2 research outputs found
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
Determination of Particle Size Distributions, Molecular Weight Distributions, Swelling, Conformation, and Morphology of Dilute Suspensions of Cross-Linked Polymeric Nanoparticles via Size-Exclusion Chromatography/Differential Viscometry
Size-exclusion chromatography (SEC),
coupled with differential
viscometry detection (SEC/DV), is applied to the dilute suspension
characterization of solvent-swollen cross-linked polymeric nanoparticles
(PNPs). Cross-linked, unimolecular polymeric nanoparticles in the
5–50 nm weight-average diameter (<i>d</i><sub>w</sub>) range were prepared by batch and semibatch microemulsion polymerization
techniques and isolated. SEC and SEC/DV characterization techniques
yield, based on the principle of universal calibration, a wealth of
information regarding the structural attributes of PNPs, including
apparent and absolute molecular weight distributions, apparent and
absolute molecular weight averages, peak and weight-average particle
diameters, particle size distributions in both the solvent-swollen
and solvent-free states, particle conformation (shape), and an estimate
of the volumetric swell factor. These structural parameters are critical
to understanding PNP performance, and all are obtained in a single
rapid chromatographic experiment, when conducted under conditions
where universal calibration applies. Particle sizes determined under
such conditions are in excellent agreement with those obtained by
dynamic light scattering, transmission electron microscopy, hydrodynamic
chromatography, and SEC/static light scattering (SEC/SLS). In addition,
Mark–Houwink exponents of approximately zero were found across
the molecular weight and size distribution of many of these tightly
cross-linked PNPs, which is consistent with a spherical particle conformation
in these dilute suspensions. The SEC/DV methods are especially valuable
to characterize the diameter, volume swell factor, and suspension
conformation of small (4–5 nm <i>d</i><sub>w</sub>) PNPs