Discrimination of Poly(ethyl methacrylate)s According to Their Molar Mass and Tacticity by Coupling Size Exclusion Chromatography and Liquid Chromatography at the Critical Adsorption Point

Abstract

A coupling of size exclusion chromatography (SEC) and liquid chromatography at the critical adsorption point (LC CAP) has been applied to simultaneous discrimination of stereoregular poly(ethyl methacrylate)s (PEMAs) according to their molar mass and tacticity. The two-dimensional SEC/LC CAP separations were carried out with a chromatographic system which consisted of two analytical columns, one SEC column (polystyrene/divinylbenzene gel) and one LC CAP column (aminopropyl bonded silica gel) connected in series. Narrow fractions of PEMA samples eluted from the SEC column were on-line forwarded into the LC CAP column to be separated according to their tacticity. The column system was flushed with tetrahydrofuran (THF)/cyclohexane mixed eluents at compositions of 64/36 and 56/44 w/w, to attain the molar-mass-independent elution of either highly syndiotactic or highly isotactic PEMAs, respectively. In these eluents, the SEC column still separated PEMAs solely according to their molar masses, while the LC CAP column system discriminated PEMAs according to their tacticity. By use of the coupled SEC/LC CAP technique, the influence of molar mass distribution of analyzed sample on its separation according to tacticity in the LC CAP column was suppressed. For the first time the separation of stereoregular polymers over the entire tacticity range has been demonstrated.

Size-exclusion chromatography—a review of calibration methodologies

“…Most interestingly, by using multiangle light scattering for direct calibration of SEC, it was recently possible to observe an unusual shape of calibration curves (molecular weight and/or radius of gyration versus retention volume) for some complex polymers [96 -98]. Furthermore, by combining SEC with other fractionation/ separation techniques, additional information about details of polymer architecture can be obtained [76,99,100].…”

Advanced fractionation methods for the microstructure analysis of complex polymers

“…[41] Following this work, Janco et al separated poly(ethyl methacrylate) (PEMA) by on-line two-dimensional LC (2D-LC) with SEC as the first dimension followed by LC at critical adsorption point as the second dimension. [42] Cho et al used TGIC with MALDI-TOF MS detection for the analysis of stereoregular PEMAs and studied the tacticity effect on the SEC behavior of such samples. [43,44] They found that TGIC alone is not sufficient to characterize both tacticity and molar mass.…”

Liquid Chromatography under Limiting Conditions of Desorption IV. Separation of Macromolecules According to Their Stereoregularity

“…The detailed molecular characteristics of both polymer groups are given in papers. [15][16][17] Polystyrene, PS ''standards'' with molar mass averages ranging from 0.8 to 498 kgÁmol À1 with narrow molar mass distribution were from Pressure Co., USA.…”

“…Other kinds of macromolecules are eluted under (prevailingly) exclusion or interaction conditions to be separated from the ''critically'' eluted species. Both EG LC 7 and LC CC [15][16][17][18] were also applied to mutual separation of macromolecules differing in their stereoregularity. A series of highly stereoregular narrow molar mass distribution isotactic, it.-, and syndiotactic, st.-poly(methacrylate)s, separately injected into the EG LC or LC CC column eluted in different retention volumes even if molar masses were almost identical.…”

“…On the other hand, the mixtures of the narrow molar mass distributed non-aggregating poly(ethyl methacrylate)s, PEMA of similar molar mass but of distinct tacticity were base line separated in the LC CC columns applying mixtures of usual solvents such as tetrahydrofuran and hexan. 17,18 Eventually, fractions of PEMA produced by SEC were on line separated according to their streoregularity with help of LC CC. Unfortunately, LC CC suffers from several drawbacks, such as -high sensitivity of many LC CC chromatographic systems toward small variations of experimental conditions, especially to fluctuations in the eluent composition, pressure, and temperature, as well as to changes in the column interactivity 19,20 -extensive broadening of the chromatographic zones [19][20][21] -reduced recovery of polymers with increased molar mass; this makes LC CC hardly applicable to molar masses over 100 kgÁmol À1 .…”