Carbon dioxide (CO₂) laser supersonic drawing is a new technique for preparation of nanofibers in a vacuum chamber using a CO₂ laser and a supersonic air jet formed directly below the fiber supply orifice. In this study, we have applied a CO₂ laser supersonic multi-drawing method to nylon 66 to produce nanofiber sheets. A fiber of 182 μm in diameter was drawn at a drawing speed of 223 m s^-1 and a draw ratio of approximately 1.3×10⁵ to obtain a nanofiber sheet having 25 cm length, 17 cm width, 61.5 μm thickness, and an average nanofiber diameter of approximately 0.5 μm. The nanofiber sheet exhibited two melting temperature (T_m), 259°C (T_m1) and 270°C (T_m2). T_m2 is approximately 10°C higher than the T_m value of nylon 66 at usual. The sheet showed no drastic fiber shrinkage during heating, and the fiber form was held even at the temperature of the usual melting temperature or higher.

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Four polyurethanes (PUs) crosslinked by polyrotaxanes (PRXs) of two filling ratios of CyD (63% for PRX4000 and 37% for PRX6000) and with modification ratios of 1 and 2 for a PU chain. The PUs were abbreviated as PU6000(1), PU6000(2), PU4000(1), and PU4000(2), in which 4000 and 6000 are the molecular weights of PEGs as an axle molecule of the PRX and the numbers in parentheses are the modification ratios of the PU chain. ATR-FT-IR, DSC, viscoelastic measurements and tensile test were carried out to investigate their thermal and physical properties. The formation of hydrogen bonds between the PU chains increased with increase in the modification ratio of the PU chain. PU4000(2) possessing the half filling ratio of CyD and higher modification ratio of the PU chain made the recrystallization of the soft segment slow. PU4000(1) with the half filling ratio of CyD and lower modification ratio of the PU chain showed the highest tensile strength among the PUs. In contrast, PU6000(2) with the lower filling ratio of CyD and higher modification ratio of the PU chain showed the highest elongation among the PUs, implying that the sliding effect based on the rotaxane structure occurred.

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