1. The properties of hydrogenated sodium polybutadienes of various degrees of unsaturation were studied. The tensile strength and relative elongation of the vulcanizates have minimum values when the degree of unsaturation has been decreased by about one half. Elasticity and gas permeability of the vulcanizates decrease and the hardness increases with diminishing unsaturation. The resistance to thermal aging also increases. Order in the polymer chains has a favorable effect on the relative elongation and tensile strength of vulcanizates even if it does not lead to crystallization. The improvement of the freeze resistance of vulcanizates made from hydrogenated sodium polybutadienes is associated with the internal plasticization effect. 2. Studies of the properties of hydrogenated cis-l,4-polybutadienes, which have appreciable crystallinity, showed that vulcanizate elasticity decreases while the hardness increases sharply with decreasing unsaturation. The rise of the glass transition temperature is due to increased rigidity of the polymer chains.

It is well known that the high strength of unfilled (pure gum) natural rubber and some synthetic rubber compounds can be explained by the homogeneity of the polymer chain which determines its ability to crystallize or to orient on stretching. The character of the vulcanization network as well as the structure of the main chain is of importance. This has been verified by the use of polyethylene polyamines and other chemical compounds as vulcanization accelerators for butadiene-styrene rubber (SKS-30A) to produce high strength (up to 200 kg/cm2) gum rubber compounds. In certain cases, only the structure of the vulcanization network obtained with carboxyl-containing rubber compounds can account for obtaining the same effects as are obtained with natural or other synthetic rubber compounds as a result of homogeneity of polymer chain. The first work done by us on carboxyl-containing (carboxylic) rubbers was done in 1954\2-1955. In this work it was shown that polymers of isoprene and of butadiene, copolymers of butadiene with styrene, butadiene with acrylonitrile, and others, which contain small quantities of methacrylic acid (1\2-2 mole %) in the chain, can be vulcanized with oxides of divalent metals to give pure gum and lightly filled compounds characterized by high strength and elasticity, good resistance to heat aging and good cut growth resistance.

The experimental evidence shows that the mechanical and elastic properties of the carboxylic rubber compounds far exceed those of the synthetic rubber type compounds. Important qualities of gum and lightly filled carboxylic rubber compounds are: good mechanical and elastic properties, high cut growth resistance and good resistance to heat aging. The disadvantage is the tendency of the carboxylic rubber mixtures to scorch. Carboxylic rubbers are of considerable interest for the preparation of general and special purpose rubber compounds.

1. The reaction between trichlorothiophenol or dienols and SO2 brings about vulcanization of rubber without separation of elemental sulfur. The mechanism of the Peachey process of rubber vulcanization is examined on the basis of concepts of the role of intermediate products of the reaction—free radicals. 2. Sulfur is found to react with many vulcanization accelerators with formation of considerable amounts of hydrogen sulfide. It is shown that hydroxycarbonyl compounds, which reduce sulfur to hydrogen sulfide, play the part of accelerators of sulfur vulcanization. Thermal breakdown of hydrogen persulfide leads to vulcanization of rubber. 3. The experimental data are applied to the consideration of the mechanism of the action of accelerators of sulfur vulcanization and of the mechanism of formation of mono- and polysulfide bonds.

No abstract