Hard elastic fibers. I. Four-component analysis of the NMR spectra of isotactic polypropylene

Abstract

Abstract Broad-line NMR spectra have been recorded from polypropylene hard elastic fibers in the temperature range from −175°C to 25°C and in the strain range 0 to 60% in an atmosphere of N2 at −60°C and air at 25°C. The analysis was carried out by using a method developed previously for polyethylene and paraffins. Four components, α, β1, β2, γ of different proton mobility can be separated uniquely: The αare rigid (crystalline) protons, β1 are amorphous chain segments of hindered mobility, and the β2 and γ are segments undergoing micro-Brownian motion. Polypropylene affords an unique possibility to study structural changes of hard elastic fibers under strain, because the CH3 groups in the amorphous regions stay mobile at least till −175°C, far below the γ process, contrary to the ─CH─CH2─ skeletal protons. With 60% strain, at temperatures below the range of the γ process, 12% of the protons change over from the crystalline to the amorphous component and become crystalline again only at higher temperatures.