Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2001-09-25
2004-08-31
Egwim, Kelechi C. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C523S201000, C523S202000, C524S458000, C524S460000, C526S083000, C526S084000, C526S085000, C526S930000
Reexamination Certificate
active
06784262
ABSTRACT:
This invention relates to processes for chemically-modifying the surface of emulsion polymer particles and to surface-modified emulsion polymer particles. More particularly, it relates to a process for chemically-modifying the surface of emulsion polymer particles which provides increased surface concentration of bound surface-modifying chemical on the particles relative to the surface concentration which would be provided by prior processes.
It is often desirable to have a particular composition or functionality, referred to herein as “surface-modifying chemical”, chemically bound to the surface of a polymer. For example, it is desirable to have acid-functionality attached to the surface of emulsion polymer particles to assist in the stabilization of the polymer particles in water. This may be effected, to varying degrees, by polymerizing acid-containing monomer throughout the polymerization of the other monomers, during portions of the polymerization of the other monomers, as a part of the polymerization of the monomers used to form an outer stage of a multi-stage polymer, or some combination thereof. However, incorporating the acid-containing monomer in parts of the emulsion polymer particle where it is not needed or desired is not only expensive and wasteful but may also cause performance problems such as reduced water-resistance and corrosion resistance and increased water sensitivity. In addition, attempts to provide bound surface-modifying chemical in a later or outer stage often leaves unincorporated or residual surface-modifying chemical in the aqueous medium. This residual surface-modifying chemical may further contribute to the water sensitivity of the system.
Even when one is successful in accomplishing complete incorporation of the surface-modifying chemical in an outer stage on the polymer particle, the polymer chains forming the outer stage may actually penetrate into the inner stage(s) of the polymer rather than forming a discrete outer stage. This penetration of the polymer chains forming the outer stage buries some surface-modifying chemical that is a part of the polymer chains within the polymer particle rather than on its surface. If the surface-modifying chemical is hydrophilic in nature or otherwise will form hydrogen bonds with water (as is the case with copolymerized acid-functional monomers), then it is believed that the polymer particle would be more thermodynamically stable if the material of interest were at the interface between the water and polymer particle surface in aqueous systems. However, because of the nature of the polymer chain entanglements, the polymer chains that contain the surface-modifying chemical may lack the necessary mobility to move to the interface between the water and polymer particle surface. Thus, it would be desirable to provide a process to improve the mobility of the polymer chains containing the bound surface-modifying chemical within the polymer particles, control the location of the surface-modifying chemical exclusively to where it is desired and thereby improve the overall efficiency of action of the material of interest.
A number of different techniques have been employed to improve the mobility of the polymer chains but each technique has serious drawbacks. For example, the polymer particles may be heated, preferably to a temperature above the glass transition temperature of the outer stage polymer, to improve the mobility of the polymer chains. However, heating involves an extra step and may degrade the polymer particles. Alternatively, the polymer particles may be permitted to age for a sufficient period of time to permit the polymer chains to move to the most thermodynamically stable configuration. This alternative is not acceptable because the time required for such movement could be unreasonably long, perhaps months or even years. A third option is to add an organic solvent to soften to the outer stage of the polymer particle and permit greater mobility of the polymer chains. This option leaves a solvent in the composition that may pose attendant safety, health and environmental problems and may need to be removed.
EP 915,108 A discloses a process for producing multistage emulsion polymers with improved extent of swelling and maintenance of dry bulking density, including the steps of:
(a) providing an aqueous emulsion of
(i) multistage emulsion polymer, containing a core stage polymer and a shell stage polymer, wherein the core stage polymer contains, as polymerized units:
(1) 5% to 100% by weight, based on the weight of the core stage polymer, of hydrophilic monoethylenically unsaturated monomer, and
(2) 0% to 95% by weight, based on the weight of the core stage polymer, of at least one nonionic monoethylenically unsaturated monomer; and
wherein the shell stage polymer contains, as polymerized units at least 50% by weight, based on the weight of the shell stage polymer, of nonionic monoethylenically unsaturated monomer; and
(ii) monomer at a level of at least 0.5% by weight based on the weight of the multistage emulsion polymer; and
(iii) swelling agent; under conditions wherein there is no substantial polymerization of the monomer; and
(b) reducing the level of monomer by at least 50%.
EP 959,176 A discloses processes to control the location of a second shell polymer in a multistaged polymer particle. The second shell polymer is formed from 93% to 99.9% by weight, based on the total weight of the second shell polymer, of at least one nonionic monoethylenically unsaturated monomer and from 0.1% to 7% by weight, based on the total weight of the second shell polymer, of an acid-functional monoethylenically unsaturated monomer. The second shell polymer has a glass transition temperature from −15° C. to −50° C.
Applicant has discovered a process to produce polymer particles having a chemically-modified surface. By employing this process, applicant produces polymer particles where the surface-modifying chemical need not be incorporated in portions of the polymer particles where it is not needed or where it is detrimental.
According to a first aspect of the present invention there is provided a process for chemically-modifying the surface of a polymer particle, including the steps of: (1) providing an aqueous emulsion comprising: (a) a multistage emulsion polymer including a core stage polymer and a shell stage polymer, wherein the core stage polymer includes, as polymerized units, from 5% to 100% by weight, based on the weight of the core stage polymer, of hydrophilic monoethylenically unsaturated monomer, and from 0% to 95% by weight, based on the weight of the core stage polymer, of at least one nonionic monoethylenically unsaturated monomer; and wherein the shell stage polymer includes, as polymerized units, at least 50% by weight of nonionic monoethylenically unsaturated monomer; (ii) a monomer at a level of at least 0.5% by weight based on the weight of the multistage emulsion polymer; and (iii) at least one surface-modifying chemical capable of chemically bonding with the monomer; under conditions wherein there is no substantial polymerization of the monomer; and (2) reducing the level of the monomer by at least 50%.
According to a second aspect of the present invention there is provided a process for chemically-modifying the surface of a polymer particle, including the steps of: (a) providing an aqueous emulsion, including: (i) a multistage emulsion polymer including a core stage polymer and a shell stage polymer; wherein the core stage polymer includes, as polymerized units, 0.1% to 100% by weight, based on the weight of the core stage polymer, of at least one nonionic monoethylenically unsaturated monomer; and wherein the shell stage polymer contains, as polymerized units: (1) at least 50% by weight, based on the weight of the shell stage polymer, of nonionic monoethylenically unsaturated monomer; and (2) at least one surface-modifying monomer; (ii) a monomer at a level of at least 0.5% by weight based on the weight of the multistage emulsion polymer; and (iii) neutralizing agent; under con
Egwim Kelechi C.
Rohm and Haas Company
LandOfFree
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