MALDI‐TOF mass spectrometry in polymer analytics, 2. Molecular weight analysis of rigid‐rod polymers

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Abstract
Molecular weight analysis of rigid‐rod polymers by gel permeation chromatography (GPC) is known to give overestimated values if polystyrene is used for calibration. In this work matrix‐assisted laser desorption/ionisation time of flight (MALDI‐TOF) mass spectrometry was applied for the first time toward direct molecular weight determination of a rigid‐rod type tetrahydropyrene (THP) polymer. The obtained results were supported by investigation of a homologous series of GPC‐separated oligomers with the respective structure. As opposed to common MALDI‐TOF mass spectra, monodisperse THP oligomers reveal two unusual facts: (i) Beside the formation of molecular ions fragmentation also takes place. (ii) The radical ions are detected instead of cationised species. The fully characterised THP oligomers were also used to calibrate the GPC measurements of the THP polymers. The number‐average molecular weight (M̄n), weight‐average molecular weight (M̄w) and polydispersity (M̄w/M̄n) data obtained from the oligomer‐calibrated GPC compare well to those values measured by MALDI‐TOF mass spectrometry.

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