A high-molecular-weight polypropylene (Mw= 83 000, Mw/M.= 3.0) has been crystallized isothermally as a function of pressure at a constant supercooling of 50°C. Wide-angle X-ray diffraction (WAXD) shows that the X-ray diffraction spectrum of the 7 phase is identical to that reported for low-molecular-weight polymers, with the exception that the peaks are broader. Calculations of the y content using WAXD show the nearly 100% 7 phase is formed at 2 kbar, but a mixture of 7 and ~ crystals are formed at lower crystallization pressures. Small-angle X-ray scattering (SAXS) studies show that 7 lamellae are approximately one-half the thickness of ~ lamellae produced at an equivalent supercooling. Morphological studies conducted using transmission electron microscopy of carbon replicas of permanganically etched surfaces confirm the thin nature of the lamellae and demonstrate their inherent waviness. Unlike ~ crystals, 7 lamellae do not form cross-hatched textures. A model is proposed, involving 7/ct lamellae and epitaxy during the growth process, to account for all the observable morphological data.
Посилання на статтю:
The gamma phase of high-molecularweight polypropylene: 1. Morphological aspects / R. Anderson Campbell and Paul J. Phillips // Polymer. – 1993. – Vol 34. – P. 4809-4816.