1. Solvent-free method for preparing a (meth)acrylic acid polymer in solution, said polymer having a molecular mass of less than 8000 g/mol and a polydispersity index (PI) between 2 and 5, comprising the following steps: a) water is introduced into a synthesis reactor, b) the reactor is heated to a temperature of at least 60 °C, c) the following compounds are introduced into the reactor in a continuous and simultaneous manner: c1) the (meth)acrylic monomer(s) to be polymerized, c2) a polymerization initiator system, c3) a compound of formula (I): S S S R COOX R XOOC (I) according to which: - X represents Na, K or H, and - R represents an alkyl chain comprising 1 to 5 carbon atoms, in an amount such that the mass percentage (weight/weight) between said compound of formula (I) and said (meth)acrylic monomer(s) is between 0.1 and 2.5%, method according to which, during step a) and/or step c), sodium hypophosphite NaPO2H2 or a derivative thereof is introduced into the synthesis reactor in a total amount such that the mass percentage (weight/weight) between NaPO2H2 and said (meth)acrylic monomer(s) is between 2.9 and 5.8% by weight.

2. Method as claimed in claim 1, according to which the polymerization initiator system c2) is hydrogen peroxide.

3. Method as claimed in claim 1 or 2, according to which the mass percentage (weight/weight) between said compound of formula (I) and said (meth)acrylic monomer(s) is between 0.15 and 2%. 24

4. Method as claimed in any one of the preceding claims, according to which said method does not comprise any step of removing the reaction by-products after the polymerization step c).

5. Method as claimed in any one of the preceding claims, according to which sodium hypophosphite NaPO2H2 is introduced into the reactor in a total amount such that the mass percentage (weight/weight) between sodium hypophosphite NaPO2H2 or a derivative thereof and said (meth)acrylic monomer(s) is between 3.3 and 5.4% by weight.

6. Method as claimed in any one of the preceding claims, according to which all of the sodium hypophosphite is introduced into the synthesis reactor during step a).

7. Method as claimed in any one of the preceding claims, according to which the (meth)acrylic acid polymer solution obtained contains unpolymerized (meth)acrylic monomer(s) in an amount of less than 1.2% by weight, as determined by highperformance liquid chromatography (HPLC).

8. Method as claimed in any one of the preceding claims, according to which the (meth)acrylic acid polymer solution obtained contains phosphate ions HPO4 2- in an amount of less than 0.4% by weight, as determined by ion chromatography.

9. Method as claimed in any one of the preceding claims, according to which the compound of formula (I) is such that R is CH3 and X is Na.

10. Use of a compound of formula (I): S S S R COOX R XOOC (I) wherein: - X represents Na, K or H, and 25 - R represents an alkyl chain comprising 1 to 5 carbon atoms, as a replacement for part of the sodium hypophosphite NaPO2H2 in a solvent-free method for preparing a (meth)acrylic acid polymer in solution, said polymer having a molecular mass of less than 8000 g/mol and a polydispersity index (PI) between 2 and 3.

11. Use as claimed in claim 10, according to which: - the mass percentage (weight/weight) between said compound of formula (I) and said (meth)acrylic monomer(s) is between 0.1 and 2.5%, and - the mass percentage (weight/weight) between NaPO2H2 and said (meth)acrylic monomer(s) is between 2.9 and 5.8% by weight.

12. Use of sodium hypophosphite NaPO2H2 or a derivative thereof and a compound of formula (I): S S S R COOX R XOOC (I) according to which: - X represents Na, K or H and - R represents an alkyl chain comprising 1 to 5 carbon atoms, to prepare a (meth)acrylic acid polymer in solution, said polymer having a molecular mass of less than 8000 g/mol and a polydispersity index (PI) between 2 and 5.

FORM 2
THE PATENT ACT 1970
(39 of 1970)
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See Section 10, and rule 13)
1. TITLE OF INVENTION
METHOD FOR POLYMERISING METH(ACRYLIC) ACID IN A SOLUTION,
POLYMER SOLUTIONS OBTAINED AND USES THEREOF
2. APPLICANT(S)
a) Name : COATEX
b) Nationality : FRENCH Company
c) Address : 35, RUE AMPÈRE,
F-69730 GENAY,
FRANCE
3. PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention
and the manner in which it is to be performed : -
2
Field of the invention
The present invention concerns the technical field of radical polymerization of (meth)acrylic
acid. More precisely, the present invention concerns a novel method of radical
polymerization, polymers thus obtained and applications thereof in industry.
Background of the invention
Radical polymerization methods conventionally require that the monomers to be
polymerized, a chain transfer agent, a source of free radicals and, optionally, a catalyst are
brought into contact in at least one solvent.
The principal objective of a polymerization method is to obtain a polymer having a molecular
mass suited to the application for which it is intended. The present invention aims to obtain
polymers having a molecular mass of less than 8000 g/mol, for example of about 6000 g/mol.
Various methods of radical polymerization exist.
Mention may be made first of methods employing organic solvents, such as secondary
alcohols like isopropanol. These methods are unsatisfactory today because they generate
volatile organic compounds (VOCs). On the one hand, these solvents must be removed at the
end of the reaction, thus complicating the industrial polymer preparation process. On the
other hand, these solvents are recognized as having very harmful effects on health and on the
environment, such that their production is sought to be avoided. Lastly, even after
purification (distillation), traces of solvent still remain in the polymer solution.
Other methods for synthesizing polyacrylic polymers take place in water and do not generate
volatile organic compounds.
Among the various radical polymerization methods, mention may also be made of reversible
addition-fragmentation chain transfer (RAFT)-type controlled radical polymerization for
carrying out the living polymerization of a monomer. Such a method also makes it possible to
3
obtain polymers having low polydispersity (polymolecularity) indices (PI), which makes
them particularly effective for certain applications.
To implement a RAFT-type controlled radical polymerization, and thus to obtain a polymer
of expected molecular mass having a good PI, it is important to add to the reaction medium
an available amount of chain transfer agent, i.e., to employ an amount of chain transfer agent
such that each chain to be polymerized is functionalized by a chain transfer agent. Moreover,
it is important that this chain transfer agent is already available when polymerization is
initiated, i.e., when the polymerization reactor is heated and radicals are generated. This
implies that large amounts of chain transfer agent must be employed in a RAFT-type
controlled radical polymerization method.
Despite all the advantages of RAFT polymerization, the use of such amounts of chain transfer
agent have a certain number of disadvantages.
First, chain transfer agents prove to be expensive products, significantly increasing the cost of
the polymer obtained.
Moreover, when sulfur-containing chain transfer agents as described in the documents
WO 02/070571, WO 2005/095466 and WO 2006/024706 are used, it is noted that a fraction
of these compounds will be broken down to free sulfur-containing by-products of the CS2 and
H2S type and be found in the aqueous solution of the final polymer and in the run-off water of
the process, and thus can have a negative impact on humans and on the environment.
Moreover, the presence of these sulfur-containing by-products in the aqueous solution, during
the use of the polymer, generates gaseous emissions harmful to humans.
Alternative RAFT-type methods of controlled radical polymerization exist. According to one,
hydrogen peroxide is used as initiator and, for example, copper sulfate as catalyst and chain
transfer agent. Nevertheless, to obtain a polymer having a molecular mass of less than
8000 g/mol, for example of about 6000 g/mol, it is necessary to use a large amount of
catalyst, which generates a large amount of polluting by-products.
4
Alternately, thiolactic acid or another RSH mercaptan is used as an additional chain transfer
agent, but, again, in order to obtain a polymer having a molecular mass of less than
8000 g/mol, for example of about 6000 g/mol, it is necessary to use large amounts of
thiolactic acid or, more generally, transfer agent.
Still other methods rely on sodium hypophosphite, having the chemical formula NaPO2H2, as
chain transfer and reduction-oxidation agent, in the presence of hydrogen peroxide or radical
generator. The document GB 771 573 A1 notably describes one such method. It has the
major disadvantage of requiring large amounts of sodium hypophosphite, a phosphorus
fraction being found grafted in the polymer, another phosphorus fraction being found in the
form of phosphate salts in the process water. This is, first, a disadvantage during the use of
the polymer and, second, an environmental pollutant.
Brief description of the invention
One object of the present invention is to propose a method for preparing a (meth)acrylic acid
polymer having a molecular mass of less than 8000 g/mol, for example of less than
7000 g/mol, this method making it possible to obtain an aqueous polymer solution containing
fewer carbon bisulfide- or hydrogen sulfide-type by-products, so as to reduce the risks to
humans and to the environment during the synthesis of the polymer, but also during the use
of the polymer solution.
Still another object of the present invention is to reduce in the process water the amount of
pollutants associated with the use of reagents containing sulfur and phosphorus.
Another object of the present invention is to propose a method for preparing a polyacrylic
polymer without solvent, i.e., one that does not generate volatile organic compounds.
Still another object of the present invention is to propose a method for producing a polymer
having a good PI while controlling the costs associated with the method.
Another object of the present invention is to propose a method for producing an aqueous
polymer solution containing few unpolymerized monomers.
5
Detailed description of the invention
The Inventor has developed a solvent-free method for preparing a (meth)acrylic acid polymer
in solution, said polymer having a molecular mass of less than 8000 g/mol and a
polydispersity index (PI) between 2 and 5, for example between 2 and 3, comprising the
following steps:
a) water is introduced into a synthesis reactor,
b) the reactor is heated to a temperature of at least 60 °C,
c) the following compounds are introduced into the reactor in a continuous and
simultaneous manner:
c1) the (meth)acrylic monomer(s) to be polymerized,
c2) a polymerization initiator system,
c3) a compound of formula (I):
S S
S R
COOX
R
XOOC
(I)
according to which:
- X represents Na, K or H, and
- R represents an alkyl chain comprising 1 to 5 carbon atoms,
in an amount such that the mass percentage (weight/weight) between said
compound of formula (I) and said (meth)acrylic monomer(s) is between 0.1 and
2.5%,
method according to which, during step a) and/or step c), sodium hypophosphite NaPO2H2 or
a derivative thereof is introduced into the synthesis reactor in a total amount such that the
mass percentage (weight/weight) between NaPO2H2 and said (meth)acrylic monomers is
between 2.9 and 5.8% by weight.
The method of the present invention indeed makes it possible to obtain polymers having a
molecular mass of less than 8000 g/mol, for example of less than 7000 g/mol, for example of
about 6000 g/mol.
6
According to an embodiment of the present invention, the polymers have a molecular mass of
more than 500 g/mol, for example of more than 1000 g/mol.
The method of the present invention is carried out without organic solvent. By “solvent” or
“organic solvent” is meant any substance that is inert with respect to liquid-phase reagents
and reaction products at its temperature of use, the function of which is to dilute other
substances without chemically modifying them and without modifying itself.
It will be noted that the method of the present invention is not a RAFT-type radical
polymerization method due, first, to the amount of the compound of formula (I) used and,
second, to the order in which the reagents are introduced into the synthesis reactor. Thus, the
method of the present invention makes it possible to obtain an aqueous polymer solution that,
advantageously, on the one hand, comprises fewer sulfur-containing (meth)acrylic acid
polymers than a polymer solution obtained from a RAFT-type radical polymerization
method; on the other hand, the solution itself obtained by the method contains fewer H2S- or
CS2-type reaction by-products than the polymer solution obtained from a RAFT-type radical
polymerization method. Although the polydispersity index of the poly(meth)acrylic polymer
obtained is higher than that obtainable by means of a RAFT-type radical polymerization
method, such an aqueous polymer solution obtained according to the method of the present
invention has a higher degree of purity than a solution obtained by a RAFT-type radical
polymerization method.
Thus, the method of the invention makes it possible to reduce the contamination of the
polymer obtained and the production of CS2- or H2S-type polluting by-products due to the
fact that the mass percentage between the compound of formula (I) and the monomers to be
polymerized is reduced to a value between 0.1 and 2.5%.
The method of the present invention also makes it possible to solve one of the major technical
problems of the present invention, namely to propose a method for preparing a polymer
having a molar mass of less than 8000 g/mol, for example of less than 6000 g/mol.
7
The method of the present invention also has the advantage of enabling a higher conversion
rate in an industry-acceptable reaction time. According to an embodiment of the method of
the invention, the reaction time of step c) is less than 4 hours, for example less than 3 hours.
Step c) of the method of the present invention also employs a polymerization initiator system.
By “polymerization initiator system” is meant a system capable of initiating the
polymerization of monomers. It is conventionally a chemical compound having the ability to
generate free radicals.
According to an aspect of the present invention, the polymerization initiator system c2) is
selected from the group consisting of hydrogen peroxide, sodium persulfates, potassium
persulfates, ammonium persulfates, hydroperoxides and a mixture of at least two of these
compounds.
According to an aspect of the present invention, the polymerization initiator system c2) is
hydrogen peroxide.
Step c) of the method of the present invention also employs at least one compound of
formula (I):
S S
S R
COOX
R
XOOC
(I)
formula (I) according to which:
- X represents Na, K or H, and
- R represents an alkyl chain comprising 1 to 5 carbon atoms.
By “alkyl chain comprising 1 to 5 carbon atoms” is meant a methyl, ethyl, propyl, isopropyl,
butyl, tert-butyl, isobutyl or pentyl chain.
8
According to the present invention, the mass percentage (weight/weight) between said
compound of formula (I) and said (meth)acrylic monomer(s) is between 0.1 and 2.5%.
According to an embodiment of the present invention, the mass percentage (weight/weight)
between said compound of formula (I) and said (meth)acrylic monomer(s) is between 0.15
and 2%.
According to another embodiment of the present invention, the mass percentage
(weight/weight) between said compound of formula (I) and said (meth)acrylic monomer(s) is
between 0.15 and 1.5%.
According to an embodiment of the present invention, said compound of formula (I) is the
compound (IV), i.e., the compound (I) wherein X represents Na and R represents CH3, and
the mass percentage (weight/weight) between said compound of formula (I) and said
(meth)acrylic monomer(s) is between 0.1 and 1.75%, for example between 0.5 and 1.5%.
According to another embodiment of the present invention, said compound of formula (I) is
the compound (IV), i.e., the compound (I) wherein X represents Na and R represents CH3,
and the mass percentage (weight/weight) between said compound of formula (I) and said
(meth)acrylic monomer(s) is between 0.15 and 1.5%.
The limits of these ranges are within the scope of the present invention.
The constituents are introduced into the synthesis reactor “continuously,” i.e., at a constant or
variable rate without stopping.
Also, the constituents are introduced into the synthesis reactor “simultaneously,” i.e., the
various constituents are introduced concomitantly.
According to an embodiment of the method of the present invention, the constituents are
introduced into the synthesis reactor “proportionally,” i.e., the proportion of each constituent
of the mixture introduced into the synthesis reactor remains constant during the reaction time,
with respect to the other constituents of the mixture.
9
By “the (meth)acrylic monomer(s) to be polymerized” is meant that the method of the
invention aims to produce either a polymer consisting exclusively of acrylic acid (acrylic acid
homopolymer), or a polymer consisting exclusively of methacrylic acid (methacrylic acid
homopolymer) or, alternately, a polymer consisting of a mixture of acrylic acid and
methacrylic acid (acrylic acid-methacrylic acid copolymer). In the latter case, according to an
aspect of the invention, the molar ratio between acrylic acid and methacrylic acid can vary
between 1:100 and 100:1, for example between 1:1 and 100:1, or between 1:1 and 50:1.
According to another aspect of the present invention, said compound of formula (I) is
dipropyl trithiocarbonate (DPTTC, CAS No. 6332-91-8) or its salts, for example its disodium
salt (sodium dipropionate trithiocarbonate, CAS No. 86470-33-2, Mw=298.31 g/mol), as
represented by the formula (IV) below:
S
S S
NaO ONa
O O
(IV)
The method of the invention is also characterized in that, during step a) and/or step c),
sodium hypophosphite NaPO2H2 or a derivative thereof is introduced into the synthesis
reactor in a total amount such that the mass percentage (weight/weight) between NaPO2H2
and said (meth)acrylic monomer(s) is between 2.9 and 5.8% by weight.
It is possible to use in the method of the invention any form of sodium hypophosphite,
hydrated or not. For example, sodium hypophosphite anhydrous NaPO2H2 or sodium
hypophosphite monohydrate NaPO2H2•H2O can be used. In this case, the amount used is such
that the mass percentage (weight/weight) between NaPO2H2•H2O and said (meth)acrylic
monomer(s) is between 3.5 and 7% by weight.
According to an aspect of the present invention, sodium hypophosphite NaPO2H2 is
introduced into the reactor in a total amount such that the mass percentage (weight/weight)
between NaPO2H2 and said (meth)acrylic monomer(s) is between 3.3 and 5.4% by weight.
10
According to another aspect of the present invention, sodium hypophosphite NaPO2H2 is
introduced into the reactor in a total amount such that the mass percentage (weight/weight)
between NaPO2H2 and said (meth)acrylic monomer(s) is between 4.1 and 5.4% by weight.
According to an aspect of the method of the present invention, all of the sodium
hypophosphite is introduced into the synthesis reactor during step a).
The polymers are generally characterized by two indices/magnitudes/values:
- polymolecularity index (PI; also called polydispersity, PD); and
- molecular mass by weight.
The polymolecularity index corresponds to the molar mass distribution of the various
macromolecules within the polymer.
If all the macromolecules have the same length (and thus the same molecular mass), this
index is close to 1. If, on the other hand, the macromolecules have different lengths (thus
different molecular masses), the PI is greater than 1.
So that the polymer is effective in various applications, it is generally attempted to bring the
PI value as close to 1 as possible.
Nevertheless, in the context of the present invention, it is sought to obtain a polymer in
solution containing few reaction by-products and a “good PI.” By “good PI” is meant a PI
between 2 and 5, in particular between 1.5 and 2.8.
According to the present invention, the polymer in solution obtained according to the method
described has a molecular mass of less than 8000 g/mol and a polydispersity index (PI)
between 2 and 3.
According to an aspect of the present invention, the reaction conditions are such that the
conversion rate of the monomers to be polymerized is greater than 98.8%.
11
In other words, the (meth)acrylic acid polymer solution obtained contains unpolymerized
(meth)acrylic monomer(s) in an amount of less than 1.2% by weight, as determined by highperformance
liquid chromatography (HPLC).
The amount of residual monomers (acrylic acid or methacrylic acid) can be evaluated by
high-pressure liquid chromatography (HPLC). In this method, the constituent components of
the mixture are separated on a stationary phase and detected by a UV detector. Once the
detector is calibrated, the amount of residual (meth)acrylic acid can be obtained from the area
of the peak corresponding to the acrylic compound. This method is described in particular in
the manual “Chimie Organique Expérimentale” by M. Chavanne, A. Julien, G.J. Beaudoin, E.
Flamand, 2nd Edition, Editions Modulo, Chapter 18, pp. 271-325.
According to another aspect of the present invention, the reaction conditions are such that the
conversion rate of the monomers to be polymerized is above 99.7%. In this case, the amount
of residual monomers is less than 0.3% or less than 3000 ppm (dry/dry).
According to another aspect of the present invention, the reaction conditions are such that the
conversion rate of the monomers to be polymerized is above 99.9%. In this case, the amount
of residual monomers is less than 0.1% or less than 1000 ppm (dry/dry).
According to an aspect of the invention, the (meth)acrylic acid polymer solution obtained
contains phosphate ions (HPO4
2-) in an amount of less than 0.4% by weight, as determined by
ion chromatography.
According to an aspect of the present invention, according to step b) of the method, the
reactor is heated to a temperature of at least 80 °C, for example 90 °C or 95 °C.
According to another aspect of the invention, the method does not comprise any step of
removing the reaction by-products after the polymerization step c).
12
Another object of the present invention resides in the use of a compound of formula (I):
S S
S R
COOX
R
XOOC
(I)
wherein:
- X represents Na, K or H, and
- R represents an alkyl chain comprising 1 to 5 carbon atoms,
as a replacement for part of the sodium hypophosphite NaPO2H2 in a solvent-free method for
preparing a (meth)acrylic acid polymer in solution, said polymer having a molecular mass of
less than 8000 g/mol and a polydispersity index (PI) between 2 and 3.
According to an aspect of the invention, the solvent-free method for preparing said
(meth)acrylic acid polymer in solution is carried out under conditions such that:
- the mass percentage (weight/weight) between said compound of formula (I) and said
(meth)acrylic monomer(s) is between 0.1 and 2.5%, and
- the mass percentage (weight/weight) between NaPO2H2 and said (meth)acrylic monomer(s)
is between 2.9 and 5.8% by weight.
Another object of the invention is the use of sodium hypophosphite NaPO2H2 or a derivative
thereof and a compound of formula (I):
S S
S R
COOX
R
XOOC
(I)
according to which:
- X represents Na, K or H and
- R represents an alkyl chain comprising 1 to 5 carbon atoms,
to prepare a (meth)acrylic acid polymer in solution, said polymer having a molecular mass of
less than 8000 g/mol and a polydispersity index (PI) between 2 and 5.
13
EXAMPLES
In each of the following examples the molecular mass of the polymers according to the
invention is determined by size-exclusion chromatography (SEC).
One such technique employs a liquid chromatography device of Waters™ trademark fitted
with a detector. This detector is a refractometric concentration detector of Waters™
trademark.
This liquid chromatography equipment is fitted with a size-exclusion column suitably chosen
by the skilled person for separating the various molecular weights of the polymers under
study.
The elution’s liquid phase is an aqueous phase adjusted to pH 9.00 with 1 N sodium
hydroxide containing 0.05 M NaHCO3, 0.1 M NaNO3, 0.02 M triethanolamine and 0.03%
NaN3.
In detail, according to a first step, the polymerization solution is diluted to 0.9%, dry basis, in
the SEC solubilization solvent, which corresponds to the SEC elution’s liquid phase, to which
0.04% dimethylformamide is added as flow marker or internal standard. The mixture is then
passed through a 0.2 μm filter. 100 μl is then injected into the chromatography device
(eluent: an aqueous phase adjusted to pH 9.00 with 1 N sodium hydroxide containing 0.05 M
NaHCO3, 0.1 M NaNO3, 0.02 M triethanolamine and 0.03% NaN3).
The liquid chromatography device contains an isocratic pump (Waters™ 515), the flow rate
of which is set at 0.8 ml/min. The chromatography device also comprises an oven, which
itself comprises the following system of columns, in series: a precolumn of the Waters™
Ultrahydrogel Guard Column type having a length of 6 cm and an inner diameter of 40 mm,
and a linear column of the Waters™ Ultrahydrogel type having a length of 30 cm and an
inner diameter of 7.8 mm. The detection system, in turn, consists of a refractometric detector
of the Waters™ 410 RI type. The oven is heated to a temperature of 60 °C and the
refractometer is heated to 45 °C.
14
The chromatography device is calibrated with sodium polyacrylate powder standards of
various molecular masses certified for the supplier: Polymer Standards Service or American
Polymer Standards Corporation.
The polydispersity index (PI) of the polymer is the ratio of the weight-average molecular
mass Mw to the number-average molecular mass Mn.
The amount of residual monomers is measured using conventional techniques known to the
skilled person, for example high-pressure liquid chromatography (HPLC).
Example 1
The purpose of this example is to illustrate the preparation of (meth)acrylic acid polymers
according to the invention, using:
- a dipropionate trithiocarbonate (DPTTC) salt with a mass percentage (weight/weight)
between said DPTTC salt and said (meth)acrylic monomer(s) between 0.1 and 2.5%
(invention) or outside this range (prior art or outside the invention), and
- sodium hypophosphite NaPO2H2 in a total amount such that the mass percentage
(weight/weight) between NaPO2H2 and said (meth)acrylic monomer(s) is between 2.9 and
5.8% by weight (invention) or outside this range (prior art or outside the invention).
Test 1 - Prior art:
This test illustrates a method for preparing a polymer by means of a RAFT-type controlled
radical polymerization.
Into the glass synthesis reactor fitted with a mechanical stirrer and an oil bath-type heater are
loaded 328 g of water and 94 g of 29% DPTTC chain transfer agent (or 27 g of 100%
DPTTC, or 0.092 mole).
Heat is applied until a temperature of 95 °C is reached.
One introduces, over a period of 2 hours, 328 g of 100% acrylic acid (or 4.558 moles) and, in
parallel:
15
- 4 g of sodium persulfate Na2S2O8 (or 0.017 mole) dissolved in 76 g of water, and
- 1.15 g of sodium metabisulfite Na2S2O5 (or 0.006 mole) dissolved in 76 g of water.
The temperature is maintained for 2 hours and then 3.2 g of 130 V hydrogen peroxide diluted
in 46 g of water is injected.
The mixture is then neutralized under stirring with 381 g of 50% sodium hydroxide diluted in
48 g of water.
Cooking resumes for 1 hour at 95 °C, followed by cooling to room temperature.
Test 2 - Outside the invention:
According to this test, the conditions of Test 1 are reproduced while decreasing by a factor of
10 the amount of DPTTC chain transfer agent used.
Into the glass synthesis reactor fitted with a mechanical stirrer and an oil bath-type heater are
loaded 328 g of water and 19 g of 14% DPTTC chain transfer agent (or 2.7 g of 100%
DPTTC or 0.0092 mole).
Heat is applied until a temperature of 95 °C is reached.
One introduces, over a period of 2 hours, 328 g of 100% acrylic acid (or 4.558 moles) and, in
parallel:
- 4 g of sodium persulfate Na2S2O8 (or 0.017 mole) dissolved in 76 g of water, and
- 1.15 g of sodium metabisulfite Na2S2O5 (or 0.006 mole) dissolved in 76 g of water.
The temperature is maintained for 2 hours and then 3.2 g of 130 V hydrogen peroxide diluted
in 46 g of water is injected.
The mixture is then neutralized under stirring with 381 g of 50% sodium hydroxide diluted in
48 g of water.
Cooking resumes for 1 hour at 95 °C, followed by cooling to room temperature.
16
Test 3 - Prior art:
This test corresponds to Test 2 of Example 2 of the document WO 2005/095466 (Coatex).
Into the synthesis reactor fitted with a mechanical stirrer and an oil bath-type heater are
loaded 150 g of water, 20.31 g of 14.4% DPTTC chain transfer agent (or 2.92 g of 100%
DPTTC) and 50 g of 100% acrylic acid.
The source of free radicals is then added, in this case 0.4 g of V501. Heat is applied until a
temperature of 95 °C is reached. The temperature is maintained for 2 hours, followed by
cooling to room temperature.
The mixture is then neutralized with 55 g of 50% sodium hydroxide.
Test 4 - Prior art:
This test illustrates a method for preparing a polymer exclusively with sodium hypophosphite
monohydrate.
Water (209 g) is loaded into a synthesis reactor fitted with a mechanical stirrer and an oil
bath-type heater. Iron sulfate heptahydrate (0.1 g) and copper sulfate pentahydrate (0.015 g)
are added.
The medium is heated to 90 °C, then the following are added simultaneously and
continuously over a period of 2 hours:
- 305 g of acrylic acid and 13 g of water, and
- 25.6 g of NaPO2H2•H2O dissolved in 32 g of water.
The mixture is cooked at 90 °C for 90 minutes.
The mixture is then neutralized to pH 8 with 50% sodium hydroxide.
Test 5 - Invention:
Into a synthesis reactor fitted with a mechanical stirrer and an oil bath-type heater are loaded
198 g of water and 13 g of NaPO2H2•H2O (or 10.8 g of NaPO2H2).
17
The medium is heated to 90 °C, then the following are added simultaneously and
continuously:
- over a period of 90 minutes:
* 208.6 g of acrylic acid diluted with 23.2 g of water,
* a stock solution of 13.41 g of 14% DPTTC disodium salt (or 1.88 g of 100% DPTTC),
- over a period of 130 minutes, 7.44 g of 130 V hydrogen peroxide diluted in 132 g of water.
The mixture is cooked at 90 °C for 90 minutes.
The mixture is neutralized with 228 g of 50% sodium hydroxide.
Test 6 - Invention:
Into a synthesis reactor fitted with a mechanical stirrer and an oil bath-type heater are loaded
198 g of water and 12 g of NaPO2H2•H2O.
The medium is heated to 90 °C, then the following are added simultaneously and
continuously:
- over a period of 90 minutes:
* 208.6 g of acrylic acid diluted with 23.2 g of water,
* a stock solution of 13.41 g of 14% DPTTC disodium salt (or 1.88 g of 100% DPTTC),
- over a period of 130 minutes, 7.44 g of 130 V hydrogen peroxide diluted in 132 g of water.
The mixture is cooked at 90 °C for 90 minutes.
The mixture is neutralized with 228 g of 50% sodium hydroxide.
Test 7 - Invention:
Water (198 g) is loaded into a synthesis reactor fitted with a mechanical stirrer and an oil
bath-type heater.
The medium is heated to 90 °C, then the following are added simultaneously and
continuously:
- over a period of 120 minutes:
* 208.6 g of acrylic acid,
* a stock solution of 10.29 g of 20% DPTTC disodium salt (or 2.05 g of 100% DPTTC),
* 12.1 g of NaPO2H2•H2O dissolved in 40 g of water.
18
- over a period of 130 minutes, 7.1 g of 130 V hydrogen peroxide diluted in 80 g of water.
The mixture is cooked at 90 °C for 90 minutes.
The mixture is neutralized with 228 g of 50% sodium hydroxide.
Test 8 - Invention:
Into a synthesis reactor fitted with a mechanical stirrer and an oil bath-type heater are loaded
198 g of water and 6.0 g of NaPO2H2•H2O.
The medium is heated to 90 °C, then the following are added simultaneously and
continuously:
- over a period of 120 minutes:
* 208.6 g of acrylic acid,
* a stock solution of 10.3 g of 20% DPTTC disodium salt (or 2.06 g of 100% DPTTC),
* 6.0 g of NaPO2H2•H2O dissolved in 40 g of water.
- over a period of 130 minutes, 7.1 g of 130 V hydrogen peroxide diluted in 90 g of water.
The mixture is cooked at 90 °C for 90 minutes.
The mixture is neutralized with 228 g of 50% sodium hydroxide.
Test 9 - Invention:
Into a synthesis reactor fitted with a mechanical stirrer and an oil bath-type heater are loaded
198 g of water and 10.4 g of NaPO2H2•H2O.
The medium is heated to 90 °C, then the following are added simultaneously and
continuously:
- over a period of 120 minutes:
* 208.6 g of acrylic acid,
* a stock solution of 15.6 g of 20% DPTTC disodium salt (or 3.12 g of 100% DPTTC),
- over a period of 130 minutes, 7.1 g of 130 V hydrogen peroxide diluted in 90 g of water.
The mixture is cooked at 90 °C for 90 minutes.
The mixture is neutralized with 228 g of 50% sodium hydroxide.
19
Test 10 - Invention:
Into a synthesis reactor fitted with a mechanical stirrer and an oil bath-type heater are loaded
198 g of water and 8.3 g of NaPO2H2•H2O.
The medium is heated to 90 °C, then the following are added simultaneously and
continuously:
- over a period of 120 minutes:
* 208.6 g of acrylic acid,
* a stock solution of 15.6 g of 20% DPTTC disodium salt (or 3.12 g of 100% DPTTC),
- over a period of 130 minutes, 7.1 g of 130 V hydrogen peroxide diluted in 90 g of water.
The mixture is cooked at 90 °C for 90 minutes.
The mixture is neutralized with 228 g of 50% sodium hydroxide.
Test 11 - Invention:
Into a synthesis reactor fitted with a mechanical stirrer and an oil bath-type heater are loaded
198 g of water and 10.4 g of NaPO2H2•H2O.
The medium is heated to 90 °C, then the following are added simultaneously and
continuously:
- over a period of 120 minutes:
* 208.6 g of acrylic acid,
* a stock solution of 26.1 g of 20% DPTTC disodium salt (or 5.22 g of 100% DPTTC),
- over a period of 130 minutes, 7.1 g of 130 V hydrogen peroxide diluted in 90 g of water.
The mixture is cooked at 90 °C for 90 minutes.
The mixture is neutralized with 228 g of 50% sodium hydroxide.
20
Test
no.
INVention
Prior Art
Mass %
DPTTC /
monomers
Mass %
NaPO2H2 /
monomers
Mw
(g/mol)
PI
SC
(%)
pH
Residual
AAs (%)
1 PA 8.23 n/a 5065 1.5 36.6 9 0.13
2 Outside INV 0.82 n/a 43400 3.5 36.6 8.5 0.03
3 PA 5.8 n/a 4947 1.55 36.6 9 0.5
4 PA n/a 7.0 4780 2.3 40.0 8.0 0.02
5 INV 0.9 5.17 4830 2.2 36.6 6.89 0.03
6 INV 0.9 4.77 5325 2.3 36.6 7.02 0.04
7 INV 0.98 4.77 7900 2.9 37.1 7.1 <0.001
8 INV 0.98 4.77 5500 2.3 37.0 7.1 <0.001
9 INV 1.5 4.14 5760 2.4 39.2 7.0 0.15
10 INV 1.5 3.30 7050 2.6 38.2 6.9 0.22
11 INV 2.5 4.14 5750 2.3 38.1 7.2 1.26
n/a: not applicable
Table 1
Example 2:
The purpose of this example is to illustrate the carbon bisulfide, hydrogen sulfide and
phosphate ion contents of various samples employing polymer solutions of the prior art or
polymer solutions according to the present invention.
The various samples are analyzed using an Agilent G1530 gas chromatograph coupled to an
Agilent G2577A mass spectrometer detector. The injection is by means of an Agilent G1888
headspace sampler. An Agilent HP5 column (30 m × 0.25 mm × 1 μm; 5% phenyl and 95%
methylsiloxane phase) is used, which allows elution of the analytes. The analysis is carried
out with 2 grams of sample as-is. The quantification is carried out using the standard addition
method.
The various samples are also analyzed using a Metrohm 761 Compact IC ion chromatograph
equipped with a conductivity detector, a chemical suppressor and a CO2 suppressor. A
21
Metrohm A Supp 5 250 anion-exchange column and two precolumns (Metrohm A supp5 and
RP) are used to elute the anions, among which HPO4
2-.
The analysis is carried out with 0.1 g of sample diluted in 60 g of distilled water. The
quantification is carried out using external standards.
Three syntheses are carried out:
- a polyacrylic dispersant prepared by means of a RAFT-type controlled radical
polymerization method, according to Test 1 of Example 1 above,
- a polyacrylic dispersant prepared by means of a polymerization method according to Test
4 of Example 1 above,
- a polyacrylic acid polymer solution prepared by means of a method according to the
present invention, according to Test 6 of Example 1 above.
Samples 1, 2 and 3, respectively, are obtained.
The results of the analyses of these samples are presented in Table 1 below.
ND: not detectable
Table 2
The analysis of Sample 1, i.e., a polyacrylic dispersant obtained by means of a RAFT
method, indicates high contents of sulfur-containing by-products H2S and CS2, which is a
major disadvantage due to their toxicity.
Samples INVention
Prior Art
HPO4
2- content
(ppm)
H2S content
(ppm)
CS2 content
(ppm)
1 PA - RAFT ND 200 1000
2 PA - hypo 5.032 ND ND
3 INV 3.500 ND ND
22
The analysis of Sample 2, i.e., a polyacrylic dispersant prepared by means of a method of the
prior art with a high NaPO2H2 content, indicates a high residual HPO4
2- ion content
(5032 ppm).
The analysis of Sample 3, namely a polyacrylic acid polymer solution prepared by means of a
method according to the present invention, shows that the H2S and CS2 contents are not
detectable. The phosphate ion content for identical molecular masses is substantially lower
than that of the polymer of Sample 2. Thus, the risks to humans and to the environment
during the synthesis of the polymer, but also during the use of the polymer solution, are
significantly reduced.
23
WE CLAIM :
1. Solvent-free method for preparing a (meth)acrylic acid polymer in solution, said
polymer having a molecular mass of less than 8000 g/mol and a polydispersity index
(PI) between 2 and 5, comprising the following steps:
a) water is introduced into a synthesis reactor,
b) the reactor is heated to a temperature of at least 60 °C,
c) the following compounds are introduced into the reactor in a continuous and
simultaneous manner:
c1) the (meth)acrylic monomer(s) to be polymerized,
c2) a polymerization initiator system,
c3) a compound of formula (I):
S S
S R
COOX
R
XOOC
(I)
according to which:
- X represents Na, K or H, and
- R represents an alkyl chain comprising 1 to 5 carbon atoms,
in an amount such that the mass percentage (weight/weight) between said compound
of formula (I) and said (meth)acrylic monomer(s) is between 0.1 and 2.5%,
method according to which, during step a) and/or step c), sodium hypophosphite
NaPO2H2 or a derivative thereof is introduced into the synthesis reactor in a total
amount such that the mass percentage (weight/weight) between NaPO2H2 and said
(meth)acrylic monomer(s) is between 2.9 and 5.8% by weight.
2. Method as claimed in claim 1, according to which the polymerization initiator system
c2) is hydrogen peroxide.
3. Method as claimed in claim 1 or 2, according to which the mass percentage
(weight/weight) between said compound of formula (I) and said (meth)acrylic
monomer(s) is between 0.15 and 2%.
24
4. Method as claimed in any one of the preceding claims, according to which said
method does not comprise any step of removing the reaction by-products after the
polymerization step c).
5. Method as claimed in any one of the preceding claims, according to which sodium
hypophosphite NaPO2H2 is introduced into the reactor in a total amount such that the
mass percentage (weight/weight) between sodium hypophosphite NaPO2H2 or a
derivative thereof and said (meth)acrylic monomer(s) is between 3.3 and 5.4% by
weight.
6. Method as claimed in any one of the preceding claims, according to which all of the
sodium hypophosphite is introduced into the synthesis reactor during step a).
7. Method as claimed in any one of the preceding claims, according to which the
(meth)acrylic acid polymer solution obtained contains unpolymerized (meth)acrylic
monomer(s) in an amount of less than 1.2% by weight, as determined by highperformance
liquid chromatography (HPLC).
8. Method as claimed in any one of the preceding claims, according to which the
(meth)acrylic acid polymer solution obtained contains phosphate ions HPO4
2- in an
amount of less than 0.4% by weight, as determined by ion chromatography.
9. Method as claimed in any one of the preceding claims, according to which the
compound of formula (I) is such that R is CH3 and X is Na.
10. Use of a compound of formula (I):
S S
S R
COOX
R
XOOC
(I)
wherein:
- X represents Na, K or H, and
25
- R represents an alkyl chain comprising 1 to 5 carbon atoms,
as a replacement for part of the sodium hypophosphite NaPO2H2 in a solvent-free
method for preparing a (meth)acrylic acid polymer in solution, said polymer having a
molecular mass of less than 8000 g/mol and a polydispersity index (PI) between
2 and 3.
11. Use as claimed in claim 10, according to which:
- the mass percentage (weight/weight) between said compound of formula (I) and said
(meth)acrylic monomer(s) is between 0.1 and 2.5%, and
- the mass percentage (weight/weight) between NaPO2H2 and said (meth)acrylic
monomer(s) is between 2.9 and 5.8% by weight.
12. Use of sodium hypophosphite NaPO2H2 or a derivative thereof and a compound of
formula (I):
S S
S R
COOX
R
XOOC
(I)
according to which:
- X represents Na, K or H and
- R represents an alkyl chain comprising 1 to 5 carbon atoms,
to prepare a (meth)acrylic acid polymer in solution, said polymer having a molecular
mass of less than 8000 g/mol and a polydispersity index (PI) between 2 and 5.