The Crystal Structure of Poly(ethylene furanoate)

The crystal structure of poly(ethylene furanoate) (PEF) has been determined using X-ray fiber diffraction (XRFD) combined with molecular modeling. Analysis of the XRFD data suggested the space group was P21, with a monoclinic unit cell where a = 5.784 Å, b = 6.780 Å, c = 20.296 Å, and γ = 103.3°, giving a calculated unit cell density of the crystal phase was 1.562 g/cm3. The repeating unit consisted of two monomers related to each other by a 21 screw axis. It was also shown that two PEF chains were included in each unit cell, with the center-chain being staggered with respect to the corner-chain. Polymer chains were found to be near planar, although careful evaluation showed that the best fit with the data required the cell to contain a mixture of 3/12 and 5/12 center-chain-staggering.