Jones Mason D, Barker Christine W, Motolani Fawaz, Patter Rakesh, Kilbey S Michael, Chandler Bert D, Long Brian K, Vogt Bryan D
Department of Chemistry, University of Tennessee, Knoxville, Tennessee 37996, United States.
Department of Chemical Engineering, The Pennsylvania State University, University Park, Pennsylvania, 16803, United States.
ACS Appl Polym Mater. 2025 Aug 1;7(16):10826-10835. doi: 10.1021/acsapm.5c02105. eCollection 2025 Aug 22.
Polyolefins, which dominate the plastics marketplace, require high-temperature size exclusion chromatography (HT-SEC) to characterize their molar masses. Chemical recycling methods designed to deconstruct plastic waste into smaller molecules (i.e., depolymerization methods) rely on HT-SEC to characterize their products, but depolymerization methods often yield a complex mixture, including components below the typical separation range of commercial HT-SEC columns. Herein, we report the accuracy and limitations of triple detection HT-SEC to analyze model chemical recycling products. We examined the chromatographic separation and quantification of individual components and mixtures of short polyethylenes (apparent = 465 and 2722 g/mol), hexatriacontane (CH, = 507 g/mol), dotriacontane (CH, = 451 g/mol), and octadecane (CH, = 254 g/mol). Despite short alkanes exhibiting molar masses below the lower molar mass limit of the columns (500 g/mol), the separation of their mixtures was resolved via refractive index (RI) detection. However, the determined molar masses of these alkane mixtures did not agree with the known molar masses of the short alkanes or their prepared mixtures. Similarly, the SEC analysis of mixtures containing discrete alkanes with low molar mass PE revealed that their individual components are easily resolved in the HT-SEC chromatogram. No obvious shift in the elution volume of the blend components versus the elution volume of the pure components was observed. However, inaccurate molar masses and molar mass distributions for these alkane-PE mixtures are calculated from the HT-SEC data. These inaccuracies are attributable to two factors: (1) molar mass-dependent for low molar mass components and (2) the small size of the molecules in solution that limits light scattering. These results highlight the importance of considering measurement limitations for quantitative interpretation of triple detection HT-SEC data obtained from chemical recycling and depolymerization experiments that commonly contain complex mixtures of polymeric, oligomeric, and small molecule alkanes.
聚烯烃在塑料市场中占据主导地位，需要高温尺寸排阻色谱法（HT-SEC）来表征其摩尔质量。旨在将塑料废物解构为较小分子的化学回收方法（即解聚方法）依靠HT-SEC来表征其产物，但解聚方法通常会产生复杂的混合物，包括商业HT-SEC柱典型分离范围以下的组分。在此，我们报告了三重检测HT-SEC分析模型化学回收产物的准确性和局限性。我们研究了短链聚乙烯（表观摩尔质量 = 465和2722 g/mol）、三十六烷（C₃₆H₇₄，摩尔质量 = 507 g/mol）、三十二烷（C₃₂H₆₆，摩尔质量 = 451 g/mol）和十八烷（C₁₈H₃₈，摩尔质量 = 254 g/mol）的各个组分及混合物的色谱分离和定量分析。尽管短链烷烃的摩尔质量低于色谱柱的较低摩尔质量极限（500 g/mol），但其混合物的分离通过示差折光（RI）检测得以实现。然而，这些烷烃混合物的测定摩尔质量与短链烷烃或其制备混合物的已知摩尔质量不一致。同样，对含有低摩尔质量聚乙烯的离散烷烃混合物的SEC分析表明，其各个组分在HT-SEC色谱图中易于分离。未观察到共混物组分的洗脱体积相对于纯组分洗脱体积有明显偏移。然而，根据HT-SEC数据计算出的这些烷烃-聚乙烯混合物的摩尔质量和摩尔质量分布不准确。这些不准确归因于两个因素：（1）低摩尔质量组分的摩尔质量依赖性；（2）溶液中分子尺寸小限制了光散射。这些结果突出了在对从通常包含聚合物、低聚物和小分子烷烃复杂混合物的化学回收和解聚实验中获得的三重检测HT-SEC数据进行定量解释时，考虑测量局限性的重要性。
