The storage modulus (E′) of nylon 6 fiber was found to increase during repeated measurements of dynamic viscoelasticity in the temperature range including the α dispersion. The fibers used in the measurements were zone-drawn at high temperatures close to the melting point; the first high-temperature zone-drawing (HT-ZD 1) was carried out at a temperature of 180°C under an applied tension of 16.6MPa, and the second (HT-ZD 2) at 210°C under 14.1MPa. The HT-ZD 1 and HT-ZD 2 fibers obtained have birefringence of 51×10^-3 and 59×10^-3, respectively. The repeated measurements were performed twice at a frequency of 110Hz; the first measurements were carried out in a temperature range from 0°C to 180°C, and the second from 0°C to 190°C. Upon repeating the measurements, E′ at 0°C of HT-ZD 1 fiber increased from 7.9GPa to 12.3GPa, and that of HT-ZD 2 fiber from 17.3GPa to 21.4GPa. These changes in E′ were irreversible. The α_a dispersion peak, which originates from the rupture of interchain hydrogen bonding due to the motion of chain segments in amorphous region, decreased in height and at the same time shifted to higher temperatures with repeated measurements. The birefringence of HT-ZD 1 fiber increased up to 56×10^-3, and that of HT-ZD 2 fiber up to 61×10^-3 after the repeated measurements. Although the birefringence increased with repeated measurements, there was no change in crystallinity.

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A theoretical equation of state (EOS) for chain molecule fluids was proposed based on a hole and cell model, which is considered as an improvement of the theories of Simha et al. and Sanchez and Lacombe. The present EOS has three characteristic parameters per pure fluid and satisfies the corresponding-state principle for pure polymeric fluids. The applicability of the present equation was investigated by fitting the experimental PVT data for nine common polymers and predicting the thermal expansion coefficient and isothermal compressibility of PVAc as well as comparing with the previously reported values. The results show that the present EOS gives the best prediction of all the EOS. Thus we conclude that the present EOS is more applicable to the predict the PVT relationship of polymeric fluids.

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