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  • Characterization of synthetic polymers by MALDI-MS

    Giorgio Montaudo a,*, Filippo Samperi b, Maurizio S. Montaudo b

    a Chemistry Department, University of Catania, Viale A. Doria 6, 95125 Catania, Italyb Institute of Chemistry and Technology of Polymers, CNR, Viale A. Doria 6, 95125 Catania, Italy

    Received 23 June 2005; received in revised form 30 September 2005; accepted 20 December 2005

    Abstract

    In recent years, matrix assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectroscopy has become a

    routine analytical tool for the structural analysis of polymers, complementing NMR and other traditional techniques, a noteworthy

    change with respect to the past, when mass spectrometry (MS) was seldom used. In this review, we discuss salient aspects of

    MALDI. First, we devote a section to fundamentals and practice in MALDI of polymers (such as the laser, ion source, ion optics,

    reflectron, detector, ionization efficiency) as well as to some basic concepts of sample preparation (such as the MALDI matrix and

    cationization agents). Then, we focus on measurable quantities of polymers: average molar masses, the chemical formula and the

    structure of the monomer (actually of the repeat unit), the masses of the chain end groups, etc. In-depth coverage is given of

    coupling MALDI with liquid chromatography (LC), since often LC offers valuable help in exploring macromolecules. The final

    section is devoted to recent applications, with a detailed discussion of MALDI of addition polymers, condensation polymers,

    polymers with heteroatoms in the chain, copolymers and partially degraded polymers.

    q 2006 Elsevier Ltd. All rights reserved.

    Keywords: MALDI; Polymers; Copolymers; Polymer degradation; LC-MALDI

    Contents

    1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 278

    2. Fundamentals and practice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279

    2.1. Ion extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279

    2.2. Detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279

    2.3. Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280

    2.4. Resolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280

    2.5. MALDI matrices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 282

    2.6. Developments in sample preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283

    2.7. Sample preparation for low molar mass compounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 286

    2.8. Doping agents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 287

    2.9. Ionization efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 287

    2.10. Measurement of molar mass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 290

    2.11. Coupling MALDI with devices that separate macromolecules by size . . . . . . . . . . . . . . . . . . . . . . . . . . . 294

    2.12. Coupling MALDI with devices that separate macromolecules by functionality or by composition . . . . . . 298

    Prog. Polym. Sci. 31 (2006) 277357

    www.elsevier.com/locate/ppolysci

    0079-6700/$ - see front matter q 2006 Elsevier Ltd. All rights reserved.

    doi:10.1016/j.progpolymsci.2005.12.001

    * Corresponding author. Tel.: C39 95339926.E-mail address: gmontaudo@dipchi.unict.it (G. Montaudo).

    http://www.elsevier.com/locate/ppolysci

  • G. Montaudo et al. / Prog. Polym. Sci. 31 (2006) 277357278

    2.13. Structure determination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 300

    2.14. End group determination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 303

    2.15. Tandem mass spectrometry for structure determination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 304

    2.16. Copolymer characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 308

    2.17. Bivariate distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309

    3. Recent applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309

    3.1. Polystyrene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309

    3.2. Polymethylmethacrylates and acrylic polymers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 311

    3.3. Other polymers with an all-carbon main chain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315

    3.4. Polymers with heteroatoms in the main chain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315

    3.5. Polysiloxanes, poly(silsesquioxane)s and polysilanes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315

    3.6. Polyethers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315

    3.7. Polyesters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 316

    3.8. Polycarbonates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 317

    3.9. Polyamides and polyimides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 317

    3.10. Polymers with phenyl and other cycles in the main chain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 319

    3.11. Copolymer studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 320

    3.12. Polymer degradation studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 327

    Appendix A. Size exclusion chromatography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 341

    Appendix B. Copolymer composition from MS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 342

    References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 344

    1. Introduction

    Polymers display a variety of structures, including

    linear, cyclic, and branched chains, copolymers with

    various architectures, dendrimers, and star polymers

    with different number of arms. The structural charac-

    terization of a polymer sample usually involves:

    evaluation of the average molar mass (MM) and of

    the molar mass distribution (MMD); determination of

    the repeat units structure; copolymers sequence

    analysis; end group identification; detection and

    identification of impurities and additives. Modern

    mass spectrometry (MS) offers the opportunity to

    explore the finest structural details in polymers [110].

    Matrix assisted laser desorption/ionization time-of-

    flight (MALDI-TOF) has dramatically increased the

    mass range of MS; it provides mass-resolved spectra up

    to 5070 kDa and above, allowing the detection of

    quite large molecules (106 Da), even in complex

    mixtures, at the femtomole level [3]. Peaks in the

    spectra originate from ions of intact polymer chains,

    and, therefore, allow structural identification of single

    oligomers. The last few years have witnessed out-

    standing progress in the application of MALDI to open

    problems concerning the characterization of polymers.

    Initially, MALDI-TOF instruments had poor spec-

    tral resolution (M/DM about 500): i.e. mass-resolvedspectra usually did not go beyond 10,000 Da. This

    caused structural identification problems, even in the

    lowest mass range. Therefore, MALDI-TOF spectral

    data on polymers that appeared in earlier papers (up to

    about 1998) may need updating. MS yields information

    on the masses of individual oligomers, a remarkable

    difference with respect to NMR, which is an averaging

    method. Therefore, besides providing unequivocal

    information on the chemical structure of polymeric

    materials, MALDI allows the identification of chain

    end groups, including species present in minor amounts

    in a polymer sample. End group identification is so

    crucial in polymer analysis that its importance cannot

    be overem

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