Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2001-09-27
2004-02-24
Cheung, William (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C525S344000, C526S234000, C526S089000, C526S090000, C526S192000
Reexamination Certificate
active
06696519
ABSTRACT:
This invention relates to a redox process for preparing an emulsion polymer having low residual monomer content. Desirably, the redox process provides an emulsion polymer having low volatile organic compound content as well as low residual monomer content. More particularly, this invention relates to a process for preparing an aqueous emulsion polymer including providing at least one ethylenically unsaturated monomer and a free radical redox initiator system under emulsion polymerization conditions, the redox initiator system including a water-soluble oxidizing agent, an water-insoluble oxidizing agent, and a sulfinic acid, or salts thereof, reducing agent; and effecting the polymerization of at least some of the ethylenically unsaturated monomer. And the invention also relates to a process for reducing the residual monomer content of an emulsion polymer.
Redox initiator systems including at least one oxidizing agent and at least one reducing agent and, optionally, a metal promotor species are advantageously used in the emulsion polymerization of ethylenically unsaturated monomers, particularly if polymerization at temperatures lower than those at which conventional thermal initiation systems provide an effective level of free radical production such as at temperatures below 85° C. is desired. However, some redox initiator systems are less efficient for reducing monomer levels, particularly for reducing the levels of certain monomers, and for reducing total volatile organic compound content, particularly since some water-insoluble oxidizing agents must be provided as solutions in water-miscible solvents in order to be easily used in aqueous emulsion polymerizations. The present invention serves to provide redox emulsion polymerization processes which desirably lead to lowered residual monomer levels and/or lowered volatile organic compound levels when compared with processes using alternative redox initiator systems.
U.S. Pat. No. 5,087,676 discloses the preparation of polymers from olefinically unsaturated monmers using a free radical initiator system which is soluble and consists of an oxidizing agent, a reducing agent, an iron salt, and a vanadium salt.
U.S. Pat. No. 5,886,140 discloses a redox process to reduce residual monomer content at the end of an emulsion polymerization process using certain oxidizing agents and reducing agents selected from complexes of formol and zinc sulfoxylate, reducing sugars or their acid derivatives, and C5-C4 carboxylic acids.
A redox emulsion polymerization process which provides even lower residual monomer levels and/or lower volatile organic compound levels is still desired. It has now been surprisingly found that lowered residual monomer levels are found in emulsion polymerization of ethylenically unsaturated monomers when certain free radical redox initiator systems are used under emulsion polymerization conditions, the redox initiator systems including a water-soluble oxidizing agent, an water-insoluble oxidizing agent, and a sulfinic acid, or salts thereof, reducing agent. An improvement is found in reducing residual monomer at the end of a emulsion polymerization as well as in an emulsion polymerization itself.
In a first aspect of the present invention there is provided a process for preparing an aqueous emulsion polymer including providing at least one ethylenically unsaturated monomer and a free radical redox initiator system under emulsion polymerization conditions, the redox initiator system composed of a water-soluble oxidizing agent, an water-insoluble oxidizing agent, and a sulfinic acid, or salts thereof, reducing agent; and effecting the polymerization of at least some of the ethylenically unsaturated monomer.
In a second aspect of the present invention there is provided a process for reducing the residual ethylenically unsaturated monomer content of an aqueous emulsion polymer including contacting the aqueous emulsion polymer with a free radical redox initiator system, the redox initiator system composed of a water-soluble oxidizing agent, an water-insoluble oxidizing agent, and a sulfinic acid, or salts thereof, reducing agent; and effecting the polymerization of at least some of the residual ethylenically unsaturated monomer.
The process for preparing an aqueous emulsion polymer of this invention includes providing at least one ethylenically unsaturated monomer and a free radical redox initiator system under emulsion polymerization conditions.
The aqueous acrylic emulsion polymer contains, as copolymerized unit(s), at least one copolymerized monoethylenically-unsaturated (meth)acrylic monomer including esters, amides, and nitriles of (meth)acrylic acid, such as, for example, (meth)acrylic ester monomer including methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, decyl acrylate, lauryl acrylate, stearyl acrylate, methyl methacrylate, butyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, aminoalkyl (meth)acrylate, N-alkyl aminoalkyl (methacrylate), N,N-dialkyl aminoalkyl (meth)acrylate; urieido (meth)acrylate; (meth)acrylonitrile and (meth)acrylamide; styrene or alkyl-substituted styrenes; butadiene; vinyl acetate, vinyl propionate, or other vinyl esters; vinyl monomers such as vinyl chloride, vinylidene chloride, and N-vinyl pyrollidone; allyl methacrylate, diallyl phthalate, 1,3-butylene glycol dimethacrylate, 1,6-hexanedioldiacrylate, and divinyl benzene; (meth)acrylic acid, crotonic acid, itaconic acid, sulfoethyl methacrylate, phosphoethyl methacrylate, fumaric acid, maleic acid, monomethyl itaconate, monomethyl fumarate, monobutyl fumarate, and maleic anhydride. The use of the term “(meth)” followed by another term such as acrylate, acrylonitrile, or acrylamide, as used throughout the disclosure, refers to both acrylate, acrylonitrile, or acrylamide and methacrylate, methacrylonitrile, and methacrylamide, respectively.
The free radical addition polymerization techniques used to prepare the acrylic emulsion polymer of this invention are well known in the art. Conventional surfactants may be used such as, for example, anionic and/or nonionic emulsifiers such as, for example, alkali metal or ammonium salts of alkyl, aryl, or alkylaryl sulfates, sulfonates or phosphates; alkyl sulfonic acids; sulfosuccinate salts; fatty acids; ethylenically unsaturated surfactant monomers; and ethoxylated alcohols or phenols. The amount of surfactant used is usually 0.1% to 6% by weight, based on the weight of monomer.
A redox initiator system composed of a water-soluble oxidizing agent, an water-insoluble oxidizing agent, and a sulfinic acid, or salts thereof, reducing agent is used. At least one sulfinic acid reducing agent, or salt thereof such as, for example, alkylsulfinic acids such as isopropyl sulfinic acid; aryl sulfinic acuds such as phenylsulfinic acid; and hydroxyalkyl sulfinic acids such as hydroxymethane sulfinic acid and 2-hydroxy-2-sulfinatoacetic acid and salts of the preceding acids typically at a level of 0.01% to 3.0%, preferably 0.01 to 0.5%, more preferably 0.025% to 0.25%, by weight based on monomer weight, is used. A preferred reducing agent is 2-hydroxy-2-sulfinatoacetic acid. Typically, 0.01% to 3.0%, preferably 0.02 to 1%, more preferably 0.05% to 0.5%, by weight based on monomer weight, of oxidizing agent is used. The oxidizing agent includes a water-soluble oxidizing agent such as, for example, hydrogen peroxide and ammonium or alkali metal persulfates, perborates, peracetates, peroxides, and percarbonates and a water-insoluble oxidizing agent such as, for example, benzoyl peroxide, lauryl peroxide, t-butyl peroxide, t-butyl hydroperoxide, 2,2′-azobisisobutyronitrile, t-amyl hydroperoxide, t-butyl peroxyneodecanoate, and t-butyl peroxypivalate. By “water-insoluble oxidizing agent” herein is meant an oxidizing agent which has a water solubility of less than 20% by weight in water at 25 C. Redox reaction catalyzing metal salts of iron, copper, manganese, silver, platinum, vanadium, nickel, chromium, palladium, or cobalt may optionally be used at a level of 0.01 t
Brown Steven Charles
Even Ralph Craig
Bakule Ronald D.
Cheung William
Rohm and Haas Company
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