Effect of molecular weight on the refractive increment of polyethylene and n‐alkanes

As in the case with other polymers previously reported, the values of the refractive index increment dn / dc of polyethylene and the n ‐alkanes change with molecular weight. Most of the variation may be understood by examination of the role of density in the Lorentz‐Lorenz mixing equation for specific refractivity, R 12 = p 1 R 1 + P 2 R 2 used to calculate dn / dc . It may also be shown that as the absolute refractive index difference between solute and solvent becomes smaller, dn / dc becomes more sensitive to density change of the solute.