Process for producing bonded macroballoon structures and resulting product

摘要

A method of making light weight flame resistant structures from bonded polyimide macroballoons and products thereof. An aromatic tetracarboxylic acid dianhydride is reacted with an oxoimine to produce an N-substituted imide, which is then esterfied with a suitable alcohol. The resulting liquid is dried and the dry residue is reduced to a uniform powder having particles with diameters generally in the 0.5 to 10 mm. range. The powder is preferably further dried, either before or after final size reduction, in a moderate vacuum at moderate temperature to remove any excess residual alcohol. The powder spontaneously expands to form a closed cell foam when heated to a temperature in the range of about 90 DEG to 150 DEG C. for a suitable period. When the powder is expanded in a closed mold, a well consolidated, uniform, closed cell foam product results. The closed cell foam produced has excellent flexibility and resistance to heat and flame, and does not shrink appreciably when exposed to flame. When expanded in an unrestricted manner, closed cell "macroballoons" having average diameters between about 0.4 and 15 mm. result. The macroballoons are useful in a number of applications, including forming a foam-like structure by bonding them together with a very small amount of a suitable resin.