| http://www.w3.org/ns/prov#value | - The temperature of this heat treatment is preferable to be in the range of 30??? to 120??? C., preferably 50??? to 80??? C. For the purpose of promoting the reaction of the acid anhydride, a catalyst, particularly the catalyst using such a tertiary amine compound as a trialkyl amine compound or pyridine, is used advantageously.
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