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 polydisper se polymer samples. Due to polydispersity the spin-labeled polymer mol ecules have a wide range of molecular weight, and this is also true fo r the matrix polymer molecules. This generally leads to a wide distrib ution in diffusion coefficients of the spin-labeled molecules. The wor k presented here includes a theoretical derivation of the new DID-ESR method in the presence of polydispersity, plus its first application f or measuring translational diffusion coefficients of liquid crystallin e (LC) polymer melts. This includes a detailed analysis of the reliabi lity of the method, the proper interpretation of average diffusion coe fficients, and how the molecular weight dependence of the diffusion co efficient may be obtained from even a single experiment on a sample wi th wide polydispersity. The results obtained by this method are compar ed with those from the FRES (forward recoil spectroscopy) technique on the same model system, but for higher molecular weight, and account i s taken of the differences in the two methods. Future experiments to f urther study LC polymer diffusion mechanisms are proposed.