Qualitative and quantitative analysis of solid state free induction decay (H-1 NMR) curves using a combination of the methods of Gardner and Prony: Isotactic polypropylene as a case study

Abstract

A combination of the methods of Gardner and Prony is used for the qualitative and quantitative analysis of solid-state free induction decay (H-1 NMR) curves of isotactic polypropylene, recorded at 40, 60, 80, and 100 degrees C at constant time intervals. These multicomponent decay curves contain information about the physicochemical structure of the polymer sample: each component is characterized by a specific model function containing a spin-spin relaxation time T-2 and an intensity as parameters depending on the properties and amount of the corresponding phase. The number of phases is still an unanswered question. Each FID curve is analyzed by using an improved method of Gardner ct al. in order to reveal the number of phases, to predict the best fitted model function, and to estimate the T-2 value of each component. The quantification of the parameters (T2 and fraction) with Prony's improved method is discussed. The presence of an intermediate phase is unambiguously demonstrated. The influence of temperature on the physicochemical structure of the polymer is examined. The precision of the computed parameters is discussed for the analyses of three consecutively measured FID curves of isotactic polypropylene at 60 degrees C.