Crystal structure and crystalline morphology of poly(hexamethylene trans-1,4-cyclohexane dicarboxylate)

The crystal structure of poly (hexamethylene trans-1, 4-cyclohexane dicarboxylate) (PHCE) was determined by X-ray fiber diffraction. Only one crystal form was observed, independent of the crystallization condition. The PHCE has a triclinic unit cell with the space group P1 ̅. The cell parameters are: a = 5.47 Å, b = 7.36 Å, c = 15.95 Å, α = 141.14°, β = 113.69°, γ = 60.70°. One chain passes through a unit cell, resulting in a crystal density of 1.203 g/cm3. To study the crystal habit, the morphology of PHCE films was studied by imaging techniques. Depending on film thickness and crystallization temperature, the morphology varied from single crystals, S-shaped crystals, branched single-layer bent crystals, branched multilayer bent single crystals, and spherulites. By investigating the crystal growth rates, two scenarios were observed, characterized by diffusion-controlled growth or secondary nucleation. The interplay between crystal bending and chain tilting was investigated by electron diffraction.