Application of the flory‐mandelkern equation to individual unfractionated polymer samples

Abstract

A method is developed for the application of the Flory‐Mandelkern equation to the determination of the weight‐average molecular weights of individual, broad, unfractionated polymer samples. The method includes appropriate averaging of the sedimentation constants and of the intrinsic viscosity of an unfractionated polymer sample in a θ solution from the velocity sedimentation data. By means of the method, individual samples of polystyrene, poly(isooctyl methacrylate) and of the copolymer of styrene with 20% isooctyl methacrylate prepared under the same emulsion polymerization conditions from commercial monomers have been investigated. Appropriate θ solvents have been found by the Elias method. Equations for the dependence of the sedimentation constants and of the intrinsic viscosities in the θ solvents on the molecular weights have been established for the polymers without fractionation. Osmometric and light‐scattering measurements as well as Archibald experiments have shown that by the proposed method the molecular weight cut‐off effect is eliminated in the above equations and in the polydispersity parameter M_w/M_n. Molecular weight distributions have been determined for the polymer samples.