Evidence for helical structures in poly(1-olefin sulfones) by transmission electron microscopy

Transmission electron microscope images were obtained of fractions of poly(1-tetradecene sulfone) and poly(cyclohexene sulfone) cast from very dilute solutions (0.007%, wt/vol) and rapidly freeze-dried on a mica surface. The samples were then vertically platinum-carbon (Pt-C) replicated with 9 +/- 0.3-A Pt-C and held together with 128 A of electron-transparent evaporated carbon. The Pt-C coating enlarges the molecular chain diameters by approximately 5 A, so that a single polysulfone chain has an apparent diameter of 9-12 A in the transmission electron microscope. Poly(1-tetradecene sulfone) forms short helical regions that show irregular helical turns of pitch 7-18 A, two to eight turns long with apparent helix diameters of 16-22 A. The n-C12H25 side chains were not obvious on the helices, but a few were visible on extended chain sections. In contrast, poly(cyclohexene sulfone) appears as a collection of Pt-C-coated single chains 10-12 A in diameter with no side-chain projections. The presence and absence of helical regions in these freeze-dried polysulfones thus reflects their solution conformations as long ago inferred on the basis of dielectric measurements.