The purpose of this work is to examine the approximation known as NMR rescaling, in which a polymer chain is replaced by a series of NMR submolecules. This coarse graining of the atomistic details makes various NMR calculations analytically possible. To test the accuracy of this approach a computer simulation of network chains consisting of freely jointed rigid rods has been carried out. The time dependence of the orientation of these rods relative to their network chain end-to-end vector has been recorded. From this the NMR Hahn spin echo sampled transverse relaxation and double quantum build-up and subsequent decay have been calculated. The simulated NMR signals are then compared with theoretical results derived from a rescaling approach. In this work we also test the Anderson-Weiss second moment approximation by using it to derive analytical expressions for the NMR signals for the simulated chains, which can then be directly compared with the simulated results. From this work it is shown that for a polymer melt above its glass transition temperature both rescaling and the second moment approximations are valid.
展开▼
