Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2000-10-26
2002-06-04
Dawson, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C528S044000, C528S048000, C528S057000, C528S055000, C524S589000, C549S512000
Reexamination Certificate
active
06399698
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention.
The present invention relates to a method of synthesizing isocyanate prepolymers for use in polyurethane synthesis. More particularly, the invention relates to the synthesis of isocyanate prepolymers from epoxidized natural oils and polyisocyanates.
2. Prior Art.
Polyurethanes comprise a wide variety of polymers. They are, in fact, the most ubiquituous polymer in the chemical industry today. Polyurethanes are defined as any polymer formed by linking isocyanic groups to hydroxyl groups present on different monomers. The polymer-forming hydroxyl and isocyanic groups can be attached to an endless variety of monomers, making the varieties of polyurethanes equally endless. Polyisocyanates and polyhydroxyl compounds may also be used to increase crosslinking in polyurethanes. Not surprisingly, uses for polyurethanes are almost as endless as their varieties. Polyurethane is used for adhesives, sealants, coatings and elastomers. The multiple uses and varieties of polyurethanes are well known in the art.
Isocyanates readily react with water, and are severe eye and skin irritants. When inhaled, they can be toxic to humans. A significant amount of isocyanate vapor is released during the synthesis of polyurethane. This poses a significant danger to humans. In order to decrease the risk of harm to persons working with polyurethanes, it has become well known in the art to use a safer isocyanate compound, known as a prepolymer, in the polyurethane polymerization reaction. Prepolymers are formed by reacting isocyanates or polyisocyanates with another compound such as a diol or an epoxide. The resulting prepolymer binds to the isocyanate and prevents the release of harmful vapors during the polymerization reaction. This safer prepolymer is then used to form polyurethane.
Epoxides are readily available, and their use in formation of prepolymers is well known in the art. When isocyanates are reacted with epoxides, prepolymers containing oxazolidone rings are formed. These oxazolidone rings not only prevent evaporation of the isocyanates, but also provide favorable thermal qualities to the resulting polyurethane. Oxazolidones may also be polymerized themselves, forming oxazolidone polymers or even oxizolidone/polyurethane combination polymers. These combinations provide for even greater variety and versatility of polyurethane chemistry. They are also well known in the art.
Reactions between monoepoxides and monoisocyanates are fairly straight forward. The reactants are heated in the presence of a catalyst, and the reaction runs to completion. However, the reactions between polyepoxides and polyisocyanates are much more complex. These reactions produce a variety of by-products that are deleterious to the final polymer. Polyisocyanates form trimers known as isocyanurates. These trimers increase the viscosity of the prepolymer and contribute to brittleness of the final product. Homopolymerization of polyepoxides results in polyethers that also reduce the quality of the final product. In addition, both of these reactions compete with the favorable oxazolidone forming reaction. The quantity of oxazolidones produced can be increased by modifying the reaction temperature and using specific catalysts. It is known in the art that various catalysts, such as halide compounds, organometal compounds, quaternary ammonia salts and organoantimony iodine, may be used to encourage the desired reaction and inhibit the formation of isocyanurate and polyethers.
The majority of epoxides used to form isocyanate prepolymers are synthetic, often derived from petrochemicals. These compounds are generally harmful to both the environment and those handling them. Safety has always been a major concern in the chemical industry. In recent years environmental concerns have also been addressed by the industry. There is an active trend toward using renewable, natural resources. This benefits the environment, and can sometimes be less expensive than using synthetic components. Natural oils, derived from plants and animals, exist in great abundance. They are readily available, inexpensive and very renewable. In addition they are easily epoxidized to form polyepoxides. As these oils are abundant, natural and renewable, it is desirable to use their epoxides in the formation of isocyanate prepolymers. Unfortunately, natural oils tend to contain ester groups. These ester groups may, under certain conditions, be hydrolyzed, decomposed or transesterified. This leads to a plethora of functional groups. When reacted with isocyanates, these additional functional groups interfere with the formation of the desired product, oxazolidones. They also cause side reactions that lead to the formation of a variety of undesirable by-products. Therefore, epoxidized natural oils have been considered poor epoxides for the formation of isocyanate prepolymers.
It is therefore desirable to develop a process whereby natural oil epoxides may by used to form isocyanate prepolymers.
It is also desirable to develop a fast, simple process for forming stable isocyanate prepolymers having a long shelf life.
It is also desirable to provide a new method for making sealants by using epoxidized natural oil based isocyanate prepolymers as the raw material.
It is also desirable to provide a new method for making coatings by using epoxidized natural oil based isocyanate prepolymers as the raw material.
It is also desirable to provide a new method for making adhesives by using epoxidized natural oil based isocyanate prepolymers as the raw material.
It is also desirable to provide a new method for making elastomers by using epoxidized natural oil based isocyanate prepolymers as the raw material.
SUMMARY OF THE INVENTION
The method of the present invention involves converting epoxidized natural plant or animal oils to isocyanate prepolymers by reaction with polyisocyanates. The reaction product comprises a mixture of chemicals including oxazolidones, urethanes, amides, urea, isocyanurates, uretdiones and esters. Oxazolidone is the dominant product of the reaction. This method takes place at atmospheric pressure.
The process of the present invention comprises mixing an epoxidized natural oil in solution with isocyanate and a catalytic amount of a Lewis acid so as to form a natural oil-based isocyanate prepolymer. An organic solvent, isocyanate and a Lewis acid are poured into a reaction vessel. The content is stirred and heated to 150-160° C. The epoxidized natural oil is then added. The reaction temperature is increased up to the boiling point of the solvent and maintained at that temperature until the completion of the reaction. The progress of the reaction may be monitored by titration. The reaction is finished when the isocyanate concentration drops to about half of the starting concentration. The reaction generally takes anywhere from 10 to 180 minutes.
Any epoxidized natural or animal oil may be used in this process. Oils extracted from vegetables, flowers, seeds and animals are all suitable for use in the present invention. These oils are both renewable and inexpensive. They are also readily commercially available in epoxidized form. The iodine values of these natural oils range from about 40 to 220 and more preferably from about 80 to 180.
Any polyisocyanate may be used. Some polyisocyanates react more quickly and/or at lower temperatures than others. This is generally due to the geometric configuration of the molecule itself. The presence of conjugated rings, aliphatic groups and steric hindrances will all affect the reactivity of an individual isocyanate. The isocyanate chosen will depend not only on its reactivity, but the use to which the prepolymer and resulting polyurethane will be put.
The catalyst may be an organometal compound, a Lewis acid or a halide compound. Preferably, aluminum trichloride is the catalyst used. Aluminum trichloride provides for a shorter reaction time. The natural oil-based prepolymer is also produced more consistently, and has a lower viscosity and longer stability when aluminum chl
Javni Ivan J.
Petrovic Zoran S.
Dawson Robert
Head Johnson & Kachigian
Peng Kuo-Liang
Pittsburg State University
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