As is well known to those skilled in the art, anhydrides of polycarboxylic acids, typified by the anhydride of maleic acid, are susceptible to deterioration when subjected to heat; and this deterioration is catalyzed by light and by chemical contaminants.
Polycarboxylic acid anhydrides including dicarboxylic acid anhydrides are subject to relatively high temperature environments in their manufacture, their purification, their use as chemical intermediates, and in cases of careless handling. These high temperatures cause deterioration which is evidenced by discoloration resulting from decomposition. Contamination can accelerate this thermal deterioration. In the case of the typical maleic anhydride, temperatures above 150.degree. C. for extended periods of time can result in extensive even violent decomposition; the upward limit of applicability of stability additives has been stated (U.S. Pat. No. 3,636,057) to be ca. 180.degree. C. due to decomposition or charring at this temperature.
The extent of deterioration and, therefore, the degree of protection required depends on the quality, method of production, feedstocks, conditions of handling and useful application as well as the nature and amount of stabilizer added and/or treatments given to the acid anhydrides to counteract this deterioration. In addition, deterioration requires definition.
Using maleic acid anhydride as an illustrative example (as it is one of the anhydrides particularly requiring thermal stabilization), thermal stability has been defined as a discoloring after 2 or more hours at 140.degree. C. as measured by APHA (American Public Health Association) Units in accordance with ASTM-1209.
It is an object of this invention to provide a novel stabilized composition containing an anhydride of a polycarboxylic acid. Other objects will be apparent to those skilled in the art.