Processability is improved.

Phenylethynyl containing reactive additive (PERA) compounds and mixtures have been found to be useful for improving the processability of oligomers, polymers, cooligomers, and copolymers that contain phenylethynyl groups. The additives can be incorporated in different forms:

• A solution of an amide acid or an imide of a PERA can be added to a solution of phenylethynyl-containing oligomer, polymer, co-oligomer, or copolymer; or
• An imide powder of a PERA can be mixed with a dry powder of a phenylethynyl-containing oligomer, polymer, co-oligomer, or copolymer.

The effects of the PERA on mechanical properties, relative to those of the host resin, depend on the amount of PERA used. Typically, the incorporation of the PERA results in

1. increases in the glass transition temperature (T_g), modulus of elasticity, and parameters that characterize behavior under compression, and
   
2. greater retention of the aforementioned mechanical properties at elevated temperatures without
   
3. significant reduction of toughness or damage tolerance.

Of the formulations tested thus far, the ones found to yield the best overall results were those for which the host resin was the amide acid form of a phenylethynyl-terminated imide (PETI) co-oligomer having a molecular weight of 5,000 g/mole [hence, designated PETI-5] and a PERA denoted as PERA-1. PETI-5 was made from 3,3',4'4'-biphenyltetracarboxylic dianhydride, 3,4'-oxydianiline (3,4'-ODA), 1,3-bis(3-aminophenoxy) benzene (1,3-APB), and 4- phenylethynylphthalic anhydride (PEPA). PERA-1 was made from 3,5-diamino-4'-phenylethynylbenzophenon and equimolar amounts of phthalic anhydride and PEPA. To make PERA-1 in the imide form, the aforementioned ingredients were processed by refluxing in glacial acetic acid. To make the amide form of PERA-1, the ingredients were reacted in N-methyl-2-pyrrolidinone (NMP) under nitrogen at a temperature of 23 °C (see figure).

On the basis of the processability and other properties, a blend comprising 20 weight percent of PERA-1 and 80 weight percent PETI-5 was selected for further evaluation. Relative to neat PETI-5, the blend exhibited an increase in T_g; improved processability; and comparable values of shear strength in adhesion to titanium panels, open-hole compressive properties, compression properties after impact, and resistance to microcracking.

This work was done by John W. Connell, Joseph G. Smith, Jr., and Paul M. Hergenrother of Langley Research Center, and Monica L. Rommel of Northrop Grumman Corp. For further information, access the Technical Support Package (TSP) free online at www.techbriefs.com/tsp under the Materials category.

This invention has been patented by NASA (U.S. Patent No. 6,441,099 B1). Inquiries concerning nonexclusive or exclusive license for its commercial development should be addressed to the Patent Counsel, Langley Research Center, at (757) 864-3521. Refer to LAR-15543.

This Brief includes a Technical Support Package (TSP).

Reactive Additives for Phenylethynyl-Containing Resins (reference LAR-15543) is currently available for download from the TSP library.

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