Method prepares aromatic polyimides with significantly reduced glass-transition temperatures and without accompanying loss of high-level thermo-oxidative stability which has been typical. This has been made possible by use of diamine monomers with specific stereoisomeric features

Bell, V. L.

English

NASA Technical Reports Server

September 1973
	 B73-10319 
O NASA TECH BRIEF 
Langley Research Center
	
_4V 
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Preparing Thermoplastic Aromatic Polyimides 
A method has been developed for preparing aromatic 
polyimides with significantly reduced glass-transition 
temperatures and without the accompanying loss of high-
level thermo-oxidative stability which has been typical. 
This has been made possible by the use of diamine 
monomers with specific stereoisomeric features. 
The reduced glass-transition temperatures lead to a 
softened state in the polyimides which permits them to 
be processed readily into such useful articles as sheets, 
thin films, fibers, foams, and molded or laminated 
•
pieces. This process also permits cross-linking or curing 
such polymers by means of a postforming step in which 
the glassy transition (softening) temperatures are in-
creased so that the shaped polymer article can be used at 
temperatures greater than those at which they were 
formed. 
Polyimides prepared by this process display out-
standing physical and chemical properties. This makes 
them suitable for fabrication into shaped articles such 
as films, fibers, and laminated composites of reinforced 
resins. These articles have high tensile and flexural 
properties as well as excellent thermal and thermo-
oxidative stability. 
The decreased glass-transition temperatures of these 
polymers result from one or both of the amine groups 
of the aromatic diamine being substituted on the 
benzene rings meta to the group connecting the benzene 
rings. This leads to softening of the polyimides when 
they are heated above the glass-transition temperatures 
and, thus, contributes to vastly improved processing 
characteristics for the polyimides. The glass-transition 
diamines are as much as 500 to 75° C lower than those 
for polyimides made from the p ,p"-diamines customarily 
used in polyimide preparation. 
.
The polyimides are prepared by reacting the m,m'-
(3,3'-) and m,p'.(3,4') diaryl diamines with pyro-
mellitic dianhydride or 3,3',4,4'-benzophenone tetra-
carboxylic acid dianhydride in an organic solvent, 
which dissolves at least one of the reactants, for a time 
and at a temperature sufficient to give a polyamide 
acid. This polyamide acid is heated to 100° C for 
sufficient time to remove the solvent after which the 
acid is converted to the polyimide by heating at 200° C 
for 1 to 2 hours. The resulting polyimide can have glass-
transition or softening temperatures from 210 0 to 
250° C, depending upon the nature of the diamine. Facile 
processing of the polyimides, such as compression 
molding, can be accomplished at this stage. A sub-
sequent post-cure of 300° C or higher serves to increase 
the glass-transition (softening) temperature of the poly-
meric article to near 300° C. 
Note: 
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Technology Utilization Officer 
Langley Research Center 
Mail Stop 139-A 
Hampton, Virginia 23665 
Patent status: 
Inquiries concerning rights for the commercial use of 
this invention should be addressed to: 
Patent Counsel 
Langley Research Center 
Code 456 
Hampton, Virginia 23665 
Source: Vernon L. Bell 
Langley Research Center 
(LAR-1137 2) 
Category 04 
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Preparing thermoplastic aromatic polyimides

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