Anionic Amphiphilic Copolymers And Solutions Comprising Thereof

Abstract

It is proposed a new family of terpolymers based on repeating units of two different types of hydrophobic moieties modified with anionic charged groups. In a preferred embodiment, the first hydrophobic moiety is an aromatic compound such as styrene and the second hydrophobic moiety is a fatty acid. Depending on the modification rate, and on the neutralization degree, the aqueous solutions of the terpolymers have different rheological behavior, ranging from yield point fluid, shear-thickening and polysoaps.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

In The above and further objects, features and advantages of the present invention will be better understood by reference to the appended detailed descriptions, and to the drawings wherein:

FIG. 1 is a schematic view of usual amphiphilic polymers (FIG. 1) compared to the highly hydrophobic polymers of the invention.

FIG. 2 is a schematic representation of the synthesis of a carboxylated polymer based on alternated styrene and maleic anhydride units.

FIG. 3 shows the variation of the specific viscosity with the polymer concentration for various modification rates; and reference data for the SMA copolymer;

FIG. 4 shows the variation of the specific viscosity with the terpolymer 60Dm concentration, for various neutralization rates; and reference data for the SMA copolymer;

FIG. 5 shows the variation of the specific viscosity with the shear rate for various concentrations of 60Dm terpolymer.

DETAILED DESCRIPTION OF THE INVENTION

Usually, amphiphilic polymers backbones are mostly hydrophilic with local hydrophobic units as schematized FIG. 1-A where the open circles represent hydrophilic monomers; the full black circles hydrophobic monomers and the scribbly line represent grafted alkyl groups. With the polymers according to the present invention and schematized FIG. 1-B, the backbone consists mostly of hydrophobic groups with a limited amount of hydrophilic units and charges to achieve solubility.

The polymers according to the present invention are terpolymers based on combination of a first and second type of hydrophobic groups and of anionic charged groups. Two types of anionic charged groups have been studied: carboxylates and sulfonates groups.

Synthesis of Carboxylated Terpolymer

FIG. 2 illustrates the main steps of a method to prepare carboxylated terpolymer according to the invention. First a copolymer styrene and maleic anhydride acid (SMA) is obtained. The synthesis was performed with an SMA copolymer in which each monomer unit consist of exactly one styrene unit and one maleic anhydride unit (in other words, z=0.5), so that the molecular mass of the repeated unit is 102 g/mol. Other commercially available SMA copolymers have higher styrene content with z varying from 0.5 to 0.75. The tested SMA copolymer had a molecular weight Mw of 150 kg/mol as measured in the laboratory.

In the second step, the SMA polymer is hydrophobically modified with an amine C_nH_2n+1NH₂. Different amines having a purity of 99% were tested with n being an even number between 8 and 18. The operative mode for dodecylamine (n=12) is the following:

In a three-necked bottle, 6 g of SMA were dissolved in 150 ml THF (tetrahydrofuran), under N2 atmosphere, at 60° C. After two hours, 3.3 g of amine, in 50 ml THF were added dropwise. The reaction was allowed to occur for 24h at 60° C. The terpolymer was recovered by precipitation in diethylether and drying over vacuum.

The general chemical formula of the synthetised polymer is thus:

with n being either 8, 10, 12 or 16. For a modification rate of 100%, x equals 0.5. Therefore x varies between 0 and 0.5 (0.5 corresponding to a modification rate equal to 100%, the modification rate is defined as 200x).

The effective modification rate is checked by ¹H NMR spectrum and reported table 1.

TABLE 1
Terpolymer	Amine	Theoretical rate	NMR rate
20Dm	Dodecylamine	20%	22%
40Dm	Dodecylamine	40%	44%
50Dm	Dodecylamine	50%	50%
60Dm	Dodecylamine	60%	62.5%
60Ocm	Octylamine	60%	64%
60Hm	Hexadecylamine	60%	60%

Note that the effective modification rate is higher than expected due to some contamination by water of the SMA polymer. The molecular weight of the terpolymer 60Dm is about 230 000 g/mol.

The last step is the hydrolysis of the polymer allowing its solubilization in water under basic conditions (addition of NaOH), at 60° C., over 6 hours under stirring. Note that sodium hydroxide can be substituted with other hydroxide of monovalent cation such as lithium hydroxide or potassium hydroxide for instance.

Depending on the neutralization rate, the polymer formula can be thus expressed by where n is either 8, 10, 12, 14 or 16, x varies between 0 and 0.5 and R is a monovalent cation or a proton.:

Rheological Properties of the Carboxylated Terpolymer

Rheological measurements were carried out. FIG. 3 shows the evolution of the specific viscosity (noted η_spe), under a shear of 3.16 rad/s, as a function of the terpolymer concentration in the solution. In FIG. 3, the full triangles correspond to the unmodified SMA polymer, the open circles to the 60Dm terpolymer, the open squares to to the 40Dm terpolymer and the open lozenges to the 20Dm terpolymer.

Compared to the SMA polymer, the addition of the alkyl pendants clearly leads to lower viscosities at low concentration (probably due to aggregation) and higher viscosities above a threshold concentration, attributed to the transformation of intra into inter molecular interactions between the polymer chains.

FIG. 4 shows the effect of the neutralization degree defined as the ratio

$\alpha =\frac{\left[\mathrm{NaOH}\right]}{\left[\mathrm{COOH}\right]}$

on the specific viscosity. Tests were carried out with the 60Dm terpolymer (with α=1 (open lozenges); α=0.9 (open triangles) and α=0.8 (open squares)). As for FIG. 3, the data are compared with those of the copolymer SMA (open squares). This test shows that the neutralization degree does not have a significant impact at lower concentration but that it allows adjusting the threshold concentration at which the intermolecular associations occur.

The flow properties of the 60Dm terpolymer are illustrated with FIG. 5 that shows the value of the specific viscosity depending on the shear rate applied to the solution for different polymer concentrations. At lower concentration, the solution has a Newtonian behavior. At intermediate concentrations, the system exhibits a Newtonian plateau at lower shear rate and becomes shear-thinning at higher shear rate. At higher concentrations, a minimum shear rate is required to cause the flow and thereafter, the system exhibit a shear-thinning behavior.

Tests repeated with various modification rates and while varying the length of the alkyl group of the amine let to the characterization of the different Theological behaviors of the solutions at room temperature (and/or more slightly higher temperature, for instance about 60° C.) as depicted table 2 in which ST stands for shear-thickening; PS for polysoaps (poorly viscous), YPF for yield point fluid and NS for non-soluble.

	TABLE 2
	Modification rate
n	10	20	30	40	45	50	60	70	80	90	100
8							YPF
12	ST	ST		PS	PS	YPF	YPF	NS	NS	NS	NS
16		ST		NS		YPF	YPF	NS	NS
18							NS

In the area corresponding to solutions with a yield point at room or slightly higher temperature, the terpolymers have a thermo-thickening behavior. In domain corresponding to a shear-thickening behavior, the terpolymers also have thermo-thinning behavior.

The influence of various factors was studied with the 60Dm terpolymer:

Influence of the Molecular Weight of the SMA Copolymer

A sample prepared from a SMA copolymer with a molecular weight around 1000 g/mol and modified at 60% (thereby similar to 60Dm) showed that a behavior similar to a viscoelastic fluid could be obtained upon addition of salt, which reinforces hydrophobic interactions.

Influence of pH

The pH of the samples is typically comprised between 11 and 12.5. Nevertheless, terpolymers which exhibit yield point keep this property when pH ranges from 9.6 to 13.1 (the change in the pH is done by addition of concentrated sodium hydroxide or hydrochloric acid). Otherwise systems show phases separations.

Influence of Salts

Terpolymers which exhibit yield point keep this property in presence of a monovalent salt (NaCl) if its concentration remains lower than 100 mM. Actually, when NaCl is added, the concentration thresholds where solutions turn into gels show lower values. Moreover, salt reinforces yield point of concentrated systems. Nevertheless, the addition of any divalent salt induces polymer precipitation.

With a lyotropic salt such as KSCN, at low concentration, the viscosity of the systems is slightly modified. When a 10 g/L (200 mmol) salt concentration is considered, the systems become biphasic after two weeks. Moreover, such a salt does not allow the increase of the solubility of insoluble systems such as 80Dm.

Influence of Surfactants

The influence of the addition of carboxylated surfactants with C8, C10, and C12 alkyl chains, was evaluated for the 60Dm at a fixed concentration equals to 6 wt %. When the C8 based surfactant is added, the systems show some turbidity. Its yield point slightly increases for a surfactant concentration of 5.8 g/l, but the system is no more soluble if the surfactant concentration is 10 times higher. When the C10 surfactant is added, no turbidity appears when surfactant concentration ranges from 0 up to 272 g/l. The yield point seems to reach its lowest value around 70 g/l, and then increases for higher surfactant concentration. Addition of C12 based surfactant induces the loss of the yield point if the concentration of surfactant is higher than 3.4 g/l.

Addition of a C10 based sulfonated surfactant to 60Dm induces a loss of the yield point as soon as a small amount is added. However, system remains monophasic up to a surfactant concentration equivalent to 25 times the critical micellar concentration.

Compatibility With Other Polymers

When PVP (polyvinylpyrrolidone with M=10 000 g/mol) is added to a 60Dm system (6% concentration), the yield point is significantly increased. However, PVP concentration should remain below 20 g/l.

Compatibility with Alcohols

Addition of three C4 based alcohol with different classes to a non-soluble 80Dm system induces the same behavior: an increase in the solubility. A gel formation is observed for a low amount of alcohol, and then, an excess of alcohol induce a destruction of the gel.

Oil Components Compatibility

With addition of aliphatic oil (dodecene), a loss of yield point is observed from 2% wt/wt oil concentration in a 60Dm (6%) system.

With addition of aromatic oil (toluene), a loss of yield point is first observed for a short period of time. Then a reorganization takes place in the system after a long period of time (weeks). Yield point is kept up to 10% wt/wt of oil.

Sulfonated Terpolymers

Equivalent sulfonated terpolymers, with sulfonate groups replacing the carboxylate groups were prepared to improve the thermal stability and the compatibility with calcium ions.

FIG. 6 shows the main steps of a first synthesis route including first the synthesis of a copolymer based on styrene and dodecylmethacrylate, using toluene as solvent, at 70° C. during 30 minutes. This step is followed by a sulfonation at 50° C., using dichloroethane as solvent in presence of H₂SO₄. The sulfonation reaction is controlled by adjusting the reaction time. The resulting polymer is obtained through evaporation and and dissolution in DMSO.

Starting with a mixture of 80% styrene and 20% dodecylmethacrylate, a 74% styrene/26% dodecylmethacrylate copolymer was prepared in step 1, leading after sulfonation to the following general chemical formula where x is the sulfonation degree.

However, with varying values for x up to 30%, no yield point is obtained with such terpolymers.

Another synthesis route is based on terpolymerization of styrene, styrene sulfonate and alkylacrylamide. The solvent is DMSO. The polymerization was allowed to proceed for 24 hours at 65° C. The resulting polymer is obtained by precipitation in ether.

The terpolymer having the following formulae was obtained:

In term of rheological behavior, this polymer is similar to a polyelectrolyte.

Claims

1. A fluid, comprising a polymer dissolved in an aqueous phase, wherein the polymer is a terpolymer based on repeating units of a first and second type of hydrophobic moieties and of anionic charged groups.

2. The fluid of claim 1, wherein the first and second type of hydrophobic moieties have different hydrophobic nature.

3. The fluid of claim 1, wherein the first hydrophobic moieties type contains an aromatic group.

4. The fluid of claim 3, wherein the aromatic hydrophobic moiety is a styrene derivative.

5. The fluid of claim 1, wherein the second hydrophobic moieties type contains a fatty acid including an alkyl side chain CnH2n+1, with n being an integer greater or equal to 6.

6. The fluid of claim 5 wherein n is selected from the group consisting of 8, 10, 12, 14 and 16.

7. The fluid of claim 5, wherein the alkyl side chains are grafted to the backbone of the polymer through hetero-functional groups.

8. The fluid of claim 7, where said hetero-functional group is selected from the list consisting of amide, ester and urethane.

9. The fluid of claim 1, wherein the anionic group is a phosphate.

10. The fluid of claim 1, wherein the anionic group is a sulfonate.

11. The fluid of claim 10, wherein the polymer is represented by the general chemical formula:

12. The fluid of claim 1, wherein the anionic group is a carboxylic group.

13. The fluid of claim 12, wherein the polymer is represented by the general chemical formula:

14. The fluid of claim 13, wherein the modification rate, defined as 200x, is 60 and n is 8, 10, 12, 14 or 16.

15. The fluid of claim 13, wherein the modification rate, defined as 200x, is 50 and n is 12, 14 or 16.

16. The fluid of claim 13, wherein the modification rate, defined as 200x, is 10 and n is 12.

17. The fluid of claim 13, wherein the modification rate, defined as 200x, is 20 and n is 12, 14 or 16.

18. The fluid of claim 13, wherein the polymer concentration is between 3 and 15% (by weight).