Impact of Chain Orientation on the Melting of the α-Form of Isotactic Polypropylene,Macromolecules

当前位置： X-MOL 学术 › Macromolecules › 论文详情

Our official English website, www.x-mol.net, welcomes your feedback! (Note: you will need to create a separate account there.)

Impact of Chain Orientation on the Melting of the α-Form of Isotactic Polypropylene
Macromolecules ( IF 5.1 ) Pub Date : 2024-08-19 , DOI: 10.1021/acs.macromol.4c01333
Damilola Ojedeji ₁ , Manolis Doxastakis ₁

Affiliation

Isotactic polypropylene (iPP) exhibits polymorphism in the crystalline state that has long been leveraged to tune the material properties. It has been established that even the most prevailing α-iPP can exhibit significant variability with two distinct melting points T_m often attributed to α₁ and α₂ forms. Several structural models with specific ordering in chain orientations and correlations along the crystals have been proposed. Precise structural investigation relies on inverse modeling of diffraction patterns, but the impact of thermal history, a potential transition between the two forms, and any existence of multiple solutions challenge characterization. Recent detailed atomistic simulations offered a direct route to link postulated structural arrangements to melting transitions with studies focusing on the α₁ and β forms of iPP. In this study, we employ atomistic molecular dynamics to examine models of α₁ and α₂ with variable levels of ordering in terms of chain axis orientation. At rapid heating rates, we find high melting points that can differ by up to 30 K depending on the fraction of the material that follows the P2₁/c structural arrangement. To contrast systems in the absence of superheating, we assembled configurations with free surfaces as well as models of semicrystalline iPP. We report melting kinetics above T_m for the P2₁/c and Cc crystals and provide T_m estimates in agreement with literature data. In addition, our study provides valuable microscopic information about the dynamics of melting of α-iPP along specific directions.

中文翻译：

链取向对α型等规聚丙烯熔融的影响

等规聚丙烯 (iPP) 在结晶状态下表现出多晶型现象，长期以来一直被用来调节材料性能。已经确定的是，即使是最普遍的 α-iPP 也可以表现出显着的可变性，具有两个不同的熔点T _m通常归因于 α ₁和 α ₂形式。已经提出了几种具有特定链方向排序和沿晶体相关性的结构模型。精确的结构研究依赖于衍射图案的逆向建模，但热历史的影响、两种形式之间的潜在转变以及任何多种解决方案的存在都对表征提出了挑战。最近详细的原子模拟提供了一条将假设的结构排列与熔化转变联系起来的直接途径，研究重点是 iPP 的 α ₁和 β 形式。在本研究中，我们采用原子分子动力学来检查链轴方向有序程度不同的 α ₁和 α ₂模型。在快速加热速率下，我们发现熔点可能相差高达 30 K，具体取决于遵循P 2 ₁ / c结构排列的材料部分。为了对比没有过热的系统，我们组装了具有自由表面的配置以及半晶 iPP 模型。我们报告了P 2 ₁ / c和Cc晶体在T _m以上的熔化动力学，并提供了与文献数据一致的T _m估计值。此外，我们的研究提供了有关 α-iPP 沿特定方向熔化动力学的有价值的微观信息。

更新日期：2024-08-19

点击分享查看原文

点击收藏

阅读更多本刊新发论文本刊介绍/投稿指南