Process for preparing comb-branched polymers

Details Process for preparing comb-branched polymers Process for preparing comb-branched polymers

1999-07-21

2001-04-10

Wu, David W. (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S319000, C526S240000, C524S005000, C560S183000

Reexamination Certificate

active

06214958

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to a method for preparing comb-branched polymers. More particularly, the invention relates to a continuous polymerization process for making a copolymer of a polyether macromonomer and an acrylic monomer. The copolymers are valuable water reducing agents for cement.
BACKGROUND OF THE INVENTION
Water reducing agents reduce the amount of water needed in cement admixtures, while maintaining good processing ability and consistency. Lignin sulfonates and naphthalene sulfonate-formaldehyde condensates have long been used as water reducing agents. These conventional water reducing agents are readily available and relatively inexpensive. However, they are used in high doses.
In contrast, newly developed polymeric water reducing agents offer high performance but are more expensive to make. U.S. Pat. No. 4,814,014, for example, teaches to graft ethylenically unsaturated monomers onto a polyether. The graft copolymer is used at a low dosage. Unfortunately, it is contaminated with a large portion of nongrafted polyether and ethylenic homopolymer. Because these nongrafted polymers do not function as water reducing agents, they reduce the effectiveness of the product.
Comb-branched copolymers of acrylic acid and polyether macromonomers have been used as high performance water reducing agents (see U.S. Pat. No. 5,834,576). The comb-branched copolymers have more uniform structures compared to the graft polymers of U.S. Pat. No. 4,814,014. Consequently, they have higher water reducing ability. An added advantage of these copolymers is the improved ability to maintain “slump.” Slump retention is the workable time after the cement admixture is mixed. Commonly used polyether macromonomers include acrylates, methacrylates, and allyl ethers of polyether.
Methods for preparing comb-branched copolymers of carboxylic monomers and polyether macromonomers are known and relatively simple. In general, free radically polymerizing a polyether macromonomer with a carboxylic monomer forms a comb-branched copolymer. While the related literature briefly mentions batch, semi-batch, and continuous processes (see U.S. Pat. No. 5,834,576, and copending Appl. Ser. No. 09/074,673), no one has suggested that a continuous process would offer comb-branched copolymers that perform better in cement compositions. Specific teachings about how to conduct a continuous process for making comb-branched copolymers are not available. U.S. Pat. No. 5,834,576, for example, only teaches details of a batch process.
SUMMARY OF THE INVENTION
The invention is a continuous process for making a comb-branched copolymer of an acrylic monomer and a polyether macromonomer. The process comprises: (a) forming a monomer stream, an initiator stream, and an optional chain transfer agent stream; (b) polymerizing the streams in a reaction zone at a temperature within the range of about −20° C. to about 150° C.; and (c) withdrawing a polymer stream from the reaction zone.
The invention also includes a multiple-zone process that comprises: (a) forming a monomer stream, an initiator stream, and an optional chain transfer agent stream; (b) polymerizing the streams in a first reaction zone at a temperature within the range of about −20° C. to about 150° C.; (c) transferring a first polymer stream from the first reaction zone to a second reaction zone wherein the polymerization continues; and (d) withdrawing a second polymer stream from the second reaction zone. The multiple-zone process enhances monomer conversion and process efficiency.
We surprisingly found that the comb-branched copolymers made by the process of the invention perform significantly better as water reducing agent in cement compared with polymers made by a batch process. They offer higher slump and flow.
DETAILED DESCRIPTION OF THE INVENTION
The continuous process of the invention uses streams of a monomer, an initiator, and, optionally, a chain transfer agent. The monomer stream contains an acrylic monomer and a polyether macromonomer. Suitable acrylic monomers derive from acrylic acid and methacrylic acid. Preferred acrylic monomers include acrylic acid, methacrylic acid, their ammonium and alkali metal salts, their C
1
to C
10
alkyl and C
6
to C
12
aryl esters, and their amides. Acrylic acid, methacrylic acid, ammonium acrylate, ammonium methacrylate, sodium acrylate, sodium methacrylate, potassium acrylate, and potassium methacrylate are preferred. Most preferred are acrylic acid and methacrylic acid.
Suitable polyether macromonomers have a polyether chain and a single carbon-carbon double bond, which can be located either at the end of or inside the polyether chain. Examples include polyether monoacrylates, polyether monomethacrylates, polyether monoallyl ethers, polyether monomaleates, and polyether monofumarates. The polyether of the macromonomer is an alkylene oxide polymer having a number average molecular weight within the range of about 500 to about 10,000. Suitable alkylene oxides include ethylene oxide, propylene oxide, butylene oxide, and the like, and mixtures thereof. The polyether macromonomers preferably have hydroxyl functionality from 0 to 5. They can be either linear or branched polymers, homopolymers or copolymers, random or block copolymers, diblock or multiple-block copolymers.
Examples of polyether macromonomers are poly(propylene glycol) acrylates or methacrylates, poly(ethylene glycol) acrylates or methacrylates, poly(ethylene glycol) methyl ether acrylates or methacrylates, acrylates or methacrylates of an oxyethylene and oxypropylene block or random copolymer, poly(propylene glycol) allyl ether, poly(ethylene glycol) allyl ether, poly(propylene glycol) monomaleate, and the like, and mixtures thereof. Preferred polyether macromonomers are poly(propylene glycol) acrylates or methacrylates, poly(ethylene glycol) acrylates or methacrylates, acrylates or methacrylates of an oxyethylene and oxypropylene block and random copolymer. More preferred are acrylates or methacrylates of an oxyethylene and oxypropylene block or random copolymer.
The ratio of acrylic monomer to polyether macromonomer is determined by many factors within the skilled person's discretion, including the required physical properties of the comb-branched copolymer, the selection of the acrylic monomer, and the properties of the polyether macromonomer. The ratio generally is within the range from 1/99 to 99/1 by weight. The preferred range is from 5/95 to 75/25.
Optionally, the monomer stream contains a third monomer. The third monomer is preferably selected from vinyl aromatics, vinyl halides, vinyl ethers, vinyl esters, vinyl pyrrolidinones, conjugated dienes, unsaturated sulfonic acids, unsaturated phosphonic acids, and the like, and mixtures thereof. The amount of third monomer used depends on the required physical properties of the comb-branched copolymer product, but is preferably less that 50% by weight of the total amount of monomers.
Optionally, the monomer stream also includes a solvent. The solvent is used to dissolve the monomer, to assist heat transfer of the polymerization, or to reduce the viscosity of the final product. The solvent is preferably selected from water, alcohols, ethers, esters, ketones, aliphatic hydrocarbons, aromatic hydrocarbons, halides, and the like, and mixtures thereof. Selections of solvent type and amount are determined by the polymerization conditions including reaction temperature. Water and alcohols, such as methanol, ethanol, and isopropanol, are preferred.
The initiator stream contains a free radical initiator. The initiator is preferably selected from persulfates, hydrogen peroxide, organic peroxides and hydroperoxides, azo compounds, and redox initiators such as hydrogen peroxide plus ferrous ion. Persulfates, such as ammonium and potassium persulfate, are preferred.
Optionally, the initiator stream contains a solvent. The solvent is used to dissolve or dilute the initiator, to control the polymerization rate, or to aid heat or mass transfer of the polymerization. Suitable solvents are d

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