长链支化聚丙烯：链结构、熔体结构、剪切改性和固溶处理对熔体松弛动力学的影响,Macromolecules

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长链支化聚丙烯：链结构、熔体结构、剪切改性和固溶处理对熔体松弛动力学的影响
Macromolecules ( IF 5.1 ) Pub Date : 2022-03-22 , DOI: 10.1021/acs.macromol.1c02113
Dietrich Gloger ₁ , Daniela Mileva ₁ , Andreas Albrecht ₁ , Gerhard Hubner ₁ , René Androsch ₂ , Markus Gahleitner ₁

Affiliation

具有大分子结构的聚合物，如长链支化聚丙烯 LCB PP，容易发生称为剪切改性的解缠结现象。挤出降低熔体粘度和弹性，通过延长熔体加热（退火）或固溶处理恢复。在这里，对于 LCB PP 和与线性等规聚丙烯 L PP 的共混物，我们研究了链结构、支链含量、线性粘弹性、剪切改性引起的变化及其在溶液中的恢复。我们的 LCB PP 是线性前体的交联产品。根据渗透理论，LCB PP 的结构和摩尔质量分布遵循随机支化，其偏差由不可忽略的线性链部分解释。溶剂不溶部分，凝胶，表示大的渗流簇。由于高摩尔质量尾部的链断裂或凝胶渗透色谱法未检测到的更大结构（渗透簇）的断裂，我们的 LCB PP 的剪切改性不是完全可逆的。我们还提出了 LCB PP 的剪切改性（i）使链构象变形，（ii）扰乱由交联反应产生的长程熔体顺序，以及（iii）影响线性和支链之间的混合质量。在解决方案中，我们提出恢复机制是链膨胀成球形构象以及线性和支链的重新分布。我们的工作表明，理解支化聚合物的剪切改性需要了解所有链种类的含量和结构、它们的分子混合质量，以及它们相互依赖的弛豫机制。

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Long-Chain Branched Polypropylene: Effects of Chain Architecture, Melt Structure, Shear Modification, and Solution Treatment on Melt Relaxation Dynamics

Polymers with large molecular structures like long-chain branched polypropylene, LCB PP, are prone to a disentanglement phenomenon known as shear modification. Extrusion decreases melt viscosity and elasticity, restored by prolonged melt heating (annealing) or a solution treatment. Here, for LCB PPs and blends with linear isotactic polypropylene, L PP, we study chain architecture, branch content, linear viscoelasticity, the changes caused by shear modification, and recovery thereof in solution. Our LCB PPs are cross-linking products of a linear precursor. The architecture and molar mass distribution of the LCB PPs followed random branching according to percolation theory, with deviations explained by a non-negligible fraction of linear chains. A solvent-insoluble fraction, gel, was indicative of large percolation clusters. Shear modification of our LCB PPs was not fully reversible due to breakage of chains in the high molar mass tail or of even larger structures (percolation clusters) not detected by gel permeation chromatography. We also propose shear modification of LCB PP (i) deforms chain conformations, (ii) perturbs the long-range melt order created by the cross-linking reaction, and (iii) affects mixing quality between linear and branched chains. In solution, we propose recovery mechanisms are chain swelling into spherical conformations and a redistribution of linear and branched chains. Our work shows that the understanding shear modification of branched polymers requires knowledge of content and architecture of all chain species, their molecular mixing quality, and consequently their mutually dependent relaxation mechanisms.

更新日期：2022-03-22

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