Scanning probe microscopy studies of isotactic polypropylene

• Published in: Ultramicroscopy 1992, Vol.42 (B), p.998-1003
• Main Authors: Zajac, G.W., Patterson, M.Q., Burrell, P.M., Metaxas, C.
• Format: Article
• Language: English
• Subjects: Applied sciences; Exact sciences and technology; Organic polymers; Physicochemistry of polymers; Properties and characterization; Structure, morphology and analysis
• ISSN: 0304-3991; 1879-2723
• DOI: 10.1016/0304-3991(92)90392-W

Scanning tunneling microscopy (STM) has been applied to the low- and high-resolution imaging of platinum-carbon-coated compression-molded isotactic polypropylene. At low magnifications we explore the spherulitic structure at the multi-micron scale. We find that the arms of the spherulite are composed of fine particles of the order of 1000 Å or less. At higher magnification within these smaller building blocks of the spherulite we find a lamellar structure composed of ordered arrays of domains with a distribution of sizes ranging from 100–250 Å in width and 500–1000 Å in length. At highest magnifications (50 nm) within these lamellae there are disordered and ordered regions. We have found the separation between characteristics features in the ordered regions to be 6–7 Å. This dimension is consistent with the separation of the pendant methyl groups between adjacent propylene monomer units in the isotactic form which is 6.6 Å from molecular modeling of the 3 1 helix. Processing of the STM digital linescan data of the ultra-microtomed samples by Fourier methods allows determination of the fractal dimension of the surface, which is representative of the bulk of the polymer. We find a fractal dimension ( D F) of the order of 1.32±0.05 for the commercial monoclinic α-polymorph i-PP. Similarly we find that the hexagonal β-polymorph of i-PP has a comparable D F = 1.23±0.05.