Stock material or miscellaneous articles – Composite – Including interfacial reaction product of adjacent layers
Reexamination Certificate
1999-11-02
2001-02-27
Robinson, Ellis (Department: 1772)
Stock material or miscellaneous articles
Composite
Including interfacial reaction product of adjacent layers
C428S035700, C428S036910, C428S034900, C428S515000, C428S516000
Reexamination Certificate
active
06194073
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a heterogeneous polymer gel comprising at least two gel networks. The heterogeneous polymer gel exhibits controlled changes in volume in response to external environmental changes.
2. Description of the Related Art
Relatively uniform or homogeneous polymer gels have attracted much interest because their volume can be changed by several orders of magnitude in response to the change of an external factor such as solvent, temperature, electric field, or light. Uses of such homogeneous polymer gels include such applications as artificial muscles, drug-delivery devices, chemical valves and actuators, and magnetic resonance monitoring agents.
It is desirable to develop and produce new polymer gels that exhibit desired reversible characteristics in response to external environmental changes.
SUMMARY OF THE INVENTION
In one aspect, the present invention concerns a heterogeneous polymer gel comprising at least two gel networks. The heterogeneous polymer gel is characterized in that it exhibits desired changes in volume in response to external environmental changes.
One embodiment of the present invention concerns a heterogeneous polymer gel comprising a first gel network comprising an environmentally-stable gel and a second gel network comprising an environmentally-unstable gel wherein the first gel network interpenetrates the second gel network.
One embodiment of the present invention concerns a heterogeneous polymer gel comprising a first gel layer comprising an environmentally-stable gel and a second gel layer comprising an environmentally-unstable gel wherein the first gel layer is attached to the second gel layer.
In another aspect, the present invention concerns a method of using a heterogeneous polymer gel comprising at least two gel networks.
In one embodiment of the present invention, a method of using a heterogeneous polymer gel, comprising an environmentally-stable gel and an environmentally-unstable gel, comprises heating the heterogeneous gel to a temperature effective to result in a desired change in volume in the environmentally-unstable gel.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention concerns a class of materials based on the spatial modulation of the chemical nature of gels. The modulation is achieved by allowing only part of one gel network to interpenetrate with another gel network. The resultant gels have an internally heterogeneous or modulated structure.
The heterogeneous polymer gel of the present invention generally comprises a first polymer gel network comprising an environmentally-stable polymer gel and a second polymer gel network comprising an environmentally-unstable polymer gel wherein the first polymer gel network interpenetrates the second polymer gel network.
As used herein, “an environmentally-stable polymer gel” is intended to represent a polymer gel that remains substantially inert or unchanged as the environment surrounding the polymer gel undergoes a change in conditions, such as in physical or chemical conditions. In particular, it is desired that the environmentally-stable polymer gel does not exhibit a substantial change in volume as the conditions of the environment surrounding the environmentally-stable polymer gel undergoes a change.
As used herein, “an environmentally-unstable polymer gel” is intended to represent a polymer gel that exhibits a substantial change in its physical characteristics as the environment surrounding the polymer gel undergoes a change in conditions, such as in physical or chemical conditions. In particular, it is desired that the environmentally-unstable polymer gel exhibits a substantial change in volume as the conditions of the environment surrounding the environmentally-unstable polymer gel undergoes a change.
Polymer gels that have been found to be useful in the present invention include N-isopropylacrylamide gels and polyacrylamide gels.
As used herein, the “environment” for a polymer gel is intended to represent the physical surroundings of the polymer gel. Generally, the environment of a polymer gel will be a liquid or a gas surrounding the polymer gel. For example, the environment of a polymer gel may be an aqueous solution or air.
In order to cause a substantial change in the physical characteristics of an environmentally-unstable polymer gel, it is generally necessary that the environment surrounding the environmentally-unstable polymer gel undergoes a change in conditions. As will be appreciated by those skilled in the art, the change in environmental conditions necessary to cause a substantial change in the physical characteristics of an environmentally-unstable polymer gel will generally be dependent on the specific environmentally-unstable polymer gel being used in a particular heterogeneous polymer gel. Such a change in conditions can, for example, be a change in the temperature, the pH, or the chemical composition of the environment.
In the present invention, it is generally desired that the environment is substantially uniform and/or that the change in conditions be applied to the environment in a substantially uniform manner. As such, it is generally not necessary to induce a gradient of an environmental property, such as temperature or electric field, to the environment in order to achieve the desired substantial change in the physical characteristics of an environmentally-unstable polymer gel.
In one embodiment of the present invention, an ionic N-isopropylacrylamide gel, prepared with sodium acrylate, shrinks substantially in volume when in an aqueous solution at temperatures higher than about 37° C. In contrast, a polyacrylamide gel does not undergo a substantial change in volume when in an aqueous solution at temperatures higher than about 37° C. As such, a heterogeneous polymer gel may be prepared comprising polyacrylamide gel as the environmentally-stable polymer gel and an ionic N-isopropylacrylamide gel as the environmentally-unstable polymer gel, wherein the environment is an aqueous solution, and the change in conditions for the environment will be a change in temperature from less than about 37° C. to greater than about 37° C.
In another embodiment of the present invention, a polyacrylamide gel shrinks substantially in volume when in a water/acetone solution that comprises at least about 34 weight percent acetone. In contrast, an N-isopropylacrylamide gel does not undergo a substantial change in volume when in a water/acetone solution that comprises at least about 34 weight percent acetone. As such, a heterogeneous polymer gel may be prepared comprising an ionic N-isopropylacrylamide gel as the environmentally-stable polymer gel and a polyacrylamide gel as the environmentally-unstable polymer gel, wherein the environment is a water/acetone solution, and the change in conditions for the environment will be a change in acetone concentration from less than about 34 weight percent to greater than about 34 weight percent.
As such, as will be appreciated by one skilled in the art, a polymer gel that is used as an environmentally-stable polymer gel in one environment, or under a particular change in conditions for that environment, may alternatively be used as an environmentally-unstable polymer gel in another environment, or under a different change in conditions for the original environment.
As also will be appreciated by one skilled in the art, it may be desirable to selectively choose the environmentally-stable polymer gel and the environmentally-unstable polymer gel that are being used so as to maximize the difference in properties between the two gels relevant to the change in conditions that are intended to be made to an environment. For example, if the temperature of the environment is to be changed so as to induce a change in the volume of the environmentally-unstable polymer gel, it may be desirable to maximize the difference in the thermal expansion coefficients of the two gels. In particular, an ionic N-isopropylacrylamide gel may shrink to half of its original size pe
Hu Zhibing
Li Yong
Zhang Xiaomin
Kilpatrick & Stockton LLP
Kimberly-Clark Worldwide, Inc
Nolan Sandra M.
Robinson Ellis
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