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
1999-04-27
2001-01-30
Sellers, Robert E. L. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S507000
Reexamination Certificate
active
06180723
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a new class of epoxy resins prepared from one or more p-hydroxystyrene polymers.
BACKGROUND OF THE INVENTION
Epoxy resins are characterized by the presence of a three-membered ring known as the epoxy, epoxide, oxirane, or ethoxyline group. Commercial epoxy resins contain aliphatic, cycloaliphatic, or aromatic backbones. The capability of the epoxy ring to react with a variety of substrates imparts versatility to the resins. Treatment with curing agents gives insoluble and intractable thermoset polymers. In order to facilitate processing and modify cured resin properties, other constituents may be included in the compositions such as for example, fillers, solvents, diluents, plasticizers, accelerators, curatives, and tougheners.
One type of epoxy resin is made from epichlorohydrin and bisphenol A. Aliphatic polyols such as glycerol may be used instead of the aromatic bisphenol A.
Another type of epoxy resin is made from polyolefins oxidized with peracetic acid. These have more epoxide groups, within the molecule as well as in terminal positions, and can be cured with anhydrides, but require high temperatures. Many modifications of both types are made commercially. Halogenated bisphenols can be used to add flame-retardant properties.
Yet another type of epoxy resin is produced from novolak compounds. Such epoxy novolak resins are typically made by the reaction of epichlorohydrin with a novolak resin, i.e a phenol-formaldehyde type resin. These have a repeating epoxide structure which offers better resistance to high temperatures than the epichlorohydrin-bisphenol A type, and are especially useful as adhesives.
Upon curing, most epoxy resins form a tight cross-linked polymer network and are characterized by toughness, good adhesion, corrosive-chemical resistance, and good dielectric properties.
The manufacture of epoxy resins and processes for their production by the reaction of di-, tri-, and tetra-phenols and epichlorohydrin in the presence of a condensing agent such as caustic soda are well known. These epoxy resins vary in physical state from liquids to solids. They are cured into a thermoset state by cross linking when reacted with tertiary, secondary or primary amines, anhydrides, lewis acids, lewis bases, amides, imidizoles, ureas, melamines, cyanate esters and other commonly used curing agents and catalysts.
The production of epoxy resins utilizing p-hydroxystyrene is known in the art. Due to the large quantity of reactive sites, this polymer, when cured, produces a relatively high crosslink density. Generally, the higher the crosslink density, the higher the chemical resistance and the higher the heat resistance.
High functionality epoxies, i.e. epoxy resins having a relatively high number of reactive sites, can be used in the manufacture of high performance coatings, adhesives, and fiber reinforced composites. One property of a cured epoxide polymer which is extremely desirable and useful is a high glass transition temperature, Tg. Generally, high Tg values impart high chemical resistance and excellent electrical properties. High functionality epoxies, upon curing, often exhibit high Tg values.
The use of epoxy resins as a matrix material for reinforced composites, molding compounds, casting resins, etc. is known. In such applications, it is desirable that the resins typically exhibit certain properties such as relatively high temperature resistance and high chemical resistance. These properties may be obtained by the use of high functionality resins such as novolak resins.
Unfortunately, conventional epoxy resins having high functionality, such as those based upon currently available p-hydroxystyrene and novolak agents, are difficult to work with due to their high melting points and relatively high viscosity prior to cure. Accordingly, there is a need for high functionality epoxy resins having a pre-cure viscosity that ranges from a low water-like liquid to a high honey-like material depending on the amount of functionality. In particular, it would be desirable to obtain a high functionality epoxy resin that has a low melt viscosity and a high Tg. Further, it would be desirable for such resins to be curable to a thermoset state by crosslinking upon reaction with tertiary, secondary or primary amines, anhydrides, acids, lewis acids, lewis bases, amides, imidizoles, ureas, meiamines, cyanate esters and other commonly used curing agents and catalysts.
SUMMARY OF THE INVENTION
It is an object of this invention to provide new high functionality epoxide polymers having low melt viscosity prior to curing, high glass transition temperatures upon curing, and a process for producing them. In a first aspect of the present invention, a process for producing such an epoxy agent is provided. The process involves providing at least one of three specific poly-p-hydroxystyrene polymers, and reacting such with epichlorohydrin.
In another aspect of the present invention, a process is provided for producing a high molecular weight epoxy agent by reacting a certain poly-p-hydroxystyrene polymer with one or more di-hydric phenol agents, and reacting such with epichlorohydrin.
The present invention also provides new classes of epoxy compounds having improved and superior properties as compared to conventional epoxy agents.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In accordance with a preferred aspect of the present invention, high molecular weight epoxy resins with high functionality, low epoxide equivalent weight, and which exhibit low melt viscosity prior to cure and high glass transition temperatures after cured, may be prepared by reacting certain poly-p-hydroxystyrene polymers and epichlorohydrin in the presence of one or more alkali agents.
Before turning attention to the details of the preferred embodiments of the present invention, it is instructive to address certain terminology utilized herein. Epoxide equivalent weight, as that term is used herein, refers to molecular weight divided by the number of reactive epoxy sites per molecule.
High functionality epoxy resins, i.e. epoxy resins having a relatively high number of reactive epoxy sites per molecule, typically have relatively low epoxide equivalent weight. Preferably, the epoxy resins according to the present invention have an average functionality of from about 5 to about 70, and most preferably up to about 100 or higher. The term glass transition temperature, as used herein, is accorded its conventional and well understood definition. Generally, this is the temperature at which an amorphous material changes from a brittle vitreous state to a plastic state. The term melt viscosity, as used herein, refers to the viscosity of the material or resin prior to curing.
The preferred embodiment epoxy agents are formed by reacting one or more particular p-hydroxystyrene polymers and epichlorohydrin. Epichlorohydrin (also known as chloropropylene oxide, CAS: 106-89-8), is an epoxide having the structure:
In reacting epichlorohydrin and p-hydroxystyrene agents(s), it is desirable to epoxidize all, or at least a majority of, phenol groups in the p-hydroxystyrene agents. Accordingly, an excess of epichlorohydrin for each equivalent of phenol is preferably employed. Thus, in a preferred process of the present invention, an excess of about 2 to about 10 moles of epichlorohydrin for each mole of total phenol groups is used.
The alkali or alkaline agent present in the reaction mixture is preferably an alkali metal hydroxide such as sodium, potassium or lithium hydroxide, and is present in an amount sufficient to neutralize the hydrochloric acid produced during the reaction, as well as to transform the chlorohydrin formed in the initial reaction of phenol and epichlorohydrin, to an epoxide-containing molecule. Preferably this amount is between about 1 mole and about 4 moles of alkali per mole of total phenolic groups that are present. In order to improve yields the alkali solution may include one or more alcohols rather than water.
The preferred poly-p-hydroxystyrene polymers that may be
Fay Sharpe Fagan Minnich & McKee LLP
Sellers Robert E. L.
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