Organic compounds -- part of the class 532-570 series – Organic compounds – Nitrogen attached directly or indirectly to the purine ring...
Reexamination Certificate
2002-07-10
2003-04-01
Bernhardt, Emily (Department: 1624)
Organic compounds -- part of the class 532-570 series
Organic compounds
Nitrogen attached directly or indirectly to the purine ring...
Reexamination Certificate
active
06541633
ABSTRACT:
RIGHTS OF THE GOVERNMENT
The invention described herein may be manufactured and used by or for the Government of the United States for all governmental purposes without the payment of any royalty.
BACKGROUND OF THE INVENTION
The present invention relates to a new quinoxaline-containing AB
2
monomer that is useful for the preparation of hyperbranched polybenzoxazoles.
Dendritic macromolecules such as dendrimers and hyperbranched polymers are a new class of highly branched polymers that have distinctly different properties from their linear analogs. Both dendrimers and hyperbranched polymers have much lower solution and melt viscosities than their linear analogs of similar molecular weights. They also have a large number of chain-ends whose collective influence dictates their overall physical and/or chemical behaviors. These features are attractive in terms of processability and offering flexibility in engineering required properties for specific applications. However, there is a practical advantage that hyperbranched polymers have over dendrimers at “raw material” level. Although dendrimers have precisely controlled structures (designated as generations), their preparations generally involve tedious, multi-step sequences that are impractical and costly in scale-up production. Synthesis of a hyperbranched polymer, on the other hand, is a one-pot process. Large quantities of hyperbranched polymers can be easily produced from AB
x
(x≧2) monomers.
Because of their excellent thermal and mechanical properties, as well as their optical and electronic characteristics, aromatic, fused heterocyclic polymers such as polyquinoxalines and polybenzoxazoles continue to attract considerable attention. However, they have limited processability due to the nature of fused ring systems. Their insolubility and their softening temperatures are generally above their degradation temperatures. Chemical modification on the these materials, for example, by the use of solubilizing pendants or flexible units in the main chain, has been successful to improve their processability, allowing the optimization of their properties as a function of processability. Another viable approach to achieving this objective is to incorporate the elements of local rigidity and global randomness into the macromolecular architecture. Local rigidity provides the thermal, electronic and optical characteristics of the aromatic fused systems while global randomness frustrates entanglement of the polymer chains, leading to greater solubility. Dendritic structures clearly embody these qualities. However, as noted previously, hyperbranched structures have greater synthetic practicality.
Accordingly, it is an object of the present invention to provide novel quinoxaline-containing AB
2
monomers that are useful for the preparation of hyperbranched polybenzazoles.
Other objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
SUMMARY OF THE INVENTION
In accordance with the present invention there are provided novel AB
2
monomers of the formula:
wherein Z is —OH, —SH or —NH
2
.HCl.
DETAILED DESCRIPTION OF THE INVENTION
The AB
2
monomer, 2,3-bis(3-amino-4-hydroxyphenyl)quinoxaline-6-carboxylic acid dihydrochloride, is synthesized by condensing 3,4-diaminobenzoic acid and 4,4′-dimethoxybenzil to afford 2,3-bis(4-methoxyphenyl)quinoxaline-6-carboxylic acid, followed by demethylation in hydrobromic acid in acetic acid to form 2,3-bis(4-hydroxyphenyl)quinoxaline-6-carboxylic acid. The latter is then nitrated using nitric acid (70% conc.) in acetic acid at room temperature, yielding 2,3-bis(3-nitro-4-hydroxyphenyl)quinoxaline-6-carboxylic acid. The desired monomer is prepared by catalytic reduction in the presence of palladium catalyst in 10% hydrochloric acid.
The AB
2
monomer, 2,3-bis(3,4-diaminophenyl)quinoxaline-6-carboxylic acid dihydrochloride, is synthesized in a similar fashion, starting with 3,4-diaminobenzoic acid and 4,4′-dinitrobenzil. The condensation product is methylated to protect the carboxy group, reduced, acetylated to protect the amino groups, nitrated and reduced to provide the desired monomer.
The AB
2
monomer, 2,3-bis(3-amino-4-mercaptophenyl)quinoxaline-6-carboxylic acid dihydrochloride, is synthesized by condensing 3,4-diaminobenzoic acid and 3,3′-diaminobenzil. The condensation product is methylated to protect the carboxy group, halogenated, treated with thiocyanate and hydrolyzed to provide the desired monomer.
The AB
2
monomers can be self-polymerized to prepare hyperbranched polymers, as shown by the following equation:
wherein Z is as described previously and Q is —O—, —S—or —NH—. Polymerization can be conducted in polyphosphoric acid (PPA) at a polymer concentration of about 6 weight percent at a temperature of up to about 130° C., or in the melt state.
REFERENCES:
patent: 4125725 (1978-11-01), Duffy
patent: 5030704 (1991-07-01), Harris et al.
Baek, J-B, Simko, S. R., Tan, L-S, Synthesis and Polymerization of a Bis(O-aminophenol)-Carboxylic Acid AB2 Monomer,Polymer Preprints2001, 42(2), 502-503 (Published Aug. 12, 2001).
Baek Jong-Beom
Tan Loon-Seng
Bernhardt Emily
Bricker Charles E.
Kundert Thomas L.
The United States of America as represented by the Secretary of
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