Modifiers with bis‐type structures are of interest as a means for conferring reactive groups onto the highest possible fraction of polymer chain ends. Various disulfides and other bis‐type compounds—some with reactive groups attached—were compared as to their effectiveness as modifiers in low conversion bulk styrene polymerizations and studies made of their mechanism of cleavage. Alkyl disulfides of primary thiols had transfer constants too low to be of much interest for this work, even when substituted at carbons near the sulfur‐sulfur bond. Aryl disulfides proved to have much higher transfer constants, and substitution on each ring with appropriate groups offered a means both of increasing the transfer constant and of incorporating desired groups. It has been shown quite conclusively that aryl disulfides cleave so as to confer one‐half the molecules onto each end of the polymer. This was demonstrated by analyzing the end group concentrations of styrene polymers of wide molecular weight range which contained various types of end groups—carboxyl, amino, naphthyl, and benzothiazyl—and comparing, wherever possible, with polymers modified with thiols containing similar groups. Polymerizations carried out at 25, 50, and 75°C. with certain of the bis‐type compounds and with a normal and a tertiary mercaptan showed that activation energies are very slight if the transfer constant is high, and begin to reach significant levels only at low levels of transfer constant.

Elastomeric tetramethylene-ethylethylene-acrylonitrile (TEAN) copolymers were prepared by quantitative selective hydrogenation of emulsion NBR polymers in solution in presence of a triphenylphosphine-liganded rhodium salt catalyst. Completeness of hydrogenation at low pressure required appreciable excess of triphenylphosphine. Physical and chemical properties of TEAN gums of varying acrylonitrile segmer content, and their sulfur- and peroxide-cured vulcanizates are characterized. As expected, both gums and vulcanizates were very resistant to attack by oxygen. The exceptionally high tensile strengths of such vulcanizates were attributed to the crystallizability of the gums on stretching. Certain peroxide-cured TEAN vulcanizates prepared from green stocks containing magnesium oxide had a combination of resistance to heat aging in air, hydrogen sulfide, and oil, suggesting their applicability to well-drilling components.

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In conclusion, we have demonstrated that modified diene elastomers containing active hydrogens and/or blocked-isocyanate derivatives can be crosslinked (cured) by three distinct methods. These methods include: 1. reaction of polymer-bound active hydrogens with monomeric polyisocyanates (Type I), 2. reaction of polymer-bound isocyanates with compounds containing two or more active hydrogens (Type II), and 3. reaction between polymer segments that contain both polymer-bound isocyanates and active hydrogens (Type III). Additionally, we have shown that the new polymerizable blocked-isocyanate derivatives (Type II and III systems) can be readily incorporated into SBR and NBR elastomers by standard emulsion-polymerization techniques. The degree and distribution of these monomers within the elastomer matrix were shown to be controlled by knowledge of their reactivity ratios. Furthermore, we have shown that the processing and properties of these systems can be readily controlled by the proper combination of isocyanate blocking group, active-hydrogen component, and catalyst. In many cases, these modified elastomers can be coagulated, dried, compounded, and cured using methods common to the rubber industry. Although not optimized, we have also shown that useful vulcanizates can be produced from extremely simple recipes. Conventional acceleration systems e.g., sulfur, accelerator, zinc oxide, are eliminated. The resulting urethane or urea crosslinks are remarkably durable under both thermal and hydrolytic conditions. Obviously, the possibilities for these uniquely reactive elastomers have not been exhausted. Many other intriguing applications of this technology are currently being explored. These applications will be the subject of future publications.