Process for preparing an aqueous composition in gel form and...

Details Process for preparing an aqueous composition in gel form and... Process for preparing an aqueous composition in gel form and...

2001-04-30

2002-10-22

Yoon, Tae H. (Department: 1714)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

At least one aryl ring which is part of a fused or bridged...

C524S394000, C524S555000, C524S556000, C524S804000, C424S070310, C424S450000, C523S102000

Reexamination Certificate

active

06469084

ABSTRACT:

The present invention concerns a novel process for preparing an aqueous composition in the form of a gel and to novel compositions which can be obtained from this process, especially compositions containing vesicles, in particular liposomes.
Water-soluble polymers have numerous applications in a wide variety of industrial fields such as cosmetics, enhanced oil recovery, and food additives.
They are often used to control the rheology of aqueous formulations, since only a little dry material is needed to produce highly viscous solutions or even gels. A particular class of those water-soluble polymers is associative water-soluble polymers.
Two recent works are cited here which particularly concern that type of polymer: “Water Soluble Polymers”, ACS Symposium Series 467, ed. Shalaby W Shalaby et al., Am. Chem. Soc. Washington (1991), pp. 82-200, and “Polymers in Aqueous Media”, ed. J. Edward Glass, Advances in Chemistry Series no. 223, Am. Chem. Soc. Washington D.C. (1989).
Associative polymers are polymers constituted by a hydrophilic main chain and hydrophobic side chains which are relatively few in number compared with the hydrophilic units of the main chain. Their behavior in solution is a result of competition between the hydrophobic and hydrophilic properties of their structure. The hydrophobic units tend to form aggregates constituting linkage points between the macromolecular chains.
From a rheological viewpoint, associative water-soluble polymers have a very high viscosifying power in water, retain their viscosity well in a saline medium, and exhibit reversible behavior under stress (rheofluidifying).
The study of aqueous systems containing polymers and surfactants is very important because of the numerous industrial applications in a wide variety of fields such as paint, cosmetics, or enhanced oil recovery.
In those systems, mixed polymer/surfactant aggregates can form, which are stabilized by different types of interactions: electrostatic interactions, dipolar interactions, or hydrogen bonds. Associative water-soluble polymers can interact more specifically with surfactants due to their hydrophobic portions.
The following publications: I. Iliopoulos et al., Langmuir 1991, 7, 617; and B. Magny et al., Prog. Colloid. Polym. Sci., 1992, 89, 118, show that the addition of a cationic, anionic, or non ionic surfactant to a hydrophobically modified sodium polyacrylate solution causes an increase in viscosity.
U.S. Pat. No. 4,432,881 describes an aqueous liquid medium with increased viscosity obtained by dispersing a water-soluble polymer containing hydrophobic pendant groups and a surfactant in that medium. The medium can in particular be used for enhanced oil recovery.
S. Evani and G. D. Rose, Proc. Am. Chem. Soc. Div. of Polym. Mater. Sci. and Eng., 1987, 57, 477 describes two systems which use reversible hydrophobic combinations to control the rheology respectively of paints containing latex and of aqueous fluids for enhanced oil recovery.
For the surfactant associative polymer couples concerned, those two documents show the favorable effect on the viscosity of the medium either of an increase in temperature or of an increase in the salt concentration in the medium.
Further, a number of studies have been devoted to the determination of interactions and phase transitions in water-surfactant systems as a function of temperature and surfactant concentration.
Particular interest has been taken in systems in which the surfactant is a polyethyleneglycol monoalkylether with formula:
H(CH
2
)
i
(OCH
2
CH
2
)
j
OH
hereinafter termed C
i
E
j
where i represents the number of carbon atoms in the alkyl chain and j represents the number of ethylene oxide groups contained in the polar head of the surfactant.
Those surfactants have the particular property of having a low segregation temperature: there is a temperature above which the micellar solution separates into two phases, one of which is dilute and the other of which is concentrated in surfactant. This temperature is termed the cloud temperature. This phenomenon is due to a reduction in hydration of the ethylene oxide groups when the temperature increases. As a result, the longer the ethyleneglycol chain, the higher the segregation temperature.
At relatively high temperatures and very low concentrations, liquid crystal phases are observed (which constitute a further specific property of those surfactants): a lamellar phase L
a
, which persists up to very high dilutions (concentrations of the order of 1% by weight for C
12
E
5
), two phases L
3
and L
a
+
constitute bilayers, and finally several regions of liquid—liquid coexistence have been shown to exist.
Phase diagrams of the surfactants C
12
E
3
, C
12
E
4
and C
12
E
5
have been published in the literature (see D. G. Hall, J. T. Tiddy, “Anionic Surfactants: Physical Chemistry of Surfactant's Action; Schick, M. J., Ed., Marcel Dekker, New York 1987, pp 55-108). More recently, a study concerning the surfactant C
12
E
5
has been published (see R. Strey, R. Schomäker, D. Roux, F. Nallet, V. Olsson, J. Chem. Soc. Faraday Trans., 1990, 86, 2253).
The C
12
E
5
/H
2
O system has been studied in detail, in particular by R. Strey et al., J. Chem. Soc. Faraday Trans., 1990, 86, 2253. It produces a lamellar phase up to a water content of 99% by weight within a narrow temperature range. This organised structure is readily evidenced by the fact that the sample appeared birefringing between crossed polarizers, and could be more precisely characterized by measuring radiation diffusion. Thus light diffusion measurements allowed the distance d separating two lamellae to be determined. For a volume fraction f=0.0125 of C
12
E
5
, d was of the order of 3×10
7
m (3000 Å). Further, since the repeat distance between lamellae was of the same order as the wavelength of visible light, the sample illuminated by white light appeared colored due to Bragg reflection.
The phase L
3
which appears on the phase diagrams is often termed the abnormal or sponge phase. It may be birefringent on stirring and highly opalescent. Those characteristics are more marked when the solution is diluted. Its structure is defined as a continuous three dimensional bilayer. The bilayers constitute a type of randomly connected network which divides the volume of the solution into two equal parts.
The existence of another phase containing bilayers, the L
&agr;
+
phase, has recently been reported by Jonströmer and Strey, J. Phys. Chem., 1992, 96, 5993. It has been observed in surfactants such as C
12
E
3
, C
12
E
4
, and C
14
E
5
, and its exact structure is currently unknown. It has the optical appearance of the L
3
phase, i.e., it can be birefringent on stirring in some cases, but it is often more viscous than the L
3
phase.
Its zone of existence is completely enclosed in that of the lamellar phase. The borders between the L
a
and L
a
+
phases are, further, difficult to determine insofar as the relaxation time at the end of which birefringence disappears after stirring has ceased can be relatively long.
The L
a
+
phase can currently be defined as a dispersion of bilayers: either in the form of vesicles (simple or multilayered), or in the form of a diphase system in which there is an equilibrium between a lamellar phase and an aqueous phase. The structure remains to be precisely determined.
We have carried out systematic studies, in particular on aqueous compositions containing non ionic surfactants and associative polymers, and surprisingly, we have discovered perfect correlation between the gelling conditions of such systems and those for the appearance of a phase corresponding to bilayers in the phase diagram of the surfactant alone in solution in water.
Our discovery has led us to define a novel process which forms the subject matter of the present invention and, in order to obtain a composition in the form of a gel containing an associative polymer at a given temperature, consists in selecting a surfactant which at that temperature is in the form of bilayers in aqueous s

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