End-Groups-Dependent MALDI Spectra of Polymer Mixtures

Abstract

During a work designed to use MALDI−TOF MS to determine the composition of an equimolar blend of nylon 6 (Ny6) and polybutyleneterephthalate (PBT), the MALDI−TOF mass spectrum showed a surprising strong imbalance between the two components. The predominance of Ny6 oligomers over the PBT oligomers terminated with hydroxyl end chains is signaled by the appearance of specific peaks in the MALDI−TOF mass spectra. Since the average molar mass and the polydispersion of the two polymers are comparable, the MALDI−TOF MS ionization efficiency is quite different for the two components of the blend. This finding prompted us to a more detailed study, and to synthesize a number of Ny6 and PBT samples terminated with different end groups, to analyze their equimolar blends by MALDI−TOF MS. The results reported in the present study may help clarifying some fundamental aspects about the mechanisms of ions formation, when MALDI−TOF mass spectrometry is applied to macromolecules. End groups ionization efficiency appears to be the most important parameter in determining the relative intensity of peaks in the MALDI−TOF mass spectra of the polymer blends investigated. End-groups-dependent ionization of MALDI−TOF mass species is the key to rationalize the relative peak intensity in MALDI−TOF mass spectra of polymer mixtures. Understanding of ionization efficiency mechanisms is essential to the quantitative applications of MALDI−TOF MS.

Quantitative analysis of polypropyleneglycol mixtures by desorption/ionization on porous silicon mass spectrometry

“…1). It is intriguing to analyze mixtures of diol and triol type PPGs and to compare the effects of DIOS-MS to those of MALDI-MS, since the ionization efficiency of the end group is an important factor for quantitative analysis by MALDI-MS [24].…”

“…The determination of the mixing ratio of different types of polymers using MALDI-MS is not easy [23]. End group ionization efficiency is the most important factor in determining the relative intensities of peaks in the MALDI mass spectra of mixtures of nylon 6 and polybutyleneterephthalate [24]. Mixtures of polystyrene and poly(␣-methylstyrene) were quantitatively analyzed by hyphenated combination of size-exclusion chromatography and MALDI-MS [25].…”

Characterization and relative ionization efficiencies of end-functionalized polystyrenes by matrix-assisted laser desorption/ionization mass spectrometry

“…For example, the ionization efficiencies of Nylon 6 and polybutyleneterephthalate oligomers have been found to vary greatly depending on the end group [22,23]. Perhaps more significantly, the addition of a so-called "covalent cation" -an organic cation, such as triphenylphosphine, covalently bonded to an oligomer as an end group -permits the ionization of polyolefins which previously gave little or no signal in normal MALDI analysis [24,25].…”

Polycondensation

“…(26)], for example, should be used instead. At low conversions, the infinite dilution is not applicable and the multicomponent Flory-Huggins equation [Eq.…”