Despite being a homopolymer, low density polyethylene (LDPE) exhibits a complex molecular structure that is determined by multiple molar mass and branching distributions. For a comprehensive microstructural analysis, preparative fractionation methods are combined with multiple advanced analysis techniques. Preparative temperature rising elution fractionation (pTREF) and preparative molar mass fractionation (pMMF) are used to fractionate three LDPE resins with different melt flow indexes into fractions with narrower branching and molar mass distributions, respectively. The chain structures of the bulk resins and their corresponding pTREF and pMMF fractions are further analyzed using size exclusion chromatography, crystallization analysis fractionation, differential scanning calorimetry, high-temperature solvent gradient interactive chromatography and SEC coupled to molar mass sensitive detectors to provide detailed information particularly on long chain branching and its correlation to molar mass. It is shown that the multiple fractionation concept is a powerful approach to generate LDPE sample libraries that may constitute fractions (samples) of comparable molar masses and different branching structures or alternatively have comparable branching but different molar masses. Cross-fractionation of these library samples with advanced analytical techniques provides in-depth information on the molecular heterogeneity of these samples as compared to bulk sample analysis.

中文翻译：

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使用多重制备分馏概念对低密度聚乙烯进行支化和摩尔质量分析

尽管是均聚物，但低密度聚乙烯（LDPE）仍显示出复杂的分子结构，该结构由多个摩尔质量和支化分布决定。对于全面的微观结构分析，将制备分级分离方法与多种高级分析技术结合使用。使用制备温度升高洗脱级分（pTREF）和制备摩尔质量级分（pMMF）分别将三种具有不同熔体流动指数的LDPE树脂分馏为具有较窄支化和摩尔质量分布的级分。使用尺寸排阻色谱，结晶分析分级分离，差示扫描量热法，进一步分析本体树脂的链结构及其相应的pTREF和pMMF馏分，高温溶剂梯度交互式色谱法和SEC与摩尔质量敏感检测器相连，可提供有关长链支化及其与摩尔质量相关性的详细信息。结果表明，多重分馏概念是产生LDPE样品库的强大方法，该LDPE样品库可以构成具有相当摩尔质量和不同支化结构的馏分（样品），或者具有具有可比支化但摩尔质量不同的馏分。与批量样品分析相比，使用先进的分析技术对这些文库样品进行交叉分级分离可提供有关这些样品分子异质性的深入信息。结果表明，多重分馏概念是产生LDPE样品库的强大方法，该LDPE样品库可以构成具有相当摩尔质量和不同支化结构的馏分（样品），或者具有具有可比支化但摩尔质量不同的馏分。与批量样品分析相比，使用先进的分析技术对这些文库样品进行交叉分级分离可提供有关这些样品分子异质性的深入信息。结果表明，多重分馏概念是产生LDPE样品库的强大方法，该LDPE样品库可以构成具有相当摩尔质量和不同支化结构的馏分（样品），或者具有具有可比支化但摩尔质量不同的馏分。与批量样品分析相比，使用先进的分析技术对这些文库样品进行交叉分级分离可提供有关这些样品分子异质性的深入信息。