S172000, C526S308000, C526S348200, C526S348300, C526S348500, C526S351000, C526S909000, C526S931000, C526S093000, C526S094000
Reexamination Certificate
active
06368708
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to polyolefin microspheres and methods of preparation therefor.
BACKGROUND OF THE INVENTION
Inherently tacky, elastomeric microspheres have been described for use, for instance, as adhesives in repositionable pressure sensitive adhesive applications. Typically, microsphere adhesives are prepared via suspension polymerization of one or more free-radically polymerizable monomers, usually acrylate or methacrylate monomers, in the presence of surfactants and/or suspension stabilizers. Suspension polymerization is particularly advantageous, since microspheres result directly from the polymerization process as opposed to post-polymerization suspension of an already-formed polymer. Microsphere adhesives described to date comprise homopolymers or copolymers of acrylate or methacrylate monomers, presumably due to the ease with which such monomers can be suspension polymerized in aqueous systems. The preparation of acrylate-based microsphere adhesives is described in, for instance, U.S. Pat. Nos. 3,691,140, 4,166,152, and 5,053,436. Microsphere adhesives prepared from alpha-olefins have not been described.
Non-free radical polymerizations of ethylenically-unsaturated monomers are well known. Typically, these polymerizations use catalysts instead of initiators to effect polymerizations. Examples of such catalyzed polymerizations include Ziegler-Natta (ZN) polymerizations of alpha-olefins, ring-opening metathesis polymerizations ROMP) of cyclic olefins, group-transfer polymerizations (GTP), and cationic and anionic polymerizations of activated olefins such as styrene or acrylate. More recently, metallocene catalysts have received considerable attention for polymerization of alpha-olefins. ZN and metallocene catalysts for alpha-olefin polymerizations are susceptible to deactivation by adventitious oxygen and water, requiring that such deactivating materials be rigorously excluded from all reagents as well as the reaction vessel.
Recently, the polymerization of ethylene, other olefins, and alkynes using a polymerization catalyst whose cationic portion has the formula
LM—R
+
wherein M is a Group VIII metal, L is a ligand or ligands stabilizing the Group VIII metal, and R is H a hydrocarbyl radical or a substituted hydrocarbyl radical, and a substituted tetraphenylborate anion as the counterion has been described in, e.g. European Patent Application No. 454231. A preferred cationic portion has the formula
wherein L′ is a two-electron donor ligand and L″ L″ are chelating ligands wherein each L″ is a neutral two-electron donor ligand, M is nickel or palladium and L is a two-electron donor ligand or the two L′ ligands together are a chelating ligand. Preparation of microspheres and, in particular, microsphere adhesives, was not disclosed.
In disclosures from the same laboratory, Johnson et al., (
J. Am. Chem. Soc
., 1995, 117, 6414-6415 and supplementary material) describe Pd(II)- and Ni(II)-based catalysts for alpha-olefin polymerizations wherein the catalysts are, for example, cationic metal methyl complexes of the general formula
{(ArN═C(R
1
)C(R
1
)═NAr)M(CH
3
)(OEt
2
)}
+BAr′
4
−
wherein M is Pd or Ni, Ar′ is 3,5-C
6
H
3
(CF
3
)
2
, Ar is 2,6-C
6
H3(R′) where R′ is isopropyl or methyl; R
1
is H. methyl, or the two R
1
groups taken together comprise a 1,8-naphthylene-diyl group. The same authors and S. J. McLain et al. reported that the same catalysts copolymerized ethylene and methyl acrylate (see PMSE Abstracts, Vol. 73, p. 458, Fall 1995, Proceedings of the American Chemical Society, Fall 1995, Chicago, Ill.). A full publication describing these findings and a catalyst {(ArN═C(R
1
)C(R
1
)═NAr)M(CH
2
CH
2
CH
2
C(OR
2
)(C═O)}
+BAr′
4
−
are reported by Johnson et al. (
J. Am. Chem. Soc
., 1996, 118, 267-268 and supplementary material), wherein R
2
can be —CH
3
, t-butyl, or —CH
2
(CF
2
)
6
CF
3
. Again, preparation of microspheres and, in particular, microsphere adhesives, was not disclosed.
SUMMARY OF THE INVENTION
Briefly, the present invention provides microspheres comprising a polymer including one or more of 1) a plurality of C
3
or larger alpha-olefin units wherein the polymer has an average number of branch points less than one per monomer unit, and 2) a plurality of C
2
alpha-olefin units wherein the polymer has an average number of branch points greater than 0.01, preferably greater than 0.05, more preferably greater than 0.10, per monomer unit incorporated into the polymer, said microspheres having an average diameter in the range of 1 to 300 micrometers. The microspheres of the invention are prepared as the polymerization product of one or more alpha-olefin hydrocarbon monomers having 2 to 30 carbon atoms, the polymerization being carried out in the presence of an effective amount of an organometallic catalyst comprising a Group VIII metal (CAS version of the Periodic Table), preferably Pd, the catalyst further comprising a polydentate ligand providing steric bulk sufficient to permit formation of polymer, and at least one liquid reaction medium in which the polymer microspheres are essentially insoluble.
In another aspect, the invention describes a method of producing the microspheres, comprising admixing, in any order, alpha-olefin monomer(s), catalyst, and at least one liquid reaction medium in which the resultant polymer is insoluble, and allowing polymerization of the alpha-olefin monomer(s) to take place.
One variation of the method comprises dispersing into an aqueous medium, in any order, one or more C
2
to C
30
alpha-olefin monomers, a polymerization organometallic catalyst comprising a Group VIII metal with which is complexed a polydentate ligand having steric bulk sufficient to permit formation of polymer, and optionally a surfactant or suspension stabilizer, and allowing the monomer(s) to polymerize, to produce polymer microspheres.
A second variation of the method comprises admixing one or more C
2
to C
30
alpha-olefin monomers, a polymerization organometallic catalyst comprising a Group VIII metal with which is complexed a polydentate ligand having steric bulk sufficient to permit formation of polymer, organic solvent in an amount sufficient to dissolve the monomer and catalyst and in which the polymer is insoluble, and allowing the monomers to polymerize to produce polymer microspheres; and optionally isolating the polymer microspheres produced by either variation of the method.
Preferably, the polymer M
w
of the microspheres is greater than 5000, preferably greater than 90,000, and most preferably greater than 100,000 up to about 5,000,000, preferably 2,000,000.
In still another aspect, the present invention provides microspheres comprising crosslinked alpha-olefin polymers. In one embodiment, a method employing high-energy irradiation of the polymer, preferably by electron beam irradiation, is used. In another embodiment, a method employing ultraviolet (UV) irradiation is used, the polymerized composition preferably further comprising UV-activated crosslinking agents.
In yet another aspect, the present invention provides films, fibers, articles and coatings comprising microspheres comprising a polymer including one or more of 1) a plurality of C
3
or larger alpha-olefin units wherein the polymer has an average number of branch points less than one per monomer unit, and 2) a plurality of C
2
alpha-olefin units wherein the polymer has an average number of branch points greater than 0.01 per monomer unit, preferably greater than 0.05, more preferably greater than 0.10, said microspheres having an average diameter in the range of 1 to 300 micrometers. Films, fibers, articles and coatings comprising the microspheres can be prepared by methods known in the art, such methods including solvent, dispersion or suspension coating, extruding, casting, melt processing, and powder coating.
In a still further aspect, microspheres comprising a polymer which is the polymerization product of
Brown Katherine A.
Kesti Michael R.
Dahl Philip Y.
Rabago R.
Wu David W.
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