Polycarbodiimide and polyimide/cyanate thermoset in situ molecular composites
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Polycarbodiimide and polyimide/cyanate thermoset in situ molecular composites D. R. Wiff a),b) Materials Directorate, WL/MLPJ, Air Force Research Laboratory, Wright-Patterson AFB, Ohio 45433
G. M. Lenkeb) 49 5th Street S.E., Massillon, Ohio 44646
P. D. Fleming IIIb) Department of Paper & Printing Science and Engineering, Western Michigan University, Kalamazoo, Michigan 49008 (Received 5 September 1997; accepted 31 October 1997)
The synthesis of polycarbodiimide and polyimide in a cyanate resin precursor was achieved. A unique procedure for achieving a high molecular weight of the molecular composite reinforcement molecules was demonstrated. In spite of phase separation being present during the processing, the final cured composites were transparent. The enhanced mechanical properties and the presence of a single Tg , which increases with rigid rod content, were indications that a molecular composite was achieved. The agreement between measured mechanical properties and those predicted using molecular mechanics simulations CERIUS2 software was encouraging.
I. INTRODUCTION
For the past decade we have been striving to produce a molecular composite via a low cost and industrially viable processing procedure.1–5 Molecular composites are dispersions of “stiff ” molecules in a matrix of flexible polymers. Attempts to make these by casting from a mutual solvent usually led to phase-separated systems,6 as predicted by the theories of Onsager7 and Flory and Abe.8,9 However, when the rigid rod molecules are formed in situ, they are completely solvated. In the reactive resin precursors the system may be biphasic, although upon curing a transparent material is usually obtained. This was true of previous systems studied in epoxy resin precursors10 and for the present system in cyanate resin precursors. However, the first in situ rigid rod molecule system studied did not yield a transparent final product. The system was polyazomethine in a-caprolactam,11 which was not transparent due to the crystallinity of the final matrix, i.e., NYRIM, nylon6. Benefits of molecular composites will eventually be manifested in highly oriented systems. For example, in addition to mechanical properties which improve with larger aspect ratio rod molecules, oriented low molecular weight (oligomers) rigid rod molecular composites could find applications in high value-added devices which utilize optical properties, such as, birefringence, dichroism, and nonlinear optical susceptibilities x s2d and x s3d . Since
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Author to whom comments should be addressed. Research was performed while employed by GenCorp Inc., Corporate Research, Akron, Ohio 44305.
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http://journals.cambridge.org
J. Mater. Res., Vol. 13, No. 7, Jul 1998
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heat conduction occurs more efficiently intramolecularly than intermolecularly, it is likely that orientation of the rodlike molecules would also impart anisotropic thermal conductivity to molded parts. Applications which could exploit this feature
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