This report deals with sulfur of thioketon type and that of crosslinked type as well as with chlorine.
(1) It was experimentally recognized that as the solution for vulcanization becomes more concentrated, so does sulfur of either type increase in quantity, on condition that vulcanization is continued only for a short period of time. When rubber is vulcanized for a long time, however, sulfur does not necessarily increases in accordance with high-concentration in the solution.
(2) Based on the quantitative experiment of aceton-extracts, free sulfur, thioketon-type sulfur, crosslinked-type sulfur, chlorine, etc., the reaction mechanism of natural rubber with S₂Cl₂ in the solution was considered as the following principal reaction:_??_

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(1) When rubber treated with hydrazine-hydrate after cold-vulcanization was compared with the untreated rubber in the swelling test, it was known that thioketon-type sulfur changes itself to constitute ketoazine crosslinkage.
(2) If thioketon groups transform into ketoazine crosslinkage, a certain kind of relation should exist between the contents of thioketon-type sulfur and N-contents. This fact was recognized in natural rubber and cis-i, 4-polybutadiene cold-vulcanizates. Principal reaction is thought as follows: _??_

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Fundamental experiments were carried out with high-pressured polyethylene in order to get rubberlike elastomer through bromination and other processes, and then to investigate some of the physical and chemical properties of the products thus obtained.
Since polyethylene is saturated hydrocarbon, it is stable chemically. But it can be changed into halide through the existence of peroxide catalyst or under the irradiation of ultraviolet ray, etc.
The experiments, therefore, were made by the following processes:
(1) After bromination, the conditions of the bromine contents of the products were considered.
(2) When polyethylene bromide was further treated in the current of N₂ gas at high temperature, HBr. was confirmed to be was confirmed to be generated.
(3) The occurrence of double-bond and cross-linkage, etc. in the produced resin by the thermal reaction, was examined.
(4) Polyethylene bromide, after mixed directly with metallic oxide (for example, MgO), was vulcanized.
(5) Some of the physical and chemical properties of the vulcanized products were tested.

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Following the previous papers1)2), some new active calcium carbonates were studied for reinforcement of SBR and NBR. These active calcium carbonates were prepared by introducing carbon dioxide gas into aqueous calcium hydroxide containing active agents.
Unsaturated fatty acids used for the active agents were maleic acid, fumaric acid, crotonic acid, methacrylic acid, sorbic acid etc. Because, the carboxyl groups of fatty acid are reactive to calcium carbonate while the double bonds of unsaturated fatty acid are reactive to rubber molecule.
SBR and NBR vulcanizates loaded with the active calcium carbonates had extremely high tensile strength and modulus. Maleic acid, maleic anhydrid, crotonic acid and sorbic acid indicated good physical properties. Sorbic acid was the most efficient of all unsaturated fatty acid. The 300% modulus (300%M.) and the tensile strength at break (T.S.) on SBR loaded with 100phr of the active calcium carbonate reached as high as 39kg/cm². and 207kg/cm²., respectively. On the other hand, those of the vulcanizate loaded with the conventional carbonate indicated only 24kg/cm². and 79kg/cm²., respectively. And the 300%M. and T.S. on NBR reached as high as 85kg/cm². and 220kg/cm²., respectively. On the other hand, those of the vnlcanizate loaded with the conventional carbonate indicated only 42kg/cm². and 102kg/cm²., respectively.

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