The permanent set, γ defined in usual methods of testing material for vulcanized rubber was studied rheologically by identifying it with the residual strain left in a viscoelastic body. After appropriate approximations the following expression was obtained.
(γ/γ₀) ≅ (ktan δ)²exp[-(ktan δ)(t/t')] |_ω=1/t'
Here γ₀ is a constant strain applied to the sample for a period of time, t', by an external force, and t stands for the time elapsed after the removal of the external force. The loss tangent and the angular frequency are symbolized by tan δ and ω, respectively.
The numerical factor, k, expects to be mainly affected by the strain dependence of tan δ in a sample.
The experimental data on several typical rubber vulcanizates checked fairly well the above equation for t'-, t- and tan δ-dependencies of γ.
An average value of 2.2 was found to be replacable for the numerical factor, k irrespective of rubber species at room temperature when t', t and γ₀ were fixed as 10 min., 10 min. and the one half of the strain at break in extension, respectively.

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A graft polymer was prepared using the coupling reaction of chlorinated ethylene-propylene terpolymer with living polystyrene obtained with a sodium-naphthalene complex initiator in tetrahydrofurane at 30°C., and the grafting efficiency and the grafting percentage were discussed.
The dried reaction product was extracted with boiling acetone to determine the weight of grafted polystyrene. The grafting was confirmed by fractionation and from infrared spectra.
The grafting efficiency at the constant living polystyrene concentration, increased with increase in the concentration of the chlorinated ethylene-propylene terpolymer and it approached an equlibrium value (37-39 %) when the ratio of chlorine to sodium in the initiator used to polymerize styrene, was unity.
At the constant concentrations of chlorinated ethylene-propylene terpolymer and living polystyrene, grafting percentage increased with increase in the degree of polymerization of living polystyrene. Crosslinking occurred during the coupling reaction and insoluble graft polymers were obtained.

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Graft polymers were prepared using the coupling reaction of chlorine-containing polymers with living polystyrene initiated with a sodium-naphthalene complex in tetrahydrofurane at 30°C.
Polychloroprene, chlorinated butyl rubber, polyvinyl chloride, polyepichlorohydrine and epichlorohydrine-ethylene oxide copolymer were used as chlorine-containing polymers.
An insoluble graft polymer was obtained in the case of polychloroprene, and in the case of chlorinated butyl rubber a soluble graft polymer was obtained.
In the cases of polyvinyl chloride, polyepichlorohydrine and epichlorohydrine-ethylene oxide copolymer, soluble graft polymers were obtained for low chlorine concentrations.
Living polyisoprene obtained with sodium-naphthalene complex initiator, was reacted with chlorinecontaining polymers in tetrahydrofurane at 30 and 50°C. No grafted polymer was obtained. When living polyisoprene, obtained with BuLi, was reacted with a chlorinated ethylene-propylene terpolymer in benzene at 30°C., an insoluble graft polymer was obtained. Grafting was confirmed by infrared spectra.

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The reinforcing abilities of carbon black against synthetic rubbers were studied. The grades of the carbon blacks used were FT, ISAF and special blacks. SBR, NBR and EPDM were used as synthetic rubbers. The stress-relaxations of the heat-treated black stocks (at 145 °C for 30 min.) were measured, and the distributions of log (H/H₀) were plotted against the relaxation time τ. Here, H and H₀ indicate the relaxation spectra of black and gum stocks, respectively. As the result, the interactions between FT black and the rubbers were found to be low. On the other hand, ISAF and special blacks indicated high interactions towards synthetic rubbers with the order of EPDM <NBR <SBR. Similar tendencies were observed in the formation of carbon gel, apparent viscosity increase of the black stock and reinforcement in tensile properties of the vulcanizates.

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