Electronhyphen;diffraction investigation of single crystals of ggr;hyphen;poly (vinylidene fluoride) grown from the melt has revealed streaking of 0k0 reflections. The threehyphen;dimensional structure of the spikes was studied by specimen tilting during electron diffraction; streaking is maximized in thebast;cast; view and disappears in theaast;bast; view, indicating that the reciprocalhyphen;lattice spikes are directed parallel toc. After exclusion of effects associated with the shape transform of our ggr; crystals, the streaks are attributed to stacking faults parallel to theabplane; such faults are consistent with incorporation of agr; sequences as defects within ggr; chains during crystallization. Conformational changes between agr; and ggr; arrangements are examined using a number of models. The simplest motions (fliphyphen;flops or rigid crankshafts) require simultaneous rotation about two noncolinear axes and are, therefore, less favored than mechanisms involving flexible chain motions as described in this report.
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