Typical Polymers Studied By Solid-State NMR

In this dissertation, various solid-state NMR spectra and NMR relaxation measurements, together with XRD and DSC, have been used to elucidate the structures and molecular dynamics in two typical polymers.Poly (ethylene-co-vinyl acetate) (EVA) is one of the most important ethylene copolymers. It has been found that the phase structure of EVA is very complex and there are five physically distinct components in all present EVA samples. Besides the familiar immobile orthorhombic and monoclinic crystalline phases as detected in PE, a third crystalline phase-mobile crystalline phase SOCP (possibly the rotator phase) was detected by solid-state NMR and then confirmed by DSC. Such a third crystalline phase has not only the well-defined melting point of its own, but also has different molecular mobility and different chemical shift from the orthorhombic phase (LOCP). In addition, the amorphous phase also contains two components: an anisotropic interfacial amorphous phase and a melt-like amorphous phase. Then, we investigated in more detail the chain dynamics in crystalline phase and the low-temperature freezing behavior of amorphous phase in the EVA. And we found that the motion of CH2 chain in rigid orthorhombic phase is the 180°filp-flop motion around its chain axis, accompanied by the simultaneous hopping motion along its axis, which causes the chain diffusion between orthorhombic and amorphous phases. This chain diffusion is evidenced by NOE measurement. Furthermore, we confirmed that the chain diffusion between two phases was restricted rather than free. The low-temperature freezing behaviors of the two amorphous components are different: below...