Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1998-12-16
2001-07-03
Yoon, Tae (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S436000, C523S500000, C523S523000, C525S064000, C525S360000, C525S370000
Reexamination Certificate
active
06255367
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to polymeric modifying agents having temperature-dependent properties.
2. Introduction to the Invention
It is known to control the rate of a chemical reaction by providing a reactant, a catalyst or other active agent in a modified form such that the availability of the active agent depends upon some external factor. For example, the active agent can be encapsulated by a protective shell which at least partly prevents access to the active agent. When release of the active agent or an increase in its concentration is desired, the shell is removed, or the shell is subjected to a treatment which does not destroy its physical integrity (i.e. the shell resins its shape and is not free to flow during the treatment), but which increases the rate at which the active agent can permeate through the shell. Removal of the shell can be effected, for example, by means of heat, solvent, or ultrasonic waves. A change in the permeation rate can, for example, be effected by using a shell having temperature-dependent permeability and by changing the ambient temperature; for further details of particularly useful temperature-dependent systems of this kind, reference may be made, for example, to commonly assigned U.S. Pat. Nos. 4,830,855 (Stewart), 5,129,180 (Stewart) and 5,254,354 (Stewart), the disclosures of which are incorporated herein by reference for all purposes.
It is also known to use so-called “latent hardeners” or “latent curing agents”, optionally in conjunction with “latent accelerators”. These “latent” compounds can be mixed with the other ingredients for a crosslinked resin, e.g. an epoxy resin or a polyurethane, to give compositions which are relatively stable at room temperature but which cure rapidly when heated to an elevated temperature, e.g. 160° C. or more. Systems of this kind are disclosed for example in U.S. Pat. Nos. 4,349,651 (Smith), 4,358,571 (Kaufman et al), 4,420,605 (Kaufman), 4,430,445 (Miyake), 4,659,779 (Bagga et al), 4,689,388 (Hirai et al), 4,701,378 (Bagga et al), 4,742,148 (Lee et al) and 4,933,392 (Andrews et al), and European Patent Publication No. 362787 A2 (Henkel), the disclosures of which are incorporated herein for all purposes.
Many attempts have been made to develop systems which are stable for extended periods at storage temperatures, but which will cure rapidly when heated to give crosslinked polymers having desired properties. However, only limited success has been achieved.
It is also known to prepare polymers containing reactive moieties which will react with other materials under appropriate conditions. For example, in the materials often referred to as “polymer-supported catalysts”, the reactive moiety is one which provides a catalytic function. Reference may be made, for example, to Encyclopedia of Polymer Science and Engineering, Vol 2, pages 702-729, the disclosure of which is incorporated herein by reference for all purposes.
SUMMARY OF THE INVENTION
We have now discovered, in accordance with this invention, that greatly improved results can be achieved through the use of polymeric materials which comprise (i) a crystalline polymeric ingredient which melts and flows over a relatively small temperature range and (ii) an active chemical ingredient which promotes or inhibits a chemical reaction of a matrix. Such materials are referred to herein as “modifying agents”. We have found that when such a modifying agent, in solid form, is in contact with the matrix (e.g. as solid particles dispersed in the matrix), the polymeric ingredient restricts the contact between the matrix and the active chemical ingredient. On the other hand, when the modifying agent is heated to the melting point of the crystalline polymeric ingredient, the modifying agent melts and flows, and as a result there is a rapid increase in the extent to which the matrix is contacted by the active chemical ingredient. A similar increase can also be achieved by other treatments, either alone or in conjunction with heating (either simultaneously or sequentially), which cause the modifying agent to lose its physical integrity, so that the polymeric ingredient and the active chemical ingredient are free to disperse into the matrix, preferably so that they become substantially uniformly distributed thereon. Such other treatments include for example, one or more of (a) addition of a solvent, (b) exposure to electromagnetic radiation, including visible and ultraviolet light, or to ultrasonic radiation, or (c) increasing or decreasing the pH. In some cases there is a chemical bond between the polymeric and active chemical ingredients; in other cases, the active chemical ingredient is merely associated with, preferably dispersed in, the polymeric ingredient.
The active chemical ingredient is one which promotes or inhibits a chemical reaction of the matrix under selected conditions. The selected conditions can result directly from the treatment which increases the availability of the active chemical ingredient, or they can involve some further change (e.g. a change in temperature, pressure, pH or radiation, or the addition of a solvent or a reactant) that does not substantially reduce the extent to which the matrix is contacted by the active chemical ingredient. The active chemical ingredient can be (1) a catalytic ingredient (i.e. an ingredient which (a) reacts chemically with an ingredient of the matrix and is thereafter regenerated or converted into another compound, or (b) reacts chemically with a material which is adjacent to or absorbed into the matrix and is thereafter regenerated or converted into another compound, and in either case does not form a permanent chemical bond with an ingredient of the matrix); or (2) a reactive ingredient (i.e. one which reacts chemically, and forms a permanent chemical bond, with an ingredient of the matrix, and is not regenerated); or (3) an inhibiting ingredient (i.e. one which reduces the rate of a chemical reaction of the matrix, optionally by itself reacting preferentially with a material, e.g. oxygen, which would otherwise react with the matrix).
In particularly preferred embodiments of the invention, the crystalline polymeric ingredient is a side chain crystallizable (SCC) polymer. SCC polymers generally contain side chains comprising substituted or unsubstituted n-alkyl groups of 6 to 50, usually 12 to 50, carbon atoms, derived, for example, from one or more n-alkyl acrylates or methacrylates. The melting point of an SCC polymer is in large measure controlled by the number of carbon atoms in the n-alkyl group or groups and is not (as in most other polymers) heavily dependent on the molecular weight of the polymer or on the presence of other comonomer units (e.g. derived from acrylic acid, acrylonitrile or an unsubstituted or substituted lower alkyl acrylate). Furthermore, SCC polymers generally melt over a small temperature range, e.g. less than 10° C. As a result, it is possible to select an SCC polymer which will cause the modifying agent to melt over a narrow and predetermined range, thus making a sharp change in the extent to which the active chemical ingredient contacts the matrix.
As explained in detail below, a number of different factors influence the extent and the speed of the change in the extent to which the active chemical ingredient contacts the matrix. These factors include (1) the form of the modifying agent (in particular the size of the particles thereof, when, as is preferred, the modifying agent is in the form of particles dispersed in the matrix), (2) whether or not there is a chemical bond between the polymeric ingredient and the active chemical ingredient, and if there is a chemical bond, the nature and the strength of the bond between the polymeric moiety and the active chemical moiety (which may be a covalent, ionic, mixed covalent-ionic, or ligand-attached bond, preferably a covalent bond), (3) the crystallinity of the crystalline ingredient and the temperature range over which it melts (which is preferably less than 10° C. between onset of
Bitler Steven P.
Stewart Ray F.
Landec Corporation
Sheldon & Mak
Yoon Tae
LandOfFree
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