Molecular weight analysis of pitches and polymeric pitches by gel‐permeation chromatography

Abstract

The technique of gel‐permeation chromatography (GPC) has been developed as a method for measuring molecular weight distribution in pitch materials. Molecular weight calibration data were obtained from measurements made on GPC fractions collected from a standard pitch. By solubilization of the polymeric portion of pitch through a reduction with lithium in ethylenediamine, the molecular weight range for analysis was extended to in excess of 3000. Mass spectroscopy has been used to further analyze some of the GPC fractions. The GPC calibration data can be employed, with the aid of computer analysis, to determine quantitatively number‐average molecular weights M̄n weight‐average molecular weights M̄w, and molecular weight distribution D (= M̄w/M̄n) in pitch materials.

Controlling the Oligomeric Composition of Carbon‐Fiber Precursors by Dense‐Gas Extraction

“…Researchers have long recognized the important role that mol wt plays in the suitability of a given pitch for a particular application, 7,8 but measuring and controlling that mol wt has long been a difficult task. The classic technique for mol wt measurement, gel permeation chromatography, is limited by the lack of calibration standards for pitches and incomplete solubility of the higher mol wt oligomers 7–9 . Solvent‐based mass spectrometry techniques are similarly limited by solubility considerations.…”

Determination of molecular weight distributions of polymerized petroleum pitch by gel permeation chromatography with quinoline eluent

“…Bergmann et al (9) have reported that the anomalous elution behavior of pitch molecules disappears when 1,2,4trichlorobenzene is used as the gel permeation chromatographic (GPC) solvent. However, interfering negative peaks were observed in 1,2,4-trichlorobenzene for the GPC elution of pitch samples (14).…”

“…The nonideal elution behavior, particularly noticeable for the pericondensed polynuclear aromatics, has been observed in tetrahydrofuran (8), toluene 0003-2700/80/0352-1877801.00/0 (9), benzene (9, 10), and methylene chloride (4, 5). This behavior, sometimes attributed to adsorption (10), generally results in a nonlinear calibration curve at low molecular weights for petroleum residuals (12,13) and polymeric pitches (14). Bergmann et al (9) have reported that the anomalous elution behavior of pitch molecules disappears when 1,2,4trichlorobenzene is used as the gel permeation chromatographic (GPC) solvent.…”

“…Lewis and Petro (14) reported the first use of GPC to obtain molecular weight distributions of polymerized pitches. In their procedures the polymeric pitch was separated into pyridinesoluble (PS) and pyridine-insoluble (PI) fractions.…”

Dense-gas fractionation of mixtures of petroleum macromolecules

“…Unfortunately, the classic technique for the separation of petroleum pitches, gel permeation chromatography [6,7], suffers from a number of disadvantages, including poor peak resolution and the incomplete solubility of higher MW pitches in even aggressive mobile phase solvents [7][8][9].…”