All purchased chemicals were used as received unless otherwise specified. Pyromellitic dianhydride (PMDA) and 4,4'-oxydianiline (ODA) were purchased from Tokyo Chemical Industry Co. and sublimated before use. Acetone was obtained from FUJIFILM Wako Pure Chemical Co. A typical experimental procedure for synthesizing polyamic acid is as follows. Initially, a human chemist prepared a 200 mmol/L solution of ODA in acetone and a 5.12 mmol/L of PDMA in acetone solution and placed them in the dispensing system. A 39 mL solution of PDMA was added to an empty sample bottle containing a stir bar rotating at 1000 rpm. The dispensing system automated the subsequent addition of reagents and stirring operations. The reaction was initiated by adding 1 mL of ODA solution so that the molar amounts of each became 0.2 mmol. A camera periodically recorded the state of the sample, and after stirring for one hour, the reaction was finished. After the reaction, an evaporator or a hot plate removed the solvent to obtain the microparticles, which were analyzed by scanning electron microscopy (Hitachi High Technologies, S-5500).