Abstract Relation between cooperativity and fragility of segmental dynamics is a crucial issue in elucidating the viscous slowdown of supercooled polymer liquids. The experimental results previously reported for p-substituted polystyrenes (PS derivatives) and poly(methacrylic acid ester)s (PMAEs) are reanalyzed based on a cooperative string model that was recently proposed on the assumption that the cooperatively rearranging region (CRR) takes a string shape. The analysis shows clear positive correlations between the cooperativity and fragility for both the polymer systems. To investigate the temperature dependence of the cooperativity, we proposed a simple model where the size of the CRR is controlled by its surface area (surface-controlled CRR model: SCC model). The analysis based on this model suggests that for many of the polymers, the CRR takes a non-compact shape with high surface-to-volume ratio. The configurational entropy of the smallest CRR is also evaluated from calorimetry based on the SCC model, and it is revealed to depend on the segmental relaxation time very weakly compared with that for typical non-polymeric glass-formers.

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过冷聚合物材料动力学的协同性及其从表面控制模型预测的温度依赖性

摘要 链段动力学的协同性与脆性之间的关系是阐明过冷聚合物液体粘性减速的关键问题。先前报道的对取代聚苯乙烯（PS 衍生物）和聚（甲基丙烯酸酯）（PMAE）的实验结果基于最近提出的协同串模型重新分析，该模型假设协同重排区域（CRR）采用字符串形状。分析显示两种聚合物系统的协同性和脆性之间存在明显的正相关。为了研究协同性的温度依赖性，我们提出了一个简单的模型，其中 CRR 的大小由其表面积控制（表面控制的 CRR 模型：SCC 模型）。基于该模型的分析表明，对于许多聚合物，CRR 采用具有高表面积与体积比的非紧凑形状。最小 CRR 的构型熵也由基于 SCC 模型的量热法评估，与典型的非聚合物玻璃形成剂相比，它显示出非常弱地依赖于分段弛豫时间。