Composition of and method for making high performance resins...

Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From carboxylic acid or derivative thereof

Reexamination Certificate

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C528S125000, C528S128000, C528S170000, C528S172000, C528S173000, C528S176000, C528S179000, C528S185000, C528S188000, C528S220000, C528S229000, C528S350000, C524S600000, C524S607000, C526S262000, C526S285000, C526S935000, C428S411100, C428S395000, C428S473500

Reexamination Certificate

active

06359107

ABSTRACT:

BACKGROUND OF INVENTION
Resin transfer molding (RTM) and resin infusion (RI) are ideally solvent-free processes for making composite parts which can have significant cost advantages over traditional autoclave methods of composite fabrication since an autoclave is not required and there are no volatiles to manage. RTM and RI enable fabrication of highly complex shapes that would otherwise be extremely difficult to fabricate using hand lay-up autoclave techniques. Typically, these processes involve the placement of a woven preform or mat (i.e. glass, carbon, polymer, etc.) in the mold cavity. The molten resin is subsequently injected or infused at an elevated temperature into the mold whereby it permeates through the woven preform. This step is usually performed under vacuum in a sealed mold so there is little opportunity for volatile components to escape. After sufficient time to allow complete wet-out of the preform, the mold is subsequently heated to a higher temperature whereby the resin reacts to crosslink the material. During this step, external pressure is often applied to the mold by means of hydrostatic pressure. It is important that there are no volatiles present either in the form of residual solvent or chemical components of the resin system as they will cause void formation in the composite part. This is a difficult feature to achieve in a resin system for RTM and/or RI processes. Commercial resins such as vinyl esters, epoxies and bismaleimides are available that are processable by RI and/or RTM and provide good mechanical performance; however, these materials are limited in their use temperatures relative to the aromatic imide based materials described herein.
Phenylethynyl containing amines have been used to terminate imide oligomers [F. W. Harris, A. Pamidimuhkala, R. Gupta, S. Das, T. Wu, and G. Mock,
Poly. Prep
., 24 (2), 325, 1983; F. W. Harris, A. Pamidimuhkala, R. Gupta, S. Das, T. Wu, and G. Mock,
J. Macromol. Sci
.-
Chem
., A21 (8 & 9), 1117 (1984); C. W. Paul, R. A. Schultz, and S. P. Fenelli, “High-Temperature Curing Endcaps For Polyimide Oligomers” in Advances in Polyimide Science and Technology, (Ed. C. Feger, M. M. Khoyasteh, and M. S. Htoo), Technomic Publishing Co., Inc., Lancaster, Pa., 1993, p. 220; U.S. Pat. No. 5,138,028 (Aug. 11, 1992) to National Starch and Chemical Co.; R. G. Byrant, B. J. Jensen, and P. M. Hergenrother,
Poly. Prepr
., 34 (1), 566, 1993; U.S. Pat. No. 5,412,066 (1995) to National Aeronautics and Space Administration]. Imide oligomers terminated with ethynyl phthalic anhydride [P.M. Hergenrother,
Poly. Prep
., 21 (1), 81, 1980], substituted ethynyl phthalic acid derivatives [S. Hino, S. Sato, K. Kora, and O. Suzuki, Jpn. Kokai Tokyo Koho JP 63, 196, 564. Aug. 15, 1988
; Chem. Abstr
., 115573w, 110, (1989)], and phenylethynyl containing phthalic anhydrides [P. M. Hergenrother and J. G. Smith, Jr.,
Polymer
, 35(22)4857 (1994); U.S. Pat. No. 5,567,800 (1996) to National Aeronautics and Space Administration, J. E. McGrath and G. W. Meyer, U.S. Pat. No. 5,493,002 (1996) to Virginia Tech Intellectual Properties, Inc., J. A. Johnson, F. M. Li, F. W. Harris and T. Takekoshi,
Polymer
, 35(22)4865 (1994), T. Takekoshi and J. M. Terry,
Polymer
, 35(22)4874 (1994), R. J. Cano and B. J. Jensen, J. Adhesion, 60, 113 (1997)] have been reported. Imide oligomers containing pendent substituted ethynyl groups [F. W. Harris, S. M. Padaki, and S. Varaprath,
Poly, Prepr
., 21 (1), 3, 1980 (abstract only), B. J. Jensen, P. M. Hergenrother, and G. Nwokogu,
Polymer
, 34 (3), 630, 1993; B. J. Jensen and P. M. Hergenrother, U.S. Pat. No. 5,344,982 (Sep. 6, 1994); J. W. Connell, J. G. Smith, Jr. R. J. Cano and P. M. Hergenrother,
Sci. Adv. Mat. Proc. Eng. Ser
., 41, 1102 (1996); U.S. Pat. No. 5,606,014 (Feb. 25, 1997) to National Aeronautics and Space Administration] and pendent and terminal phenylethynyl groups, [J. G. Smith, Jr., J. W. Connell and P. M. Hergenrother,
Polymer
, 38(18), 4657 (1997)] have been reported.
A high temperature resin system designated as phthalonitrile has been developed that exhibits low melt viscosity. This material however suffers from poor melt stability and lacks suitable toughness after thermal cure. Simple laminates have been fabricated by RTM, however mechanical properties were low and the resin exhibited microcracking upon thermal cycling (D. E. Duch,
Sci. Adv. Mat. Proc. Eng. Ser
., 44, 705 (1999).)
The present invention constitutes a new composition of and method for preparing a mixture of imide random co-oligomers and imide compounds that exhibit a unique combination of properties that make them particularly useful in the fabrication of composite parts via RTM and/or RI processes. These materials can be readily synthesized and isolated in a solvent-free and moisture-free form, exhibit the proper flow, melt stability and lack of volatile formation to allow for processing using RTM and/or RI techniques. Upon thermal curing, these materials exhibit sufficient thermal stability, toughness and mechanical properties so as to be useful as composite matrix resins in high performance applications. They are also useful as adhesives, coatings, films, foams and moldings (both filled and unfilled).
SUMMARY OF INVENTION
According to the present invention, a composition of and method for making high performance resins that are processable by resin transfer molding (RTM) and resin infusion (RI) techniques were developed. Materials with a combination of properties, making them particularly useful for the fabrication of composite parts via RTM and/or RI processes, were prepared, characterized and fabricated into moldings and carbon fiber reinforced composites. These materials are particularly useful for the fabrication of structural composite components for aerospace applications. This method produces aromatic imide based resins that are processable into complex composite parts using RTM and/or RI.
The method for making high performance imide resins for RTM and/or RI processes is a multi-faceted approach. It involves preparation of a mixture of products from a combination of aromatic diamines with aromatic dianhydrides at relatively high stoichiometric offsets and endcapping with latent reactive groups. The combination of aromatic diamines includes at least over approximately 50 molar percent of a flexible diamine. It also may include less than approximately 50 molar percent of a rigid diamine. Alternatively, or in conjunction with the rigid diamine, a diamine containing pendent phenylethynyl groups comprising less than approximately 20 molar percent of the total diamine combination can also be utilized. This combination of monomers provides a balance of properties that impart flexibility (melt flow) with those that impart rigidity for sufficiently high glass transition temperature (T
g
) and results in a mixture of products, in the imide form, that exhibit a stable melt viscosity of less than approximately 60 poise below approximately 300° C. The use of a high stoichiometric offset produces a mixture of products consisting of different molecular weight imide oligomers and simple imide compounds. This mixture of products can be detected through gel permeation chromatographic (GPC) analyses that indicate multi-modal molecular weight distributions. Additional experimental observations also indicate that there are components in the mixture of products that significantly contribute to the low melt viscosities exhibited by the materials described herein.
The selection of the monomers used to prepare the imide oligomers desires a balance of monomers that impart flexibility (i.e. melt flow) with those that impart rigidity (high cured Tg). The resultant mixture of products from their reaction should exhibit a stable melt viscosity of less than approximately 60 poise below approximately 300° C. In addition, the mixture of products formed does not contain components that are volatile under the processing conditions. A flexible diamine is described herein as an aromatic d

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