Stimulated echo method for investigation of structural and dynamic characteristics of branched polymers

Abstract

The theory of stimulated echo (SE) without magnetic field gradient is proposed. The theory made it possible for the first time to establish a relationship between the stimulated echo signal and correlation function of molecular mobility. Signals of free induction decay (FID) and SE in polymer networks and branched polymers were modeled. The type of the correlation function at different average chain lengths N₀ between knots and different distribution functions of the knots was determined. A strong influence of the molecular weight distribution (MWD) on the type of the correlation function in polymer melts was shown. Two methods were proposed for the numerical determination of the correlation function from the observed FID and SE signals. These methods gave an information about the molecular mobility and topological structure in the samples of branched polymethyl methacrylates of different structures and various molecular weights.