Biexponential 13C spin–lattice relaxation behavior of the crystalline region of ethylene copolymers and its origin

Abstract

In this work, two series of ethylene–dimethylaminoethylmethacrylate (EDAM) and ethylene–methyl acrylate copolymers (EMA) with different comonomer content were studied by high-resolution solid-state 13C NMR spectroscopy. Biexponential 13C spin–lattice relaxation behaviors of the crystalline region were observed for all copolymer samples either melt-quenched or isothermally crystallized. The relative content of the shorter 13C T 1 component to that of the longer 13C T 1 component was found to increase with comonomer content. By employing a new pulse sequence which can be considered as a combination of Goldman–Shen's and Torchia's pulse sequences, it was demonstrated that the shorter 13C T 1 component is corresponding to the intermediate part of the crystalline region. The thickness of the intermediate part is estimated to be about 0.85 nm.