Abstract
A variety of solid‐state NMR techniques were used to characterize the chain dynamics, miscibility and the micro‐phase structure of a polypropylene (PP) in‐reactor alloy system. The alloy was physically separated into three fractions, and the molecular dynamics and relaxation behavior of the pure fractions was then compared with the components in the alloy to achieve comprehensive understanding of the phase structure of the PP in‐reactor alloy. The miscibility among different components of the alloy was studied by the rotational frame spin‐lattice relaxation time. Proton spin‐diffusion methods were used to quantify the domain thicknesses of different regions in the alloy. The results show that the alloy is composed of three phases, namely, a homo‐polyethylene (HPE) matrix, a homo‐polypropylene (HPP) dispersed phase, and a linear low‐density polyethylene (LLDPE) interphase. The thickness of the LLDPE interphase is estimated to be 7.7 nm at room temperature, and changes dramatically with temperature. Finally, based on all the solid‐state NMR results, a model for the micro‐phase‐structure of the PP in‐reactor alloy is proposed, and a correlation between the micro‐phase structure and the excellent mechanical property is established.
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