The mechanism of plasticizer action has been discussed for linear, slightly and highly crosslinked polymers. The important factors considered are the flexibility of the polymer chain, the polar interaction of groups along the chain, the masking of these interactions by plasticizer molecules, and the importance of the relative shape of polymer unit and plasticizer in the effectiveness of separating the chains. For nonpolar polymers, without secondary valence cross links, the plasticization is largely an entropy effect since no secondary valence bonds are broken or formed.

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Compounding studies are presented, showing the effect of several variables on the compression properties of cellular ebonites cured at 325°F ., including choice of nitrile-tvpe rubber, amounts of sulfur, diazoaminobenzene (blowing agent), and several selected plasticizers, pigments, and accelerators.Effects of some of these variables on the exothermic heat of vulcanization were also briefly studied . ACELLULAR ebonite is an expanded hard rubber, produced by combining the techniques for producing a hard rubber product with those for "blowing" a soft rubber or plastic sponge or foam. Cellular ebonite was made from natural rubber as early as 1931, when Beckmann (1) reported on the electrical properties of accumulator separator diaphragms made from "mieroporous" hard rubber. Little technical information has been published on the application of nitrile-type synthetic rubbers to the production of cellular ebonites, although such products have been used for radomes, flotation material, thermal insulation, and Sandwich-type structures.

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