Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1998-01-15
2001-10-02
Richter, Johann (Department: 1613)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S086000, C524S174000, C524S186000, C524S401000, C558S420000, C558S421000, C522S006000
Reexamination Certificate
active
06297298
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to polymerizable phthalonitrile compositions, and in particular to storable mixtures of phthalonitrile monomers and curing agents.
2 Description of the Related Art
Phthalonitrile polymers of various types are described generally in U.S. Pat. No. 3,730,946, U.S. Pat. No. 3,763,210, U.S. Pat. No. 3,787,475, U.S. Pat. No. 3,869,499, U.S. Pat. No. 3,972,902, U.S. Pat. No. 4,209,458, U.S. Pat. No. 4,223,123, U.S. Pat. No. 4,226,801, U.S. Pat. No. 4,234,712, U.S. Pat. No. 4,238,601, U.S. Pat. No. 4,259,471, U.S. Pat. No. 4,304,896, U.S. Pat. No. 4,307,035, U.S. Pat. No. 4,315,093, U.S. Pat. No. 4,351,776, U.S. Pat. No. 4,408,035, U.S. Pat. No. 4,409,382, U.S. Pat. No. 4,410,676, U.S. Pat. No. 5,003,039, U.S. Pat. No. 5,003,078, U.S. Pat. No. 5,004,801, U.S. Pat. No. 5,132,396, U.S. Pat. No. 5,159,054, U.S. Pat. No. 5,202,414, U.S. Pat. No. 5,208,318, U.S. Pat. No. 5,237,045, U.S. Pat. No. 5,242,755, U.S. Pat. No. 5,247,060, U.S. Pat. No. 5,292,854, U.S. Pat. No. 5,304,625, U.S. Pat. No. 5,350,828, U.S. Pat. No. 5,352,760, U.S. Pat. No. 5,389,441, U.S. Pat. No. 5,464,926, U.S. patent application by Satya B. Sastri and Teddy M. Keller for “FIBER-REINFORCED PHTHALONITRILE COMPOSITE CURED WITH LOW-REACTIVITY AROMATIC AMINE CURING AGENT” filed Oct. 2, 1997 and U.S. patent application by Satya B. Sastri and Teddy M. Keller for “PHTHALONITRILE THERMOSET POLYMERS AND COMPOSITES CURED WITH HALOGEN-CONTAINING AROMATIC AMINE CURING AGENTS” filed Oct. 2, 1997. All of these patents and applications are incorporated herein by reference.
The above references teach an in situ method of polymerization wherein a phthalonitrile monomer is heated to a temperature above the melting point of the monomer and a curing agent is added to the melt stage to promote polymerization of the phthalonitrile monomer. A method wherein the curing agent is added immediately before the heating step has also been described. These methods of polymerization can be inconvenient in some circumstances, particularly in the fabrication of composites by methods such as resin transfer molding (RTM), filament winding, injection molding, or prepreg formulation, where it may be difficult or cumbersome to mix the monomer and the curing agent on site or to add the curing agent to the melt after the heating step is begun. Alternatively, many of the above references teach that a frangible B-stage polymer can be created by heating the phthalonitrile monomer with a curing agent to initiate the polymerization process and then quenching the reaction before the polymerization goes to completion. The B-stage polymer created by this process can be stored indefinitely at room temperature. However, creation of a B-stage prepolymer involves the additional time-consuming and cost-consuming step of partial polymerization of the monomer.
In conventional resin systems such as epoxies, polyimides, vinyl esters, cyanate esters, etc., a mixture of a monomer and a curing agent must be used fairly soon after the mixture is created because the monomer begins to immediately polymerize in the presence of the curing agent. Even under freezer conditions, the mixture has a short shelf life. As the material polymerizes, it becomes highly viscous and unprocessable. Thus, long term storage of a mixture of the monomer and a curing agent in these conventional resin systems is not possible.
SUMMARY OF THE INVENTION
It has now been discovered that phthalonitrile monomers can be combined with curing agents below the melting temperatures of the monomer and curing agent without polymerization taking place, and that the mixture can be maintained in an unreacted state for an indefinite period of time.
Accordingly, the present invention is directed to a polymerizable composition suitable for storage prior to polymerization, made by a process comprising the steps of mixing a phthalonitrile monomer and a curing agent under non-reactive conditions below the melting temperatures of the phthalonitrile monomer and the curing agent and in the absence of a solvent to create a homogeneous, unreacted mixture. The invention further relates to an article comprising a dry, homogeneous, unreacted mixture of a phthalonitrile monomer and a curing agent in a storage container. The invention further relates to a stored polymerizable composition made by a process comprising the steps of mixing a phthalonitrile monomer and a curing agent under non-reactive conditions in the absence of a solvent to create a homogeneous, unreacted mixture and storing the unreacted mixture under non-reactive conditions. The invention further relates to a method of making a phthalonitrile polymer comprising the steps of mixing a phthalonitrile monomer and a curing agent at a first location under non-reactive conditions to create a homogeneous, unreacted mixture, transporting the mixture to a second location remote from the first location, and polymerizing the phthalonitrile monomer by heating the mixture at the second location to a temperature above the melting point of the mixture.
By creating a prepolymer mixture for long-term storage according to the present invention, the extra step of creating a B-stage prepolymer as described in the above-cited references is avoided.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention relates to a polymerizable composition suitable for storage prior to polymerization, made by a process comprising the step of mixing a phthalonitrile monomer and a curing agent under non-reactive conditions to create a homogeneous, unreacted mixture. The phthalonitrile monomer may be any phthalonitrile monomer described in the above referenced patents. Preferably, the phthalonitrile monomer is a compound of the formula:
wherein A is any divalent organic radical. More preferably, A is selected from the group consisting of substituted or unsubstituted phenyl radicals, polyphenyl radicals, polyphenoxy radicals, fused aromatic poly-ring radicals and radicals of the general form —Ar—Z—Ar— where Ar is a substituted or unsubstituted aromatic group and Z is
any alkylene of up to six carbon atoms, any halogenated alkylene of up to six carbon atoms, an imide-containing group or a connecting bond. By the word “substituted”, it is meant that any known substituent could be attached to the aromatic moiety. Substituents include but are not limited to halogens, chalcogens, and organic radicals such as phenyl, alcohol, carboxyl, carbonyl, or aliphatic groups of less than 10 carbon atoms. Phthalonitrile monomers of the above description are dry solids, typically powders, below their melting temperature.
The curing agent may be any curing agent useful in promoting the polymerization of the phthalonitrile monomer under reactive conditions, such as temperatures above the melting point of the monomer. The curing agent should be a dry solid, for example, a powder, and should be stable and nonvolatile under storage conditions, during the heat up to the polymerization temperature and during polymerization of the monomer. Preferably, the curing agent is selected from the group of curing agents consisting of aromatic amines, phenols, inorganic acids, strong organic acids, metals, metallic salts and combinations thereof. Most preferably, the curing agent is an aromatic amine.
According to the invention, the phthalonitrile monomer and the curing agent are mixed and stored under non-reactive conditions, that is, under conditions wherein the phthalonitrile monomer and the curing agent do not react and the phthalonitrile monomer does not polymerize. Generally, this will be at a temperature below the melting temperatures of the phthalonitrile monomer and the curing agent. Preferably, the monomer and the curing agent are mixed and stored at room temperature or at the ambient temperature depending on the location. For an additional precaution against reactivity, the monomer and the curing agent may be mixed and stored in an inert atmosphere. The monomer and the curing agent may be mixed by any method known in the art for creating a d
Keller Teddy M.
Sastri Satya B.
McDonnell Thomas E.
Richter Johann
Sackey Ebenezer
The United States of America as represented by the Secretary of
Webb Ralph T.
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