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Matrix assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) allows detection of large molecules such as those present in synthetic and natural macromolecules. Until recently, it was reported that MALDI-TOF measurements can provide correct molecular weight (MW) averages only for samples with a narrow MW distribution (MJMn < 1.20). We have now developed a methodology for polydisperse samples. We recorded the GPC trace of two polydisperse polymeric samples, namely, poly(butylene adipate) (PBA) and poly(butylene adipate-co-butylene succinate) (PBAS), collecting about 40-50 fractions per run. Selected fractions were analyzed by MALDI-TOF, and the average MW of each fraction was determined, allowing calibration of the GPC curves against absolute MW. The two calibrated GPC traces were then used to compute average MW and molecular weight distributions (MWD) of the unfractionated samples. End group analysis from MALDI-TOF spectra revealed that the PBA sample is composed of seven different types of chains. For the copolymer sample, PBAS, analysis of the MALDI spectra established a random sequence distribution of comonomer units. The succinate/adipate molar ratio calculated from the MALDI spectra is in good agreement with the molar ratio found by NMR.

The structural characterization and composition of five random copolyesters, originating from 1,4-butanediol and mixtures of succinic, adipic, sebacic, and terephthalic acids, were obtained by analysis of their fast atom bombardment (FAB) and their matrix-assisted laser desorption ionization (MALDI) mass spectra. Multicomponent condensation copolymers may sometimes prove difficult to characterize by conventional techniques, whereas mass spectrometry is able to handle them. Once the choice between Bernoullian or Markoffian models has been made, the determination of copolymer composition, number-average sequence length, and related quantities can be achieved by applying well-defined analytical equations. The theoretical mass spectra of multicomponent copolymers are remarkably simple, and the number of peaks appearing in each copolymer mass spectrum is easily predictable. Different kinds of spectral fitting algorithms may help in the actual computations, and it has been shown that the apparent complexity of mass spectra of copolymers is due to the presence of mass series bearing different end groups. By selecting a single mass series, one obtains an experimental spectrum immediately comparable to the theoretical one. Detailed examples, together with a discussion on the reliability of results, are given to apply the computation procedures and to gain proper understanding of the concepts involved.

Four samples of Ny6, each terminated by different end groups, i.e., diamino terminated, monoamino terminated (monocapped), dicarboxyl terminated, and amino‐carboxyl terminated, were synthesized and analyzed by MALDI‐TOF Mass Spectrometry, in order to accurately characterize their structure by direct identification of mass resolved chains. A self‐calibrating method for the MALDI‐TOF mass spectra of polymeric samples was used in order to distinguish the end groups existing in the four samples of Ny6. The MALDI‐TOF spectra showed the presence of protonated, sodiated, and potassiated ions that were assigned to Ny6 chains containing the expecteted end groups. Furthermore, the MALDI‐TOF spectra made possible the simultaneous detection of the cyclic oligomers of Ny6 present in these samples, thus achieving the full structural characterization of the molecular species present in these polyamides. © 1996 John Wiley & Sons, Inc.