Translational Diffusion in Polydisperse Polymer Samples Studied by Dynamic Imaging of Diffusion ESR

A new methodology utilizing the DID-ESR (dynamic imaging of diffusion by ESR) technique has been developed for its application to polydisperse polymer samples. Due to polydispersity the spin-labeled polymer molecules have a wide range of molecular weight, and this is also true for the matrix polymer molecules. This generally leads to a wide distribution in diffusion coefficients of the spin-labeled molecules. The work presented here includes a theoretical derivation of the new DID-ESR method in the presence of polydispersity, plus its first application for measuring translational diffusion coefficients of liquid crystalline (LC) polymer melts. This includes a detailed analysis of the reliability of the method, the proper interpretation of average diffusion coefficients, and how the molecular weight dependence of the diffusion coefficient may be obtained from even a single experiment on a sample with wide polydispersity. The results obtained by this method are compared with those from the FRES (forward recoil spectroscopy) technique on the same model system, but for higher molecular weight, and account is taken of the differences in the two methods. Future experiments to further study LC polymer diffusion mechanisms are proposed. 1