Note: Descriptions are shown in the official language in which they were submitted.
-"`` 1328~31
.
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
i patent on "~ater Soluble Modified PVA Films" (U.S. Patent
~,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 100C tmolecular 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
100C. For example, PVA having a MW of 3.5x105 at 90% hydrolysis
requires greater than 120C for its dissolution. At the same
molecular weight and at 99% hydrolysis its dissolution temperature
is greater than 160C. 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 wei~ht PVA having a high degree of hydrolysis (99%) can be
modified with acrylamide in a simple one-step, low-temperature
reaction tless than 100C) 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
by low temperature (less than 100C) reaction, producing high
molecular weight modified PVA with minimal thermal degradation, and
eliminating the need to dissolve PVA at high temperatures prior to
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F-4114 -~- 13 2 8 ~ 31
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its reaction with modifying compounds, thereby reducing production
costs.
Accordingly, the present invention provides a one-step
process for the preparatio~ of high viscosity modified polyYinyl
alcohols comprising forming at room temperature a water slurry of
a polyvinyl alcohol having a degree of hydrolysis varying from
about 90% to about 95% or more, an alpha, beta-u~saturated
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 100C 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.
, .
~ ;''~'.
OH OH .
(Eq. 1)
' . '
O OH O
~ ' .
R X
2û wherein n=a+b;
x = -N~2 , -NHR , H,
~H
-NH-C-CH2SO3 Na (AMPS);
. CH3
! 25 - ;
-S~ where
R and R2 in~ependently are selected from H, alkyl, aryl or
A alkylaryl with from about 12 oarbons or less, preferably about 8 to
_ _.. _. _ . . . . _ ... , . _
F-4114 -3- 1328~3~
abcut 12 carbon atoms. A~rylonitr;le or substituted acrylonitrile
m~y also be advantageously used.
Modified products are cold water soluble contrary to the
high molecular weight parent PVA which has very low solubility in
' 5 cold water, especially when the degree of hydrolysis is high (more
than 90%). 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 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 thls method. Py high molecular weight PVA's is
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 100C
dependlng on the particular PVA. Preferred is a temperature of from
about 80-95C with pressures varying from amblent. 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 tlmes, higher molar
ratios, etc., will provide higher degrees of modificatlon.
Any suit~ble 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.
~A :-
~2~Q~
- F-4114 ~4~
EXAMPLE 1
A 59 sample of 3.5x105 molecular weight PVA, 99~
hydrolyzed was dissolved in 959 of deaired distilled water in an
autoclave under argon atmosphere at 160C for two hours. The
resulting PVA solution was reacted with 2ûg of acrylamide and 19 of
NaOH for 10 hours at about 85C. 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
10.7% acrylamide incorporation. A 5% water solution of the
copolymer had a viscosity of 70 cp.
EXAMPLE 2
59 of 3.5x105 molecular weight PVA, 99% hydrolyzed, 209
acrylamide and 19 NaOH formed a slurry in 959 of water at room
temperature. This mixture was heated to 85C 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 3.2%N 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.
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