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As the most consumed synthetic polymers globally, polyolefins provide tunable performance at a low production cost. This tunability is achieved by modifying polymer molecular weight or branching characteristics, the latter of which can be quantified by chemical composition distribution (CCD). CCD can be measured using interaction-based techniques relying on graphite-based material as the stationary phase. Interaction-based techniques are classified as solvent gradient or thermal gradient according to the type of gradient that is used to enable the separation of polyolefins. High-temperature thermal gradient interactive chromatography (HT-TGIC) has been the preferred technique as it overcomes the detector shortcomings of solvent gradient interactive chromatography. This work focuses on the HT-TGIC technique and strives to improve the separation resolution by adopting improvements in the stationary-phase packing material. Resolution is greatest with a substrate consisting of nonporous and homogeneous, spherical particles. However, the synthesis of such material with naturally occurring graphite has been a challenge. Here, an innovative yet simple approach to make such particles is described. A core–shell particle with nonporous silica as the core and graphene nanopowder (GNP) as the shell provides this solution. This novel method does not require chemical modification of graphene or silica particles, which has been explored previously as a potential avenue. These core–shell particles were packed into columns and showed an increase in chromatographic performance and separation resolution versus the best HT-TGIC columns currently available.

Crystallization-based separation techniques are widely used for chemical composition distribution (CCD, also often referred as short chain branching distribution SCBD) measurement in the polyolefin industry, in which CCD is among the most critical structural parameters to define their properties and applications. The desire to improve the sample throughput rate by shortening the analysis time in the current CCD techniques would normally sacrifice measurement accuracy due to the cocrystallization phenomena, in which the polymer chains with similar molecular architectures will cocrystallize or coelute enigmatically in the CCD analysis. Herein, we reported the investigation by exploring various separation packing materials on the cocrystallization phenomena. In comparison with the commercially available Crystallization Elution Fractionation (CEF) technique, an improved technique for CCD measurement (iCCD) was developed using the columns packed with gold-coated nickel substrate or spherical gold particles with or without the dynamic cooling process. With iCCD, it was observed with equivalent cocrystallization degree to the industrial gold standard benchmark Wild-TREF method but with over 70+ times improved sample throughput rate (62 vs 4500 min). The experimental CCD chromatogram for a polyolefin blend similarly assembled to the mathematically constructed result further demonstrated the minimized cocrystallization and measurement accuracy in the iCCD method. In addition, the superior mechanical properties of gold-coated nickel particles enabled the long-term robustness and enhanced measurement precision of the iCCD technique during the repeated thermal treatment cycles and pressure variations.

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