Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G73/00—Macromolecular compounds obtained by reactions forming a linkage containing nitrogen with or without oxygen or carbon in the main chain of the macromolecule, not provided for in groups C08G12/00 - C08G71/00
  • C08G73/06—Polycondensates having nitrogen-containing heterocyclic rings in the main chain of the macromolecule
  • C08G73/10—Polyimides; Polyester-imides; Polyamide-imides; Polyamide acids or similar polyimide precursors
  • C08G73/1003—Preparatory processes
  • C08G73/1007—Preparatory processes from tetracarboxylic acids or derivatives and diamines
  • C08G73/101—Preparatory processes from tetracarboxylic acids or derivatives and diamines containing chain terminating or branching agents
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
  • C08J5/04—Reinforcing macromolecular compounds with loose or coherent fibrous material
  • C08J5/0405—Reinforcing macromolecular compounds with loose or coherent fibrous material with inorganic fibres
  • C08J5/043—Reinforcing macromolecular compounds with loose or coherent fibrous material with inorganic fibres with glass fibres
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
  • C08J5/24—Impregnating materials with prepolymers which can be polymerised in situ, e.g. manufacture of prepregs
  • C08J5/241—Impregnating materials with prepolymers which can be polymerised in situ, e.g. manufacture of prepregs using inorganic fibres
  • C08J5/244—Impregnating materials with prepolymers which can be polymerised in situ, e.g. manufacture of prepregs using inorganic fibres using glass fibres
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J2379/00—Characterised by the use of macromolecular compounds obtained by reactions forming in the main chain of the macromolecule a linkage containing nitrogen with or without oxygen, or carbon only, not provided for in groups C08J2361/00 - C08J2377/00
  • C08J2379/04—Polycondensates having nitrogen-containing heterocyclic rings in the main chain; Polyhydrazides; Polyamide acids or similar polyimide precursors
  • C08J2379/08—Polyimides; Polyester-imides; Polyamide-imides; Polyamide acids or similar polyimide precursors

Definitions

• Embodiments of the present invention relate to single-step processes for synthesizing polyimide oligomers having high thermal and oxidative stability and improved mechanical properties.
• polyimides exhibit properties desirable for high- temperature applications such as those demanded in the aerospace industry.
• Existing materials are primarily based on Polymerization of Monomeric Reactants (PMR) chemistry and are, with a few exceptions, only suitable for prepreg. Additionally, these materials are plagued with various deficiencies.
• PMR-15 which is described in U.S. Pat. No. 3,745,149, contains a known carcinogen 4,4-methylene dianiline (MDA), is prone to microcracking, difficult to handle during processing and has a short shelf life.
• MDA carcinogen 4,4-methylene dianiline
• Many PMR materials cannot be used for thick composites due to unwanted reaction byproducts.
• the utilization of polyimides in high-temperature composite applications has been limited due to their processing cost and difficulties. Problems associated with processing polyimides for such applications include poor solubility in many solvents, evolution of volatiles during imidization and the high-temperatures necessary for processing.
• a fundamental problem withal of the PMR-based chemistries is that multiple reactions take place during the curing and crosslinking of these resins. Having multiple reactions taking place means that reactions other than those principally desired may take place. Furthermore, reactions at temperatures below the desired processing and cure temperatures can increase resin viscosity unacceptably. Accordingly, it is desirable to have resin systems for polymers that only have one reaction mechanism during curing. Moreover, it is highly desirable to have the single reaction mechanism occur between endcaps that have difunctionality.
• Embodiments of the present invention satisfy the aforementioned needs by providing a process for synthesizing formulations for polyimides suitable for use in high-temperature composites in which all reactions other than chain-extension have already taken place prior to making a composite.
• the resulting resin systems have only the single step of endcap-to-endcap reactions during composite processing.
• the resins prior to the initiation temperature of these endcap- to-endcap reactions, the resins are stable affording the composite manufacturer a very large processing window, which is clearly highly advantageous to anyone skilled in the art.
• One process for producing suitable polyimides comprises the pre-imidization of at least one endcap monomer with a chemical backbone / precursor suitable for composite manufacturing prior to making a composite; wherein the resulting resin system is subsequently heated to initiate the single step of endcap-to-endcap reactions upon making a composite.
• precursors with moderate-to-lower molecular weights allows easier melt-processability and increased crosslink density. Accordingly, formulations can be specifically prepared, without sacrificing crosslink density, to address diverse applications requiring stability at various temperatures, application- specific mechanical properties, as well as different chemical resistances. Therefore, polymeric resins manufactured according to various embodiments of the present invention are ideal for high-performance composites as presently needed by the aerospace industry.
• embodiments of the present invention comprise the sequential reaction of monomers such that the monomers are pre-imidized prior to the making of a composite. Accordingly, the pre-imidized resin system exhibits only one reaction mechanism, namely the single step of endcap-to-endcap reactions, during the curing and crosslinking of the resin to form a composite. Below temperatures for initiating the endcap-to-endcap reactions, the polyimide compositions are easily processable, unreactive and otherwise latent.
• the present invention is directed to a process for synthesizing polyimide oligomers suitable for high-temperature polymeric composites, wherein all reactions except for chain-extension reactions have been performed prior to composite fabrication.
• monomelic reactants are imidized prior to composite manufacturing and subsequently the remaining single step of endcap-to- endcap reactions is initiated during composite manufacturing for the following: wherein R is selected from the group consisting of
• L is -CH 2 -, —(CH 3 ) 2 C— , — (CH 3 ) 2 C— , -O-, -S-, — SO 2 — or -O-; wherein y is —SO 2 —, — S—, -(CF 3 ) 2 C-, — O—, or — (CH 3 ) 2 C— ; and in certain embodiments n is selected such that the molecular weight ranges from about 1000 to about 5000.
• monomeric reactants are imidized prior to composite manufacturing and subsequently the single remaining step of endcap-to-endcap reactions is initiated during composite manufacturing for the following:
• R is selected from the group consisting of wherein L is wherein y is and in certain embodiments n is selected such that the molecular weight ranges from about 1000 to about 5000.
• x, y and z are each selected such that the molecular weight of the resulting pre-imidized material ranges from about 1000 to about 5000.
• R is selected from the group previously described.
• embodiments of the present invention comprise a process for synthesizing polyimide oligomers comprises the sequential reaction of monomers such that the monomers are pre-imidized prior to the making of a composite resulting in a pre-imidized resin system exhibiting only one reaction mechanism, namely endcap-to-endcap reactions, during the curing and crosslinking of the resin to form a composite.
• a list of exemplary monomers suitable as chemical backbones include, but are not limited to: a dialkyl ester of an aromatic tetracarboxylic acid; 4,4 methylene dianiline (MDA); a dialkyl, trialkyl or tetraalkylester of biphenyltetracarboxylic acid; phenylenediamine; 3,4'-oxydianiline (3,4'-ODA); a dimethyl ester of 3,3',4,4'-benzophenonetetracarboxylic acid (BTDE); 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA), 3,4,3',4'-biphenyltetracarboxylic dianhydride (BPDA), 2,2 bis (3',4'- dicarboxy phenyl) hexafluoro propane dianhydride (6FDA), 2-(3,4-dicarboxyphenyl)-1- phenylacetylene anhydr
• the chemical backbones / precursors that are reacted with at least one endcap comprise a moderate molecular weight between about 1000 and about 5000.
• the chemical backbone comprises a molecular weight of about 2500 to about 5000.
• the chemical backbones comprises a lower-molecular weight between about 1000 to about 3000.
• Other embodiments may comprise a chemical backbone from about 1000 to about 2000, from about 2000 to about 3000 or alternatively from about 1500 to about 2500.
• the chemical backbone comprises a molecular weight that does not exceed about 3000.
• the endcaps comprise difunctional endcaps.
• the endcaps comprise a dinadic material such as a dinadic acid chloride, a dinadic phenol or a dinadic amine.
• Endcaps suitable for specific embodiments of the present invention include but are not limited to, for example, the following compounds:
• suitable endcaps include difunctional imidophenols, which are condensation products of diamino-phenols and anhydrides, as follows:
• X is selected from the group consisting of:
• Ri is a lower alkyl, lower alkoxy, aryl, substituted aryl, or mixtures thereof; G is -SO 2 -, -S-, -O-, Or -CH 2 -; andj is 0, 1, or 2.
• Another aspect of the present invention pertains to producing high-temperature composites. Resin systems produced in accordance with embodiments of the present invention exhibit densities less than those of metal counterparts. Accordingly, composites comprising polyimide resins formed by a single-step process are ideal for replacing metallic structures to reduce weight. Where high-temperature strength also drives the design, a material with higher allowable strength at elevated temperatures, such as composite embodiments of the present invention, will reduce overall structural weight.
• Composites and prepregs comprising polyimide oligomer compositions formulated according to embodiments of the present invention can by prepared by any conventional technique known in the art.
• the polyimide oligomers exhibit a melt viscosity such that a composite can be prepared by known liquid-molding techniques such as resin-transfer molding and resin film infusion among others.
• the reinforcement materials can include, for example, woven fabrics, continuous or discontinuous fibers (in chopped or whisker form), ceramics, organics, carbon (graphite), or glass.
• a composite can be manufactured by impregnating reinforcing materials with a pre-imidized composition according to embodiments of the present invention and cured anaerobically and under sufficient pressure to prevent the creation of voids. If the polyimide oligomers are nadic endcapped, the curing process will initially release cyclopentadiene. In such cases, the applied pressure during the curing process should be sufficient to re-dissolve the cyclopentadiene, which will react with the resin itself and become incorporated into the backbone. Suitable pressures for composite fabrication range from atmospheric to 1 ,000 psi. depending upon the nature of the polyimide composition.
• the pre-imidized resin systems may be cured at temperatures known in the art.
• the pre-imidized resin systems by be cured by subjecting them to temperatures ranging from about 200°C to about 350°C.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Health & Medical Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Medicinal Chemistry (AREA)
• Polymers & Plastics (AREA)
• Organic Chemistry (AREA)
• Inorganic Chemistry (AREA)
• Manufacturing & Machinery (AREA)
• Reinforced Plastic Materials (AREA)
• Macromolecular Compounds Obtained By Forming Nitrogen-Containing Linkages In General (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=39681047

Family Applications (1)

Country Status (2)

Cited By (1)

Families Citing this family (3)

Citations (4)

Family Cites Families (74)

• 2007
  • 2007-06-22 US US11/767,077 patent/US7825211B2/en active Active
• 2008
  • 2008-05-19 WO PCT/US2008/064057 patent/WO2009002633A1/en active Application Filing

Patent Citations (4)

Also Published As

Similar Documents

Legal Events