Abstractcis‐1,4‐Polybutadiene andtrans‐1,4‐polybutadiene were mixed at the ratio in weight of 100/0, 75/25, 50/50, 25/75 and 0/100, and various problems related to the mixing were studied. The mixing was carried out by the three methods, i.e., (1) by rolling, (2) by filler batch polymer, and (3) by coprecipitation of the solution. For the mixed compound and vulcanized rubber, such characteristics as the viscosity of the solution, the Mooney viscosity, x‐ray diffraction, infrared spectra phase separation of the solution, tensile strength, and the swelling ratio in benzene were observed. No marked difference in the state of mixing was noted, regardless of the method of mixing. However, the mixing of filler batch polymer was accomplished more easily than by the rolling method. A 50/50 blend rubber was microheterogeneous and contained particles about 0.5 μ in length, but these did not affect the crystallization, as judged from the observation of the state of dispersion, by means of electron microscopy, x‐ray diffraction, and infrared analysis. Thetrans‐4 polymer, vulcanized at a much slower rate than Cis‐4. This was revealed by comparing infrared spectra of extracts obtained from the unvulcanized portion after various vulcanization times. The Cis‐4 vulcanizate did not show any crystalline pattern even
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