Crystal Structure and Morphology of Poly(11-undecalactone) Solution-Grown Single Crystals

Abstract

Solution-grown lamellar single crystals of poly(11-undecalactone) (PUDL) have been prepared in 1-hexanol. The lozenge and hexagonal-shaped single crystals were grown simultaneously, and these crystals gave well-resolved electron diffraction diagrams from which the orthogonal reciprocal lattice with the parameters a* = 1.346 nm-1, b* = 2.004 nm-1, and γ* = 90° could be determined. The growth faces of both crystals were considered as mainly {110}, and the average chain-folding direction was parallel to these growth planes, suggesting that the hexagonal crystal has pseudohexagonal symmetry but actual orthogonal packing of the PUDL molecules. The diffraction analysis combined with X-ray and electron diffraction diagrams indicated that PUDL crystallized in the orthorhombic system which had the lattice parameters of a = 0.743 ± 0.001 nm, b = 0.499 ± 0.001 nm, and c(chain axis) = 1.519 ± 0.003 nm. There are two chains per unit cell, which existed in an antiparallel arrangement. The fiber repeat distance is appropriate for an all-trans backbone conformation for the straight stems. Molecular packing of this structure has been studied in detail, taking into account both diffraction data and energy calculations. The setting angles, with respect to a axis, were 59° for the corner and center chains according to intensity measurements and structure factor calculations. A final model was obtained to yield R = 0.173 with X-ray diffraction data and R = 0.152 with electron diffraction data. A brief comparison is also made with related polymer structures.