Electron and X-ray diffraction study on poly(4-hydroxybutyrate)

Lozenge-shaped poly(4-hydroxybutyrate) single crystals, showing spiral growth, were obtained from a dilute ethanol solution. The crystals gave well-resolved electron diffraction patterns from which the reciprocal lattice parameters a∗=1.305 nm−1, b∗=2.085 nm−1 and γ∗=90° could be determined. Systematic absences occurred at every odd reflection along the two orthogonal axes a∗ and b∗. Therefore, the P(4HB) electron diffraction pattern is consistent with a p2gg two-dimensional symmetry. The unit cell of P(4HB) is orthorhombic with space group P212121 and lattice constants a=0.775±0.002 nm, b=0.477±0.002 nm and c (fiber axis)=1.199±0.002 nm, which is determined by X-ray fiber diagram of a stretched-annealed film combined with electron diffraction patterns of single crystals. There are two chains in one unit cell, which exist in antiparallel arrangement.