GB2199834A

GB2199834A - Modified polyvinyl alcohols

Info

Publication number: GB2199834A
Application number: GB08729181A
Authority: GB
Inventors: Paul Shu
Original assignee: Mobil Oil Corp
Current assignee: ExxonMobil Oil Corp
Priority date: 1986-12-22
Filing date: 1987-12-15
Publication date: 1988-07-20
Anticipated expiration: 2007-12-15
Also published as: GB8729181D0; CA1328031C; NO875231D0; NO172647B; NO875231L; NO172647C; GB2199834B

Abstract

High molecular weight polyvinyl alcohols can be modified with alpha, beta-unsaturated carbonyl- or nitrogen-containing compounds such as acrylamide or acrylonitrile in a one-step low temperature reaction to produce products having higher viscosity than those prepared in 2-step high temperature modification reaction.

Description

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 filed a patent on "water Soluble Modified PVA Films" (U.S. Patent 3,505,303). In these reports, PVA is first dispersed in water at low temperature followed by high temperature dissolution to obtain a PVA solution after which the modifying agent is added to start the reaction. The above process is useful for PVA which are soluble in water below lOO0C (molecular weight less than 1 X 105 and degrees of hydrolysis less than 90%.) As PVA molecular weight and degree of hydrolysis increase, its dissolution temperature requirement becomes much greater than 1000C. For example, PVA having a MW of 3.5x105 at 90% hydrolysis requires greater than 1200C for its dissolution.At the same molecular weight and at. 99% hydrolysis its dissolution temperature is greater than 160or. For both cases, a pressurized reactor is reauired. Precautions must be taken to prevent oxidative degradation of PVA at these temperatures. We now find that high molecular weiaht PVA having a high degree of hydrolysis (99%) can be modified with acrylamide in a simple one-step, low-temperature reaction (less than 100 C) to produce acrylamide modified PVA (AMPVA) which has a much higher viscosity than a sample prepared via a two-step, high-temperature dissolution-modification reaction process.

The concept of the present invention involves modifying PVA with acrylamide and other alpha, beta-unsaturated carbonyl compounds hy low temperature (less than lOO C) reaction, oroducino high molecular weight modified PVA with minimal thermal deoradatlon, and eliminating the need to dissolve PVA at high temperaturec prior tn its reaction with modifying compounds, thereby reducing production costs.

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, (i.e. greater than 90%) a modifying aqent and a base, heating said mixture to temperatures of 1000C for a time sufficient to obtain the resultant modified high viscosity, high molecular weight product.

Modifying PVA with alpha, beta-unsaturated carbonyl compounds as modifying agent produces a class of very useful materials.

wherein n=a+b; x = NP? , -NHR-, H,

-5 where P rnd R2 independently are selected frcn H, alkyl, aryl or alkylaryl with from ahout 12 carbons or less, preferably about Q to about 12. Acrylonitrile or substituted acrylonitrile 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 (more than 90%). They are also more tolerant to brine (including NaCl, KC1 solutions) than the unmodified PVA. Furthermore, these materials are thermally and hydrolytically stable in concentrated brines, which makes them potentially useful as oilfield 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 lower molecular weight and lower degree of hydrolysis can also be modified by this method. By high molecular weight PVA's is 5 meant a molecular weight at least of 1 x 105.

The general reaction conditions for these highly hydrolyzed PVA's (99%+) include temperatures up to but not including 1000C depending on the particular PVA. Preferred is a temperature of from about 80-950C 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 t! modification reaction may be used. Preferred are such bases as NaOH.

The following examples are illustrative of the invention embodied herein.

EXAMPLE 1 5 A 5g sample of 3.5x105 molecular weight PVA, 99% hydrolyzed was dissolved in 95g of deaired distilled water in an autoclave under argon atmosphere at 1600C for two hours. The resulting PVA solution was reacted with 209 of acrylamide and lg of NaOH for 10 hours at about 850C. The product was isolated by precipitating from i-propanol. Crude product was purified by redissolving in cold water and reprecipitating in i-propanol three times. Nitrogen analysis showed 2.99% N which is equivalent to 10.7bio acrylamide incorporation. A 5% water solution of the copolymer had a viscosity of 70 cp.

EXAMPLE 2 5 5g of 3.5x105 molecular weight PVA, 99% hydrolyzed, 209 acrylamide and lg NaOH formed a slurry in 95g of water at room temperature. This mixture was heated to 850C for ten hours. During the process of heating, PVA solid particles gradually disappeared.

The product was collected and purified as in Example 1. Analysis showed 3,2it or 11.5% acrylamide. A 5% solution has a viscosity of 294cp.

The method of Example 2 produces a more viscous product than does the method of Example 1. It is obvious that the lower temperature process of Example 2 which is in accordance with the invention is, among other advantages, significantly more cost efficient.

AMPVA and AMPS PVA in particular are therefore viewed as important profile control gel precursors. The ability to modify these highly hydrolyzed, high molecular weight PVAs conveniently and economically enhances the attractiveness of these copolymers compared with other candidate systems, such as the AMPS-vinyl pyrrolidone- acrylamide copolymers.

Although the present invention has been described with preferred embodiments, it is to be understood that modifications and variations may be resorted to, without departing from the spirit and scope of this invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the appended claims.

Claims

CLAIMS:

1. A one-step process for the preparation of high viscosity modified polyvinyl alcohols comprising forming at room temperature a water slurry of a polyvinyl achohol having a degree of hydrolysis varying from about 90% to about 95% or more, an alpha, beta-unsaturated carbonyl compound modifying agent wherein said polyvinyl alcohol and said modifying agent are present in a molar ratio of from about 10:1 to about 1:10 and a base, and heating said mixture to a temperature of less than 1000C for a time sufficient to obtain the resultant modified high viscosity high molecular weight product.

2. The process of claim 1 wherein the base is sodium hydroxide.

3. The process of claim 1 or 2 wherein the modifying agent is selected from açrylamide, methacrylamide, acrylonitrile and sodium 2 - acrylamido - 2 methyl-propane - 3-(sulfonate).

4. The process of any of the preceding claims wherein the polyvinyl achohol molecular weight ranges from 1 to 5.0 x 105.

5. The process of any of the preceding claims wherein the temperature ranges from ambient to about 900C.