Solid‐state NMR characterizations on phase structures and molecular dynamics of poly(ethylene‐co‐vinyl acetate)

Abstract

Solid-state nuclear magnetic resonance spectroscopy and relaxation measurements, together with DSC, have been used to elucidate the structures and molecular dynamics in poly(ethylene-co-vinyl acetate) (EVA). It has been found that besides immobile orthorhombic and monoclinic crystalline phases, the third mobile crystalline phase (possibly the phase) of a considerable amount (36% of total crystalline phases) appears in the EVA samples, which forms during room-temperature aging as a result of the secondary crystallization and melts at temperature somewhat higher than room temperature. Such a mobile crystalline phase has not only the well-defined chemical shift of its own, but also has different molecular mobility from the orthorhombic phase. The mobile crystalline phase is characterized by the rapid relaxation of the longitudinal magnetization, which is caused by conventional spin-lattice relaxation, while the slow relaxation of the longitudinal magnetization occurring in the orthorhombic phase is originated from the chain diffusion. In addition, the amorphous phase also contains two components: an interfacial amorphous phase and a melt-like amorphous phase.

Effect of hot air aging on the properties of ethylene‐vinyl acetate copolymer and ethylene‐acrylic acid copolymer blends

“…However, no well-resolved reflections from monoclinic phase and SOCP phase were detected by WAXD at room temperature. 30,31 This is conformed by our experiment results of WAXD as shown in Table III, the grain size L hkl (Å ) of (110) crystal plane of various EAA/ EVA blends is listed. It is observed that the L hkl of (110) crystal plane has the same tendency to increase with the hot air aging time, which indicates the completion of secondary crystallization.…”

Review and critical analysis of the morphology of random ionomers across many length scales

“…From a critical perspective, there does not seem to be any piece or pieces of evidence that could not be explained either by water absorption and/or slow crystallization of ethylene segments. Further, this same peak at $508C that grows with room temperature annealing occurs in both unneutralized acid copolymers [112] as well as other ethylene copolymers, [113][114][115], although the effect is not nearly as dramatic. The best way to prove that such a transition exists is to choose a system that cannot crystallize, and rigorously exclude water to eliminate these two possible explanations.…”

Quantitative NMR investigation on the low-temperature dissolution mechanism of chitin in NaOH/urea aqueous solution

“…For the spin 3/2 nucleus of 23 Na, the solid-state NMR signal of 23 Na was recorded with half of the liquid-state NMR 90°pulse length (i.e., 1.75 ls corresponding to 90°pulse length for central-selective excitation) (Causemann et al 2011). The 23 Na spinlattice relaxation time in the rotating frame (T 1q ) was measured using a spin-lock pulse sequence (Wang et al 2006).…”