AbstractThe alternating copolymer was prepared from butadiene (BD) and acrylonitrile (AN) with ethylaluminum dichloride as a complexing agent and with vanadyl chloride as a catalyst, and was investigated to explain effects of composition and sequence distribution on the physical properties, especially the viscoelastic properties and the ultimate mechanical properties. In the unvulcanized state, the viscoelastic properties of the alternating rubber is not essentially different from the random one, except for a slight difference in the relaxation spectra. However, the vulcanized rubbers show different shift factors. The latter depends upon the glass transition temperature (Tg.) Since the alternating copolymer possesses aTglower than the random one, the nature of the alternating copolymer corresponds to that of the random copolymer having an AN content of 40. The difference in dynamic properties can be expressed with the different shift factors. In the isofree‐volume state or at the temperatureTg+ 25°C, the rubbers having various acrylonitrile contents and various degrees of alternation exhibit almost the same dynamic properties. However, the strain at break of the alternating rubber is higher than that of the random one. The temperature of maximum strain increases with increasing degree of alternation. The alternating rubber shows higher stress at break than the random one. The stiffness of the chain of the alternating copolymer is smaller than the random copolymer; in other words, the molecular chain of the former is more flexible than the latter. It can be said that the alternating copolymer is an excellent rubber having high tensile strength and elongation at bre
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