Turbidimetric titration method for determining solubility distributions of polymers

A turbidimetric titration method for determining solubility distributions (which are closely related to molecular weight distributions) has been developed. In this method, polymer is precipitated from its solution by addition of a nonsolvent of the same refractive index as that of the solvent. The precipitating particles of swollen polymer are allowed to agglomerate until the turbidity reaches a maximum. It is shown by the use of light‐scattering theory that under these conditions the concentration of polymer which is precipitated can be calculated from the maximum turbidity on an absolute basis. The effects of particle size and particle size distribution are discussed. The method was tested by using polystyrene, and is shown to be accurate. In principle the method is applicable to most kinds of polymers.