Development of high temperature comprehensive two-dimensional liquid chromatography hyphenated with infrared and light scattering detectors for characterization of chemical composition and molecular weight heterogeneities in polyolefin copolymers

On the feasibility of determining polymer chemical heterogeneity by SEC with continuous off-line Raman detection

Examined here is the feasibility of employing Raman spectroscopy as a detection method in size-exclusion chromatography (SEC) and related macromolecular separations, for the purposes of determining the chemical heterogeneity of copolymers.

State-of-the-art analytical methods for assessing dynamic bonding soft matter materials

Dynamic bonding materials are of high interest in a variety of fields in material science. The reversible nature of certain reaction classes is frequently employed for introducing key material properties such as the capability to self-heal. In addition to the synthetic effort required for designing such materials, their analysis is a highly complex--yet important--endeavor. Herein, we critically review the current state of the art analytical methods and their application in the context of reversible bonding on demand soft matter material characterization for an in-depth performance assessment. The main analytical focus lies on the characterization at the molecular level.

Toward absolute chemical composition distribution measurement of polyolefins by high-temperature liquid chromatography hyphenated with infrared absorbance and light scattering detectors

Chemical composition distribution (CCD) is a fundamental metric for representing molecular structures of copolymers in addition to molecular weight distribution (MWD). Solvent gradient interaction chromatography (SGIC) is commonly used to separate copolymers by chemical composition in order to obtain CCD. The separation of polymer in SGIC is, however, not only affected by chemical composition but also by molecular weight and architecture. The ability to measure composition and MW simultaneously after separation would be beneficial for understanding the impact of different factors and deriving true CCD. In this study, comprehensive two-dimensional chromatography (2D) was coupled with infrared absorbance (IR5) and light scattering (LS) detectors for characterization of ethylene-propylene copolymers. Polymers were first separated by SGIC as the first dimension chromatography (D1). The separated fractions were then characterized by the second dimension (D2) size exclusion chromatography (SEC) with IR5 and LS detectors. The concentrations and compositions of the separated fractions were measured online using the IR5 detector. The MWs of the fractions were measured by the ratio of LS to IR5 signals. A metric was derived from online concentration and composition data to represent CCD breadth. The metric was shown to be independent of separation gradients for an "absolute" measurement of CCD breadth. By combining online composition and MW data, the relationship of MW as a function of chemical composition was obtained. This relationship was qualitatively consistent with the results by SEC coupled to IR5, which measures chemical composition as a function of logMW. The simultaneous measurements of composition and MW give the opportunity to study the SGIC separation mechanism and derive chain architectural characteristics of polymer chains.

Multi-dimensional separations of polymers

Synthetic polymers and comprehensive two-dimensional liquid chromatography (LC × LC) are a synergistic combination. LC × LC provides unique insights in mutually dependent molecular distributions. Synthetic polymers offer clear demonstrations of the value of LC × LC.