| Abstract: | In the use of refractometry for polymer characterization, it is shown that interpretation of data through use of a molar refractivity as defined by the Lorenz-Lorentz equation is more accurate than by use of the parachor. The disagreement between experimental and calculated values of the unit molar refractivity may be attributed to the arbitrary definition of the residue unit and the method of summation of group refractivities. In general, refractive index should depend on molecular weight and the conditions of polymerization, but this may depend on the dielectric properties and volume fraction of the domains comprising chain ends, initiator fragments, and free volume. The effect of polymer conformation on the molar refractivity of polyisoprene is found to be slight. For copolymer systems, there is a linear dependence of refractive index on weight fractional composition only where there is little order. The refractive index of a copolymer is not independent of the nature of the distribution of the residues along the chain. |
