EPITAXIAL CRYSTALLIZATION AND AFM INVESTIGATION OF A FRUSTRATED POLYMER STRUCTURE - ISOTACTIC POLY(PROPYLENE), BETA-PHASE

The metastable phase of isotactic polypropylene (beta iPP) is crystall ized epitaxially on two specific nucleating agents: gamma-quinacridone and dicyclohexylterephthalamide (DCHT). The resulting thin films are investigated by electron microscopy and atomic force microscopy. Epita xial crystallization yields a biaxially oriented sample of beta iPP, a n orientation which cannot be achieved by mechanical means due to the beta --> alpha phase transformation on stretching. Electron diffractio n indicates that the beta iPP (110) plane is the contact face involved in both epitaxies. AFM investigation with methyl group resolution rev eals a lateral periodicity of 19 Angstrom in that (110) contact face, which corresponds to the distance between three chains and is a tradem ark indicator of the frustrated packing of beta iPP. AFM further indic ates some variability of the surface pattern, suggesting that two diff erent frustrated structures may coexist in the surface layer; this, in turn, suggests some type of surface reconstruction. Structural requir ements that efficient beta iPP nucleating agents must meet are analyze d.