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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.

Mechanisms operating in the exchange reactions occurring in the melt mixing processes of Bisphenol A polycarbonate (PC) with poly(butylene terephthalate) (PBT) and poly(ethylene terephthalate) (PET) blends have been investigated making use of appropriate polymer samples, capped or containing reactive chain end groups. The exchange process may proceed by two different mechanisms:  a direct exchange reaction between inner functional groups located inside the polymer chains, i.e., inner−inner, or by attack of reactive chain ends functional groups (outer) on inner groups, i.e., outer−inner. It is shown that the distinction between the two processes can be conveniently made by determining the composition of the copolymer formed in the exchange reaction. The inner−inner mechanism occurs only in the reaction between end-capped or high molar mass PBT/PC or PET/PC samples, and it was found that the molar composition of the copolymer formed is always equal to the feed ratio of the two homopolymers and independent from the reaction time. The outer−inner mechanism occurs in the presence of hydroxyl or carboxyl reactive chain ends in PBT and PET samples. The reaction proceeds by the attack of the reactive end groups on the PC chains, originating block copolymers of PC and PBT and low molar mass PC with phenol end groups which are unreactive. The reaction stops right after the reactive end groups are consumed. The amount and the composition of the copolymers generated in the reactions are found to be constant as a function of time. The copolymer composition shows an excess of PBT or PET units with respect to the feed molar ratio. These results indicate that monitoring the composition of the copolymer formed in each case is diagnostic for establishing the mechanism of the reaction. The approach used here allows control of the composition and yield of the copolymer to be produced, and it is applicable to other systems where exchange reactions occur.

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Four polylactide samples, obtained by ring-opening polymerization with an aluminum alkoxide initiator derived from a Schiff's base, were characterized by MALDI-TOF mass spectrometry. The MALDI mass spectra of these polylactides show well-resolved signals that can be reliably assigned to polylactide oligomers. Remarkably, both even-membered and odd-membered oligomers are present in these MALDI spectra. The presence of odd-membered oligomers cannot be explained on the basis of the lactide ring-opening polymerization, and one must admit that ester-exchange reactions do occur parallel to the polymerization process, causing a random cleavage of the polylactide chain. Furthermore, evidence for the presence of cyclic lactides was found in the MALDI-TOF spectrum of a low molecular weight polylactide fraction, indicating that ester exchange occurs also in polylactides by intramolecular endbiting reactions (ring-chain equilibration), with formation of cyclic oligomers.