Crystal Structure of a γ Form of Poly(butylene trans -1,4-cyclohexane dicarboxylate) Grown from Solution

Poly(butylene trans-1,4-cyclohexane dicarboxylate) (PBCE) is a type of sustainable polyester, with favorable thermal, mechanical, and biodegradation properties. As a semicrystalline polymer, PBCE has been reported to exhibit two crystal modifications (α, β) when crystallized from the bulk. In this work, single crystals of PBCE were grown in solution by a self-seeding method. By combining electron diffraction with molecular simulation, a different crystal structure was identified. This crystal modification, designated as the γ form, adopts a triclinic system with space group P1– and chain symmetry ti, with unit-cell parameters a = 6.19 Å, b = 5.91 Å, c = 11.52 Å, α = 54.73°, β = 73.09°, and γ = 62.69°. The structural model was further verified by powder X-ray diffraction. The γ form was found to undergo an irreversible transition to the β form upon heating, indicating that the γ form is thermodynamically less stable than the β form. These findings extend the current understanding of the crystal structure and transitions of alicyclic polyester materials.