Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
2002-09-09
2004-04-27
Le, H. Thi (Department: 1773)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
C428S407000, C525S902000
Reexamination Certificate
active
06726991
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to porous polymer particles. More particularly, this invention relates to porous polymeric particles having a core/shell structure and a method for preparation thereof.
BACKGROUND OF THE INVENTION
The present invention relates to polymer particles, in particular porous polymeric particles having a core/shell structure which are useful as packing materials for liquid chromatography, pigments for ink jet receiving layers, adsorbents, cosmetics, paints, building materials, controlled release devices, pharmaceuticals, and the like.
Porous polymer particles are useful for oral, injectable and implantable devices because they have a long circulation time in the body and are efficient drug, enzyme, and protein carriers. The particles form a porous network capable of retaining large amounts of inert and active substances. Such controlled release delivery systems for drugs have a wide variety of advantages over conventional forms of drug administration. Some of these advantages include: decreasing or eliminating the oscillating drug concentrations found with multiple drug administrations; allowing the possibility of localized delivery of the drug to a desired part of the body; preserving the efficacy of fragile drugs; reducing the need for patient follow-up care; increasing patient comfort and improving patient compliance.
The porous polymer particles must be small in size in order to circulate in the body. A problem with prior art particles is that although small in median size, the quality of the particle size distribution may be inadequate. In particular, there may be a tail of larger particles which can give a gritty feel during oral administration, plug needles used for injection, or inhibit circulation in the body. Extensive and tedious filtration may be required in order to remove these larger particles.
Another problem with prior art particles is that some porous polymer particles may be stabilized by small surfactant molecules or by water-soluble polymers. These prior art stabilizers or emulsifiers are sometimes not desired because they may be toxic or create surface properties on the porous polymer particle which are inappropriate for the application.
Porous polymer particles are also useful as pigments for ink jet receivers. While a wide variety of different types of image-recording elements for use with ink jet devices have been proposed heretofore, there are many unsolved problems in the art and many deficiencies in the known products which have limited their commercial usefulness. One such problem is that larger than desired particles create visible defects.
U.S. Pat. No. 5,583,162 relates to porous crosslinked microbeads, about 10 &mgr;m to about 5 mm in diameter, having cavities joined by interconnecting pores. The microbeads are made by polymerization of high internal phase emulsions where about 70% to about 98% water is dispersed as a discontinuous phase in a continuous monomer phase. Finely-divided, water-insoluble inorganic solids, such as silica, are used as suspending agents for the microbeads. However, the particle size of the water-insoluble inorganic solids is not specified or its importance affecting the particle size distribution of the microbeads.
In addition, the process for making porous crosslinked microbeads described in U.S. Pat. No. 5,583,162 requires two separate shearing steps for forming discontinuous phases and also requires an emulsifier. It would be desirable to provide a process for making such microbeads which only has one shearing step and is free of emulsifiers.
It is an object of this invention to provide porous polymeric particles having a core/shell structure. It is another object of this invention to provide porous polymeric particles having a core/shell structure and narrow particle size distribution. It is another object of this invention to provide a method for preparing porous polymeric particles having a core/shell structure which only has one shearing step and is free of emulsifiers.
SUMMARY OF THE INVENTION
These and other objects are achieved in accordance with the invention which comprises core/shell particles having a core of a porous polymer and a shell of an inorganic colloid, the inorganic colloid having a median diameter of less than about 0.07 &mgr;m, and the core/shell particles having a median diameter of less than about 50 &mgr;m.
Using the invention, porous particles are obtained which have narrower particle size distributions than prior art core/shell particles.
In another embodiment of the invention, a method for preparing core/shell particles having a core of a porous polymer and a shell of an inorganic colloid, comprises:
a) forming a suspension or dispersion of ethylenically unsaturated monomer droplets containing a crosslinking monomer and a porogen in an aqueous medium containing an inorganic colloid; and
b) polymerizing the monomer to form core/shell particles having a core of a porous polymer and a shell of an inorganic colloid.
By use of the method of the invention, core/shell particles are obtained which are not limited to inorganic colloids having a median diameter of less than about 0.07 &mgr;m or core/shell particles having a median diameter of less than about 50 &mgr;m.
DETAILED DESCRIPTION OF THE INVENTION
As noted above, the core/shell particles of this invention have a core of porous polymer. This core can be porous beads of essentially spherical shape, porous irregularly shaped particles, or is an aggregate of emulsion particles. Preferred are porous beads. By porous is meant polymers that have voids. They may also be thought of as cavities joined by interconnecting pores.
Suitable cores of a porous polymer used in the invention comprise, for example, acrylic resins, styrenic resins, or cellulose derivatives, such as cellulose acetate, cellulose acetate butyrate, cellulose propionate, cellulose acetate propionate, and ethyl cellulose; polyvinyl resins such as polyvinyl chloride, copolymers of vinyl chloride and vinyl acetate and polyvinyl butyral, polyvinyl acetal, ethylene-vinyl acetate copolymers, ethylene-vinyl alcohol copolymers, and ethylene-allyl copolymers such as ethylene-allyl alcohol copolymers, ethylene-allyl acetone copolymers, ethylene-allyl benzene copolymers, ethylene-allyl ether copolymers, ethylene acrylic copolymers and polyoxy-methylene; polycondensation polymers, such as, polyesters, including polyethylene terephthalate, polybutylene terephthalate, polyurethanes and polycarbonates.
In a preferred embodiment of the invention, the porous polymers suitable for the core are made from a styrenic or an acrylic monomer. Any suitable ethylenically unsaturated monomer or mixture of monomers may be used in making such styrenic or acrylic polymers. There may be used, for example, styrenic compounds, such as styrene, vinyl toluene, p-chlorostyrene, vinylbenzylchloride or vinyl naphthalene; or acrylic compounds, such as methyl acrylate, ethyl acrylate, n-butyl acrylate, n-octyl acrylate, 2-chloroethyl acrylate, phenyl acrylate, methyl-&agr;-chloroacrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate; and mixtures thereof. In another preferred embodiment, methyl methacrylate or styrene is used.
Typical crosslinking monomers used in making the porous polymer core used in the invention are aromatic divinyl compounds such as divinylbenzene, divinylnaphthalene or derivatives thereof; diethylene carboxylate esters and amides such as ethylene glycol dimethacrylate, diethylene glycol diacrylate, and other divinyl compounds such as divinyl sulfide or divinyl sulfone compounds. Divinylbenzene and ethylene glycol dimethacrylate are especially preferred. The porous polymer core has a degree of crosslinking of about 27 mole % or greater, preferably about 50 mole %, and most preferably about 100 mole %. The degree of crosslinking is determined by the mole % of multifunctional crosslinking monomer that is incorporated into the porous polymeric particles.
The core of porous polymer used in this invention can be prepared, for example, by pulverizing
Kaeding Jeanne E.
Smith Dennis E.
Cole Harold E.
Eastman Kodak Company
Le H. Thi
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