The crystal structure analysis of a cycloaliphatic polyester, poly(butylene-trans-1,4-cyclohexane dicarboxylate) (PBCE), is performed by X-ray fiber diffraction. Depending on the cooling condition, two crystal forms are identified (α and β). The α form is obtained by slow cooling from the melt, while the β form is generated during fast cooling. The α form has a triclinic unit cell with a P1̅ space group, with parameters of a = 5.46 Å, b = 6.89 Å, c = 13.51 Å, α = 138.37°, β = 109.42°, and γ = 63.30°. One PBCE chain is located in the unit cell with the chair conformation aliphatic rings and all-trans-conformation methylene segmental parts. The structural transition and polymorphic transition during the heating and stretching process of PBCE are investigated by in-situ X-ray scattering. During heating, both the α and β forms show significant lattice distortion and eventually transform directly into the isotropic melt state. The volumetric thermal expansion coefficient of the PBCE α form was twice that of its unsaturated analogue, poly(butylene terephthalate). On the other hand, the irreversible β–α transition occurs during stretching, indicating that the β form is a metastable phase.

中文翻译：

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聚(反式1,4-环己烷二甲酸丁二醇酯)的晶体结构和多晶型

通过 X 射线纤维衍射进行脂环族聚酯聚（反式-1,4-环己烷二甲酸丁二醇酯）（PBCE）的晶体结构分析。根据冷却条件，可鉴定出两种晶型（α 和 β）。 α型是通过熔体缓慢冷却获得的，而β型是在快速冷却过程中生成的。 α 型具有P 1̅ 空间群的三斜晶胞，参数为a = 5.46 Å、b = 6.89 Å、c = 13.51 Å、α = 138.37°、β = 109.42° 和 γ = 63.30°。一条PBCE链位于具有椅式构象脂肪环和全反式构象亚甲基片段部分的晶胞中。通过原位X射线散射研究了PBCE在加热和拉伸过程中的结构转变和多晶型转变。在加热过程中，α和β形式均表现出明显的晶格畸变，并最终直接转变为各向同性熔融态。 PBCE α 形式的体积热膨胀系数是其不饱和类似物聚对苯二甲酸丁二醇酯的两倍。另一方面，拉伸过程中发生不可逆的β-α转变，表明β形式是亚稳态相。