It remains elusive about the modification selection of polymers under coupled fields prevalent in actual polymer processing. In this work, we investigated the effect of pressure, flow, and temperature (the three most essential parameters in polymer processing) on the polymorphic behavior of syndiotactic polystyrene (sPS) that is a representative model polymer due to its complicated yet diverse modifications. Unlike the β crystal usually observed under pressure or flow alone, the α crystal was induced with the coupling of pressure and flow. The critical shear rate for the formation of α crystals showed a negative dependence on the imposed pressure. Such a promotion became more pronounced at lower crystallization temperature. The phase diagram for the formation of α/β crystals was drawn with respect to three coupled variables for the first time. There was a strong synergy between pressure and shear on the formation of α crystals, where lowering the temperature intensified this effect. The exclusive formation of α crystals was attributed to the enhanced nucleation competitiveness under high pressure and at low T_c and the orientation of chains induced by flow, where pressure and T_c played an essential part by slowing down the orientation relaxation. Our current effort provides a deep insight into polymorphism selection of sPS under melt processing-related conditions by which the structure manipulation can be directed.

中文翻译：

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在压力、流量和温度的耦合下促进间聚聚苯乙烯多晶型选择中α晶体的形成

在实际聚合物加工中普遍存在的耦合场下聚合物的改性选择仍然难以捉摸。在这项工作中，我们研究了压力、流量和温度（聚合物加工中三个最重要的参数）对间规聚苯乙烯 (sPS) 的多晶型行为的影响，间规聚苯乙烯 (sPS) 是一种具有代表性的模型聚合物，由于其复杂而多样的改性。与通常仅在压力或流动下观察到的β晶体不同，α晶体是通过压力和流动的耦合诱导的。形成α晶体的临界剪切速率与施加的压力呈负相关。这种促进在较低的结晶温度下变得更加明显。首次绘制了关于三个耦合变量的α/β晶体形成的相图。压力和剪切力对α晶体的形成有很强的协同作用，降低温度会增强这种作用。α 晶体的专有形成归因于在高压和低压下增强的成核竞争力T _c和流动引起的链取向，其中压力和T _c通过减缓取向弛豫发挥了重要作用。我们目前的努力提供了对熔融加工相关条件下 sPS 多态性选择的深入了解，通过这些条件可以指导结构操作。