Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2002-09-20
2004-12-07
Wyrozebski, Katarzyna (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S445000, C524S447000, C501S145000, C501S148000
Reexamination Certificate
active
06828367
ABSTRACT:
BACKGROUND OF THE INVENTION
A. Origin of the Invention
The invention described herein was made by an employee of the United States Government and may be manufactured and used by and for the Government for Government purposes without payment of any royalties thereon or therefore.
B. Field of Invention
This invention pertains to the art of modified silicate clays for dispersion in polymeric matrices. In particular, the present invention is directed to a modified silicate clay formed by a co-ion exchange process with a mono-protonated diamine and alkyl ammonium ions.
C. Description of the Related Art
The nanometer level dispersion of a layered silicate into a polymer matrix typically requires organic modification of the silicate interlayer surface. This modification is easily achieved by ion exchange of the interlayer metal cations found naturally in the silicate, with a protonated organic cation, typically a protonated amine. Long chain alkyl ammonium ions are commonly chosen as the ion exchange material as they effectively lower the surface energy of the silicate and ease the incorporation of organic monomers or polymers into the silicate galleries.
However, in high temperature thermosetting polymers, use of long chain alkyl ammonium ions poses two problems. First, the decomposition temperature of the alkyl chain is commonly lower than the processing temperature of the polymers. Degradation of the organic modifier can result in aggregation of the silicate layers leading to micron level dispersion, rather than nanometer level dispersion of the individual clay platelets. Secondly, the presence of the flexible chains in the rigid polymer matrix has plasticizing effects which can lower the strength and use temperature of the material.
Previous work has demonstrated that ion exchange with an aromatic diamine is a viable method of achieving irreversible swelling of the silicate in a thermoplastic polyimide matrix. However, in a thermosetting polyimide, silicate modification with only the diamine tends to increase the melt viscosity of the system and may affect the polymer structure on curing. As a result, dispersion of this organically modified silicate into a thermosetting polymer matrix may not enhance polymer properties such as strength, modulus, or thermal stability.
The present invention provides a synergistic co-ion exchange process using a mono-protonated aromatic diamine and alkyl ammonium ions. A relatively low level of alkyl ammonium ions is utilized to minimize oligomer melt viscosity without the downfalls of low degradation temperature and plasticization effects.
The co-ion exchange of a protonated aromatic diamine and an alkyl ammonium ion into a silicate clay is unique. This organic modification optimizes the benefits of silicate dispersion into a highly-crosslinked, thermosetting polymer. Co-ion exchange allows irreversible swelling of the silicate layers under elevated processing temperatures, without adversely increasing the melt viscosity. Therefore, the present invention provides a nanocomposite exhibiting improved properties and unexpected results.
SUMMARY OF THE INVENTION
According to one aspect of the present invention, a new and improved clay/organic chemical composition is provided. The clay/organic chemical composition for dispersion in a polymer matrix, wherein the clay/organic chemical composition comprises an ion-exchanged reaction product produced by the intercalation and reaction of:
(a) a clay having a cation exchange capacity;
(b) a synergistically effective amount of alkyl ammonium ion to ion-exchange with interlayer cations to provide minimized oligomer melt viscosity of the polymer matrix without adverse plasticizing effects; and,
(c) a synergistically effective amount of a mono-protonated aromatic diamine to provide irreversible swelling of the polymeric matrix, by providing a free amine site that can react with polymer precursors.
According to another aspect of the invention, there is provided a nanocomposite comprising:
(a) a polymer matrix comprising the polymerization of monomer reactants where the monomers are 3,3′,4,4′-benzophenonetetracarboxylic acid, methylene dianiline, and 2-carbomethoxy-3-carboxy-5-norbornene (hereinafter, PMR-15); and
(b) a layered clay material dispersed in the polymer matrix, the layered clay material being a clay/organic chemical composition comprising an ion-exchanged reaction product produced by the intercalation and reaction of:
(i) a clay having a cation exchange capacity;
(ii) a synergistically effective amount of alkyl ammonium compound to ion-exchange with interlayer cations to provide minimized oligomer melt viscosity of the polymer matrix without adverse plasticizing effects; and,
(iii) a synergistically effective amount of a mono-protonated aromatic diamine to provide irreversible swelling of the polymeric matrix.
According to another aspect of the invention there is provided a process for producing a nanocomposite comprising the steps of:
(a) modifying a layered clay material by co-ion exchange with an alkyl ammonium ion and a mono-protonated aromatic diamine;
(b) dispersing the modified layered clay material into a mixture of monomers; and
(c) in-situ polymerizing the monomer to obtain a composite having the modified clay material dispersed in a polymeric matrix.
According to another aspect of the invention, there is provided a clay/organic chemical composition formed by reaction of a mono-protonated aromatic di amine and an alkyl ammonium ion with a silicate clay having exchangeable metal cations within the silicate galleries at a plurality of cation exchange sites where interlayer cation exchange takes place, the clay/organic chemical compound comprising:
(a) surface modification by ionic interaction at the silicate surface;
(b) a free (react-able) amine site;
(c) a mono-protonated diamine ion exchanged at a first cation exchange site; and,
(d) an alkyl ammonium ion exchanged at a second cation exchange site.
According to another aspect of the invention, there is provided a process for synthesizing a silicate clay reinforced polymer comprising the steps of:
(a) providing a silicate clay having an overall negative charge and interlayer cation exchangeable sites;
(b) modifying the silicate surface by interaction of one amine group of a mono-protonated aromatic diamine with the silicate surface and leaving one amine group free for subsequent interaction;
(c) exchanging cations at the cation exchangeable sites with alkyl ammonium ions;
(d) providing a monomer capable of interaction with the free amine group; and,
(e) in situ polymerizing a monomer.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Definitions:
Whenever used in this specification, the terms set forth shall have the following meanings:
“T
g
” refers to a “glass transition temperature”. A preferred method of measuring the T
g
is by using a differential scanning calorimeter at a heating rate of 10° C. per minute. “Layered clay,” “layered clay material,” or “clay material” refers to any organic or inorganic material or mixtures thereof, such as smectite clay mineral, which is in the form of a plurality of adjacent, bound layers. The layered clay comprises platelet particles and is typically swellable.
“Platelet particles,” “platelets” or “particles” shall mean individual or aggregate unbound layers of the layered clay material.
“Dispersion” or “dispersed” is a general term that refers to a variety of levels or degrees of separation of the platelet particles. The higher levels of dispersion include, but are not limited to, “intercalated” and “exfoliated.”
“Intercalate” is defined as the situation where a material is inserted between the platelets or layers of another material. When a material is intercalated between the platelets of clay it means the material is inserted between the layers such that the distance between the platelets of clay is increased a measurable amount.
“Exfoliate” or “exfoliated” shall mean platelets dispersed predominantly in an individual state throughout a carrier material, such as a matrix polymer.
“Nanocomposite” o
Emerson Roger D.
McDowell Brouse
The United States of America as represented by the United States
Thomson Daniel A.
Wyrozebski Katarzyna
LandOfFree
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