Jin Tianyi, Coley Connor W, Alexander-Katz Alfredo
Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States.
Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States.
ACS Macro Lett. 2023 Nov 21;12(11):1517-1522. doi: 10.1021/acsmacrolett.3c00553. Epub 2023 Oct 27.
We unveil a unified view on the effect of side chains on the glass transition temperatures () in polymer melts by using molecular dynamics simulations, density functional theory calculations, and available experimental data. We use acrylates as a model system and evaluate the effect of -alkyl side chains on . We find that backbone dihedral angle fluctuations follow established patterns due to sterics, as expected. However, we also find that the dihedral angle orthogonal to the backbone, which normally is neglected when discussing the effect on , introduces a secondary rotational degree of freedom which strongly impacts . These results are in agreement with experiments and generalize to multiple other polymer systems, as is demonstrated using available experimental data. Conversely, -alkyl pendant groups attached to the side group reduce . Our work establishes a coherent framework that unifies previously established trends, emphasizing the polarity and size effects of -alkyl chains on .
我们通过分子动力学模拟、密度泛函理论计算以及现有的实验数据，揭示了侧链对聚合物熔体玻璃化转变温度（）影响的统一观点。我们以丙烯酸酯为模型体系，评估 - 烷基侧链对的影响。正如预期的那样，我们发现主链二面角波动因空间位阻遵循既定模式。然而，我们还发现，在讨论对的影响时通常被忽略的与主链正交的二面角，引入了一个对有强烈影响的二级旋转自由度。这些结果与实验结果一致，并如利用现有实验数据所证明的那样，推广到多个其他聚合物体系。相反，连接到侧基上的 - 烷基侧基会降低。我们的工作建立了一个连贯的框架，统一了先前确立的趋势，强调了 - 烷基链对的极性和尺寸效应。
