Abstract
The imidization reaction of various polyamic acids having different chemical structures has been followed by measuring the weight losses that occurred during dehydro-cyclization. From these studies it was found that when polyamic acids were heated rapidly to a given temperature, the imidization reaction proceeded during the temperature rise but slowed down very markedly after the given temperature was reached. The temperature at which the imidization reaction ended was closely related to the glass transition temperature of the resulting polyimide. Based on these observations, it is concluded that the imidization reaction slows down markedly because the glass transition temperature of the polymer rises as the reaction proceeds, and molecular motion is frozen. In other words, the free rotation of amide bonds in the main chain is frozen. As a result, suitable conformation for imidization cannot take place any more.
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