Herein, we study comparatively melt-memory effects on recrystallization of two sets of linear low-density polyethylenes (LLDPE) synthesized with Ziegler–Natta (ZN-LLDPE) and with metallocene catalysts (M-LLDPE), respectively. All copolymers have M_w ∼ 120,000 g/mol, M_w/M_n ∼ 4, and very similar average comonomer content (∼2 mol % branches) but different comonomer composition distribution (CCD). While all types of copolymers display the strong melt-memory effect of the initial crystallites enhancing the recrystallization rate from melt temperatures (T_melt) up to ∼160 °C, a subsequent retardation of the rate associated with liquid–liquid phase separation (LLPS) is found mainly in ZN-LLDPEs. Only one M-LLDPE displays the retardation of the recrystallization rate. The conclusion from a detailed quantitative analysis of the TREF profiles is that copolymers with inversion of crystallization rate, characteristic of LLPS, have CCD comprising 15–25 wt % molecules in the 12–6 mol % comonomer range and <50 wt % in the 6–1.5 mol % comonomer range. The rest (30–50 wt %) are lowly branched molecules (<1.5 mol %) that comprise the high-crystallinity component. Characterization of the spherulitic crystalline morphology with polarized optical microscopy allows us to extract the exponential variation of the number of residual clusters (self-nuclei) in the melt as a function of decreasing T_melt within the melt-memory range. The comparative CCD-crystallization analysis carried out in this work serves as a guideline to design LLDPEs with distributions prone to LLPS during processing.

中文翻译：

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具有双峰共聚单体组成分布的齐格勒-纳塔和茂金属乙烯共聚物对熔融记忆重结晶和液相分离的比较作用

在本文中，我们研究了熔体记忆对分别用齐格勒-纳塔（ZN-LLDPE）和茂金属催化剂（M-LLDPE）合成的两组线性低密度聚乙烯（LLDPE）重结晶的影响。所有共聚物具有中号_瓦特〜120000克/摩尔，中号_瓦特/中号_Ñ〜4，和非常相似的平均共聚单体含量（〜2％（摩尔）的分支），但是不同的共聚单体组成分布（CCD）。虽然所有类型的共聚物都显示出初始微晶的强大的熔体记忆效应，但可提高熔体温度（T_熔体）的重结晶速率）直至约160°C，随后发现的液相-液相分离（LLPS）速率的随后降低主要出现在ZN-LLDPE中。仅一种M-LLDPE显示出重结晶速率的延迟。通过对TREF分布图进行详细定量分析得出的结论是，具有结晶速率倒置（具有LLPS特征）的共聚物的CCD包含12–6 mol％共聚单体范围内的15–25 wt％分子，而6内的<50 wt％ –1.5摩尔％共聚单体范围。其余（30–50 wt％）是组成高结晶度组分的低支链分子（<1.5 mol％）。_熔融的熔融存储器范围内。在这项工作中进行的比较CCD结晶分析可作为设计LLDPE的指南，该LLDPE在加工过程中倾向于LLPS分布。