Stable emulsions, preparation methods and applications

Details Stable emulsions, preparation methods and applications Stable emulsions, preparation methods and applications

2000-02-07

2002-05-21

Lovering, Richard D. (Department: 1712)

Drug, bio-affecting and body treating compositions

Preparations characterized by special physical form

Biocides; animal or insect repellents or attractants

C424S445000, C428S321500, C514S772700, C514S937000, C514S953000, C516S020000, C516S030000, C523S122000

Reexamination Certificate

active

06391326

ABSTRACT:

This application is a 371 of PCT/FR99/00586 filed Mar. 16, 1999.
The present invention relates to stable emulsions comprising a continuous phase formed from a solution of an elastomer in an organic solvent and a dispersed phase, in the form of droplets with a diameter greater than or equal to 10 &mgr;m; said droplets comprise an active chemical substance in a solvent which is immiscible with the elastomer solution and are capable of being converted into elastomeric films.
The present invention also relates to the process for preparing said emulsions, as well as to elastomeric films containing them: said emulsions can give, after evaporation of the solvent for the elastomer, an elastic film containing stable droplets of liquid, with a diameter of greater than or equal to 10 &mgr;m.
International patent application WO 95/17453 in the name of the Applicant describes the preparation of a two-phase solid material containing a dispersion of liquid droplets of an active chemical substance, which are stabilized by means of a block or grafted copolymer comprising at least a number of sequences polyB which are compatible with said droplets and a number of polyA sequences, which are immiscible with these droplets, in an elastomer. The droplets generally have a diameter of less than 10 &mgr;m. Under these conditions, the block or grafted copolymer effectively stabilizes the emulsion, which is thus distributed homogeneously in said film.
That international patent application WO 95/17453 also describes the process for preparing said elastomeric material; this process essentially comprises two steps:
(1) the preparation of an emulsion which comprises:
the preparation of a phase A by dissolving the elastomer in an organic solvent a (phase A: solution of elastomer in the organic solvent a)
the preparation of a phase B, by mixing an active chemical substance in an organic solvent b which is immiscible with phase A (phase B: solution or dispersion of active substance in an organic solvent b which is immiscible with the phase A)
the addition to phase A or phase B, in proportions of from 0.1 to 50%, preferably from 0.1 to 25%, of a block or grafted copolymer comprising at least a number of polyA sequences, which are miscible with the phase A, and a number of polyB sequences, which are miscible with the phase B, as defined above
the dispersion of phase B in phase A to give an emulsion in which phase A constitutes the continuous phase and phase B constitutes the dispersed phase, as represented in
FIG. 1
, and
(2) evaporation of the organic solvent a to give an elastomeric film containing, in the form of a stable dispersion, droplets of solvent b generally less than 10 &mgr;m in diameter, loaded with active chemical substance.
Continuing its research, the Applicant became interested more particularly in improving the stability of emulsions B in A in step (1), in particular those with droplets at least equal to 10 &mgr;m in diameter and preferably between 10 and 50 &mgr;m in diameter.
The various elastomeric materials usually used in the medical or paramedical field (in particular hygiene) can be modified so as to be combined with active chemical substances, having a protective effect, during the use of this [sic] materials (gloves, fingerstalls, condoms, strips and various dressings). Specifically, both in the case of examination or surgery or in odontology, and for protection against pathogenic agents such as, for example, bacteria, viruses and fungal spores, a rupture or sometimes even simply the pores or a crack in the elastomeric membrane can result in the wearer of said material becoming contaminated by being pricked with syringes, suture needles, trocars, bone splinters, etc.
Now, if the droplets containing the active chemical substance, which may be released in the event of rupture of the protective elastomeric material, do not release a sufficient amount of active substance, the protective effect will not be sufficient.
Moreover, if the diameter of the droplets is increased, so as to allow the release of a sufficient effective amount of active substance to rapidly neutralize the pathogenic agent which may thus have been accidentally introduced into the wearer, the problem of the stability of the emulsion may become crucial.
According to the literature (P. Becher,
Emulsion: Theory and Practice, ACS Monogr
., 162, 1965), an emulsion can be defined as “a heterogeneous system consisting of at least one immiscible liquid intimately dispersed in another in the form of droplets”. These systems generally contain one or more surfactants, like the block or grafted copolymers described in international patent application WO 95/17453. In this case, the particles are subjected to Van der Waals attraction forces and electrostatic or steric repulsion forces associated with the presence of copolymer, as well as to gravitational forces, if the densities of the phases present are different.
The equilibrium between the forces of attraction and repulsion is the origin of stabilization or destabilization of the emulsions.
Two main destabilization mechanisms should be envisaged for these systems:
flocculation, which is reflected by an aggregation of particles in the form of clusters, and
coalescence, which is the result of thinning of the liquid film separating the particles and is reflected by fusion of the particles to form a single particle of larger size.
The block or grafted copolymers as described in international patent application WO 95/17453 are particularly suitable for stabilizing emulsions comprising droplets less than or equal to 10 &mgr;m in diameter, by reducing the phenomena of coalescence and/or flocculation.
The Applicant has now found that to stabilize droplets of a phase B (containing an active chemical substance x and a solvent b) with a diameter ≧10 &mgr;m, dispersed in an organic phase A (elastomer+solvent a), said block or grafted copolymers must be used as a mixture with other compounds of particle-stabilizing type, in order to effectively obtain stabilization of the emulsion.
The Applicant has also found that, when the emulsion comprises certain chemical substances x which have surfactant properties, it is possible to reduce the content of block or grafted copolymer, or even to dispense with it altogether. In such a case, said chemical substance included in phase B and combined with the particulate stabilizer also makes it possible to obtain a stable emulsion.
A subject of the present invention is a stable emulsion of at least one chemical substance x in an elastomer solution, which can be used for the preparation of an elastomeric film, comprising (1) a phase A comprising an elastomer dissolved in an apolar or relatively nonpolar organic solvent a, in which is dispersed (2) a phase B comprising at least said chemical substance x dissolved or dispersed in a polar solvent b, which is immiscible with phase A, and (3) at least one dispersing agent selected from the group consisting of block or grafted copolymers, this emulsion being characterized:
in that the droplets of dispersed phase B have a diameter ≧10 &mgr;m,
in that said emulsion comprises, for the stabilization of said dispersed phase B, besides at least one block or grafted copolymer (also referred to as dispersing copolymer) comprising polyA sequences which are compatible with phase A and polyB sequences which are compatible with phase B, at least one particulate stabilizer selected from the group consisting of solid organic compounds of between 30 nm and 10 &mgr;m in size or solid inorganic compounds of between 5 nm and 10 &mgr;m in size, of any geometry (sphere, parallelepiped, finely divided solid, etc.), whose surface is organophilic in nature,
in that the mass fraction &phgr;
B
of dispersed phase (phase B) in the emulsion, expressed by:
φ
B
=
m
B
m
B
+
m
A
+
m
elastomer
 is between 0.01 and 0.2,
with m
B
=mass of phase B (solvent b+active chemical substance x)
m
A
=mass of solvent a
m
elastomer
=mass of the elastomer dissolved in a;
in that the mass fraction of the

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