Polyimide is a generic name of polymers having imide bonds. Typically they have excellent heat resistance, chemical resistance, electrical insulation, and mechanical strength. Moreover, they have a relatively low coefﬁcient of thermal expansion in organic compounds. And since they have only a few errors from expansion when used at high temperatures, they have been widely used for industrial products. For example, polyimides are used for ﬂexible printed wiring boards in electronic devices, insulating material for electronic circuits and protection ﬁlms for semiconductors, etc. Also, in the area of liquid crystal displays, polyimides are used as the alignment ﬁlm to arrange liquid crystal molecules in one direction.