WO1999045037A1

WO1999045037A1 - High molecular weight poly(dialkyldiallylammonium halide)

Info

Publication number: WO1999045037A1
Application number: PCT/US1999/005006
Authority: WO
Inventors: Jeffrey D. Williams; Elizabeth Robles Foy; Jackson A. Ransohoff
Original assignee: Neutron Products, Inc.
Priority date: 1998-03-05
Filing date: 1999-03-05
Publication date: 1999-09-10
Also published as: AU2989599A

Abstract

Polymers of dialkyldiallylammonium halide are economically prepared in bulk form by subjecting an aqueous monomer solution having a monomer concentration of at least about 60 percent by weight, to an effective dose of gamma radiation. The resulting polymer product is characterized by its solid form and hardness.

Description

High Molecular Weight Poly (Dialkyldiallylammonium Halide)

CROSS-REFERENCE TO RELATED APPLICATION

This application is related to provisional U.S. patent application serial no. 60/076,933, filed March 5, 1998.

BACKGROUND OF THE INVENTION

1. Technical Field The invention relates generally to the production of polymers of dialkyldiallylammonium halides. More specifically, the invention relates to the economically efficient production of a solid solution of poly (diallyldimethylammonium chloride> (pDMDAAC) in bulk form by polymerization of a solution containing in excess of about 60 percent by weight diallyldimethylammonium chloride monomer.

2. Description of the Background Art

It is well known that dialkyldiallylammonium halide salts having the general formula: (CH₂=CH-CH₂)₂N⁺(R)₂ X^" where R is an alkyl group and X is a halogen, may be polymerized using free-radical initiators to produce essentially linear water soluble polymers. The polymerization of dimethyldiallyl-ammonium bromide was first reported in 1949 by G.Butler et al. Poly (dimethyldiallylammonium chloride) (pDMDAAC) has become a commercially available product with an annual domestic production in excess of one hundred million pounds with principal application as a coagulant of suspended fine particles in potable water treatment and various industrial processes, emulsion breaking, and as a retention aid in papermaking. At present, the majority of pDMDAAC is produced by solution polymerization and supplied in the form of viscous aqueous solutions having polymer concentrations of about twenty to about forty percent by weight, with one manufacturer supplying a dry solid bead produced by suspension polymerization. The concentration of polymer in solution is inherently limited by the molecular weight, because the solution viscosity increases approximately with the square of the average molecular weight. Thus, as molecular weight increases, the viscosity of higher concentration solutions becomes too great for the material to be handled and shipped as a bulk liquid. Therefore, commercial products in the higher molecular weight ranges are limited in aqueous solution to a concentration of about twenty percent. Moreover, solutions of the still higher molecular weights achievable by the present invention would be limited to about ten percent or less and therefore become uneconomic to ship as a bulk liquid as the shipping distance increases.

It is common practice to determine the intrinsic viscosity, IV or [η] , of pDMDAAC and other high molecular weight water soluble polymers rather than measure the molecular weight directly. The intrinsic viscosity is defined as:

[ (η/rio - 1) /c]_c,₀ where η is the kinematic viscosity of a dilute polymer solution, η₀ is the kinematic viscosity of the pure solvent, and c is the polymer concentration generally given in g/dl. The expression:

(η/η₀ - 1) /c is referred to as the reduced specific viscosity or RSV. To determine the IV, the RSV is determined at several dilute concentrations and extrapolated to infinite dilution. The IV is related to the average molecular weight by the Mark-Houwink equation:

[η] = β ₂° where M_z is the average molecular weight and and β are empirically determined constants specific to the polymer, solvent, and conditions of the analysis, and valid over a defined molecular weight range. Often the actual determination of average molecular weight is omitted and the intrinsic viscosities are used as an indicator. Furthermore, it is common to avoid the time consuming practice of determining the IV in favor of a single RSV at a defined dilute concentration. The higher the RSV the higher the average molecular weight of the polymer, and thus this method can be used to compare quantitatively polymers of similar formulation but differing average molecular weights. For the purpose of this disclosure, all RSV's were determined with a No. 1 Ubbelohde viscometer at a temperature of 30° C and a polymer concentration of 0.05 g/dl in 2 molal sodium chloride. Commercial pDMDAAC solutions are available in several molecular weight ranges. While a specific molecular weight range will usually provide optimum performance for a given application, the selection of a specific product may also be influenced by the available polymer concentration and its effect on shipping and handling costs. Furthermore, although it is widely speculated that still-higher molecular weight pDMDAAC would yield improved performance in certain applications, we are not aware of any commercially available pDMDAAC with an RSV above about 1 dl/g, as determined by the method given above. It is likely that benefits would be derived from the availability of pDMDAAC products of higher molecular weights and in forms which overcome the viscosity related shortcomings of solutions. While the bead form is one possible alternative to solutions, it is costly and the commercially available molecular weights do not exceed that of the highest available solutions. SUMMARY OF THE INVENTION

The present invention provides water soluble polymers of poly (dialkyldiallylammonium halide) and, in preferred embodiments, polymers of poly (dimethyldiallylammonium chloride) produced in a novel form as a bulk solid. The physical ^" properties of these bulk solids in some embodiments are that of a pliable gel with a typical Shore A hardness of about 30. In other embodiments, the bulk solid is more characteristic of a hard material with Shore A hardness greater than about 75. In this hardness range the polymer product will not cohere to itself, so that it can be comminuted into small pieces which can be packaged, shipped, and handled by a variety of known means and then readily dispersed and dissolved in water.

The present invention also provides a process for preparing water soluble polymers of poly (dialkyldiallylammonium halide) and in preferred embodiments polymers of poly (dimethyldiallylammonium chloride) in bulk solid form. The process comprises providing an aqueous dialkyldiallylammonium halide solution (and in preferred embodiments, a dimethyldiallylammonium chloride solution) at concentrations greater than about 60 percent and exposing the solution to an effective dose of gamma radiation thereby converting monomer to polymer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS We have discovered that it is possible to improve upon the prior art by using gamma radiation to initiate free radical polymerization of dimethyldiallylammonium halide in aqueous solution. Using radiation-initiated polymerization, in contrast to conventional chemical catalysts, e.g. azobis compounds, peroxides, or hydroperoxides, we have found that it is possible to react dimethyldiallylammonium halide monomer at concentrations in excess of 60 percent by weight to high conversions to produce polymer over a wide range of molecular weights. The polymer product thus obtained is in a solid form and, when the initial monomer concentration exceeds about 65 percent by weight, the solidity is such that the product will not fuse to itself. Furthermore, we have discovered that it is possible to produce pDMDAAC s by this method with RSV's and therefore average molecular weights far in excess of those currently known. One attractive embodiment of the process of the present invention involves exposing a deoxygenated aqueous solution of DMDAAC monomer with an initial monomer concentration of about 60 percent by weight or higher to gamma radiation for a period of time, or total absorbed dose, sufficient to convert a significant portion of the monomer to polymer. An upper limit on the total absorbed dose is determined by the tendency of the polymer to form insoluble crosslinked gels when exposed to very high doses of radiation. This upper limit is inversely dependant on the initial monomer concentration. Those skilled in the art will be able to select suitable radiation doses that will provide the desired polymer characteristics.

We have found that the average molecular weight (or, more precisely, the RSV) increases with monomer concentration and decreases with the gamma radiation dose rate to which the monomer solution is exposed. For example, at dose rate of 35 kilorad/hr the RSV of a polymer obtained by irradiating a 55 percent monomer solution approximates that of the prior art product, namely 0.9 dl/g. In other embodiments the RSV is greater than about 2 dl/g., and in some embodiments is greater than about 3 dl/g. At about 65 percent monomer, which is the concentration of commercially available DMDAAC monomer solutions, the RSV thus obtained increases to 3.9 dl/g. At 72 percent monomer, the RSV of polymer produced under similar conditions was 7.7 dl/g. These are far greater than the molecular weights known from either the literature or from commercially available sources. Thus, in one embodiment, the invention provides poly (dialkyldiallylammonium halide) compositions having an RSV greater than about 1.5 dl/g. At dose rates higher than 35 kilorad/hr, the RSV's are reduced, but remain higher than those of the prior art products. We have found that it is practical to irradiate the monomer at a lower radiation dose rate until substantial conversion to higher molecular weight polymer occurs and then to increase the dose rate in order to reduce the overall time required to obtain high monomer conversions.

One major discovery of the present invention is the remarkable extent to which the form (physical properties) of the resulting polymer changes dramatically when the concentration of the monomer solution exceeds 60 percent by weight. Products obtained from a 55 percent monomer solution have been semi-solid with a consistency similar to petrolatum. This form is difficult to package and handle via conventional means.

At 60 percent monomer the products are solid and gel-like; however, they tend to deform under moderate pressure and, to some extent, they will cohere to themselves. Dilute solutions of these materials could be prepared by a process similar to that described in U.S. patent no. 4,113,688. At 65 monomer percent or higher, the products, when produced across a broad dose rate range, have invariably been hard solids characterized by their resistance to cold flow or deformation under normal (ambient) conditions. Nor will these materials fuse or cohere to themselves. In other words, two or more pieces of the aqueous gel held together under moderate pressure at ambient temperature will not stick together. Thus it is possible by a variety of means to reduce the bulk solid to small pieces of about 1.0 centimeter or less, to package, ship and store this reduced particle size material, and then at some later time to disperse the material in water and through conventional agitation for a modest period of time consistent with the current art, to thereby produce a diluted solution at a concentration suitable for metering to an application process. Thus, we have prepared a novel form of pDMDAAC which makes possible the shipping and practical use of materials of high molecular weight without limiting the active concentration and without necessarily subjecting the material to any further drying process. However the product could readily be further dried by conventional means, if so desired. The advantages of such a form over the presently- available commercial forms of this polymer will be immediately apparent. For example, the storage and shipping costs will be reduced. The polymer product of the present invention is characterized by its solid form and relative hardness, even though it can contain up to about 35 percent by weight of water. Shore A hardness can range from about 30 to about 100, or harder. It is practical to produce pDMDAAC by means of the present invention as a bulk solid material so that the properties of the solid, for example, hardness and cohesion, can be selected across a range that allows for the product to handled and used by a variety of readily available means. Likewise, the average molecular weight as indicated by the RSV can be controlled and varied across a wide range by controlling the parameters of the polymerization process by measures known to those skilled in the art . The process of the invention has been practiced at monomer concentrations as high as 72 percent by weight. However, an upper limit to initial monomer concentration has not been established. Such an upper limit, if existent, will be determined by factors such as monomer solubility and reaction kinetics .

The following examples are illustrative of the invention. The monomer conversion was determined by high pressure liquid chromatography using a LC-CN column at 30° C and a mobile phase of 50% acetonitrile: 50% 0.1 N sodium chloride in deionized water. The polymer RSV was determined under the conditions given above. Shore A hardness was determined using a Shore Instrument & Mfg. Co. Type A durometer. Example 1 60 ml of a commercially available 65 percent by weight DMDAAC solution containing about 4 percent by weight sodium chloride and about 31 percent by weight water was deoxygenated with high purity nitrogen through a gas dispersion tube and charged into a 60 ml syringe which was then sealed. The syringe was exposed to gamma radiation from a cobalt-60 source at a dose rate of 35 kilorads per hour for 20 hours and then at 350 kilorads per hour for three hours. The resulting product was a hard solid, which when reduced to smaller pieces of about 2-5 millimeters in each dimension was readily soluble in deionized water. The monomer conversion to polymer was 90.9 percent and the polymer RSV was 3.8 dl/g. The Shore A hardness was 90.

10 Example 2

60 ml of a commercially available 65 percent by weight DMDAAC solution containing about 4 percent by weight sodium chloride and about 31 percent by weight water was deoxygenated with high purity nitrogen through a gas dispersion tube and charged into a 60 ml syringe which was then sealed. The syringe was exposed to gamma radiation from a cobalt-60 source at a dose rate of 350 kilorads per hour for 7 hours and then at 1,000 kilorads per hour for three hours. The resulting product was a hard solid, which when reduced to smaller pieces of about 2-5 millimeters in each dimension was readily soluble in deionized water. The monomer conversion was 93.4 percent and the polymer RSV was 3.0 dl/g. The Shore A hardness was 80. Example 3 60 ml of a commercially available 65 percent by weight DMDAAC solution containing about 4 percent by weight sodium chloride and about 31 percent by weight water was deoxygenated with high purity nitrogen through a gas dispersion tube and charged into a 60 ml syringe which was then sealed. The syringe was exposed to gamma radiation from a cobalt-60 source at a dose rate of 1,000 kilorads per hour for 8 hours. The resulting product was a hard solid, which when reduced to smaller pieces of about 2-5 millimeters in each dimension was readily soluble in deionized water. The monomer conversion was 97.5 % and the

11 polymer RSV was 2.5 dl/g. The Shore A hardness was 75. Example 4

A commercially available 65 percent by weight DMDAAC solution was diluted to 60 percent by weight with deionized water. 60 milliliters of said dilution was deoxygenated with high purity nitrogen through a gas dispersion tube and charged into a 60 ml syringe which was then sealed. The syringe was exposed to gamma radiation from a cobalt-60 source at a dose rate of 1,000 kilorads per hour for 8 hours. The resulting product was a pliable gel like solid, which when reduced to smaller pieces of about 2-5 millimeters in each dimension was readily soluble in deionized water. The monomer conversion was 94.6 percent and the polymer RSV was 1.2 dl/g. The Shore A hardness was 30. Example 5

A commercially available 65 percent by weight DMDAAC solution was diluted to 55 percent by weight with deionized water to serve as a comparative example. 60 milliliters of said dilution was deoxygenated with high purity nitrogen through a gas dispersion tube and charged into a 60 ml syringe which was then sealed. The syringe was exposed to gamma radiation from a cobalt-60 source at a dose rate of 1,000 kilorads per hour for 8 hours. The resulting product was a semisolid with a petrolatum like consistency, which was readily soluble in deionized water.

12 The monomer conversion was 94.7 percent and the polymer RSV was 0.9 dl/g. The Shore A hardness of this semisolid was measured as 0.

Example 6 A commercially available 65 percent by weight DMDAAC solution was concentrated to 72 percent by weight by vacuum distillation of part of the water fraction at 70° C and 10 millimeters of mercury absolute pressure. 60 milliliters of said dilution was deoxygenated with high purity nitrogen through a gas dispersion tube and charged into a 60 ml syringe which was then sealed. The syringe was exposed to gamma radiation from a cobalt-60 source at a dose rate of 1,000 kilorads per hour for 8 hours. The resulting product was a hard solid consisting of crosslinked polymer which, when reduced to smaller pieces of about 2-5 millimeters in each dimension, was insoluble in deionized water. The Shore A hardness was 98. Example 7

A commercially available 65 percent by weight DMDAAC solution was concentrated to 72 percent by weight by vacuum distillation of part of the water fraction at 70° C and 10 millimeters of mercury absolute pressure. 60 milliliters of said dilution was deoxygenated with high purity nitrogen through a gas dispersion tube and charged into a 60 ml syringe which was then sealed. The syringe was exposed to gamma radiation from a

13 cobalt-60 source at a dose rate of 35 kilorads per hour for 20 hours. The resulting product was a hard solid which, when reduced to smaller pieces of about 2-5 millimeters in each dimension, was readily soluble in deionized water. The monomer conversion was 94.9 percent and the polymer RSV was 7.7 dl/g. The Shore A hardness was 95.

While the present invention has been described by reference to certain preferred embodiments, including preferred materials and methods, it is not thereby limited. Modifications within the scope of the following claims will be apparent to persons skilled in this branch of science.

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Claims

We claim:

1. A polymer of dialkyldiallylammonium halide in the form of a bulk solid.

2. The polymer according to claim 1, having an RSV at 0.05 g/dl in 2 molal sodium chloride at 30 degrees C. greater than about 1.5 dl/g.

3. The polymer according to claim 1, wherein said dialkyldiallylammonium halide is diallyldimethylammonium halide.

4. The polymer according to claim 1, having an RSV greater than about 2 dl/g.

5. The polymer according to claim 1, having an RSV greater than about 3 dl/g.

6. The polymer according to claim 3, wherein said dialkyldiallylammonium halide is diallyldimethylammonium chloride .

7. The polymer according to claim 4, wherein said dialkyldiallylammonium halide is diallyldimethylammonium chloride.

8. The polymer according to claim 1, wherein said bulk solid has a Shore A hardness greater than about 30.

9. The polymer according to claim 1, wherein said bulk solid has a Shore A hardness between about 30 and about 100.

10. The polymer according to claim 3, wherein said bulk solid

15 has a Shore A hardness between about 30 and about 100.

11. The polymer according to claim 4, wherein said bulk solid has a Shore A hardness between about 30 and about 100.

12. A process for producing a polymer of dialkyldiallylammonium halide in the form of a bulk solid, comprising exposing an aqueous solution of dialkyldiallylammonium halide monomer to an effective dose of gamma radiation, wherein said aqueous solution of dialkyldiallylammonium halide monomer has a monomer concentration of at least about 60 percent by weight.

13. The process according to claim 12, wherein the monomer is dimethyldiallylammonium halide.

14. The process according to claim 12, wherein the monomer is dimethyldiallylammonium chloride.

15. The process according to claim 12, wherein said aqueous solution of dialkyldiallylammonium halide monomer has a monomer concentration of at least about 65 percent by weight.

16. The process according to claim 12, wherein said effective dose rate of gamma radiation is at least about 5 kilorads per hour.

17. The process according to claim 12, wherein the resulting polymer has an RSV at 0.05 g/dl in 2 molal sodium chloride at 30 degrees C. of at least about 1.5 dl/g.

18. The process according to claim 17, wherein said RSV is at least about 2.

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19. The process according to claim 17, wherein said RSV is at least about 3.

20. The process according to claim 12, wherein the resulting bulk solid has a Shore A hardness of at least about 30.

21. The process according to claim 12, wherein the resulting bulk solution has a Shore A hardness of between about 30 and about 100.

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