Thermorheological evidence and structure of heterogeneity in syndiotactic polypropylene melts with strong memory effects
Thermorheological evidence and structure of heterogeneity in syndiotactic polypropylene melts with strong memory effects
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具有强记忆效应的间规聚丙烯熔体的热流变证据和异质性结构
DOI：
10.1016/j.polymer.2021.123484
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发表时间：
2021-02
期刊：
影响因子：
4.6
通讯作者：
Feng Jiachun
中科院分区：
文献类型：
--
作者：
Wang Xinxin;Yi Jianjun;Yuan Yuan;Wang Li;Feng Jiachun
半结晶聚合物的记忆效应通常与自成核（SN）熔体的异质性有关。在这项研究中，系统地研究了间规聚丙烯（sPP）的强记忆效应和SN熔体的异质性，在很宽的温度范围内，甚至高于其平衡熔融温度（Tmo）。流变测量表明，SN 熔体表现出复杂的热流变行为，表明 SN 熔体中存在不均匀性。从相角(δ)与复数模量(G*)的流变图中，确定参数Δln G*δ=45°值，并用于比较SN熔体在加热过程中热流变复杂程度的变化。结果发现，随着Δln G*δ=45°值的增加，记忆效应促进结晶过程的效率提高，这表明记忆效应取决于SN熔体的不均匀性。样品纯化后，强烈的记忆效应仍然存在，说明这不是杂质的稳定作用造成的。广角/小角 X 射线散射和红外光谱的结果表明，我们研究的 SN 熔体中不存在部分残留微晶或规则的链构象。基于我们研究的 sPP 的复杂链结构，我们推测 sPP 熔体的异质性是由长可结晶序列和无规立构序列之间的分离引起的。
The memory effect of semi-crystalline polymers is usually related to the heterogeneity in self-nucleated (SN) melts. In this study, the strong memory effects of syndiotactic polypropylene (sPP) and the heterogeneity in SN melts were systematically investigated in a wide temperature range even above its equilibrium melting temperature (Tmo). The rheological measurements revealed that the SN melts exhibited thermorheologically complex behaviors, indicating that the presence of the heterogeneity in the SN melts. From the rheological plots of phase angle (δ) with the complex modulus (G*), the parameterΔln G*δ=45°values were determined and used to compare the change of the degree of thermorheological complexity in the SN melts during the heating process. It was found that the memory effect's efficiency to promote the crystallization process improved as the increase ofΔln G*δ=45°values, which suggested that the memory effect depended on the heterogeneity in the SN melts. After purifying the sample, the strong memory effect still existed, which indicated that it was not caused by the stabilization effect of impurities. The results of wide/small-angle X-ray scattering and infrared spectroscopy revealed that there were no partial residual crystallites or regular chain conformation in our investigated SN melts. Based on the complex chain structure of our investigated sPP, we speculated that the heterogeneity in sPP melts was caused by the separation between the long crystallizable sequence and the atactic sequence.
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