Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Reexamination Certificate
2001-04-05
2002-11-26
Berman, Susan W. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Compositions to be polymerized by wave energy wherein said...
C522S181000, C522S182000, C528S220000, C526S316000
Reexamination Certificate
active
06486230
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
Polymers having high-temperature characteristics are required to improve the performance and to reduce the weight of industrial materials in electronic devices, aeronautical equipment and some machinery. The polyamides and polyesters are polymers known to have the required mechanical strength, dimensional stability, low coefficient of thermal expansion, and electrical insulation properties in addition to high-temperature resistance.
The preparation of high performance polymers, however, requires cure temperatures in excess of 200° C. This leads to high tooling costs, high processing costs, and processing induced thermal stresses that can compromise component durability. The process of this invention allows the curing of high performance polyimides and polyesters at or near room temperature. This invention enables the cure of high performance polyimides and polyesters at or near room temperature by using ultraviolet light or some other radiation sources, such as electron beams rather than heat to provide the cure energy. Specifically, this invention relates to the Diels-Alder cyclopolymerization of a photochemically generated diene with dienophiles, such as di(acrylates), tri(acrylates), di(methacrylates), tri(methacrylates), and mixtures thereof with monoacrylates. Irradiation of aromatic diketones produces two distinct hydroxy o-quinodimethane (photoenol) intermediates. The intermediates are trapped via a Diels-Alder cycloaddition with appropriate dienophiles, e.g. di(acrylates) and/or tri(acrylates) to give the corresponding polyesters in quantitative yields. When acrylates such as di(acrylate) or di(methacrylate) are used as the bisdienophile, the resulting polyesters of this invention were found to have glass transition temperatures, (Tg), as high as 200° C.
2. Description of the Prior Art
The preparation of high performance polymers such as the polyimides and polyesters are typically prepared by condensation reactions. In the case of polyimides, the reaction involves diamines and dianhydrides or dianhydride derivatives e.g., the diester of tetracarboxylic acids. This process suffers from several problems in that aromatic diamines are toxic, mutagenic, or carcinogenic. Safe handling and disposal of these material requires the implementation of costly engineering controls. Further, processing of condensation reaction systems also can be a problem, since this chemistry leads to low molecular weight by-products, e.g., water and alcohols. Evolution of these by-products and high processing temperatures lead to voids and defects in the polymer and composites prepared with these polymers.
Some of these processing problems can be overcome, however, by combining addition chemistry with condensation chemistry, as is the case for PMR-15 polyimides. With this approach, low molecular weight oligomers (short chain polymers) are prepared by the condensation of diamines with dianhydrides or their derivatives and a suitable endcapping group. The endcaps undergo a cross-linking reaction at high temperatures (typically in excess of 300° C.) to provide a polymer network having good solvent resistance and high temperature performance. Prior to cross-linking, however, the imide oligomers are somewhat fluid and volatile condensation by-products can be removed from the polymer. While this approach overcomes some of the processing difficulties, it requires higher processing temperatures and monomer toxicity is still a concern.
It is known in the prior art that Diels-Alder polymerization reactions have been used to prepare high performance polymers such as the polyimides and polyacrylates. Typical Diels-Alder reactions used to obtain polyimides have involved the reaction of a bismaleimide with a suitable bisdiene such as a bisfuran. Other Diels-Alder reactions use a bisdiene precursor, such as a bis(benzocyclobutane), that forms the bisdiene upon heating to temperatures of 250° C. or higher. Using these Diels-Alder cyclopolymerization reactions overcome the health and safety problems associated with other methods of preparing polyimides, since these reactions do not involve the use of aromatic amines as one of the reactants. However, these methods still require high cure and processing temperatures, see, for example, U.S. Pat. Nos. 5,338,827; 5,322,924; 4,739,030 and the Annual Reviews in Materials Science, 1998, 28, 599-630 by M. A. Meador.
In the case of polyesters, these systems are generally prepared by a polycondensation process involving the reaction of diols and diacids or diesters producing water or alcohol as byproduct. Unsaturated polyesters are similarly prepared with the exception that the diacids are unsaturated. It is known also that ethylenically unsaturated compounds, and in particular acrylate derivatives, can be polymerized by irradiation with ultraviolet light in the presence of a photoinitiating system. The photoinitiating system includes a diaryl ketone photoinitiator and a coinitiator, i.e. a molecule that serves as a hydrogen donor. The coinitiators are typically alcohols, or ethers which have available hydrogens attached to carbon atoms adjacent to heteroatoms.
SUMMARY OF THE INVENTION
The unique feature of this invention is that the process employs energy from ultraviolet light, rather than heat to form the polymers. While other radiation curable polymers have been developed, these methods employ either free radical or cationic-based polymerization chemistries. The present invention utilizes photochemically generated dienes (not free radicals or carbocations) and standard Diels-Alder cycloaddition chemistry in the polymerization process.
More specifically, this invention relates to polyesters i.e. polyacrylates and to the method of preparing these polymers derived from the photochemical cyclopolymerization of stoichiometric amounts of at least one aromatic diketone having the formula:
wherein Ar is the same or a different aromatic or substituted aromatic radical e.g., a lower alkyl substitutent and R is the same or a different radical selected from the group consisting of hydrogen, aromatic radicals, substituted aromatic radicals, lower alkyl radicals of 1 to 8 carbons, O
2
CR
1
and —OR
2
radicals where R
1
and R
2
are the same or different organic radicals selected from the group consisting of lower alkyl radicals of 1 to 8 carbons e.g. 1 to 4 carbons, aryl and substituted aryl radicals and x in the diketone formula is selected from the group consisting of nil, oxygen, sulfur, —C═O, —CH
2
—, alkyl radicals of 1 to 8 carbons, ether radicals, aryl radicals and substituted aryl radicals with at least one dienophile selected from the group consisting of di(acrylates), tri(acrylates), di(methacrylates), tri(methacrylates) and mixtures of monoacrylates or mono(methacrylates) with the di(methacrylates), tri(methacrylates), di(acrylates) and/or tri(acrylates) wherein the monoacrylates range from 0 to about 25 molar percent of the mixture to obtain polyacrylates having glass transition temperatures (Tg) as high as 200° C., high thermal-oxidative stability and decomposition-stability temperatures ranging up to about 300° C.
Accordingly, it is an object of this invention to employ energy from ultraviolet light rather than heat to obtain polyesters having glass transition temperatures as high as 200° C.
It is another object of this invention to provide a novel method of preparing polyesters at ambient temperatures by using radiant energy to photochemically cyclopolymerize aromatic diketones and one or more acrylic dienophiles.
It is another object of this invention to provide a method of preparing radiation curable polyesters that do not have the health risk associated with conventional methods.
It is a further object of this invention to provide polyesters and a novel process of preparing cured polyesters by using radiation energy at ambient temperatures to obtain acrylic polymers derived from the polymerization of at least one aromatic diketone and acrylic dienophiles without using free radical or cationic polymerizati
Berman Susan W.
Stone Kent N.
The United States of America as represented by the Administrator
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