Chemical reactions to produce polyimide foams for application as thermal insulation and fire prevention materials are discussed. Thermal and physical properties of the polyimides are described. Methods for improving basic formulations to produce desired qualitites are included

Rosser, R. W.

English

NASA Technical Reports Server

September 1972
	 B72-10300 
NASA TECH BRIEF 
Ames Research Center
	 -4r 
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be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Polyimide Foams Provide Thermal Insulation and Fire Protection 
Polymer foams may be used as flame-resistant insu-
lative materials. When exposed to intense heat or 
flame, properly formulated foams maintain dimen-
sional stability and provide an efficient thermal barrier 
because they form stable, integral chars which insu-
late and protect the substrates. New types of semi-
rigid polyimide foams have been developed which 
have markedly improved thermal and physical prop-
erties in comparison to other polyimide foams. Under 
standard test conditions in a smoke chamber, an index 
of zero is registered, implying that negligible smoke 
is evolved by the new types of semi-rigid polyimide 
foams; the results of other standard tests indicate a 
low flame-spread index. Moreover, the foams retain 
resiliency and good dimensional stability at cryogenic 
temperatures. 
The new polyimide foams can be prepared by mix-
ing 100 parts by weight of an aromatic anhydride, such 
as pyromellitic anhydride, with 100 to 500 parts by 
weight of an aryl polyisocyanate, such as poly(meth-
ylenephenylene) polyisocyanate. From 2 to 40 parts 
by weight of a sioxane-oxyalkylene copolymer are 
added to this mixture as a foam stabilizer and initi-
ator. Alkanolamines may be added in small amounts 
(0.1 to 10 percent by weight) to catalyze reaction. The 
materials are mixed at room temperature and then 
transferred to low or vertical-rise molds of any desired 
shape. The density of the resulting semi-rigid foams 
[about 0.2-0.08 g/crn3(1-5 lb/ft3)] can be varied by 
keeping the mixture at different temperatures during 
the rise; however, more precise control can be exer-
cised by adjusting the concentration of surfactant in 
the mixture. Mixtures will cure slowly at 98°C or 
more rapidly at temperatures up to 316°C.
Preferred materials and ratios are briefly outlined 
below: 
Ratio of diisocyanate to dianhydride: 150-300 parts 
by weight. 
Water: a small amount should be present. 
Ratio of foam stabilizer to polymer-forming species: 
5-20 parts by weight silicone—glycol copolymer (2% 
or more hydroxyl termination) to 100 parts anhydride-
isocyanate mixture. 
Surfactant: DC193. 
Alkanolamine: 1-Hydroxyethyl-3-heptadecenyl glyox-
alidine, which can be added from 0.1 to 10 parts by 
weight of total reactants. The alkanolamine is also 
an effective emulsifier, and it. contributes significantly 
to cell quality and texture; it also terminates the poly-
mer chain, thereby increasing char yield. Other al-
kanolamines are effective as initiators, for example, 
triethanolamine and dimethylethanolamine. Conven-
tional emulsifiers such as sulfonates, epoxidized soy 
bean oil, and blends of polyol carboxylic acids and 
their esters are less effective in the new foam mixture 
than in other foam compositions. 
The basic formulation can be improved by adding 
silica or carbon fibers (0.8 to 6.35 mm long) at a con-
centration of from 5 to 8% of the total formulation. 
The fibers improve mechanical and physical prop-
erties such as strength, density, and char integrity 
during combustion of the cured polyimide foam. 
Notes: 
1. The developed formulations are especially attrac-
tive because they utilize commercially available 
materials and because there is no need to use com-
plicated mixing procedures during polymerization. 
(continued overleaf) 
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rected to:	 - 
Technology Utilization Officer 
Ames Research Center 
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Reference: TSP 72-10300
Patent status: 
No patent action is contemplated by NASA. 
Source: Robert W. Rosser 
Ames Research Center 
(ARC-10464) 
B72-10300	 Category 04


Polyimide foams provide thermal insulation and fire protection

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