Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymerizing in tubular or loop reactor
Reexamination Certificate
2000-05-03
2003-02-04
Henderson, Christopher (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymerizing in tubular or loop reactor
C526S200000
Reexamination Certificate
active
06515082
ABSTRACT:
This invention relates to a process for preparing polymers. In particular, the invention relates to a process for preparing polymers which contain as polymerized units hydrophobic monomers. As used herein, by hydrophobic monomer is meant a monomer containing a C
8
to C
28
(meth)acrylic acid ester or a monomer with low water solubility such as styrene. By (meth)acrylic is meant both acrylic and methacrylic.
Polymers may be made by various processes, which include solution and emulsion polymerization. Many solution polymerization processes utilize organic solvents, whereas emulsion polymerization processes utilize water and surfactants. Due to environmental concerns over volatile organic compounds, emulsion polymerization processes are preferred.
Until recently, polymers which contain as polymerized units hydrophobic monomers were only known to be made through solution polymerization processes. This was because there are difficulties with emulsion polymerization processes. There are three problems associated with the emulsion polymerization of hydrophobic monomers. The first problem is that it is difficult to disperse the hydrophobic monomer in water and transport the monomer to the forming polymer. The second problem is in forming small enough monomer droplets to form a stable monomer emulsion. The third problem is that some suspension polymer, which has a larger particle size than emulsion polymer forms. The suspension polymer may cause problems such as forming a “cream” layer on top of the latex or a sedimentation layer upon storage. The suspension polymer may also cause problems in downstream application properties.
Therefore, there is a need for a process for preparing polymers which contain as polymerized units hydrophobic monomers, wherein a stable emulsion is formed and suspension polymer formation is minimized.
One emulsion polymerization approach to dispersing the hydrophobic monomer and transporting it to the forming polymer was taught in U.S. Pat. No. 5,521,266. The process disclosed in that patent generates a latex, and utilizes cyclodextrin to transport the monomer through the water phase to the polymer phase. The monomer and cyclodextrin were combined in an emulsion with a monomer concentration ranging from 69 weight percent to 77 weight percent. The monomer emulsion was not pre-diluted prior to feeding it to the reactor.
One problem associated with the approach of U.S. Pat. No. 5,521,266 is that some suspension particles are formed. Another problem associated with this approach is that upon dilution of the concentrated monomer emulsion with water, a highly viscous dispersion is formed. The high viscosity requires more energy to disperse the monomer emulsion in the reactor, and therefore more cost to agitate the dispersion during the polymerization. If higher agitation rates are used in the reactor, there is a potential for shear coagulation of the latex.
U.S. Pat. No. 3,637,563 disclosed a process for preparing polymers which may contain as polymerized units hydrophobic monomers. The process was designed to make higher solids containing polymer emulsions. The process includes premixing monomers, surfactant, and water in a tank to form a concentrated monomer emulsion, then feeding the concentrated monomer emulsion containing from 75 percent by weight to 94 percent by weight monomer to a reactor containing water and polymerizing the monomers. The process does not include a step of pre-diluting the concentrated monomer emulsion with water through a mixer prior to feeding the monomer emulsion to the reactor. Therefore, the process has the problem of forming a highly viscous dispersion upon dilution of the concentrated monomer emulsion with water.
U.S. Pat. No. 3,296,168 disclosed a continuous process for preparing polymers. The process utilizes an in-line mixer to create continuously a monomer emulsion from one monomer feed and a second feed of surfactant and water. A process for preparing polymers from concentrated monomer emulsions containing hydrophobic (meth)acrylic acid ester monomers was not disclosed.
U.S. Pat. No. 4,355,142 disclosed a process of preparing monomer emulsions for making polyvinyl chloride latexes. The process utilizes in-line rotating shearing means to prepare the monomer emulsion. The reference disclosed a drastic reduction in polymer build-up on the reactor interior and coagulum in the latex. The reference did not disclose the applicability of this process to hydrophobic monomers.
Despite the disclosure of the references, there is a continuing need for a process of preparing polymers containing as polymerized units hydrophobic monomers, wherein a stable emulsion is formed and suspension polymer formation is minimized.
The present invention provides a process including: preparing a concentrated monomer emulsion including at least one monomer; diluting the concentrated monomer emulsion with water; feeding the diluted monomer emulsion to a reactor; and polymerizing the monomer.
As indicated above, the first step in the process of the invention involves preparing a concentrated monomer emulsion. By concentrated is meant that the monomer emulsion contains from 76 percent by weight to 95 percent by weight, preferably from 80 percent by weight to 90 percent by weight of at least one monomer. The monomer is combined with water and emulsifiers or dispersing agents to form the concentrated monomer emulsion.
The concentrated monomer emulsion may be prepared by admixing the monomer, water, and emulsifiers or dispersing agents in a tank.
Alternatively, the concentrated monomer emulsion may be prepared through the use of in-line mixing. The in-line mixing process is characterized by separate feeds of monomer and a solution of water and emulsifiers or dispersing agents being fed continuously through an in-line mixer contained in the line and then to the reactor.
The preferred mixers are high shear mixers, such as, but not limited to an IKA multi-teeth high shear mixer (ULTA-TURRAX in line or the like), or Series 400 IN-LINE, X-Series Mixer Emulsifiers by Charles Ross & Son Company. This kind of mixer can produce high shear and energy density in a small space to emulsify the monomer in water.
The concentrated monomer emulsion may also be prepared by utilizing a high pressure homogenizer. A homogenizer is a device that pumps monomers, water, and surfactant through a valve at a high pressure. The pressure typically ranges from 1000 to 30000 psi. Suitable homogenizers include, but are not limited to those from EmulsiFlex such as the EmulsiFlex C-160 or the EmulsiFlex C-50.
The emulsifiers or dispersing agents employed for preparing the concentrated monomer emulsions may be anionic, cationic or non-ionic types. Also a mixture of any two types may be used. Suitable nonionic emulsifiers include, but are not limited to, ethoxylated octylphenols, ethoxylated nonylphenols, ethoxylated fatty alcohols and the like. Suitable anionic emulsifiers include, but are not limited to, sodium lauryl sulfate, sodium dodecylbenzene sulfonate, sulfated and ethoxylated derivatives of nonylphenols, octylphenols and fatty alcohols, esterified sulfosuccinates and the like. Suitable cationic emulsifiers include, but are not limited to, laurylpyridinium chlorides, cetyldimethyl amine acetate, (C
8
-C
18
) alkyldimethylbenzylammonium chlorides and the like. The level of emulsifier may be from about 0.1% to about 10% by weight, based on total monomer charged.
Among the monomers that may be useful in the concentrated monomer emulsion are ethylenically unsaturated monomers which include, but are not limited to (meth)acrylic ester monomers including methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, decyl acrylate, methyl methacrylate, butyl methacrylate, hydroxyethyl methacrylate, and hydroxypropyl acrylate; acrylamide or substituted acrylamides; styrene or substituted styrene; vinyl acetate or other vinyl esters; vinyl monomers such as vinyl chloride, vinylidene chloride, N-vinyl pyrolidone; and acrylonitrile or methacrylonitrile. Butyl acrylate, methyl methacrylate,
Brown Jeffrey Lewis
Stack Dennis Patrick
Wu Richard Shu-Hua
Bakule Ronald D.
Greenblatt Gary D.
Henderson Christopher
Rohm And Haas Company
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