New solutions to the problems of chain orientation and chain continuity in structure analysis of fibrous polymers. A reconsideration of the structure of polyisobutene.

Two points of general interest in structural refinement of polymers based on internal coordinates are discussed: the chain orientation and the chain continuity. Using a proprietary computer program, based on revised approaches to these questions, the structure of polyisobutene has been reconsidered, using new X-ray diffraction measurements (Fuji image plate) and performing a structure refinement based on internal coordinates. Three refinement schemes, with a decreasing number of degrees of freedom, have been considered, with the conclusion that the distortion from the 83 regular helix, claimed by Tadokoro [(1979). Structure of Crystalline Polymers, p. 136. New York: Wiley-Interscience], is confirmed, though lower than supposed. The new procedures implemented for chain orientation and chain continuity work excellently.