Electron crystallography of linear polymers: direct structure analysis of poly(epsilon-carprolactone)

Three-dimensional electron diffraction intensity data from poly(epsilon-caprolactone) are used for an ab initio phase determination based on the probabilistic estimate of three- and four-phase structure invariants in space group P212121. From the initial phase set of 30 reflections (two of which are incorrect) of the 47 in the total data set, computed electrostatic potential maps produce a recognizable structure that can be refined by Fourier techniques and atomic displacement. The final structure (R = 0.21), which is very similar to one found in an earlier fiber x-ray study, shows that the polymer chain must adopt a nonplanar conformation around the ester linkage.