N. Jourdan et al., STRUCTURAL STUDY OF LINEAR POLYESTERS .1. CRYSTAL-STRUCTURE OF POLY(TRIMETHYLENE SEBACATE), ESTABLISHED FROM X-RAY AND ELECTRON-DIFFRACTIONDATA, Macromolecules, 28(24), 1995, pp. 8086-8091
The crystal structure of the poly(trimethylene sebacate) polyester, PE
(3,8), was arrived at through a combined analysis of its electron, pow
der, and fiber diffraction patterns. PE(3,8) has an orthorhombic unit
cell of dimensions a = 5.032, b = 7.532, and c = 31.33 Angstrom (fiber
axis) and belongs to the P2(1)2(1)2(1) space group. There are two che
mical units per fiber repeat and the two chains within the unit cell a
re positioned on 2(1) screw axes, parallel to the c direction. The fib
er repeat is 2.50 Angstrom shorter than that for an all-trans conforma
tion. The non-trans torsion angles are located in the glycolic moiety
of the chemical repeat. A conformational analysis revealed several ene
rgy minima which, after minimization, yielded 18 potentially acceptabl
e conformations. The most likely conformation for the -O-(CH2)(3)-O-fl
exible segment of the polyester is g(+)tg(-)g(+), while the sebacate g
roup is in the all-trans conformation. The final structure and its ori
entation and position within the unit cell were arrived at by a compar
ison of the theoretical and experimental intensities recorded on singl
e crystal electron diffractograms and on X-ray diffraction powder patt
erns. The proposed structure;is confirmed by the small values taken by
the conventional R factor, R = 0.108 for 19 powder diffraction arcs a
nd R = 0.136 (R(w) = 0.096) for 12 independent spots on the electron d
iffraction recording.