Abstract

Polybutadiene samples may be analyzed by a refractive-index method, except at low levels of polystyrene—where the method becomes insensitive due to the very small changes in refractive index. Small concentrations of polystyrene are sometimes encountered in polybutadiene, in the range of 5% or less. These levels of polystyrene may be detected and determined by ultraviolet spectrophotometric examination of samples of sheets prepared from the latex by the ASTM procedure. These sheets are translucent, but are insoluble in the usual ultraviolet-transparent solvents. It was found that the sheet samples become transparent upon compression. The sample was placed between the internal surfaces of the quartz windows of a micrometer Baly cell and compressed by turning the micrometer screw. The polystyrene content was determined from the absorbance at 269 mμ, as measured on a Cary model 11 or 14 recording spectrophotometer.

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