Olefin copolymers are complex polymer materials that exhibit multiple distributions in molecular properties such as molar mass, chemical composition, and branching. To address the multivariate molecular compositions, chromatographic protocols have been developed that synergistically combine solvent and temperature gradients. As representative examples, blends of olefin copolymers have been fractionated on porous graphitic carbon stationary phases. This is the first study that makes complementary use of solvent and temperature gradient interaction chromatography (SGIC and TGIC, respectively) to capitalize on the advantages of both techniques. In a first experimental setup, solvent and temperature gradients were used simultaneously and complex blends of low molar mass polyethylene and ethylene-co-1-octene copolymers were separated with high efficiency. The separation of oligomers was observed to be significantly better in SGIC as compared to TGIC, while comonomer blends could be separated in either TGIC or SGIC mode. In another innovation, a two-column setup was employed where the columns were placed in different temperature zones. It was demonstrated that the separation of both low and high comonomer content blends was improved significantly when the temperatures of the two zones were manipulated reasonably.

Chain-walking (CW) catalysis applied to α-olefin polymerization gives rise to structurally unparalleled macromolecules with diverse topological and rheological properties. The specific motion pattern of the CW catalyst along the polymer chain is easily manipulated by varying synthesis parameters such as monomer concentration, temperature, and time or by adjusting the steric and electronic effects of the catalyst's ligands or choice of central metal. While their structural potential has been extensively studied, the experimental identification has often been single-sided. Modern techniques in liquid chromatography provide a suitable approach to investigate the complex dimensions of CW polyethylene (PE). In this study, advanced interaction chromatography in temperature and solvent gradient modes as well as comprehensive two-dimensional chromatography (2D-LC), coupling of interaction (IC), and size exclusion chromatography (SEC) are combined with multidetector high-temperature SEC (HT-SEC) to characterize the multidimensional heterogeneity of CWPE. Nuclear magnetic resonance and Fourier transform infrared spectroscopy provide quantitative information about the types and numbers of branches. The complementary characterization techniques give insight into highly diverse branching topologies within narrow molar mass distributions of the CW polyethylene.

Olefin plastomers/elastomers are typically copolymers with high comonomer contents and low crystallinities. Therefore, the fractionation of these materials with crystallization-based methods is not feasible. On the other hand, solvent and temperature gradient interaction chromatography (SGIC and TGIC, respectively) are suitable techniques for the separation of olefin copolymers with regard to their chemical composition. In this study, the application ranges of both techniques are investigated and compared for ethylene-propylene (EP) copolymers. A linear dependency of ethylene content versus elution volume is obtained with SGIC in practically the whole ethylene range. In the case of TGIC, a linear dependency is obtained within certain ethylene content limits. The accessible ethylene content separation range for TGIC is 50-100 mol% ethylene, and a broader 26-100 mol% ethylene range is accessible for SGIC, the latter being the technique of choice in the analysis of EP rubbers.

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Classical linear low density polyethylenes (LLDPEs) are copolymers of ethylene and 1-octene or 1-hexene, respectively. In the past, other 1-olefins have been tested as comonomers but the resulting LLDPEs were never commercialized as large scale products. The present study focuses on the use of 1-heptene as an interesting comonomer for the synthesis of LLDPE. For a comparison of the molecular structure and the physical properties of 1-heptene-and 1-octene-based LLDPEs, five Ziegler-Natta LLDPEs of varying comonomer contents based on 1-heptene and 1-octene, respectively, were acquired and analysed using advanced methods. The comonomer contents of the resins were between 0.35 and 6.4 mol %. Crystallization-based techniques revealed similar bimodal distributions that are due to the formation of copolymer and polyethylene homopolymer fractions. The compositional distribution of the copolymers was studied by high-temperature (HT) HPLC and HT-2D-LC. The analytical results indicate similar chemical heterogeneities and molar mass distributions of the two sets of LLDPE up to a comonomer content of 3 mol %. Similar to the molecular structure, the physical properties of the materials are quite similar. At comonomer contents of 3 mol % differences between the two sets of samples are seen that are attributed to differences in the abilities of 1-heptene and 1-octene in disrupting the crystal arrangements of the polymer chains in solid state. V C 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 962-975