Scanning transmission electron microscopy (STEM) dark field images reveal that within the essentially amorphous matrix of quench-cooled isotactic polypropylene (iPP) there exist microcrystalline regions, 100 to 200 A in size, that have the ~-monoclinic crystal form (a = 6.67 + 0.01, b =20.89 + 0.05, c= 6.48 +0.01 A, /~=98.4+0.6°). Regions of lower crystalline order are also observed which, according to micro-micro diffraction, also possess the c~-monoclinic crystal structure but with substantially larger unit cell constants (a = 7.03 ± 0.01, b = 2 i. 1 ± 0.1, c = 6.47 + 0.02 &, fl = 99 ± 2°). Differential scanning calorimetry studies indicate that during quench cooling to the glassy state iPP samples attain a low degree of crystalline order to an extent that depends on sample mass. Upon heating from the glassy state, these samples exhibit exothermic transitions, between - 15 and 120°C, that correspond to the formation and subsequent perfection of the microcrystalline regions observed by STEM dark field.
Посилання на статтю:
The structure of the mesomorphic phase of quenched isotactic polypropylene / V. Caldas and G. R. Brown and R. S. Nohr and J. G. MacDonald // Polymer. – 1994. – Vol 35. – P. 899-907.