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
2003-07-15
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...
C522S063000, C522S167000, C522S178000, C522S180000, C522S181000, C522S183000, C526S316000, C528S220000, C528S228000
Reexamination Certificate
active
06593389
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 polyimides and polyacrylates 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 polyacrylates at or near room temperature. This invention enables the cure of high performance polyimides and polyacrylates 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 a dienophile, such as bismaleimide and mixtures thereof with a maleimide end-cap and trismaleimide. Irradiation of an aromatic diketone produces two distinct hydroxy o-quinodimethane (photoenol) intermediates. The intermediates are trapped via a Diels-Alder cycloaddition with appropriate dienophiles, e.g., bismaleimide and/or trismaleimide to give the corresponding polyimides in quantitative yields. When maleimides such as bismaleimide and/or trismaleimide are used as the bisdienophile, the resulting polyimides of this invention have glass transition temperatures, (Tg), as high as 300° C.
2. Description of the Prior Art
High performance polymers such as polyimides or 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 materials 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.
It is known that 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 its 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 also in the prior art that the Diels-Alder polymerization reaction has been used to prepare high performance polymers such as the polyimides and polyesters. Typical Diels-Alder reactions used to obtain polyimides have involved the reaction of bismaleimides with a suitable bisdiene such as a bisfuran. Other Diels-Alder reactions use a bisdiene precursor, such as bis(benzocyclobutane), to form 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.
SUMMARY OF THE INVENTION
The unique feature of this invention is that it 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-Aider cycloaddition chemistry in the polymerization process.
More specifically, this invention relates to polyimides and to the method of preparing polyimides derived from the photochemical cyclopolymerization of stoichiometric amounts of at least one aromatic diketone selected from the group consisting of:
wherein Ar is the same or a different aromatic or substituted aromatic radical e.g., p-methoxy phenyl, p-tolyl, p-cyano-phenyl, and R is the same or a different radical selected from the group consisting of aromatic radicals, substituted aromatic radicals, lower alkyl radicals of 1 to 8 carbons, O
2
CR
1
and R
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, ester radicals, aryl radicals and substituted aryl radicals with at least one dienophile selected from the group consisting of bismaleimide, trismaleimide and mixtures of a maleimide end-cap with bismaleimide and/or trismaleimide in various molar ratios to obtain polyimides having glass transition temperatures (Tg) as high as 300° C., high thermal-oxidative stability and decomposition-stability temperatures ranging up to about 350° C.
Accordingly, it is an object of this invention to employ energy from ultraviolet light rather than heat to obtain polyimides having glass transition temperatures as high as 300° C.
It is another object of this invention to provide a novel method of preparing polyimides at ambient temperatures by using radiant energy to photochemically cyclopolymerize aromatic diketones and one or more dienophile.
It is another object of this invention to provide a method of preparing radiation curable polyimides that do not have the health risk associated with conventional methods that utilize toxic aromatic diamines.
It is a further object of this invention to provide polyimides, and a novel process of preparing cured polyimides by using radiation energy at ambient temperatures to polymerize at least one aromatic diketone and a dienophile without using free radical or cationic polymerization methods.
These and other objects of this invention will become apparent from a further and more detailed description of the invention as follows:
DESCRIPTION OF THE PREFERRED EMBODIMENTS
This invention enables the curing of high performance polymers 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. In general, the invention involves the Diels-Alder cyclopolymerization of photochemically generated bisdienes with dienophiles, such as bismaleimides. The general chemistry is described in Scheme 1, for a representative polyimide. The irradiation of an aromatic diketone produces two distinct hydroxy o-quinodimethane (photoenol) intermediates. These intermediates are trapped via a Diels-Alder cycloaddition with appropriate dienophiles, e.g., bismaleimide, added prior to irradiation, to give the corresponding polymers in quantitative yields. For example, when bismalei
Berman Susan W.
Stone Kent N.
The United States of America as represented by the Administrator
LandOfFree
Polyimides by photochemical cyclopolymerization does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Polyimides by photochemical cyclopolymerization, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Polyimides by photochemical cyclopolymerization will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3045084