Relation between refractive index and density of polymer solutions

The relation between the fractive index n and the density ρ of a liquid mixture is formulated as where wi and Rsi are the weight fraction and the specific refraction, respectively, of component i. The calculation of the specific refraction of straight-chain polyethylene and polystyrene from data for pure compounds of low molecular weight is discussed. The result is applied to dilute solutions of polystyrene in toluene. The calculated values of (dp/dw)0 and (d2ρ/dw2)0 at three different temperatures are compared with measured values. The agreement is satisfactory.