Structural Studies of Polyesters. III. Crystal Structure of Poly-ε-caprolactone

Abstract

In the course of structural studies of aliphatic polyesters, the crystal structure of poly-ε-caprolactone, [–(CH2)5–CO–]n, was determined by interpretation of X-ray diffraction patterns. The crystallographic data are: a=7.47Å, b=4.98Å, c(fiber axis) =17.05Å, the orthorhombic space group P212121-D24, two molecular chains in the unit cell. The chain conformation of poly-ε-caprolactone is almost planar zigzag, but evidently deviates from the fully extended form, i.e., the CH2 sequences are planar but the plane of atoms of the ester group tilts slightly to the fiber axis. The molecular chains are arranged side by side in the same way as in polyethylene, but the carbonyl groups of the two chains in the unit cell are separated by an amount of 3/14c along the fiber axis.