Characterization of linear low‐density polyethylene: Cross‐fractionation according to copolymer composition and molecular weight
Characterization of linear low‐density polyethylene: Cross‐fractionation according to copolymer composition and molecular weight
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线性低密度聚乙烯的表征：根据共聚物组成和分子量进行交叉分级
DOI：
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发表时间：
1987
期刊：
影响因子：
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通讯作者：
E. Ford
中科院分区：
文献类型：
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作者：
F. Mirabella;E. Ford
自从所谓的线性低密度聚乙烯（LLDPE）树脂成功商业化以来，α-烯烃改性乙烯共聚物的结构已成为一个激烈的研究领域。研究了一系列典型商品LLDPE共聚物的分子结构，并与LDPE和HDPE进行了比较。所研究的商业LLDPE树脂含有约7重量%的丁烯-1。根据短链支化含量，通过称为升温洗脱分级的技术对树脂进行分级。尺寸排阻色谱法，X-射线衍射，13 C核磁共振，特性粘度，和差示扫描量热法被用来充分表征整个聚合物，以及选定的LLDPE树脂的馏分。在这项工作中收集了大量的数据，以研究这些商业树脂的短链支化、长链支化和分子量分布。发现LLDPE树脂的熔融行为与LDPE和HDPE的熔融行为有显著不同。发现LLDPE树脂的宽的和多峰的熔融包络是由于宽的和多峰的短链支化分布。在LLDPE树脂中没有发现显著的长链支化。在典型的商业LLDPE树脂中，发现短链支化随着分子量的增加而减少。这些树脂的独特的物理性能肯定是强烈控制的表达的独特的异质共聚单体掺入的固态形态结构。这些材料的物理和机械性能最终应基于独特的形态学来理解，所述独特的形态学是由这些商业LLDPE树脂中的改性α-烯烃的极其不均匀的结合而产生的。
The structure of ethylene copolymers modified by α-olefins has become an area of intense investigation since the successful commercialization of so-called linear low-density polyethylene (LLDPE) resins. The molecular structure of a series of typical commercial LLDPE copolymers was investigated and compared to LDPE and HDPE. The commercial LLDPE resins studied contained about 7% by weight of butene-1. The resins were fractionated according to short-chain branching content by a technique called temperature rising elution fractionation. Size exclusion chromatography, x-ray diffraction, 13C nuclear magnetic resonance, intrinsic viscosity, and differential scanning calorimetry were used to fully characterize the whole polymers as well as fractions of a selected LLDPE resin. A broad set of data was assembled in this work to investigate the short-chain branching, long-chain branching, and the molecular-weight distribution of these commercial resins. The melting behavior of the LLDPE resins was found to be strikingly different from that of LDPE and HDPE. The broad and multimodal melting envelope of the LLDPE resins was found to be due to a broad and multimodal short-chain branching distribution. No significant long-chain branching was found in the LLDPE resins. The short-chain branching was found to decrease with the increase of molecular weight in a typical commercial LLDPE resin. The unique physical properties of these resins are certainly strongly controlled by the expression of the distinctive heterogeneous comonomer incorporation in the solid-state morphological structure. The physical and mechanical properties of these materials should be ultimately understandable on the basis of the unique morphology which results from the extremely heterogeneous incorporation of modifying α-olefin in these commercial LLDPE resins.