| Abstract
| - A preliminary crystal structure of syndiotactic poly(β-hydroxybutyrate), syn PHB, wasderived by using X-ray fiber and powder diffraction data in conjunction with computational modeling.The X-ray fiber diagram of highly stretched 69% syn PHB gave 23 reflections and a fiber repeat of 7.69Å. The diffraction trace of a powder syn PHB octamer provided well-resolved d spacing measurementsfrom which an orthorhombic unit cell of dimensions a = 7.84 Å, b = 14.90 Å, c = 7.69 Å is proposed.Conformational analysis with a syndiotactic diad repeat unit gave six low-energy chains with a fiberrepeat of 7.69 Å. The most favorable chain conformation had dihedral angles similar to isotactic PHBbut with a more extended integral helix. There is no energy preference for a right-handed or left-handedhelix. The P212121 space group was selected based on observed systematic absences, the tentativeorthorhombic unit cell, and favorable packing energies. The 21 symmetry in the chain direction is betweenneighboring sets of anticline packed helices of syn PHB. The structural model of syn PHB put forth isbased on favorable packing energies and a reasonable fit of simulated X-ray diffraction data with theexperimental results, which were further evaluated by a Rietveld analysis.
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