Tuning block copolymer structural information by adjusting salt concentration in liquid chromatography at critical conditions coupled with electrospray tandem mass spectrometry (original) (raw)
Related papers
Journal of The American Society for Mass Spectrometry, 2008
Electrospray ionization tandem mass spectrometry has been used to characterize the microstructure of a nitroxide-mediated poly(ethylene oxide)/polystyrene block copolymer, called SG1-capped PEO-b-PS. The main dissociation route of co-oligomers adducted with lithium or silver cation was observed to proceed via the homolytic cleavage of a C-ON bond, aimed at undergoing reversible homolysis during nitroxide mediated polymerization. This cleavage results in the elimination of the terminal SG1 end-group as a radical, inducing a complete depolymerization process of the PS block from the so-formed radical cation. These successive eliminations of styrene molecules allowed a straightforward determination of the PS block size. An alternative fragmentation pathway of the radical cation was shown to provide structural information on the junction group between the two blocks. Proposed dissociation mechanisms were supported by accurate mass measurements. Structural information on the SG1 end-group could be reached from weak abundance fragment ions detected in the low m/z range of the MS/MS spectrum. Amongst fragments typically expected from PS dissociation, only β ions were produced. Moreover, specific dissociation of the PEO block was not observed to occur in MS/MS, suggesting that these rearrangement reactions do not compete effectively with dissociations of the odd-electron fragment ions. Information about the PEO block length and the initiated end-group were obtained in MS3 experiments.
Macromolecules, 2012
Separation of functional poly(ethylene oxide) PEO and PEO block copolymers was investigated using liquid chromatography under critical conditions (LCCC) with a mixture of organic solvents as eluent. The optimum eluent is a mixture of 58.05% chloroform, 6.45% methanol, and 35.50% n-heptane (v/v/v) using a reverse phase (C 8) column. Unlike what was expected, the elution mechanism is governed by the interaction of a polar endgroup with the column. In these conditions, poly(ethylene oxide) (PEO) functionalized with either an acrylate or alkoxyamine moieties were separated. This allows us to investigate the efficiency of the synthesis of poly(ethylene oxide)-b-polystyrene (PEO-b-PS) and polystyrene-b-poly(ethylene oxide) b-polystyrene (PS-b-PEO-b-PS) block copolymers prepared via the combination of 1,2 radical intermolecular addition followed by the nitroxide-mediated polymerization NMP of styrene. Amphiphilic diblock PEO-b-PS and triblock PS-b-PEO-b-PS copolymers were also separated from PEO homopolymers using the same experimental conditions. We showed that the PEO block is then invisible, and the calibration curve obtained using PS homopolymer standards could be used to determine the whole molar mass of the PS block in block copolymers with PS and PEO segments, with a weak influence of the architecture.
Tandem mass spectrometry of poly(ethylene glycol) lithium-attachment ions
Journal of the American Society for Mass Spectrometry, 1994
A study of the fast-atom bombardment tandem mass spectrometry behavior of a number of ethylene glycol polymers (PEGs) has been carried out. Both linear (hydroxyl, amino, and/or alkyl end groups) and cyclic (crown ether) polymers were studied. One of the materials is a block copolymer of ethylene and propylene oxides. Collisional activation was carried out in the collision octapole of a BEoQ hybrid mass spectrometer at a translational energy of 50 eV, with collision gas air. For the linear polymers, the most intense product ions are Iithiated, linear polyglycol oligomers, These ions are formed via internal hydrogen transfer reactions that are facilitated (charge-induced) by lithium. This series of product ions allows for the observation of consecutive losses of monomer units from the chain end; this is useful to determine the sequence of monomers in a copolymer. The most abundant product ions from cyclic PEGs are lithiated radical cations. An especially interesting finding in this work is the preferential loss of two internal ethylene oxide (EO) units (dioxane, 88 u) from some 1M + Li]" precursors. Factors that influence this loss include (a) the sequence length of EO repeat units in the oligomer and (b) the identity of the end groupts) on the oligomer. It is proposed that this elimination of dioxane involves a six-membered ring intermediate; this decomposition reaction is believed to be a lithium-mediated (charge-induced) rearrangement.
Macromolecular Research, 2003
A poly(ethylene oxide)-b-poly(L-lactide) diblock copolymer (PEO-b-PLLA) is characterized by matrixassisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) and a block length distribution map is constructed. Although the MALDI-TOF mass spectrum of PEO-b-PLLA is very complicated, most of the polymer species were identified by isolating the overlapped isotope patterns and by fitting the overlapped peaks to the Schulz-Zimm distribution function. Reconstructed MALDI-TOF MS spectrum was nearly identical to the measured spectrum and this method shows its potential to be developed as an easy and fast analysis method of low molecular weight block copolymers.
Sequence analysis of styrenic copolymers by tandem mass spectrometry
Analytical chemistry, 2014
Styrene and smaller molar amounts of either m-dimethylsilylstyrene (m-DMSS) or p-dimethylsilylstyrene (p-DMSS) were copolymerized under living anionic polymerization conditions, and the compositions, architectures, and sequences of the resulting copolymers were characterized by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) and tandem mass spectrometry (MS(2)). MS analysis revealed that linear copolymer chains containing phenyl-Si(CH3)2H pendants were the major product for both DMSS comonomers. In addition, two-armed architectures with phenyl-Si(CH3)2-benzyl branches were detected as minor products. The comonomer sequence in the linear chains was established by MS(2) experiments on lithiated oligomers, based on the DMSS content of fragments generated by backbone C-C bond scissions and with the help of reference MS(2) spectra obtained from a polystyrene homopolymer and polystyrene end-capped with a p-DMSS block. The MS(2) data provided con...
Tandem Fourier transform mass spectrometry of block and random copolymers
International Journal of Mass Spectrometry, 2011
In recent years, many fragmentation techniques have been developed for use with Fourier transform mass spectrometry (FTMS) in sequencing polymers. Tandem mass spectrometric techniques such as collision-induced dissociation (CID) and electron capture dissociation (ECD) were used to fragment high mass polyether and polyacrylate copolymer ions produced using external electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI) sources. High resolution FTMS analysis of fragments produced by collision cell CID (QCID) is available in a new generation hybrid FTMS instrument. Although tandem QCID-TOF techniques have been used heavily to explore copolymer fragmentation, we report the first QCID-FTMS analysis of such systems. The high fragmentation efficiency of QCID combined with the high mass resolution and mass accuracy of FTMS reveals a novel fragmentation pattern of selected oligomers. This method provided evidence of re-combination of fragments in the gas phase, in that some fragments have higher mass and charges than the isolated precursor ions. QCID fragmentation of oligomers of varying size was studied in the presence of Li, Na, or Cs salts. The ECD-FTMS spectra of polyacrylates showed only side group losses. Accordingly, this technique can be used for an unknown polyacrylate sample analysis and has the potential for side group determination.
Analytical Chemistry, 2008
Complex copolymers are heated to slowly increasing temperatures on a direct probe (DP) inside the plasma of the atmospheric pressure chemical ionization (APCI) source of a quadrupole ion trap. Slow heating allows for temporal separation of the thermal degradation products according to the stabilities of the bonds being cleaved. The products released from the DP are identified in situ by APCI mass spectrometry and tandem mass spectrometry. DP-APCI experiments on amphiphilic copolymers provide conclusive information about the nature of the hydrophobic and hydrophilic components present and can readily distinguish between copolymers with different comonomer compositions as well as between cross-linked copolymers and copolymer blends with similar physical properties. The dependence of DP-APCI mass spectra on temperature additionally reveals information about the thermal stability of the different domains within a copolymer. Electrospray ionization (ESI) 1 and matrix-assisted laser desorption/ionization (MALDI) 2,3 have made it possible to form intact gas-phase ions from most classes of synthetic polymers, enabling mass spectrometry (MS) analyses on such macromolecules. 4-20 MS experiments provide the masses of the individual oligomers contained in a polymer, from which important compositional and structural information about the polymer can be deduced, for example, its (co)monomer composition, end groups, compositional heterogeneity, and molecular weight distribution. Still, numerous synthetic polymers designed for important industrial or biomedical applications cannot be analyzed by MS, because they are too large or too polar to be dissolved (for ESI) or desorbed (for MALDI), or they are unable to form gas-phase ions due to the lack of functional groups that can attract and bind a charged particle, such as a proton or metal cation. Fortunately, most large or unionizable polymers become amenable to MS analysis by pyrolysis, i.e., thermal degradation. 9,21-30 Depending on the thermal stability of the polymer and the temperature used (typically within 150-1000°C), pyrolysis leads either to small fragments that can be ionized by electron ionization, chemical ionization (CI), field ionization, or photoionization, or to higher-mass pyrolyzates that can be subjected to ESI, MALDI, or both. The resulting mass spectra unveil the composition of the polymer sample. Molecular weight information is lost, but information about the thermal stability and degradation pathways of the polymer is gained. Rapid heating of the sample to a high temperature, via hightemperature Curie-point or resistive heating flash pyrolysis,