Branched polymers stress relaxation is at the center to their function as viscosity modifiers, though the fundamentals that underlie the correlation between the polymer topology and their impact on viscosity remains an open question. Here, the stress relaxation of short, branched polyethylene comb polymer melts is studied by molecular dynamics simulations. A coarse-grained model where four methylene groups constitute one bead is used, and the results are transposed to the atomistic level. For arms of length comparable to entanglement length n_e of the linear polymer, we show that while increasing the number of branches with the same arm length decreases the plateau modulus, the terminal diffusive time does not change significantly. Increasing the arm length decreases the plateau modulus and increases the terminal time. As arms shorter than n_e relax by the entanglement time, both the chain mobility and stress relaxation can be described by reptation of the backbone with an increased tube diameter and an increased friction coefficient; or in other words, the branches act as a solvent.

Graphic Abstract

中文翻译：

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梳型聚合物熔体的应力松弛

支链聚合物应力松弛是其作为粘度调节剂的核心功能，尽管聚合物拓扑结构及其对粘度影响之间相关性的基础仍然是一个悬而未决的问题。在这里，通过分子动力学模拟研究了短支化聚乙烯梳状聚合物熔体的应力松弛。使用其中四个亚甲基构成一个珠的粗粒度模型，并将结果转换为原子级。对于长度等于缠结长度n _e的臂对于线性聚合物，我们发现虽然在相同臂长的情况下增加支链数会降低平稳模量，但末端扩散时间不会明显改变。臂长的增加会降低平台模量，并增加终端时间。当比n _e短的臂在缠结时间内松弛时，链的运动性和应力松弛都可以通过增加骨架直径和增大摩擦系数的骨架来描述。换句话说，支链起溶剂的作用。

图形摘要