THE STRUCTURE OF THE MESOMORPHIC PHASE OF QUENCHED ISOTACTIC POLYPROPYLENE

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 angstrom in size, that have the alpha-monoclinic crystal form (a = 6.67 +/- 0.01, b = 20.89 +/- 0.05, c = 6.48 +/- 0.01 angstrom, beta = 98.4 +/- 0.6-degrees-). Regions of lower crystalline order are also observed which, according to micro-micro diffraction, also possess the alpha-monoclinic crystal structure but with substantially larger unit cell constants (a = 7.03 +/- 0.01, b = 21.1 +/- 0.1, c = 6.47 +/- 0.02 angstrom, beta = 99 +/- 2-degrees-). 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-degrees-C, that correspond to the formation and subsequent perfection of the microcrystalline regions observed by STEM dark field.