Yasuji Kobayashi

Change of amorphous state of poly(ethylene terephthalate) by heat treatment below the glass transition temperature

Abstract Several papers have demonstrated that structural changes in the amorphous regions of semicrystalline polymers can be produced by heat treatment below the glass transition temperature (Tg). In this paper, we report structural change in the amorphous phase of poly(ethylene terephthalate), heat-treated below and above Tg. The density, the Tg, the endothermic peak at Tg and the relative spectral intensity in the 973 cm−1 band (due to the CO stretching vibration), all increased with heat treatment below Tg, but the specific heat decreased. The stability of the amorphous state was examined by further heat treatment at temperatures above Tg and sufficiently high for crystallization, and it was verified that structural changes in the amorphous regions do not result in acceleration of the rate of crystallization. We therefore suggest that the amorphous region is one phase, rather than two phases consisting of random and regular regions.

Effect of side chains on molecular motion of poly (alkyl methacrylates) with isothermal annealing at temperatures below glass transition temperature

Abstract In this study, an estimation was made of the effect of side chains on the rate of enthalpy relaxation that occurred during isothermal annealing at temperatures below Tg. For the purpose of the analysis of the relaxation process, the relaxation time and activation energy obtained assuming a single relaxation time were used. Bulk-polymerized atactic poly(methyl methacrylate), poly(ethyl methacrylate), poly(isopropyl methacrylate), and poly(tert-butyl methacrylate) were used as samples. The enthalpy change that occurred during annealing in the glassy state was expressed in terms of variations in the enthalpy displacement from the equilibrium glassy state (excess enthalpy). The kinetics of the enthalpy relaxation was analyzed in terms of the excess enthalpy, δHt. δHt = δHO exp(-t/τ) From the relaxation time at a constant degree of enthalpy decrease, it was shown that the rate of the relaxation was influenced by the side chain. With a larger side chain, the relaxation time became longer. Considering t...

Change of the amorphous state by heat treatment below the glass transition temperature

Abstract This study was undertaken to elucidate the state of a polymer in the amorphous state through a change of motion of the molecular chain caused by heat treatment below the glass transition temperature. From dielectric measurements of amorphous poly(ethylene terephthalate) heat-treated below T g , it was found that the average relaxation time, the distribution of relaxation time and the dielectric strength increase with increase of heat treatment. From these results, it was concluded that the amorphous state becomes more random by heat treatment.