Spectrophotometric determination of the styrene content of butadiene–styrene copolymers

The ultraviolet absorption of polystyrene, with maximum absorption at 262 mμ, is due to the presence of phenyl residues in the polymer. The specific extinction coefficient is constant, i.e., independent of the molecular weight of the polymer. This shows that the extinction of the phenyl residues is additive. On the basis of this fact, it is shown that the styrene content of a butadiene–styrene copolymer (such as GR‐S rubber) can be determined by ultraviolet spectrophotometry. The relative precision of the determination is about 1%, the probable relative accuracy is about 3%.