Crystal Structure Determination of Poly(1,4-trans-cylcohexylenedimethylene 2,6-naphthalate) by X-ray Diffraction and Molecular Modeling

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The crystal structure of poly(1,4-trans-cyclohexylenedimethylene 2,6-naphthalate) (PtCN) was identified by X-ray diffraction and molecular modeling, and the effect of the trans/cis ratio of 1,4-cyclohexylenedimethyl unit on the crystal structure of PtCN was also investigated. The unit cell of PtCN is found to be a triclinic with dimensions of a = 0.638 nm, b = 0.657 nm, c = 1.661 nm, α = 83.41°, β = 43.92°, and γ = 106.02°, and the space group of the crystal is identified as P1̄. The calculated crystal density of 1.313 g/cm3 indicates that there is one repeating unit in a unit cell. The crystal structure of PtCN was also determined by using the molecular modeling technique and then confirmed by comparing the calculated structure factors with the ones obtained from the X-ray fiber diagram. The flexible unit, a 1,4-trans-cyclohexylenedimethoyl group [−O−CH2−(C6H10)−CH2−O−] in the PtCN backbone, is in the conformation of (t ± gt t (g, gauche; t, trans), and the naphthalene rings are in a face-to-face arrangement. It was observed that the crystal structures of polymers containing above 70% 1,4-trans-cyclohexylenedimethyl groups are nearly the same as that of the crystal structure of PtCN.