Hyphenated Polymer Separation Techniques

Journal of Chromatography A, 2008

Size-exclusion chromatography (SEC) separates polymers by hydrodynamic volume (the universal calibration principle). Molecular weights can be determined using viscometry (relying on universal calibration) and light scattering (independent of universal calibration). In the case of complex branched polyacrylates with tetrahydrofuran as eluent, universal calibration is valid, although the separation in term of molecular weight is incomplete: a given elution slice contains a range of molecular weights, described in terms of a 'local polydispersity'. The local polydispersity index decreases when the number of branches per chain increases and complete separation is reached for highly branched chains.

Journal of Polymer Science Part B: Polymer Physics, 1991

The relationship between viscosity constants, k', a and K,, from the equations of Huggins and Mark-Kuhn-Houwink has been considered. It is shown, theoretically, that the sum of k' and a must be constant for all flexible-chain macromolecules irrespective of the solvent used. On this basis, a combination of chromatography and viscometry measurements can be used to characterize a new species. The method has been applied to the new polymer, poly [ methyl (pyridin-3-yl) siloxane] (1) where no suitable calibration standards are available. The value of a , k', and K,, for 1 has been calculated. The calculated constants enabled an estimation of different average molecular weights (M,,, M,, M ,) and polydispersity (M , / M ,) from a minimum of experimental data. The new method is general and can be applied to any homogeneous linear flexible-chain nondraining macromolecule.

Macromolecular Theory and Simulations, 2007

Macromolecular Symposia, 2008

Summary: This paper discusses the analysis of star‐branched and dendritic polyisobutylenes (PIBs) using branching parameters based on radii of gyration Rg,z and hydrodynamic radii Rh,z. Rg,z and Rh,z were measured by Size Exclusion Chromatography equipped with a Wyatt Technology Viscostar viscometer (VIS), a Wyatt Optilab DSP RI detector, a Wyatt DAWN EOS 18 angle Multiangle Light Scattering (MALS) detector and a Wyatt Quasi‐elastic Light Scattering QELS detector. Branching parameters were calculated from these measurements and compared with those computed for these architectures.

Journal of Polymer Science Part A: Polymer Chemistry, 2000

Rapid high-performance liquid chromatography (HPLC) of polystyrenes, poly(methyl methacrylates), poly(vinyl acetates), and polybutadienes using a monolithic 50 ϫ 4.6 mm i.d. poly(styrene-co-divinylbenzene) column have been carried out. The separation process involves precipitation of the macromolecules on the macroporous monolithic column followed by progressive elution utilizing a gradient of the mobile phase. Depending on the character of the separated polymer, solvent gradients were composed of a poor solvent such as water, methanol, or hexane and increasing amounts of a good solvent such as THF or dichloromethane. Monolithic columns are ideally suited for this technique because convection through the large pores of the monolith enhances the mass transport of large polymer molecules and accelerates the separation process. Separation conditions including the selection of a specific pair of solvent and precipitant, flow rate, and gradient steepness were optimized for the rapid HPLC separations of various polymers that differed broadly in their molecular weights. Excellent separations were obtained demonstrating that the precipitation-redissolution technique is a suitable alternative to size-exclusion chromatography (SEC). The molecular weight parameters calculated from the HPLC data match well those obtained by SEC. However, compared to SEC, the determination of molecular parameters using gradient elution could be achieved at comparable flow rates in a much shorter period of time, typically in about 1 min.

2019

Poly (lactide-co-glycolide acid) ( PLGA) is an extraordinary well-described polymer and has excellent pharmaceutical properties like high biocompatibility and good biodegradability. Hence, it is one of the most used materials for drug delivery and biomedical systems, also being present in several US Food and Drug Administration approved carrier systems and therapeutic devices. For both applications, the quantification of polymer is important. During the development of the production process, parameters like yield or loading efficacy are essential to be determined. Although PLGA is a well-defined biomaterial, it still lacks a sensitive and convenient quantification approach for PLGA-based systems. Thus, we present a new method for fast and precise quantification of PLGA by HPLC-SEC. The method includes a shorter run time of 20 minutes with a size exclusion column of 300mm x 8.0mm diameter, tetrahydrofuran as mobile phase and diluent, the detection was carried out using the refractive...

Journal of Polymer Science Part A: Polymer Chemistry, 2011

This article presents the SEC analysis of branched polyisobutylene PIB and polystyrene PS with high molecular weight and broad multimodal molecular weight distribution. Both polymers were synthesized using an inimer technique, which results in long-chain branched polymers with statistical branching and broad multimodal distributions. Using high resolution multidetector Size Exclusion Chromatography SEC the polymers were analyzed based on three branching factors: g ¼ (R 2 g z,br /R 2 g z,lin) Mw ; h ¼ (hR h i z,br /hR h i z,lin) Mw ; and q ¼ (R 2 g 1/2 /hR h i z). It is generally accepted that for monodisperse branched polymers g and h < 1. In the case of our polydisperse PIB and PS, it was seen that g and h > 1, and q increases with molar mass and the number of chain ends as predicted earlier. The multidetector SEC system allowed for the separation of branching and polydispersity, reported here for the first time experimentally. The g parameter as a function of DP i was compared to the theory developed by Zimm and Stockmayer. The plots followed a similar trend, but were shifted by a factor related to the average chain length between branching points. The q parameter decreased with increasing DP i , as predicted theoretically by Kajiwara. V

Journal of Chromatography A, 2005

Macromolecules, which stay adsorbed within the active size-exclusion chromatography (SEC) column packings may strongly reduce effective volume of the separation pores. This brings about a decrease of retention volumes of the non-retained polymer samples and results in the increased apparent molar mass values. The phenomenon has been demonstrated with a series of poly(methyl methacrylate)s (PMMA) and a polyethylenoxide (PEO) fully retained by adsorption within macroporous silica gel SEC column from toluene or tetrahydrofuran, respectively. The non-retained probes were polystyrenes (PS) in toluene and both PS and PMMA in THF eluents. The errors in the peak molar mass values determined for the non-retained polymer species using a column saturated with adsorbed macromolecules and considering calibration curves monitored for the original "bare" column packing assumed up to several hundreds of percent. Errors may appear also in the weight and number averages of molar masses calculated from calibration dependences obtained with columns saturated with adsorbed macromolecules. Moreover, the SEC peaks of species eluted from the polymer saturated columns were broadened and in some cases even split. These results demonstrate a necessity not only to periodically re-calibrate the SEC columns but also to remove macromolecules adsorbed within packing in the course of analyses.

Journal of Chromatography A, 1984

The separation of synthetic polymers of different molecular weight by nonaqueous, gradient liquid chromatography does not follow traditional chromatographic mechanisms. As a result one can produce separations where late eluting solutes have narrower bandwidths than early eluting solutes, where shorter columns result in higher resolution than identical longer columns, and where the selectivity and resolution are independent of the type of stationary phase used. These results are explained for polystyrene, poly-a-methylstyrene and polyisoprene using recently developed theory. The results of this work are not only pertinent to the practice and theory of chromatography but also to the study of polymers.

Journal of Chromatography A, 2016

This work describes the applicability of common reversed phase and HILIC columns for size exclusion chromatography of synthetic and natural polymers. Depending on the nature of the solute and column stationary phase, a "non-retention" condition must be created with the aid of the mobile phase to achieve a unique size-based separation in isocratic mode. The various bonded phases show remarkable differences in size separations that are controlled by mobile phase conditions. Polymer-mobile phase and columnmobile phase solvation interactions determine polymer hydrodynamic volume (or solute bulkiness) and polymer-column steric interaction. Solvation interactions in turn depend on polymer, mobile phase and stationary phase polarities. Column-mobile phase solvation interactions determine the structural order of the bonded ligands that can vary from ordered (extended, aligned away from the silica substrate) to disordered (folded, pointing toward the silica substrate). Chain order increases with increased solvent penetration into the bonded phase. Increased chain order reduces pore volume, and therefore decreases the size-separation efficiency of a column. Conversely, decreased chain order increases pore volume and therefore increases the size-separation efficiency. The thermodynamic quality of the mobile phase also plays a significant role in the separation of polymers. "Poor" solvents can significantly reduce the hydrodynamic diameter of a solute and thus change their retention behavior. Medium polarity stationary phases, such as fluoro-phenyl and cyano, exhibit a unique retention behavior. With an appropriate polarity mobile phase, polar and non-polar synthetic polymers of the same molecular masses can be eluted at the same retention volumes.