Addition of polar modifiers to alkyllithium‐initiated homopolymerizations of butadiene causes substantial changes in the microstructure of the polymers produced. These changes are shown to depend not only on the concentration of modifier, but also on the polymerization temperature. The combined effects of modifier concentration and reaction temperature have been considered, and a method is presented for quickly determining the proper conditions for preparation of a polybutadiene of any 1,2‐microstructure within a range of 10–80%. It is also shown that in anionic polar‐modified copolymerizations of butadiene–styrene, the reaction temperature is again critical. Within a certain concentration range of modifier, the temperature will influence the rate of styrene incorporation or the randomness of styrene units in the resulting copolymers.
Many commercial elastomers exhibit good solvent resistance and high temperature stability but have limited use at low temperature. Fluorosilicone, which exhibits good low temperature properties, is limited in many dynamic applications by its poor physical strength. Phosphonitrilic fluoroelastomers are being developed for applications which require solvent resistance, low temperature flexibility, and good physical strength over a broad range of service conditions. A brief description of the synthesis and characterization of these new polymers has been presented in the forms of chemical, chromatographical, spectroscopical, physical testing, and rheological studies. The main object of this paper has been to provide an introduction to the art of processing, vulcanization, and reinforcement of these elastomers to produce useful commercial items. These fluoroelastomers can be processed on conventional equipment for dry-mixing rubber. Vulcanization can be effected with either organic peroxides or sulfur-accelerator cure systems. These vulcanizates can be reinforced with silicas, carbon blacks, or silane-treated clays to give stocks with a wide range of modulus, strength, hardness, and service temperatures (−80 to 400° F) in many service fluids and atmospheres. The exceptional solvent resistance, low temperature flexibility, and wide temperature service range indicate that phosphonitrilic fluoroelastomers should find use in items such as O-rings, Arctic fuel hose, lip seals, gaskets, and vibration damping services.
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