Fischer‐tropsch waxes. IV. Qualitative and quantitative investigation of chain branching

Abstract

The degree of branching of waxes, expressed as the number of branches per 100 carbon atoms, is important because it determines crystallinity, which in its turn influences physical properties. Among several methods available for the study of branching, an infra-red spectrometric method was chosen. It consisted of the determination of methyl groups. It was also necessary to determine molecular weight. The most serious problem encountered was the variation of the specific absorbance at the chosen frequency (1379 cm⁻¹) with the structural position of the methyl group, which necessitated a thorough qualitative investigation of the branches, using infra-red, nuclear magnetic resonance and mass spectrometry. It was shown that branches in the Fischer-Tropsch waxes are almost entirely methyl and that the branching is seemingly distributed statistically along the chains. Calibration was effected with pure n- and mono-methyl paraffins, making the determination of degree of branching possible. This method can be applied to other materials provided that certain structural features about them are known.