ブテン低重合体の動的粘弾性

抄録

According to the works of Barlow et al. on amorphous polymers in molecular weights ranging from 448 to 7. 13×10^4, the shifted curves of shear data follow the Lamb spectrum in transition region from glassy to flow state independently of chemical or molecular structure. Whereas our data on polyvinyl-i-butyl ethers (number average molecular weight M_n=2. 66×10^3 and 1. 2×10^6) and poly-i-butyl methacrylate (M_n=4. 72×10^3) show rather contradictorily that the shifted curves are represented by the Davidson-Cole spectrum which indicates broader distribution of relaxation times than that of the Lamb spectrum. Hence it would be of interest to make a measurment on a series of polybutenes of low molecular weight and a comparison with Barlow's data. The modified rotating plate method was used to determine precisely shear wave velocity at frequencies of 1, 3 and 5 MHz. A reflection method was used to measure the real part of the acoustic impedance in a frequency range from 8. 6 to 102 MHz. Three Kinds of polybutene, LV-50, HV-100 and HV-1900, offered by Furukawa Chemical Co. were used, whose characteristics are listed in Table 1. Viscosity was measured by Cannon-Fenske Viscometer. The real parts of shear impedance in various frequencies are plotted against temperature in Fig. 4. A secondary dispersion on primary dispersion is found in the samples of HV-100 and HV-1900 around the glass transition temperature T_g as shown in Figs. 4 and 5 ; its magnitude in HV-1900 is the highest. It is found that molecular weight dependence of limiting shear modulus G_∞ is similar to those of Barlow et al. As shown in Fig. 7, the differences between the values of G_∞ derived from Litovitz's and Lamb's method reaches 15% at the most. The shifted curves of LV-50, HV-100 and HV-1900 are shown in Figs. 8, 9 and 10, using G_∞ derived from Litovitz's method. The shifted curve of LV-50 agrees well with the theoretical curve derived from Lamb spectrum shown by the solid line in the whole frequency region, while those of HV-100 and HV-1900 deviate from the theory in the region of log ωτ_H&gt0. 5. The shifted curves of HV-100 and HV-1900 in a higher frequecy fit the Davidson-Cole spectrum shown by dotted lines. It is clear from Fig. 11 that the width of distribution which is expressed by the parameter β become broader as the molecular weight increases. Hirai and Eyring proposed that G_∞=RT/(V_0)exp(E_h/(RT)), where R is the gas constant, V_0=M_0/ρ the volume of monomer unit and E_h the energy necessary to create hole per mole. Value of E_h/(RT_g) for HV-1900 is found to be 4. 25 which is grater than the universal constant (3. 69±0. 12)