Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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PRECIPITATION POLYMERIZATION OF CQPOLYMERS OF
VINYL LACTAM AND A POLYMERIZABLE CARBOXYLIC ACID
IN AN ALIPHATIC HYDROC~RBON SOLVENT
BACKGROUND OF THE INVENTION
l. Field of the Invention
This invention relates to precipitation
polymerization of copolymers of a vinyl lactam and a -
polymerizable carboxylic acid, and, more particularly, to
such copolymers having a wide compositional range, prepared
in high yield, as a white powder, which can be filtered and
dried easily, and which have advantageous physical
properties.
2. Description of the Prior Art
Copolymers of vinyl lactams,- e.g. vinyl
pyrrolidone (VP) or vinyl caprolactam (VCL), and
polymerizable carboxylic acids, e.g. acrylic acid (AA) or
methacrylic acid (MAA), have found application in the
photographic industry, as coatings, as biological
membranes, in drug release systems, as preservatives, in
oil recovery processes, in immunochemicals, and in cosmetic
materials.
Solution polymerization and precipitation
polymerization are two available methods for making these
copolymers; see in U.S. Patent Nos. 3,044,873; 3,862,915;
and 4,283,384; and articles by Takeski, in J. Makromol.
Chem. 148, 205 (1971); and by Uelzmann, in J. Polymer Sci.
33, 377 (1958).
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The solution polymerization process is used when
both reactant monomers and the copolymer product are
soluble in a reaction solvent. However, this method
suffers from the following disadvantages:
(1) Desirable compositions of the copolvmer may
not be soluble in a selected solvent; (2) the yields of
such copolymer may be low; (3) the copolymer may be
colored; (4) the solvent may be a high boiling liquid which
is difficult to separate from the copolymer; and (5) the
solvent may be a protic liquid, e~g. water or mixtures
thereof, which causes considerable hydrolysis of the vinyl
lactam under acidic reaction conditions.
The precipitation polymerization method is useful
when the monomers are soluble in the reaction solvent and
the copolymers are insoluble in the solvent. Benzene,
tetrahydrofuran, acetone and methyl ethyl ketone are known
precipitation polymerization solvents. Unfortunately,
these solvents have one or more of the following
disadvantages:
(1) Useful copolymer compositions may not be
insoluble in a selected reaction solvent, which restricts
the process to a narrow copolymer compositional range;
(2) the copolymer may precipitate only as a gelatinous mass
which is difficult to filter; (3) low yields of polymer may
be obtained; and (4) the solvent may be toxic.
For these and other reasons, present solution
polymerization and precipitation polymerization processes
for making copolymers of a vinyl lactam and an acrylic acid
have not been very successful on a commercial scale.
Accordingly, it is an object of this invention to
provide an improved method of making copolymers of a vinyl
lactam and a polymerizable carboxylic acid.
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Another object of the present invention is to
provide an effective reaction solvent in a precipitation
polymerization process which will provide copolymers having
advantageous physical properties, including low
hygroscopicity, high glass transition temperatures, a high
average molecular weights, polyelectrolyte behavior.
Yet another object herein is to provide a
precipitation polymerization process in which the
copolymers will precipitate in high yield as a fine white
powder which i9 insoluble in the reaction solvent over the
entire compositional range of the copolymer.
A feature of the invention is the provision of a
precipitation polymerization process for making copolymers
of a vinyl lactam and a polymerizable carboxylic acid in
which an aliphatic hydrocarbon is used as the reaction
solvent.
Another feature of the invention is the provision
of copoly~ers of a vinyl lactam and a polymerizable
carboxylic acid made by a precipitation polymerization
process in which the reaction solvent is selected from
heptane and cyclohexane.
Still another feature of the invention is the
provision of copolymers of a vinyl lactam and a
polymerizable carboxylic acid over the complete
compositional range of monomers, which copolymers are
characterized by having a high average molecular weight,
low hygroscopicity, a high glass transition temperature,
being a white powder, exhibiting polyelectrolyte behavior,
and which are soluble in an aqueous basic solution of pH 8
and insoluble in an aqueous acid solution of pH 3.
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SUMMARY OF THE INYENTION
What is described herein is a precipitation
polymerization process and copolymer products produced
thereby. The polymerization is carried out in reaction
mixture of a vinyl lactam, e.g. vinyl pyrrolidone or vinyl
caprolactam, and a polymerizable carboxylic acid, e.g.
acrylic acid or methacrylic acid, in the presence of a
polymerization initiator, e.g. a free radical initiator, in
an aliphatic hydrocarbon solvent, preferably, a C3-C10
saturated, branched or unbranched, cyclic or acyclic, and
preferably heptane or cyclohexane.
The process herein provides copolymers having a
weight ratio of vinyl lactam to polymerizable carboxylic
acid of 1:99 to 99:1, and as a white powder, which powder
precipitates readily from the aliphatic hydrocarbon solvent
and is easily filtered and dried.
The copolymers herein have a uni~ue set of
physical and chemical properties which are advantageous for
commercial use.
DETAILED DESCRIPTION OF THE INVENTION
In accordance with the invention, copolymers of a
vinyl lactam and a polymerizable carboxylic acid are made
by a precipitation polymerization process in an aliphatic
hydrocarbon solvent in the presence of a polymerization
initiator.
Suitable vinyl lactams for use herein include
vinyl pyrrolidone, vinyl caprolactam and alkylated vinyl
derivatives thereof. Suitable polymerizable carboxylic
acids include e.g. acrylic acid, methacrylic acid, itaconic
acid, maleic acid, and crotonic acid. Acrylic acid itself,
or methacrylic acid, is a preferred coreactant monomer in
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the polymerization. These monomers may be employed in
weight ratios over the entire compositional range of the
copolymers, i.e. from 1-99 weight percent vinyl lactam and
99:1 weight percent of acrylic acid. Accordingly, weight
ratios of VP:AA in the copolymer of 99:1, 75:25, 50:50,
25:75 and 1:99, for example, may be conveniently prepared
in this invention in substantially quantitative yields.
The reaction solvent of the invention suitably is
a C~-C10 saturated hydrocarbon which is branched or
unbranched, cyclic or acyclic. Preferably the solvent is a
C5-C8 aliphatic hydrocarbon or mixtures thereof.
A preferred aliphatic hydrocarbon solvent over
other known precipitation polymerization solvents is
selected from heptane and cyclohexane. Heptane, the most
preferred solvent provides high yields of a precipitate of
the desired copolymer composition as a fine white powder
which is easy to filter and dry. This advantageous result
is surprising since vinyl pyrrolidone itself readily -
homopolymerizes in heptane to produce gummy products.
The amount of solvent used in the process of the
invention should be sufficient to dissolve an appreciable
amount of the reactants and to maintain the copolymer
precipitate in a stirrable state at the end of the
polymerization. Generally, up to about 40% solids,
preferably 15-20% solids, is maintained in the reaction
mixture.
The precipitation polymerization process of the
invention is carried out in the presence of a
polymerization initiator, preferably a free radical
initiator, and most suitably, a peroxy ester, e.g.
t-butylperoxy pivalate, although other free radical
initiators such as acylperoxides, alkyl peroxides and
azo-nitriles, known in the art or described in the
aforementioned references, may be used as well.
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The amount of such initiator may vary widely;
generally about 0.2-5.0% is used, based on the weight of
total monomers charged.
The reaction temperature may vary widely;
generally the reactants are maintained at about 50-150C.,
preferably 60-70C., during the polymerization. Pressure
usually is kept at atmospheric pressure, although higher -
and lower pressures may be used as well.
The reaction mixture should be stirred vigorously
under an inert atmosphere, e.g. nitrogen, during the
polymerization. A stirring rate of about 400-600 rpm in a
1-liter lab reactor is quite adequate to effect the desired
polymerization and to keep the precipitate in a stirrable
state during the polymerization.
The monomers and initiator used herein are
commercially available materials, as described below.
Monomers Source Form
Vinyl pyrrolidone GAF Liquid
or
Vinyl caprolactam Aldrich Solid
Acrylic acidRohm and Haas Liquid
or
Methacrylic acidAldrich Liquid
Initiator
t-Butylperoxy Pennwalt Corp. Liquid; 75% solution
pivalate (Lupersol 11) in mineral spirits
The precipitation polymerization process of the
invention may be carried out by first precharging a
suitable reactor with a predetermined amount of a vinyl
lactam in the aliphatic hydrocarbon solvent, and heating
the solution to a desired reaction temperature while
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stirring vigorously under an inert gas atmosphere. The
initiator is then charged into the reactor. Then a
selected amount of the polymerizable carboxylic acid, e.g.
acrylic acid, is admitted into the reactor over a period of
time, generally about an hour or more. Then the reaction
mixture is held for an additional period of time for
polymerization to occur. Finally, the mixture is cooled to
room temperature. Filtering, washing with solvent, and
drying provides the copolymer in yields approaching
quantitative, and, substantially, in a composition
predetermined by the weight ratio of monomers introduced
into the reactor.
Alternatively, the aliphatic hydrocarbon solvent
can be precharged into the reactor, purged with nitrogen,
heated to reaction temperature, the initiator added, and
then separate streams of the vinyl lactam monomer and the
acryl,c acid monomer are introduced over a period of time
into the precharged reactor. Other process variations will
be apparent to those skilled in the art.
The copolymers of the invention are generally
characterized by their having high average molecular
weights, low hygroscopicity, high glass transition
temperatures, and exhibiting polyelectrolyte behavior in
water, as described below.
a. Molecular Weight
The weight average molecular weight for a
75:25 wt. ratio VP:AA copolymer, for example, having a
Fikentscher K-value of about 70, was about 180,000, as
determined by light scattering.
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b. HygroscoPicitY
The hygroscopicity of the copolymers is lower
than the weighted average of the homopolymers. This effect
is maximized for copolymers, for example, having a VP:AA
mole ratio of about 1:1, where the hydroscopicity may be
actually lower than the value of either homopolymer.
Hygroscopicity is measured by the equilibrium moisture
pickup of the copolymer powders at 50% relative humidity.
c. Glass Transition Temperature, Tg
This property shows the effect of strong
hydrogen bonding in the copolymer which causes a strong
positive deviation from typical behavior, which is most
prominent at a vinyl lactam:acrylic or methacrylic acid
mole ratio of about 1:1.
d. Solubility
The copolymer exhibits very unusual
solubility characteristic-: it is insoluble in aqueous acid
solution of pH 3 but soluble in basic solution of pH 8.
Table I below illustrates the solubility characteristics of
copolymers of different compositions in several aqueous and
organic solvents.
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TABLE I
P(VP/AA~ SOLUBILITY
VP/AA W/W 95/5 85/15 75/25 50/50 25/75 10/90
VP/AA M/M 92/8 79/21 66/34 39/61 18/82 7/93
WATER S
0.lN NaOH S S S S S S
ETHANOL PS
DMF S S S S S S
NMP S S S S S S
ACETONE
CHLOROFORM PS
TOLUENE
HEPTANE
SYMBOLS
P = Polymer
VP = Vinyl Pyrrolidone
AA = Acrylic Acid
DMF = Dimethylformamide
NMP = N-methylpyrrolidone
W/W = Weight to weight
M/M = Mole to mole
S = Soluble
I = Insoluble
PS = Partly soluble
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e. Viscosity
The viscosity in water is pH dependent
in the pH range of about 4-12. The maximum viscosity
occurs at a pH of about 8-9. Dilute aqueous solutions
exhibit polyelectrolyte behavior.
The invention will be illustrated hereinafter
by the following working examples.
EXAMPLE 1
1. PREPARATION OF COPOLYMERS OF VINYL PYRROLIDONE AND
ACRYLIC ACID
A l-liter, 4-necked reaction kettle was
equipped with a mechanical stirrer, thermometer, dropping
funnel and a nitrogen purge tube. The reactor was
precharged with 75 g. of vinyl pyrrolidone in 500 g. of
heptane. The solution then was heated to 65C. during 20
minutes and held there for 30 min., while stirring under
nitrogen gas. Then 260 microliter (0.3 g.) of
t-butylperoxy pivalate initiator was added. Then 25 g. of
acrylic acid was admitted during a period of 1 hour and the
mixture was held for an hour. Then an additional 140
microliter (0.2 g.) of initiator was admitted into the
reaction mixture and the solution was maintained at 65C.
with stirring for another 2 hours. Then another 100
microliter of initiator was added and the mixture held for
2 hours.
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The reaction product then was cooled to room
temperature during a period of about an hour. A fine white
powder precipitate of copolymer product was obtained which
was filtered, washed twice with heptane and dried overnight
at 100C. and then overnight again in a vacuum oven at
100 C .
A 75:25 VP:AA copolymer (wt. ratio) was
obtained in 97% yield.
PROPERTIES OF COPOLYMER PRODUCT
K-VALUE AND AVERAGE MOLECULAR WEIGHT
The product had a K-value of about 70 (1%
copol~mer in 0.1 N NaOH and 0.2N LiNo3 aqueous solution).
The weight average molecular weight of the
copolymer was about 180,000, as measured by light
scattering in dimethylformamide solvent.
EXAMPLES 2-6
The procedure of Example 1 was followed using
g9, 95, 50, 25 and 1 g. of vinyl pyrrolidone and 1, 5, 50,
75 and 99 g. of acrylic acid, to produce the corresponding
99:1, 95:5, 50:50, 25:75 and 1:99 wt. ratio VP:AA
copolymers.
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EXAMPLES 7-8
The procedure of Examples 1-6 was followed
using cyclohexane and hexane in place of heptane, with
similar results.
EXAMPLE 9
. . _
The procedure of Examples 1-8 was repeated
using vinyl caprolactam in place of vinyl pyrrolidonè to
produce the corresponding vinyl caprolactam/acrylic acid
copolymer in 95-100% yield.
EXAMPLE 10
The procedure of Examples 1-8 was repeated
using methacrylic acid in place of acrylic acid to produce
the corresponding vinyl pyrrolidone/methacrylic acid
copolymer in 95-100% yield.
COMPARATIVE EXAMPLES 11-14
The procedure of Example 1 was followed to
compare the efect of usinq different reaction solvents at
various copolymer compositions. The results are shown in
Table 2 below.
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The results in comparative Examples 11-14 above
show that heptane is the solvent of choice in the
precipitation polymerization of copolymers of vinyl
pyrrolidone and acrylic acid. Successful products were
obtained in heptane over the entire compositional range of
monomers, whereas failure in one or more respects was
evident with either tetrahydrofuran, acetone or benzene as
the solvent.
The copolymer products of the invention find
particular utility in such applications as thickeners,
adhesives, in paper manufacture and coatings thereon, in
ion-exchange resins and membranes, in controlled release
polymers, in textile sizings, as dispersants, in oil
recovery chemicals, in surface cleaning, as anti-scaling
agents in boilers, and in personal care products.
While the invention has been described with
particular reference to certain embodiments thereof, it
will be understood that changes and modifications may be
made which are within the skill of the art. Accordingly, ~-
it is intended to be bound only by the following claims, in
which:
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