Fast and Accurate Determination of Absolute Individual Molecular Weight Distributions from Mixtures of Polymers via Size Exclusion Chromatography−Electrospray Ionization Mass Spectrometry

Abstract

We present a method to determine accurate and absolute molecular weight distributions (MWDs) as well as absolute concentrations of the individual macromolecular components in mixtures of polymers of the same monomer class yet differing in their end groups. Data gained from size exclusion chromatography coupled online to refractive index (RI) detection and electrospray ionization mass spectrometry (ESI-MS) are processed by a sophisticated computer algorithm based on the maximum entropy principle. The procedure yields, for the first time, absolute molecular weight distributions of each component corrected for chromatographic band broadening. Molecular weights of up to 10 kDa are accessible with a conventional quadrupole ion-trap mass analyzer. The method is applicable to variable polymer systems regardless of the monomer class and without the need for an external calibration or additional model assumptions. It was validated using binary and ternary mixtures of poly(methyl methacrylate) carrying labile functional groups. For the ternary mixture, maximum deviations of the reconstructed molecular weight averages and mass concentrations from the original values were 8% and 5%, respectively.

A Perfect Couple: PLP/SEC/ESI‐MS for the Accurate Determination of Propagation Rate Coefficients in Free Radical Polymerization

“…However, in the case of poly(ethyl methacrylate) (pEMA) and poly(butyl methacrylate) (pBMA), peak clusters in the mass spectrum are well separated, thus enabling retention time, bandbroadening and area data corresponding to products from disproportionation and combination to be extracted individually using the previously developed Maximum Entropy (MaxEnt) approach. [59,60] The results of this can be seen in Figure 2, where the individual MWD of the species formed by disproportionation and by combination have been extracted. In PLP, a very high concentration of initiator radicals is formed at each pulse.…”

“…[57,58] We have recently extended the method to provide molecular weight analysis in mixtures of polymers, making use of the potential of soft ionization mass spectrometry to distinguish polymers differing in their endgroups. [59] In the current manuscript we report the application of SEC/ESI-MS for the determination of highly accurate MWD in PLP. Errors in the determined rate coefficients due to band broadening and calibration issues encountered in traditional size exclusion chromatography are successfully eradicated.…”

Mass spectrometry in polymer chemistry: a state-of-the-art up-date

“…The unique capability of online mass spectrometry to identify these functional polymers as well as to quantify them with respect to each other was used by the same authors to restore individual molecular weight distributions of binary and ternary mixtures of functional PMMA. 92 Restoration of the individual MWDs is possible by a simple weighting procedure of the total molecular weight distribution derived by the MaxEnt algorithm with the relative peak areas recorded by mass spectrometry (see Fig. 5, lower right).…”

A broad-standard technique for correcting for band broadening in size-exclusion chromatography

“…Methods employing various types of mass spectrometry can be very accurate (e.g. [5][6][7]), but these techniques cannot be applied to many polymer systems, e.g. those containing very high molecular weights.…”