Microcapsule having temperature-dependent permeability profile
First Claim
1. A microcapsule comprised of a crystallizable polymer, the crystallizable polymer being comprised such that it has a first permeability at a temperature below a first order phase transition temperature of the polymer and a second permeability at a temperature at or above the first order phase transition temperature, wherein the second permeability is at least three times that of the first permeability and wherein the permeability of the microcapsule can be repeatedly and reversibly changed between the first and second permeability by changing the temperature of the microcapsule above and below the first order transition temperature.
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Abstract
The microcapsules of the invention are comprised of crystallizable polymers which are preferably side-chain crystallizable polymers or cross-linked, side-chain crystallizable polymers having a specific first order transition point or "melt" temperature. The polymers are caused to form microcapsules and thereby encapsulate one or more compounds generally referred to herein as an active ingredient such as a herbicide, insecticide, fungicide, or fertilizer. The polymer of the microcapsule surrounds the active ingredient separating it from the outside environment. Crystallizable polymers used herein have temperature-dependent permeabilities with respect to a given component such that this component is kept out of contact with the active ingredient at a temperature below a given first order transition point and (due to increased permeability) is allowed to contact the active ingredient at a temperature at or above the transition point. The permeability of the polymer is not only temperature-dependent but reversible. The microcapsules are less than 200 microns in median diameter, more generally less than 100 microns in median diameter and preferably less than 50 microns in median diameter. By varying the polymer and reactants used in the formation of the microcapsules, the release rate and timing of the release of active ingredient from the microcapsule can be temperature controlled to obtain the various objects, advantages and features of the present invention.
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Citations
30 Claims
- 1. A microcapsule comprised of a crystallizable polymer, the crystallizable polymer being comprised such that it has a first permeability at a temperature below a first order phase transition temperature of the polymer and a second permeability at a temperature at or above the first order phase transition temperature, wherein the second permeability is at least three times that of the first permeability and wherein the permeability of the microcapsule can be repeatedly and reversibly changed between the first and second permeability by changing the temperature of the microcapsule above and below the first order transition temperature.
- 19. A microcapsule comprised of a side-chain crystallizable polymer having a reversible temperature-dependent permeability such that a first permeability of the polymer as regards a liquid at a temperature below the melt temperature of the polymer is increased five times as regards the liquid at a temperature at or above the melt temperature, a plurality of microcapsules enclosing an active ingredient therein and having a median microcapsule diameter of less than 100 microns.
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30. A method for improving plant growth, comprising the steps of:
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providing a plurality of microcapsules comprising a sphere of a solid side-chain crystallizable polymer enclosing an active ingredient which affects plant growth, the polymer having a reversible temperature-dependent permeability such that a first permeability of the polymer, as regards a liquid at a temperature below the melt temperature of the polymer, is increased five times as regards the liquid at a temperature at or above the melt temperature, wherein the plurality of microcapsules have a median microcapsule diameter of less than 100 microns; dispersing the microcapsules in an area of a plant; and allowing the microcapsules to remain in the area of the plant for sufficient time and under such conditions that active ingredient in the microcapsules permeates out of the microcapsules into the area of the plant and affects plant growth.
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Specification