Claims
- 1. A one-step process for the preparation of high viscosity modified polyvinyl alcohols comprising forming under atmospheric or autogeneous pressure, at room temperature with minimal thermal degradation a water slurry of
- (1) a normally water insoluble high molecular weigh polyvinyl alcohol having a high degree of hydrolysis,
- (2) a modifying agent, selected from alpha, beta-unsaturated carbonyl compounds, and
- (3) a base, heating said mixture to temperatures varying from about 50.degree. to 100.degree. C. for a time sufficient to obtain the resultant modified high viscosity, high molecular weight product wherein the molecular weight of said polyvinyl alcohol varies from at least about 1.0 to about 5.0.times.10.sup.5 and, wherein the molar ratio of the polyvinyl alcohol to the modifying agent varies from about 10:1 to about 1:10.
- 2. The process of claim 1 wherein the base is NaOH.
- 3. The process of claim 1 wherein the modifying agent is selected from the group consisting of acrylamide, methacrylamide, acrylonitrile, methyacrylonitrile and sodium 2-acrylamido-2-methyl-propane-3-(sulfonate).
- 4. The process of claim 3 wherein the modifying agent is acrylamide.
- 5. The process of claim 3 wherein the modifying agent is methacrylonitrile.
- 6. The process of claim 3 wherein the modifying agent is 2-acrylamido-2-methyl-propane-3-(sulfonate).
- 7. The process of claim 6 wherein the polyvinyl alcohol has a molecular weight of at least about 3.5.times.10.sup.5.
- 8. The process of claim 1 wherein the degree of polyvinyl alcohol hydrolysis varies from about 90 to about 95% or more.
- 9. The process of claim 8 wherein the degree of hydrolysis is about 99%.
- 10. The process of claim 1 wherein the temperature varies from ambient to about 90.degree. C. or less.
- 11. The process of claim 10 wherein the temperature varies from about 60.degree. to about 85.degree. C.
- 12. The process of claim 11 wherein the temperature varies from about 60.degree. to 70.degree. C.
- 13. The process of claim 12 wherein the temperature varies from about 50.degree. to 60.degree. C.
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation-in-part of Ser. No. 307,143, filed Feb. 6, 1989,.which is now pending, entitled, PREPARATION OF COPOLYMERS OF POLYVINYL ALCOHOLS.
This invention is directed to a simplified method of preparing improved copolymers of polyvinyl alcohols (PVA). More specifically, it is directed to the modification of PVA with various alpha, beta-unsaturated carbonyl compounds.
It is known that PVA may be modified, e.g., by chemical means such as grafting and hydrolysis. Modification of PVA with acrylamide was first reported by H. Ito, et al. Lindemann has obtained a patent on "Water Soluble Modified PVA Films" (U.S. Pat. No. 3,505,303). In this prior art, PVA is first dispersed in water at low temperatures followed by high temperature dissolution to obtain a PVA solution. Thereafter which the modifying agent is added to start the reaction. The above process is useful for PVA soluble in water below 100.degree. C., molecular weight less than 1.times.10.sup.5 and degree of hydrolysis less than 90%.
The PVAs utilized herein are not, without the instant modification, soluble in water at ambient temperatures. As PVA molecular weight and degree of hydrolysis increase, its dissolution temperature requirement becomes greater than 100.degree. C. For example, PVA having a MW of 3.5.times.10.sup.5 at 90% hydrolysis requires greater than 120.degree. C. for its dissolution. At the same molecular weight and at 99% hydrolysis its dissolution temperature is greater than 160.degree. C. For both cases, a pressurized reactor is required. Precautions must be taken to prevent oxidative degradation of PVA at these temperatures. We now find that high molecular weight PVA having a high degree of hydrolysis from about 90% up to 99% can be modified with acrylamide in a simple one-step, low-temperature reaction (less than 100.degree. C. such as 50.degree. to 60.degree. C.) to produce acrylamide modified PVA (AMPVA) which has a much higher viscosity than samples prepared via a two-step, high-temperature dissolution modification reaction) process.
According to the teaching of the aforementioned Lindemann, PVA will not be dissolved at 50.degree.-100.degree. C. under atmospheric pressures. Therefore, Lindemann's procedure is not applicable to the grade of specific PVA used in the instant invention. As previously mentioned, it is possible to prepare a dilute aqueous PVA solution (less than 5%) of such high molecular weight and degree of hydrolysis at greater than 160.degree. C. in a pressurized vessel or an autoclave. This procedure is rather tedious and inefficient. Degradation of polymer can also occur under such severe conditions. Surprisingly, we have found that the PVA dissolution procedure in Lindemann could be eliminated by carrying out a heterogeneous reaction at low temperatures under atmosphere pressures. We have accordingly, prepared acrylamido-PVA ethers at temperatures lower than that of Lindemann's examples and having higher acrylamide content. Therefore, the process in accordance with this invention is an unexpected and surprising improvement over such prior art.
The concept of the present invention involves modifying PVA with acrylamide and other alpha, betaunsaturated carbonyl compounds by a low temperature (less than about 50.degree. to 60.degree. C.) reaction, producing high molecular weight modified PVA with minimal thermal degradation, and eliminating the need to dissolve PVA at high temperatures prior to its reaction with modifying compounds.
Accordingly, the invention is directed towards a one-step process for the preparation of high viscosity modified polyvinyl alcohols comprising forming a water slurry at room temperature of a PVA having a high degree of hydrolysis, a modifying agent and a base, heating said mixture to temperatures of less than 50.degree. to 60.degree. C. for a time sufficient to obtain the resultant modified high viscosity, high molecular weight product. The molecular weight of the product varies from at least about 1.0 to about 5.0.times.10.sup.5 or more.
Modifying PVA with alpha, beta-unsaturated carbonyl compounds produces a class of very useful materials. They may be used for example as precursors in a number of chemical processes. The concept generally involves modifying high molecular weight PVA with acrylamide and other alpha, beta-unsaturated carbonyl compounds by low temperature (<50.degree.-60.degree. C.) reaction, producing high molecular weight modified PVA with minimal thermal degradation, and eliminating the need to dissolve PVA at high temperatures prior to its reaction with modifying compounds, thereby reducing production costs. ##STR1##
R and R.sub.2 are independently selected from H, alkyl, aryl or alkylaryl with from about 12 carbons or less, preferably from about 8 to about 12. Acrylonitrile or substituted acrylonitrile such as methacrylonitrile may also be advantageously used.
Modified products are cold water soluble contrary to the high molecular weight parent PVA which has very low solubility in cold water, especially when the degree of hydrolysis is high (greater than 90% e.g., 90 to 95% or more). They are also more tolerant to brine (including NaCl, KCl solutions) than the unmodified PVA. Furthermore, these materials are thermally and hydrolytically stable in concentrated brines, which makes them potentially useful as oil field chemicals, adhesives, etc. In addition, the added functional groups can be used as synthetic handles for further reactions. Other modifying agents also can be used to modify the high molecular weight, highly hydrolyzed PVA; e.g., methacrylamide, 2-acrylamido-2-methyl-propane-3-(sulfonate) (AMPS), acrylonitrile and others described in Equation 1. It also should be noted that PVA having a lower molecular weight and a lower degree of hydrolysis can also be modified by this method. By high molecular weight PVA's is meant a molecular weight at least of 1.0.times.10.sup.5 up to about 5.0.times.10.sup.5 or more, highly suitable is a PVA of 3.5.times.10.sup.5 molecular weight.
The general reaction conditions for these highly hydrolyzed PVA's (99%+) may include temperatures up to but not including 100.degree. C. depending on the particular PVA. Preferred is a temperature of from about 80.degree.-95.degree. C. to as low as 50 to 60.degree. C. with pressures varying from ambient, higher pressures may be used if desired but usually the pressure is autogeneous; reaction times vary from about 2 hours to 24 hours or more. The molar ratio of PVA to modifying agent varies from about 10:1 to about 1:10 and preferably from about 2:1 to about 1:3 depending upon the desired degree of modification. Higher reaction parameters, i.e., higher temperatures, longer reaction times, higher molar ratios, etc., will provide higher degrees of modification.
Any suitable basic substance which will not interfere with the modification reaction may be used. Preferred are such bases as NaOH.
The following examples are illustrative of the invention embodied herein.
US Referenced Citations (2)
| Number |
Name |
Date |
Kind |
| 3505303 |
Lindensann |
Apr 1970 |
|
| 4775716 |
Beresniewicz et al. |
Oct 1988 |
|
Continuation in Parts (1)
|
Number |
Date |
Country |
| Parent |
307143 |
Feb 1989 |
|
Patent Grant
5104933
