Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Removing only nonpolymerized or nonpolymerizable material...
Reexamination Certificate
2000-04-06
2002-06-11
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Removing only nonpolymerized or nonpolymerizable material...
C526S317100, C526S307300, C526S307400, C526S307700, C526S072000
Reexamination Certificate
active
06403731
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a process for preparing a polymer solution. More particularly, it relates to radical polymerization of unsaturated monomers in a solvent to prepare a polymer solution having a reduced content of the unreacted unsaturated monomers.
BACKGROUND OF THE INVENTION
Several methods for obtaining a polymer solution having a reduced content of an unreacted unsaturated monomer have been proposed to date. Known processes include (1) feeding nitrogen, etc. to vaporize an unsaturated monomer, (2) simple distillation to distill off an unsaturated monomer together with a solvent, (3) addition of a small amount of a polymerization initiator at the final stage of polymerization to accelerate polymerization of the remaining unsaturated monomer, (4) blowing ozone, etc. into the system at the final stage of polymerization to remove an unreacted unsaturated monomer, (5) addition of a basic substance capable of reacting with an acrylic ester monomer (i.e., unsaturated monomer), such as hydrazine, and (6) irradiation with an ionizing radiation, such as &ggr;-rays.
However, any of these known methods cannot be recognized as a method providing a polymer solution having its unsaturated monomer content reduced sufficiently and therefore easy to handle, highly safe, and almost odorless.
JP-A-
10-87738
(the term “JP-A” as used herein means an “unexamined published Japanese patent application”) discloses a continuous polymerization process for obtaining a resin with excellent optical characteristics, in which polymerization is carried out in a system comprising not more than 25% by weight of a solvent, and the reaction mixture is distilled while withdrawing the bottom of a distillation column to remove the impurities, etc. by-produced in the polymerization. However, the polymer solution prepared by this method contains a large amount of unreacted monomer and therefore it is difficult for use in the fields where weight is: put on safety, such as the medical field and the cosmetic field.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a process for preparing a polymer solution which has a sufficiently reduced residual unsaturated monomer content and therefore is easy to handle, highly safe, and almost odorless.
As a result of intensive studies, the present inventors have found that a polymer solution meeting the above object can be obtained by limiting the weight ratio of an unsaturated monomer(s) and a solvent to be charged and defining the conversion of an unsaturated monomer that has the lowest conversion of the other unsaturated monomers whose boiling point is lower than that of the solvent. The present invention has been completed based on this finding.
The gist of the invention resides in a process for preparing a polymer solution comprising radically polymerizing a monomer mixture comprising at least one unsaturated monomer in a solvent for the unsaturated monomer(s) and the polymer in the presence of a radical polymerization initiator, whereby at least one unsaturated monomer has a lower boiling point than that of the solvent, and wherein the weight ratio of the total amount of the unsaturated monomers to the solvent is in a range of from 1/9 to 7/3, the polymerization is carried out until the conversion of the unsaturated monomer having the lowest conversion of all the other unsaturated monomers whose boiling point is lower than that of the solvent reaches at least 85%, and, after completion of the polymerization, the unreacted unsaturated monomer(s) is removed under rectification conditions.
DETAILED DESCRIPTION OF THE INVENTION
The unsaturated monomers which can be used in the invention are not particularly limited. A monomer mixture comprising at least one unsaturated monomer whose boiling point is lower than that of the solvent used can be used. Therefore, the monomer mixture can contain an unsaturated monomer which has a higher boiling point than the solvent as long as the monomer is so polymerizable as to remain unreacted in only a trace amount. Further, the monomer mixture can contain an unsaturated monomer having a molecular weight of not less than 1000, such as a silicone macro-monomer, because such a macro-monomer has no problem of smell nor of safety even if it remains unreacted.
Examples of useful unsaturated monomers include unsaturated carboxylic acids, unsaturated carboxylic acid alkyl esters, N-alkyl-substituted amides of unsaturated carboxylic acids, alkyl vinyl esters, styrene derivatives, and alkyl vinyl ethers.
The unsaturated carboxylic acids include acrylic acid, methacrylic acid, and vinylacetic acid.
The term “alkyl” as used herein means a straight-chain or branched saturated hydrocarbon group which may be substituted with a functional group containing a nitrogen atom, an oxygen atom, etc. The alkyl group preferably contains 1 to 12 carbon atoms, particularly 1 to 8 carbon atom. Specific examples of the alkyl group are methyl, ethyl, propyl, n-butyl, isobutyl, t-butyl, 2-ethylhexyl, hydroxyethyl, and dimethylaminoethyl. The alkyl esters of the unsaturated carboxylic acids include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, t-butyl acrylate, t-butyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate, dimethylaminoethyl acrylate, and dimethylaminoethyl methacrylate.
The N-alkyl-substituted amides of the unsaturated carboxylic acids include N-methylacrylamide, N-t-butylacrylamide, and N,N-dimethylacrylamide. The alkyl vinyl esters include vinyl acetate, vinyl propionate, and vinyl butyrate. The styrene derivatives include styrene and &agr;-methylstyrene. The alkyl vinyl ethers include methyl vinyl ether, ethyl vinyl ether, propyl vinyl ether, and butyl vinyl ether.
Of these unsaturated monomers preferred are unsaturated carboxylic acids, such as acrylic acid and methacrylic acid; alkyl esters thereof, such as t-butyl acrylate, t-butyl methacrylate, 2-ethylhexyl acrylate, and 2-ethylhexyl methacrylate; N-alkyl-substituted amides thereof, such as N-methylacrylamide, N-t-butylacrylamide, and N,N-dimethylacrylamide; and styrene.
The solvent which can be used in the present invention is not particularly limited. Solvents generally employed in solution polymerization can be used. Those capable of dissolving all the unsaturated monomers to be polymerized and the produced polymer are preferred. Examples of suitable solvents include alcohols, such as ethanol, isopropanol, t-butanol, 3-methoxy-3-methyl-1-butanol, 3-methyl-1,3-butanediol, and 2-methyl-1,3-propanediol; aliphatic hydrocarbons, such as heptane, isoparaffin, and n-paraffin; aromatic hydrocarbons, such as toluene and xylene; esters, such as ethyl acetate, n-propyl acetate, isopropyl acetate, butyl acetate, and 3-methoxy-3-methylbutyl acetate; ketones, such as methyl ethyl ketone and methyl isobutyl ketone; and cyclic silicone solvents, such as octamethylcyclotetrasiloxane and decamethylcyclopentasiloxane. These solvents can be used either individually or as a mixture of two or more thereof.
Preferred among these solvents are multi-component aliphatic: hydrocarbons such as isoparaffin and n-paraffin. Multi-component aliphatic hydrocarbons having 8 to 18 carbon atoms, such as isoparaffin, are particularly preferred.
As the radical polymerization initiator which can be used in the present invention, any radical polymerization initiator known in the art can be used in the present invention. Suitable initiators include peroxides such as benzoyl peroxide and lauroyl peroxide, and azo compounds such as 2,2′-azobisisobutyronitrile, 2,2′-azobis-2,4-dimethylvaleronitrile, and dimethyl 2,2′-azobisisobutyrate.
The polymerization reaction is usually carried out by heating the reaction system comprising the solvent, the unsaturated monomer or monomers, and the radical polymerization initiator to a necessary temperature. The manner of charging the unsaturated monomers or the initiator is not particularly restricted. For example, the requisite amount may be pre
Hayama Kazuhide
Kawaguchi Shigeoki
Kondou Tadahiko
Saitou Yukio
Sawa Kouhei
Mitsubishi Chemical America, Inc.
Sughrue & Mion, PLLC
Wu David W.
Zalukaeva Tanya
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