Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2001-02-20
2003-01-14
Nutter, Nathan M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S293000, C525S294000, C525S296000, C525S299000
Reexamination Certificate
active
06506837
ABSTRACT:
The present invention relates to a gelled aqueous composition comprising a block copolymer containing at least one water-soluble block and one hydrophobic block.
Amphiphilic molecules are molecules having different water-solubility regions which give them special properties. A known example of an amphiphilic molecule is that of surfactants which may have a hydrophilic and a hydrophobic region.
Because of their amphiphilic character, these molecules come together and organize themselves in solution in water to form micelles. These micelles may be of various morphologies, such as spherical micelles or anisotropic micelles (for example lamellar or vermicular micelles). Spherical micelles are the most common as they are the most accessible.
These micelles are in equilibrium, which means that dilution or addition of a solvent or of a cosurfactant to the medium containing these micelles results in a variation in the size of the micelles or in their morphology.
One objective of the present invention is to provide amphiphilic block copolymers of hydrophobic/hydrophilic structure which can form a gel when they are in water.
Another objective is to be able to obtain easily preparable aqueous gels whose elastic modulus can be adjusted.
To achieve the above objectives, the purpose of the invention is the use of a block copolymer containing at least one block water-soluble in nature and at least one block predominantly hydrophobic in nature, which copolymer is in the form of micelles when it is in water.
This block copolymer forms a viscoelastic gel when it is in solution in water.
This block copolymer contains at least one block predominantly hydrophobic in nature and at least one water-soluble block, the predominantly hydrophobic block having hydrophilic units preferably in an amount of less than 33% by weight with respect of the total weight of the units of said predominantly hydrophobic block. This amount may be equal to 0 but is preferably at least 1% by weight and less than 25% by weight, even more preferably between 2 and 15%, with respect to the total weight of the units of said predominantly hydrophobic block.
This block copolymer contains at least one block predominantly hydrophobic in nature and at least one water-soluble block, the water-soluble block having hydrophobic units in an amount which may be small, about 1% of the total weight of the units of said water-soluble block. The maximum amount of hydrophobic units depends on the nature of the units and is in most cases less than 70% by weight and at least 1% by weight, and even more preferably less than 50% by weight and at least 10%, with respect to the total weight of the units of said water-soluble block.
The invention also relates to a process for preparing these block copolymers by so-called living or controlled polymerization.
The invention also relates to a process for controlling the hydrophilic/hydrophobic balance of amphiphilic block copolymers having at least one block coming from the polymerization of hydrophilic monomers and at least one block coming from the polymerization of hydrophobic monomers, in which process:
hydrophilic units are introduced into the block coming from the polymerization of hydrophobic monomers, and/or
hydrophobic units are introduced into the block coming from the polymerization of hydrophilic monomers.
Finally, the invention relates to the use of these block copolymers as gelling agents or as thickeners for aqueous medium.
The invention firstly therefore relates to a block copolymer containing at least one block water-soluble in nature and at least one block predominantly hydrophobic in nature. According to a first embodiment, the copolymer contains only a single hydrophobic block and a single water-soluble block. According to another embodiment, the copolymer contains a water-soluble block having a hydrophobic group at each end or vice-versa.
In the description which follows, the expression “block water-soluble in nature” should be understood to mean a polymer block containing a number of hydrophilic groups sufficient to obtain a water soluble block well dissolved in water. Solubility in water of the water soluble block means a block copolymer containing such a water-soluble block, when mixed with water, gives a translucent monophasic system. Usually such a translucent monophasic system is obtained from a water soluble block comprising at least 30%, preferably at least 50% by weight of hydrophilic units with respect to the totality of units of the water-soluble block. The block water-soluble in nature is therefore soluble in water. The term “unit” should be understood to mean that part of the block corresponding to a monomeric unit.
Likewise, the expression “block predominantly hydrophobic in nature” should be understood to mean a polymer block preferably containing at least 67% by weight hydrophobic units with respect to the totality of units. The block predominantly hydrophobic in nature is not soluble in water. This block copolymer containing at least one block water-soluble in nature and at least one block predominantly hydrophobic in nature forms a viscoelastic gel when it is in solution in water.
The term “viscoelastic gel” should be understood to mean a liquid medium for which the viscous modulus G″ and the elastic modulus G′ are such that G′>G″. This gel behaviour is manifested by a flow threshold and even, in some cases, by a shear-thickening effect (an increase in the viscosity with flow). This gel effect is obtained when the polymer concentration exceeds a certain threshold called the critical gelling concentration.
The block copolymers according to the present invention have the advantage of making the aqueous media viscoelastic when they are used in only a small amount with respect to the aqueous medium. The copolymer is preferably used at a concentration higher than 0.1% by weight and even more preferably at a concentration from 1 to 10% by weight.
The properties of the copolymers according to the present invention may be obtained by selecting the nature of the soluble blocks and the nature of the predominantly hydrophobic blocks, at least the hydrophilic block having to contain hydrophobic groups in an appropriate amount.
According to one embodiment of the invention, the weight ratio of the block water-soluble in nature to the completely hydrophobic block is between 95/5 and 20/80, even more preferably between 90/10 and 40/60.
According to a first version of the preparation, the blocks water-soluble in nature and the blocks predominantly hydrophobic in nature of the above copolymers may come from the copolymerization of hydrophilic and hydrophobic monomers. The amounts of hydrophilic and hydrophobic units in each of the said blocks can then be controlled by the respective contents of hydrophilic monomers and hydrophobic monomers during the polymerization of the blocks.
Thus, the blocks predominantly hydrophobic in nature may come from the copolymerization of hydrophobic monomers and of hydrophilic monomers, the hydrophilic monomers being present in an amount of less than 33% by weight, preferably at least 1% by weight, even more preferably between 2 and 15%, with respect to the total weight of the units of the hydrophobic block.
In addition, the blocks water-soluble in nature may come from the copolymerization of hydrophilic monomers and of hydrophobic monomers, the hydrophobic monomers being present in an amount of less than 70% by weight, preferably at least 1% by weight, even more preferably between 50 and 25%, with respect to the total weight of the units of the water-soluble block.
According to a second version of the preparation, the blocks water-soluble in nature may come:
from the polymerization of monomers that may be rendered hydrophilic by hydrolysis and optionally of non-hydrolysable hydrophobic monomers and/or of hydrophilic monomers, and then
from the hydrolysis of the polymer obtained.
During the hydrolysis, the units corresponding to the hydrolysable monomers are hydrolysed into hydrophilic units.
The amounts of hydrophilic and
Destarac Mathias
Joanicot Mathieu
Reeb Roland
Asinovsky Olga
Nutter Nathan M.
Rhodia Chimie
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