Polyacylureas were prepared by the polyaddition reaction of diamides with diisocyanates and the rel tionship between chemical structure and chemical property was discussed.Fumaramide, succinamide and azobisformamide were used as diamide.The reactivity of amides is influenced by the structure of being squeezed between two amide groups and fumaramide is the most reactive of the three diamides.The obtained polymers are light yellow or light brown powder, which has an intrinsic viscosity of about0.15dl/g.

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In the previous paper, it was found that when heated by a hot press (200-340°C), unvulcanized BR or SBR hardened with an increase in temperature.
In this paper, vulcanized BR or SBR heated by a hot press (200-340°C) and the change of each property is examined.From data on swelling with benzene, specific gravity, and hardness, it is found that vulcanized BR or SBR is also hardens (seems to cross-link) with an increas in temperature, but unvulcanized and vulcanized IR soften.The changes of these properties are particularly remarkable in the range of 250°Cto300°C, and the changes of properties of BR are more remarkable than those of SBR.From the result of the infrared spectrum analysis, it is found that vulcanized BR also isomerized from cis-1.4to trans-1.4 and afterwards double bond decreases, and this isomerization of vulcanized BR is less remarkable than that of unvulcanized BR.
These results suggest that BR can chip more easily than SBR.

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Synthetic natural rubber vulcanized by sulfur was ozonized and reduced by lithium aluminum hydride to give a liquid rubber possessingahydroxyl a group. The liquid rubber was revulcanized by the reaction with tolylene diisocyanate. The treatment of the ozonized rubber with hydrogen peroxide gave a liquid rubber containing a carboxylgroup. The liquid rubber was revulcanized by the reaction with tris [1-(2-methyl) aziridinyl] phosphine oxide.

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1-chlorobutadiene (CB)-butadiene copolymers with high chlorine contents (high-C1 CB-BR) were prepared by emulsion polymerization at 50°C (hot rubber) or at 5°C (cold rubber).The rubbers, thus obtained, contained more gel fraction than low-C1 CB-BR which contained virtually no gel.This difference is assumed to be due to the higher concentration of active chlorine atoms attached to CB units.
Thermally the high-C1 CB-BR was not stable enough, showing an exothermic peak near 145°C in DSC charts.Some of metal soaps and organic tin compounds, which are known as stabilizing agents for poly (vinyl chloride), are effective for stabilizing high-Cl CB-BR.
This rubber can be cured not only with sulfur but also with the curing agents employed for CR, among which 2-mercaptoimidazoline/Pb₃O₄ is the most effective.Usual sulfur vulcanization is too fast, even when carried out at 90°C. Oil resistant property is much improved by the presence of CB unit.Glass transition temperature of the vulcanizates measures with the temperature dispersion of dynamic loss increased with an increase in CB content.These data indicate that the higher the CB content, the higher the oil resistance but the lower the thermal stability.

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The relation between the shear modulus of elasticity and the indentation hardness of vulcanized rubber is derived, from the theory of elasticity.Hooke's law, isotropy and incompressibility of rubber are assumed in the derivation.Indentor shape is presumed as a cylinder of average diameter instead of a truncated cone. An approximate conclusion is expressed as follows.
H_s=G/G+G₅₀×100
where H_s is indentation hardness degree of rubber, G is shear modulus of rubber and G₅₀ is a constant.
(If G=G₅₀, then H_s=50 and it shows the meaning of the constant G₅₀.) The calculated value of G₅₀ for JIS A hardness scale is 7.53kgf/cm², but the measured value of shear modulus for rubber of hardness degree 50is sometimes smaller than the calculated G₅₀.The disagreement is caused by the stress relaxation, because the measurement of modulus of elasticity requires longer time than that of indentation hardness.
The above expression for Shore A scale agrees fairly well with the IRHD probit curve shown in ISO Recommendation R48.

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The phenylhydrazine-ferrous chloride system was shown to be a very effective reagent for the reclamation of synthetic rubber vulcanizates regardless of the structure of main chain and that of cross-links.That is, the following ten types of gum vulcanizates were easily softened by treating with the reagent at room temperature for 4-24 hr: sulfur vulcanizates of IR, SBR, NBR, EPDM and IIR, organic peroxide vulcanizates of SBR, CR and EPDM, sulfur donor vulcanizate of SBR, and 2-mercaptoimidazoline vulcanizate of CR. Revulcanization of these reclaim gave good elastomers.

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