Helical chain assembly has a great influence on the physical properties of polymeric materials. It has been known that the newly developed, anisotropic nanostructure of polymers in nanoconfinement is significantly different from that in the bulk. In this research, we demonstrate 3₁ helical chain assembly in isotactic polypropylene (i-PP) under 2D confinement in two main crystalline phases: α- and γ-phase crystals. Samples synthesized with a metallocene catalyst yield the γ-phases. We found the integrated assembly of the threefold helical chains in both α- and γ-phase crystals under confinement. The helical chain packing at the “four-methyl growth face” prefers to be aligned with the rod long axis. Furthermore, we demonstrate two unit-cell orientations of the γ-phase crystal in which the c_γ-axis is consistent with the radial or axial direction under cylindrical confinement. The formation mechanism for the radial γ-phase crystals lies in that the rapid growth direction of the α-phase lamellar from which the γ-phase crystals are epitaxially grown is kinetically favored to be consistent with the rod long axis. More interestingly, the new axial γ-phase crystal reflects a complex, multi-fold structural ensemble of threefold helices in two phases via epitaxial relationships.

中文翻译：

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圆柱约束下全同立构聚丙烯分子链的结构整合

螺旋链组装对聚合物材料的物理性能有很大的影响。众所周知，纳米约束中聚合物的新开发的各向异性纳米结构与本体中的显着不同。在这项研究中，我们展示了在等规聚丙烯（i-PP）中在两个主要结晶相（α和γ相）的二维约束下3 ₁螺旋链组装。用茂金属催化剂合成的样品产生γ相。我们发现在约束条件下，α相和γ相晶体中三重螺旋链的整合组装。“四甲基生长面”处的螺旋链堆积更倾向于与杆的长轴对齐。此外，我们展示了γ相晶体的两个晶胞取向，其中c在圆柱约束下，_γ轴与径向或轴向一致。放射状γ相晶体的形成机理在于，外延生长γ相晶体的α相薄片的快速生长方向在动力学上有利于与棒长轴一致。更有趣的是，新的轴向γ相晶体通过外延关系在两个相中反映了一个复杂的，多重折叠的三重螺旋结构整体。