Organic compounds -- part of the class 532-570 series – Organic compounds – Chalcogen in the nitrogen containing substituent
Reexamination Certificate
2000-11-03
2002-11-19
Raymond, Richard L. (Department: 1624)
Organic compounds -- part of the class 532-570 series
Organic compounds
Chalcogen in the nitrogen containing substituent
C528S129000, C528S137000, C528S145000, C528S146000, C528S150000, C528S408000, C544S069000, C544S090000
Reexamination Certificate
active
06482946
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to benzoxazines, high char yield polybenzoxazines formed therefrom and method of forming said polybenzoxazines.
BACKGROUND OF THE INVENTION
Benzoxazines are a class of phenolic resins that are generally formed by the reaction of a phenol, primary amine and formaldehyde or paraformaldehyde. The benzoxazine may be polymerized by simple heating to open the oxazine ring. This leads to the formation of a chemical bond between the phenolic groups. Cross-linked (i.e., thermoset) polybenzoxazines generally require multi-functional benzoxazine monomers (i.e., they contain more than two reactive sites). Generally, cross-linked polybenzoxazines are formed from benzoxazine monomers having more than one benzoxazine rings.
Benzoxazines exhibit several advantages for forming thermally stable polymers compared to resole phenolics and novolacs. For example, benzoxazines do not form any volatile reaction products upon polymerization, which is, for example, an advantage for forming composite parts (i.e., no out-gassing). In addition, they do not require the use of strong acid polymerization catalysts; such as used to cure resoles, which can cause corrosion of a mold.
One of the desirable traits of the cured benzoxazines is their potential to achieve high char yields, which are indicative of their thermal stability. However, many of the benzoxazine monomers that give cured products with high char yields often have limited processability because of their high viscosity below their reaction temperature. This makes them more suitable for processing methods, such as compression molding, rather than high speed processing methods, such as pultrusion. That is to say, they do not achieve desirable processing viscosities (i.e., sufficient to easily impregnate fiber matrices) without the aid of a solvent or substantial heating.
Unfortunately, the use of a solvent adds processing steps to remove it. The disadvantage of applying heat to the neat resin (benzoxazine) is that at the temperatures (e.g., about 160° C.) needed to achieve a reasonable processing viscosity (e.g., <1000 centipoise) the benzoxazines autopolymerize resulting in a very short processing time. As a result, the viscosity builds faster than the ability to efficiently impregnate the fiber mat because of polymerization. Consequently, a method of obtaining both high char yields and good processability, without the use of solvents, is desirable for extending the utility of benzoxazines into applications, such as structural composites.
A recent attempt to increase the char yield of polybenzoxazines has been described by Ishida in WO 99/18092. Ishida describes incorporating a pendant reactive group, either to the phenolic or amine reactants, to create the benzoxazine monomer. The pendant reactive group is a group that is reactive with itself (e.g., acetylene group) or is a first reactive pendant group that is reactive with a second pendant reactive group, neither being reactive with itself. Unfortunately, even though these benzoxazines are reported to increase the char yield, they fail to address the processing problems described above.
Accordingly, it would be desirable to provide a polybenzoxazine that overcomes one or more of the problems of the prior art, such as one of those described above. It would be particularly desirable to provide an easily processed benzoxazine composition that still forms a high char yield polybenzoxazine.
SUMMARY OF THE INVENTION
A first aspect of the present invention is a polybenzoxazine comprised of the reaction product of a mixture comprised of (i) a benzoxazine compound, (ii) a furan compound, (iii) a benzoxazine-furan compound or (iv) combinations thereof, wherein the mixture has a furan ring to benzoxazine ring ratio of at least about 0.001 to at most about 10.
A second aspect of the invention is a method of forming a polybenzoxazine comprised of:
mixing (i) a benzoxazine compound, (ii) a furan compound, (iii) a benzoxazine-furan compound or (iv) combinations thereof, wherein the mixture has a furan ring to benzoxazine ring ratio of at least about 0.001 to at most about 10 and
heating the mixture for a sufficient time to form the polybenzoxazine.
A third aspect is a mixture useful for preparing a polybenzoxazine comprised of (i) a benzoxazine compound, (ii) a furan compound, (iii) a benzoxazine-furan compound or (iv) combinations thereof, wherein the mixture has a furan ring to benzoxazine ring ratio of at least about 0.001 to at most about 10.
In the broadest sense, the benzoxazine compound is a compound that contains at least one benzoxazine ring, but fails to have a furan ring. Similarly, the furan compound is a compound that contains at least one furan ring but fails to have a benzoxazine ring. Finally, the benzoxazine-furan compound contains at least one furan ring and at least one benzoxazine ring. Practically, each of the compounds, generally, has at most about 100 carbon atoms.
Surprisingly and unknown until the present invention, it has been discovered that a furan group, which does not react with itself, can be combined with a benzoxazine to give polymers with improved char yields after curing. Furthermore, it is unnecessary and may even be detrimental to add a compound containing a group that is reactive with the furan (i.e, maleimide) to the benzoxazine compound or benzoxazine-furan compound to obtain increased char yield. That is to say, the mixture preferably fails to have a benzoxazine compound that contains a maleimide group when the benzoxazine-furan compound is present in the mixture. It is even more preferable to have the mixture devoid of any maleimide.
In addition, the invention allows, for example, the use of certain benzoxazine-furan compounds that have only one benzoxazine ring and one furan group to unexpectedly form a thermoset polymer by itself. This type of compound also has been found to reduce the viscosity of a benzoxazine compound or benzoxazine-furan compound containing more than one benzoxazine ring without being detrimental to the final properties, such as char of the resultant polybenzoxazine.
These new polybenzoxazines may be used in the same applications as polymers, such as polyimide, phenolics, epoxies and other thermally stable polymers. In particular, they may be used in applications that take advantage of properties, such as fire resistance and low water absorption. Examples of applications include brake pads or composite applications, such as interiors and structural components of an aircraft, piping, ladders, ship masts, gratings, table trays, ducts, beams, ship housings, and printed wiring boards.
DETAILED DESCRIPTION OF THE INVENTION
The polybenzoxazine is comprised of the reaction product of a mixture comprised of (i) a benzoxazine compound, (ii) a furan compound, (iii) a benzoxazine-furan compound or (iv) combinations thereof, wherein the mixture has a furan ring to benzoxazine ring ratio of at least about 0.001 to at most about 10.
Because of the furan ring to benzoxazine ring ratio limitation, it is understood that the mixture must contain at least some amount of either the furan compound or benzoxazine-furan compound. That is to say, one of these has to be present in the mixture to provide the furan ring required by the furan/benzoxazine ring ratio. The mixture preferably contains the benzoxazine compound and the furan compound. In addition, it is preferred to have a benzoxazine compound or benzoxazine-furan compound that has more than one benzoxazine ring in the mixture. More preferably, the mixture contains a benzoxazine-furan compound that has at least two benzoxazine rings and at least one furan ring. Even more preferably, the mixture contains a benzoxazine-furan compound having at least two benzoxazine rings, in combination with a benzoxazine-furan compound that has one benzoxazine ring and one or more furan rings.
To reiterate, the ratio of furan to benzoxazine rings in the mixture is at least about 0.001 to at most about 10. Preferably, the ratio is at least about 0.1, more preferably at least about 0.2
Dettloff Marvin L.
Null Marty J.
White Jerry E.
Dow Global Technologies Inc.
Nilsen Kevin J
Raymond Richard L.
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