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ABSTRACT The phase appearance during the synthesis of fluorinated polyamic acid (PAA) from 2,2-bis(3,4-anhydrodicarboxyphenyl)-hexafluoropropane (6FDA) and 2,2′-bis(trifluoromethyl)−4,4′-diaminobiphenyl (TFDB) in supercritical carbon dioxide (scCO2) was investigated to obtain fundamental data for the deposition of fluorinate polyimides (PI) using scCO2. All polymerizations were carried out at 30 MPa for 60 min. The experimental temperatures ranged from 50 to 70 °C, and each of the monomer concentrations ranged from 0.67 × 10−5 to 3.3 × 10−5 mol cm−3. The holding time of the transparent phases, which was the time from the beginning of the polymerization to the appearance of a turbid phase, was increased with either a decrease in the polymerization temperature or a decrease in the initial monomer concentration. The holding time of the fluorinated PAA was longer than that of the monomers of Kapton-type PAA. The deposition of PI into the microscopic-scale trenches that had formed on the silicon wafer was successful in scCO2. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43334. [ABSTRACT FROM AUTHOR]

ABSTRACT To develop a microscale processing technique for aromatic polyimides (APIs) in supercritical carbon dioxide (scCO2), the relationships between the polymerization condition, the phase behavior during polymerization and the molecular weight of polyamic acid (PAA)-an intermediate in the production of polyimides-were investigated in scCO2 at 50°C. 4,4′-Diaminodiphenyl ether (ODA) and pyromellitic dianhydride (PMDA) were used as monomers of aromatic diamine and tetracarboxylic dianhydride, respectively, and 19 mol % of N,N-Dimethylformamide (DMF) was added to scCO2 as a cosolvent. The cloudy phase appeared immediately when ODA and PMDA were mixed under any experimental conditions. However, the appearances of the phase behaviors during polymerization differed depending on the polymerization pressure and the initial monomer concentration. The number average molecular weight of PAA increased as the monomer concentration was increased in scCO2, as was the case with polymerization in pure DMF at atmospheric pressure, despite differences in the phase behavior. On the other hand, the weight average molecular weight of PAA depended on the phase behaviors during polymerization along with the monomer concentration. Moreover, API obtained from the PAA synthesized in scCO2 was analyzed using a Fourier transform infrared spectrophotometer and thermogravimetric analyzer, and the results were compared with those of APIs obtained by the solution polymerization. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 39878. [ABSTRACT FROM AUTHOR]

In hard disk drives, it is important to enlarge the control bandwidth in order to shorten the track pitch for larger data capacity. However, it is difficult for the H∞ control method to increase the control bandwidth if the mechanical resonance modes have uncertainty. This is because the robustness of the H∞ control method is assured by the small-gain theorem for additive or multiplicative perturbation and the control bandwidth is limited by the uncertainty. In this study, we propose an H∞ control method for high-bandwidth design by introducing a new uncertainty model with a feedforward and a feedback path in order to reduce the conservatism of robust design. The effectiveness is shown by numerical simulations. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 173(4): 54–62, 2010; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.21025 [ABSTRACT FROM AUTHOR]