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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.

During a work designed to use MALDI−TOF MS to determine the composition of an equimolar blend of nylon 6 (Ny6) and polybutyleneterephthalate (PBT), the MALDI−TOF mass spectrum showed a surprising strong imbalance between the two components. The predominance of Ny6 oligomers over the PBT oligomers terminated with hydroxyl end chains is signaled by the appearance of specific peaks in the MALDI−TOF mass spectra. Since the average molar mass and the polydispersion of the two polymers are comparable, the MALDI−TOF MS ionization efficiency is quite different for the two components of the blend. This finding prompted us to a more detailed study, and to synthesize a number of Ny6 and PBT samples terminated with different end groups, to analyze their equimolar blends by MALDI−TOF MS. The results reported in the present study may help clarifying some fundamental aspects about the mechanisms of ions formation, when MALDI−TOF mass spectrometry is applied to macromolecules. End groups ionization efficiency appears to ...

Progress in understanding the thermal decomposition processes occurring in Nylon 66 (Ny66) was obtained by using matrix assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry techniques. Ny66 samples were subjected to thermal degradation under inert atmosphere heating them at 290 and 315 °C. The formation of a gel fraction was observed after about 15 min of heating and the addition of a condensing agent such as triphenyl phosphite (TPP) made the gelation complete in a few minutes. The MALDI-TOF mass spectra of the soluble fraction showed that secondary amino groups and cyclopentanone chain ends were generated in the heating process. The gel fraction was partially hydrolysed to destroy the network structure and the soluble material was analysed by MALDI-TOF. The spectra revealed the presence of N,N-substituted amide as side chains generated by the condensation of carboxyl end groups with secondary amino groups and azomethine structures originating from the reaction of cyclopentanone moieties with the terminal amino groups. These structures were most likely responsible for the gel formation on heating Ny66 samples. Comparison with similar experiments conducted on Ny6, showed that only secondary amino groups were formed in Ny6, leading to branched structures but not to crosslinking.

We report here a case of apparent failure of the size exclusion chromatography/matrix-assisted laser desorption/ionization (SEC/MALDI) method to provide polymer fractions with narrow molar mass distribution, showing that intermolecular chain association is responsible for this phenomenon. Poly(bisphenol A carbonate) (PC) chains terminated with hydroxyl groups undergo self-association by hydrogen bonding, providing macromolecular aggregates with higher hydrodynamic volume. These aggregates are eluted through SEC columns at the same volume as higher molar mass chains, which remain non-associated. Thus, self-association affects negatively the SEC fractionation experiments, and even the sharpest SEC fractions contain a heterogeneous mixture of PC chains of different size. When the off-line SEC/MALDI procedure is applied, the SEC fraction is diluted in the matrix which, being a dissociating medium (carboxylic acid) for hydrogen-bonded aggregates, suppresses the chains' self-association. Therefore, the MALDI spectra of these PC fractions indicate a polydisperse character, with irregular bimodal distributions of peaks. As a consequence, in the presence of chain association, the SEC/MALDI method for the calculation of molar masses of polymers cannot be directly applied. In the present case we have found that, under opportune experimental conditions, self-association in polycarbonates can be avoided, so that nearly monodisperse SEC fractions can be obtained and the SEC/MALDI method can be applied. Our results also show that MALDI is a very sensitive technique for the detection of association of polymers in dilute solutions. Copyright 1999 John Wiley & Sons, Ltd.

The determination of molar mass (MM) data for polydisperse polymers by SEC/MALDI involves the fractionation of samples through analytical size exclusion chromatography (SEC). Selected SEC fractions are then analyzed by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) and the mass spectra of these nearly monodisperse samples allow the determination of the average molar masses. The SEC/MALDI procedure has now been applied to two polycarbonate samples, PC1 and PC2. The results show that the MALDI spectra of the SEC fractions allow not only the detection of linear and cyclic oligomers contained in these samples, but also the simultaneous determination of their average molar masses. Two slightly differing SEC calibration plots were obtained, due to the smaller hydrodynamic volume of the polycarbonate cyclic chains with respect to the linear ones. In agreement with theory, the ratio (M(cycle)/M(linear))(Ve) at a fixed elution volume was found to be 1.22, independent of the molar mass values. Copyright 1999 John Wiley & Sons, Ltd.

High conversion copolymers may experience a strong variation in composition as a function of monomer conversion, and since the compositional heterogeneity of copolymers varies as the size of the chains grows, this poses a problem in determining the bivariate distribution of masses and composition in copolymers. Although several methods have been proposed to determine bivariate distributions, relatively little data are available on this important aspect of copolymer characterization, perhaps because of the complexity of the methods available up to the present time. We propose here a generally applicable method to determine bivariate distribution of masses and composition in copolymers. SEC fractionation of two random copolymers, poly(methyl methacrylate)/polybutyl acrylate (PMMA/PBA) obtained at high and low conversions, respectively, was used to collect nearly monodisperse fractions that allowed the computation of the corresponding molar masses (by matrix-assisted laser desorption ionization mass spectrometry, MALDI, measurements) and of compositions (by NMR measurements) for the two copolymers. Bivariate distribution maps were derived by combining SEC/NMR and SEC/MALDI data with Stockmayer's theoretical distribution to estimate the composition distribution of each fraction.

The PROLOG programming language was used for the construction of the Expert System (ES) HEPHESTUS used in the interpretation of pyrolysis mass spectra of condensation polymers, such as polyamides, polycarbonates, polyethers, polyesters, polyureas, polyurethanes, polyimides, polysulphides, polysulfones, polyschiff bases, polysiloxanes and polyphosphagenes. The ES can be applied to Pyrolysis Mass Spectrometry (PyMS) spectra of polymers using Electron Impact, Chemical Ionisation or Desorption Chemical Ionisation modes. The sample is introduced and pyrolysed directly in the source of the mass spectrometer. The ES knowledge base is organised in a tree form, based on polymer structures. The inference mechanism uses empirical algorithms and the autocorrelation algorithm to determine important information present in the unknown polymer spectrum. Possible solutions are proposed using the Certainty Factor model and based on the rules of the knowledge base. The autocorrelation algorithm, used to determine the repeating unit, gave 57.3% of successes and 42.7% not best choices. Among the not best choices the 23.3% were failures. For the same purpose, the empirical algorithm gave 68.5% successes and 31.5% not best choices (among them 35.7% were failures). User interaction improves the ES's performance to propose the correct polymer (94.4% of the trials were the best choices).

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 (M w /M n ≤ 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.

To explore the possibility of using the partial pyrolysis of microbial poly(hydroxybutyrates) (PHBs) for obtaining single 3HB, 4HB, and mixed 3HB/4HB oligomers, the pyrolysis of P(3HB), P(4HB), and P(3HB-co-4HB) was performed and the products obtained were analyzed by HPLC and fast atom bombardment mass spectrometry (FAB-MS). Our results show that the partial pyrolysis of P(3HB) and P(4HB), followed by HPLC separation of the products, affords a suitable route for the synthesis of linear 3HB oligomers and of 4HB oligolides, respectively. The thermal degradation of P(3HB), P(4HB), and P(3HB-co-4HB) copolymers containing 3-34% of 3HB units was investigated by using several techniques: monitoring the time-dependent changes in molecular weight of melt samples in the range 180-200 °C ; direct pyrolysis mass spectrometry ; preparative pyrolysis and subsequent IR, NMR, HPLC, and FAB-MS analysis of the pyrolysate. Contrary to the claim that the rate constant (K d ) of chain scission is not influenced by the composition of the copolyesters, our results show that the rate of chain scission is influenced by the composition of copolyesters and that a mixture of cyclic and open chain oligomers is formed in the pyrolysis process. These findings indicate that P(3HB-co-4HB) copolymers undergo thermal degradation by two competitive random chain scission mechanisms : a β-CH hydrogen transfer at the 3HB units and an ester exchange cyclization at the 4HB units.

A new method for the interpretation of pyrolysis-mass spectra of polyesters is described. The method is based on the use of table of pyrolysis-mass spectral data of polyesters. It has two steps: first, the examination of the unknown pyrolysis-mass spectrum in order to extract information about the relationship of specific ion masses with particular polyester structures; second the recongnition and the identification of mass series in the spectrum. Tables of pyrolysis-mass spectrometry (Py-MS) data of polyesters are presented. Examples of the application of the interpretation method are given. The advantages in limitations of the method are presented and discussed.

Mass Spectrometry, being able to look at the mass of individual molecules in a mixture of homologues, is particularly suitable for the detection of a series of oligomers. However, mass spectra had not been exploited to estimate oligomers distributions, due to the diffuse notion that a lack of correlation existed between peak intensities and concentration of the oligomers in the mixture. The introduction of soft-ionization techniques has largely eliminated this problem. A novel method for the determination of the microstructure of copolymers is presented here. We have recently found that opportune decoding of the information contained in the mass spectral intensities leads to the determination of composition and microstructure in copolymers, and this represents a significant progress. Statistical modeling of the mass spectral intensities of copolymers has been used to derive information on the distribution of monomers along the copolymer chain, and an automated procedure to find the composition and the sequence of the copolymers analyzed has been developed. The statistical analysis of copolymers makes use of Bernoullian and Markovian models in order to characterize the microstructure of copolymer samples, and assuming a theoretical distribution and then fitting the calculated oligomer abundances with the experimental MS peak intensities, the copolymer composition can be determined. A method is also reported to obtain the copolymer conposition by direct analysis of the mass spectra. These theories have been applied to determine the composition and the microstructure of several copolymers whose mass spectra have been reported in the most recent literature.

Two different terpolyesters were obtained by fermentation of Rhodospirillum rubrum fed either with 4-pentenoic acid alone or with an equimolar mixture of 4-pentenoic and valeric acids. Sequence distributions of these two polyesters were determined by fast atom bombardment mass spectrometry (FAB-MS) of the oligomers prepared by partial methanolysis and separated by HPLC. The distributions in both polymers follow Bernoullian statistics, indicating that both are random terpolyesters

Matrix-assisted laser desorptionhonization time-of-flight mass spectrometry (MALDI-TOF MS) allows the detection of large molecules such as those present in synthetic and natural macromolecules. Synthetic polymers may show a wide range of molecular weight distributions (MWD), according to the synthetic method used in their preparation. We have studied several poly(methylmethacry1ate) (PMMA), poly(styrene) (PS) and poly(ethyleneg1ycol) (PEG) samples with varying MWD, and also a number of condensation polymers such as Nylon-6, poly(carbonate) and poly(ester). Measurements of MALDI-TOF spectra in the linear mode were used in our work to estimate the molecular weight (MW) and MWD of the polymer samples. Our results show that the molecular weight estimates provided by MALDI-TOF measurements agree with the values obtained by conventional techniques, such as gel-permeation chromatography (GPC), only in the case of polymer samples with very narrow molecular weight distribution. However, when the polydispersity reaches values around 1.10 the difference between the MW measured by GPC and measured by MALDI may amount to up to about 20%. At higher dispersions, the MALDI spectra fail to yield reliable MW values.

The thermal degradation products of two sulfur polymers, poly(styrenedisulfide) (PSD) and poly(styrenetetrasulfide) (PST), were investigated in parallel by direct pyrolysis-mass spectrometry (DPMS) and by flash pyrolysis-GC/MS (Py-GC/MS). The time-scale of the two pyrolysis techniques is quite different, and therefore they were able to detect significantly different products in the pyrolysis of PSD and PST because of the thermal lability of sulfur-containing compounds. However, the results obtained are not contradictory, and satisfactory mechanisms for the thermal degradation of PSD and PST have been derived from the overall evidence available. Pyrolysis compounds containing sulfur, styrene, and a number of cyclic styrene sulfides and diphenyldithianes have been observed by DPMS. However, in flash pyrolysis-GC/MS, styrene, sulfur, only one cyclic styrene sulfide, and two isomers of diphenylthiophene have been detected. These thiophene derivatives were indeed absent among the compounds obtained by DPMS because they were the terminal (most thermally stable) species arising from further decomposition of the cyclic styrene sulfides formed in the primary thermal degradation processes of PSD and PST.

Fast atom bombardment mass spectrometry (FAB-MS) has been used to identify oligomers with different end groups obtained by the carbonate interchange reaction of bisphenol-A with dimethyl carbonate and the partial methanolysis of poly(bisphenol-A carbonate)s. Based on the FAB-MS data, a reaction pathway for the formation of compounds in the synthesized oligomers is proposed.

Poly(β-hydroxybutyrate-co-β-hydroxyvalerate) of microbial origin has been analyzed by matrix-assisted laser desorption/ionization (MALDI) in a time-of-flight mass spectrometer, after partial methanolysis, using two different instruments, Our results show that the mass spectral intensities recorded in the MALDI mode correlate with previously reported fast-atom bombardment and direct chemical ionization data. MALDI compares favourably with these other two techniques in that it is more suitable to the analysis of complex mixtures and of higher molecular masses.

This study shows that is possible to determine the composition and microstructure of the copolyester formed in the melt-mixing process of poly(ethylene truxillate)1 (PETx) and poly(ethylene terephthalate) (PET), by applying a novel method of statistical modeling of mass spectra of copolymers. The peak intensities of molecular ions appearing in the fast atom bombardment mass spectrum of the melt-mixed equimolar mixture of PETx and PET were found to reflect the relative amounts of oligomers present in the sample and to be directly related to the microstructure of the copolymer formed. The statistical analysis of copolymers allows one to generate a number of different theoretical mass spectra that can be fitted with the experimental mass spectrum data, thus determining the most likely copolymer composition.

The sequence distributions of microbial copolyesters produced by Pseudomonas oleovorans grown with (a) nonanoic acid (NA) (b) an equimolecular mixture of NA and octanoic acid (OA) or (c) 2:1 mixtures of 10-undecenoic acid with either NA or OA were determined by analyzing the oligomers prepared by partial pyrolysis of these copolymers using FAM mass spectrometry. the sequence distributions in these copolyesters followed Bernoullian statistics, indicating that they were random copolymers

The recent finding that significant information on copolymer microstructure can be obtained by using mass spectrometry has stimulated our work toward developing appropriate algorithms to match the experimental mass spectra to those theoretically calculated. A novel program for the determination of microstructure in copolymers by computer simulation of mass spectra is reported. The statistical model used to describe copolymer distributions is reported in detail in the text. The computer simulation program (MACO3) is discussed, and three illustrative examples are given.

The assumption on which both the structural analysis of polymers and the sequential of co-polymers by fast-atom bombardment mass spectrometry (FAB-MS) is based, is that the ion detected in the FAB spectra do originate from species already present in the polymeric samples, and that the bombardment by fast atoms does not produce the fragmentation of macromelecules. FAB spectra do not yield direct structural information on large macromolecules, but such information can be deduced from the structural analysis of relatively low molecular weight species. Therefore, in a series of recent studies, FAB-MS has been used to identify the oligomers formed in the partial degradation of several co-polymers, and the results obtained have yieled detailed information on the microstructure of the materials investigated.

Etude de copolymeres statistiques, d'un poly(1,4-butadiene) cis et d'un copolymere trisequence SBS. Les resultats montrent que la spectrometrie de masse des produits de lozonolyse permet de distinguer une structure statistique d'une structure sequencee et d'evaluer la proportion et la distribution des monomeres. La cinetique d'ozonolyse est etudiee

We report matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) and off-line coupling of size-exclusion chromatography with MALDI-TOFMS analysis (SEC/MALDI-TOFMS) methods for the detailed characterization of poly[(R,S)-3-hydroxybutyrate-co-L-lactic acid], P[(R,S)-3HB-co-LA], and poly[(R,S)-3-hydroxybutyrate-co-epsilon-caprolactone], P[(R,S)-3HB-co-CL], copolymer samples which are expected to be used in special medical application as scaffolds for cartilage and soft tissue engineering. The novel copolyesters contained randomly distributed (R,S)-3-hydroxybutyrate structural units, were synthesized by transesterification of the corresponding homopolymers, i.e. atactic poly[(R,S)-3-hydroxybutyrate], a-PHB, and poly(L-Lactide) (PLLA) or poly(epsilon-caprolactone) (PCL), respectively. The MS methods used for the characterization of the resulting polydisperse copolyester samples were supported by classical methods (NMR, SEC). The structures of individual copolyester macromolecules, including end-group chemical structures, were established using initially MALDI-TOFMS and then SEC/MALDI-TOFMS. The compositions of the copolyesters were determined by two methods, namely based on 1H NMR and MALDI-TOF spectra. The two sets of values showed good agreement. The sequence distribution was determined using the signal intensities of individual copolyester macromolecules, which appeared in MALDI-TOF mass spectra. Furthermore, sequence analysis gave information about the degree of transesterification. The copolyesters synthesized, with only one exception, were demonstrated to be almost random, which implies that the ester-ester exchange was close to completion.

In the last few years, mass spectrometry has rapidly become indispensable in polymer analysis and complements, in many ways, the structural data provided by nuclear magnetic resonance. Mass spectrometry of polymers is emerging as a revolutionary technique, capable of challenging the techniques and protocols established for years for the characterization of synthetic polymers. Matrix-assisted laser desorption/ionization (MALDI) has become a widely applied method for the structural characterization of synthetic polymers. The primary aim of this review is to illustrate some recent advances in the study of macromolecular systems by MALDI. MALDI allows the identification of repeat units and end groups, the structural analysis of linear and cyclic oligomers and the estimate of composition and sequence for co-polymers. MALDI is also quite useful for the measurement of molar mass and bivariate distributions in polymers and for the detection of self-association in macromolecules, performed by coupling MALDI with size exclusion chromatography (SEC). Recently MALDI has been applied, with remarkable success, to the study of thermal and oxidative processes in polymers and to the characterization of co-polymers obtained by reactive polymer blending. Selected applications of MALDI to polymers are illustrated herewith.

Matrix-Assisted Laser Desorption/Ionization (MALDI) allows the identification of repeat units and end groups, the structural analysis of linear and cyclic oligomers, and the estimate of composition and sequence for copolymers. MALDI has also been applied to the measurement of molar mass distributions in polymers and to the study of thermal and oxidative processes in polymers. This paper illustrates the detection of self-association in macromolecules made by coupling MALDI and Size Exclusion Chromatography (SEC), the investigation of polymer oxidation phenomena, and the characterization of copolymers formed in the processing of reactive polymer blends.

Matrix-assisted laser desorption ionization mass spectrometry (MALDI-TOF-MS) has been found to be an excellent method to det. the structure of the mols. produced in the photooxidative degrdn. of poly(butylene succinate) (PBSu) at 60 °C in air. Over 20 compds. are present in the MALDI spectrum of the oxidized sample, as compared to only 4 in the original PBSu sample. The MALDI spectra present many new well-resolved peaks, which provide information on the structure and end groups of the oxidn. products. The MALDI peaks correspond to sodiated ions of oxidized oligomers, and they have been assigned to polymer chains contg. succinic and malonic acid, Bu ester, Et ester, and Bu formate end groups. These oligomers had not been revealed before. The mechanisms accounting for the formation of photooxidn. products of PBSu involve the operation of several reactions: (i) oxidn. of hydroxyl end groups; (ii) a-H abstraction decompn.; (iii) Norrish I photocleavage. Our results establish the photooxidn. mechanisms of PBSu. The novelty of our approach consists of using a nonaveraging technique, such as mass spectrometry, which allows the detection of individual compds. formed during the oxidn. process. This is a remarkable result, and it should be expected that future MALDI studies might have an impact on the current views on photooxidn. processes of other polymer systems.

In the attempt to find evidence on the structure of the species produced in the thermal oxidative degradation of Bisphenol A-Polycarbonate (PC), two polycarbonate samples, one capped (incompletely) with phenyl groups at both ends (PC1) and the other one capped (incompletely) with tert-butyl phenyl groups at both ends (PC2), were used. The two PC samples were heated at 300°C and 350°C under atmospheric air up to 180 min producing a THF insoluble gel at the longer heating times. The oxidative process was followed as a function of the exposure time by SEC, 1H-NMR , MALDI and SEC/MALDI techniques. The SEC curves showed extensive degradation, up to the formation of very low molar mass oligomers. Highly valuable structural information on the thermal oxidized PC species was obtained by using MALDI mass spectrometry. The MALDI spectra of the thermal oxidized PC1 and PC2 samples showed the presence of polymer chains containing acetophenone, phenyl substituted acetone, phenols, benzyl-alcohol and biphenyl terminal groups. Formation of acetophenone and phenol end groups was confirmed by 1H-NMR analysis. The mechanisms accounting for the formation of thermal oxidation products of PC involve the operation of several simultaneous reactions: i) hydrolysis of carbonate groups of PC to form free Bisphenol A end groups; ii) oxidation of the isopropenyl groups of PC; iii) oxidative coupling of phenols end groups to form biphenyl groups. The presence of biphenyl units among the thermal oxidation products confirmed the occurrence of cross-linking processes, which is responsible for the formation of the insoluble gel fraction.. The MALDI analysis of the oxidation products of PC2 sample, capped with tert-butyl phenyl groups at both ends, unveiled a specific antioxidant action of these terminal groups, which are able to slow down the rate of thermal oxidation of PC2 compared to PC1 sample.

The positive ion matrix-assisted laser desorption/ionization (MALDI) spectrum of an equimolar blend of Nylon 6 (Ny6) and hydroxyl-terminated polybutyleneterephthalate (PBT) shows a surprisingly strong imbalance between the two components. Since the average molar masses and the polydispersions of the two polymers are comparable, it follows that the efficiency of MALDI is quite different for the two components of the blend. This finding prompted us to a more detailed study, and to synthesize Ny6 and PBT samples terminated with different end groups, in order to analyze their blends by MALDI. The negative ion MALDI spectra of the mixtures investigated show that PBT samples do not yield signals, so that only Ny6 peaks appear in these spectra. By comparing positive and negative ion MALDI spectra of mixtures of Ny6 terminated with various end groups, it was found that the peak intensity depends on the nature of the end groups. The results reported in the present study may help to clarify some fundamental aspects of the mechanisms of ion formation, when MALDI mass spectrometry is applied to macromolecules. End group ionization efficiency appears to be the most important parameter in determining the relative intensity of peaks in the MALDI spectra of the polymer blends investigated. End-group-dependent ionization is the key to the rationalization of the relative peak intensities in MALDI spectra of polymer mixtures. Copyright (C) 2002 John Wiley Sons, Ltd.

This chapter devotes to the discussion of the direct pyrolysis of polymers in the ion source of a mass spectrometer. The specific thermal decomposition pathways occurring in these polymers largely depend upon the nature of the functional groups present and also upon the chemical structure of the monomer units, which causes drastic changes in the pyrolysis mechanisms even within the same class of condensation polymers. The polymeric material is deposited on a filament, which is rapidly heated to the degradation temperature. Blends of condensation polymers such as polyesters, polyamides, polycarbonates, and in general polymers bearing reactive backbone or pendant functional groups, may yield chemical exchange reactions in the molten state. The thermal degradation of polymers was an active field of investigation long before modern instrumental techniques were available. Earlier studies generally involved the pyrolysis of large samples and off-line degradation.

Preface, G. Montaudo and R.P. Lattimer Introduction to Mass Spectromety of Polymers, M.J. Polce and C. Wesdemiotis Polymer Characteriztion Methods, G. Montaudo and M.S. Montaudo Pyrolysis Gas Chromatography/Mass Spectrometry (Py-GC/MS), S. Tsuge and H. Ohtani Electrospray Ionization (ESI-MS) and On-Line Liquid Chromatography/Mass Spectrometry (LC/MS), L. Prokai Direct Pyrolysis into the Ion Source (DPMS), G. Montaudo and C. Puglisi Field Ionization (FI-MS) and Field Desorption (FD-MS), R. P. Lattimer Fast Atom bombardment (FAB-MS), G. Montaudo and F. Samperi Time-of-Flight Secondary Ion Mass Spectrometry (FT-MS), S.J. Pastor and C.L. Wilkins Laser Fourier Transform Mass spectrometry (FT-MS), S.J. Pastor and C.L. Wilkins Matrix-Assisted Laser Desorption/Ionizationi Mass Spectrometry (MALDI-MS), G. Montaudo, M.S. Montaudo, and F. Samperi Two-Step Laser Desorption Mass Spectrometry, M.S. deVries and H.E. Hunziker

Matrix-assisted laser desorption ionisation (MALDI) mass spectrometry was used, in an attempt to find firm evidence for the structure of the species produced in the thermal oxidative degradation of Nylon 6 (Ny6), at 250°C in air. The MALDI spectra of the products showed the presence of polymer chains containing aldehydes, amides, methyl and N-formamide terminal groups. The aldehydes undergo further oxidation to produce carboxylic end groups. The formation of azomethines, from the further reaction of aldehydes with amino-terminated Ny6 chains, is also supported by the appearance of specific peaks in the MALDI spectra.

The thermal decomposition pathways leading to the formation of volatile compounds and to char residue in poly(bisphenol A carbonate) (PC), poly(resorcinol carbonate) (PRC), and poly-(hydroquinone carbonate) (PHC) have been investigated by mass spectrometry. The structure of the volatile compounds obtained in the temperature range 300-700 degrees C, by direct pyrolysis mass spectrometry (DPMS), suggests that these polycarbonates undergo thermal decomposition by a number of different pyrolysis processes. In the initial stage of the thermal degradation are generated cyclic oligomers by an intramolecular exchange reaction, whereas the evolution of CO2 and H2O is spread over all the pyrolysis temperature range, being responsible for the formation of ether bridges (decarboxylation) and phenolic end groups (hydrolysis). A disproportionation reaction of the BPA isopropylidene bridges of PC itself takes place at higher temperature yielding phenyl and isopropylidene end groups, whereas pyrolysis products containing dibenzofuran units are formed by dehydrogenation of ether units. The formation of compounds containing xanthone and fluorenone units, most likely generated by isomerization of the aromatic carbonate functional groups and successive condensation reaction, has also been observed. In an additional set of experiments, the isothermal pyrolysis of PC was achieved, isothermally, at 350 and 400 degrees C, and then the exhaustive and selective aminolysis of the carbonate functional groups, still present in the pyrolysis residue, has been performed. The aminolyzed residue was then analyzed by fast atom bombardment (FAB) mass spectrometry to detect the compounds eventually formed by molecular rearrangements of PC chains. The FAB-MS spectra showed the presence of compounds containing several consecutive xanthone and ether units, indicating that at this temperature the isomerization and the condensation processes leading to these structures are quite extensive. These units undergo aromatization and cross-linking processes, leading to a graphite-like charred residue as the temperature increases.

A method for the determination of molecular weight distribution data for polydisperse polymer samples by MALDI-TOF is reported that involves the fractionation of polydisperse samples through analytical GPC columns and collection of fractions. Selected fractions are then analysed by MALDI-TOF and the mass spectra of these nearly uniform samples allow the determination of M-n and M-w averages. The GPC tracing, calibrated against molecular weight values obtained by MALDI, was used to compute molecular weight distribution data of the unfractionated sample. To test the reliability of the molecular weight estimates by the GPC/MALDI-TOF method, a sample of poly(methyl methacrylate) and two samples of poly(dimethyl siloxane), both with wide polydispersity, were analyzed. The results show that the molecular weights of PMMA fractions obtained by MALDI coincide with the GPC calibration plots obtained with anionic PMMA standards, In the case of the two poly(dimethyl siloxanes), two slightly different GPC calibration plots were obtained owing to the different structures of the polymer chains of the two samples. In fact, the MALDI spectra of low MW fractions of these polymers, showed that one sample consists essentially of linear oligomers, whereas the other sample contained cyclic oligomers.

The sequence distributions of four poly(ether-sulfone)/poly(ether-ketone) (PES/PEK) copolymer samples were determined by means of fast atom bombardment mass spectrometry (FAR-MS) and by C-13 NMR spectroscopy. The controlled partial degradation of the copolymer chains to produce oligomers suitable of FAB-MS analysis was performed with sodium methoxide in dimethyl sulfoxide solution at 130 degrees C, and the experimental conditions were optimized. The sequential arrangements of ether-sulfone/ether-ketone units present in these materials were estimated by a best-fit minimization method using the MACO4 computer program which compares the experimental FAB-MS spectral intensities with theoretical intensities. Random PES/PEK copolymer samples showed quite the same sequence arrangements as expected from monomer feed-ratios used in the syntheses. Instead, a PES/PEK copolymer sample expected to be exactly alternating (from the synthesis procedure) showed 44% of random sequences owing to the transetherification reaction which occurred in the synthesis. The results of sequential analysis obtained from C-13 NMR data compare well with the data obtained by the FAB-MS analysis.

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) estimates only for nearly monodisperse polymer samples. We have now developed a methodology for polydisperse samples. We recorded the gel-permeation chromatography (GPC) trace of a polydisperse polymeric sample of poly(dimethylsiloxane) (PDMS), collecting 42 fractions. Selected fractions were analyzed by MALDI-TOF and the average MW of each fraction was determined, allowing a calibration of GPC curves against absolute MW. The calibrated GPC trace was then used to compute average MW and molecular-weight distribution (MWD) of the unfractionated poly(dimethylsiloxane) sample. In the spectra of low molecular-weight fractions, the resolution is high enough to resolve the contributions of the various PDMS oligomers as separate signals.

A novel calibration procedure is introduced that allows one to obtain absolute mass values in MALDI-TOF spectra of polymeric materials. The masses of the oligomers are written as the sum of two masses: mu(n) = sigma(n) + theta, where theta is the mass of the first oligomer and sigma(n) is a multiple of the polymer repeat unit and represents the distance in daltons from the first oligomer. The new calibration procedure considers theta as a variable parameter and performs a best-fit minimization. Two examples of application of the new procedure are given. Two synthetic polymers, poly(caprolactone) and poly(Bisphenol A carbonate), were analyzed by MALDI-TOF, and complex spectra showing one or more mass series up to 20 kDa were obtained. Application of this procedure allowed the interpretation of each single peak in the mass spectra and established that none of the peaks in the spectrum corresponds to fragments. It was found that the poly(caprolactone) sample consists of a series of oligomers with H and OH as terminal groups, which form sodium-cationized ions in the MALDI process. The composition of the poly(Bisphenol A carbonate) sample was more complex, since it contains a series of cyclic oligomers desorbing as sodium-cationized ions, plus two series of oligomers bearing H/phenol and phenyl/phenol as terminal groups, respectively, which form ions by capturing a proton in the MALDI process.

The sequence distributions of poly(beta-hydroxyalkanoate) copolymers were determined by analyzing oligomers obtained by the pyrolysis direct-chemical-ionization (DCI) mass spectrometry technique. Oligomers up to nonamers were identified and the comparison between the experimental and calculated peak intensities makes it possible to calculate repeating unit compositions and sequence distributions. Comparisons with other earlier methods are given.

Statistical modeling of the mass spectral intensities of copolymers has been used to derive information on the distribution of monomers along the copolymer chain, and an automated procedure to find the composition and the sequence of the copolymers analyzed has been developed. A deconvolution method to determine the microstructure of copolymers when different chemical species contribute to the same mass spectral peak (that is, when a mass spectroscopic peak has an equivocal structural assignment) is presented. The effect of the partial degradation process on the mass spectra of copolymers is discussed, and a theory is given for the interpretation of the mass spectra of copolymers when the cleavage of the copolymer chain occurs by a selective or nonselective mechanism. A method is also reported to obtain the copolymer composition by direct analysis of the mass spectra. All these theories have been applied to determine the composition and microstructure of several copolymers (both addition and condensation types) whose mass spectra have been reported in the most recent literature.

The thermal decomposition mechanisms of poly(trimethylene carbonate), poly(neopentylene carbonate), poly(t2-phentlrimethylene carbonate) and poly(p-xylylene carbonate) have been investigated by EI/CI direct pyrolysis mass spectrometry and by desorption chemical ionizatio (DCI) mass spectrometry. The results ....

The partial methanolysis and the partial pyrolysis of bacterially synthesized copolyesters of β-hydroxybutyrate (HB) and β-hydroxyvalerate (HV) have been performed and the oligomers produced have been analyzed by fast atom bombardament mass spectrometry (FAB-MS). An algorithm has been developed to distinguish pure random copolymers from mixtures of random copolymers, using the relative abundances of the oligomers which can be deduced from the FAB-MS spectra.

Linked scanning mass spectrometry was applied to the analysis of the mixture of pyrolysis products obtained from some polyamides, pyrolyzed directly in a mass spectrometer. Collision activated decomposition spectra were obtained in order to induce a higher intensity in the metastable transition. The results indicate that linked scanning mass spectrometry provides a fast method for unambiguously assigning chemical structures through the study of molecular ions, characteristic fragmentations and comparisons of daughter and parent ions of authentic samples.

The primary fragmentation mechanisms in the thermal decomposition of several polyurethanes were studied by direct pyrolysis into the mass spectrometer. Ester exchange reactions predominate in the primary thermal fragmentation process, causing the formation of cyclic oligomers, which are subsequently cleaved to open-chain oligomers containing hydroxyl end groups.

Spectrometrie de masse et chromatographie sur gel des oligomeres cycliques formes dans cette reaction conduisant a des polysulfures aliphatiques

Fast atom bombardament mass spectrometry (FAB-MS) has been used to identify the low molecular weight compounds produces in the partial ammonolysis of an essentially alternating copolycarbonate containing resorcine and Bisphenol A (BPA) units. The FAB-MS spectra allow to identify sequences with an exactly alternating structure. Furthermore, some spurious sequences containing blocks of 2-4 consecutive BPA units are detected.

Als Modellverbindungen zur Differenzierung von thermischen und elektronenstosinduzierten Abbaureaktionen von entsprechenden Polymeren im Massenspektrometer wurden die Fragmentierungsreaktionen oligomerer 1,4-Phenylene mit Sauerstoff-, Schwefel- und Disulfidbrucken sowie eine Reihe alternierender Co-oligomersysteme untersucht. Bei verringerter Ionisationsenergie (15 eV) treten in den Massenspektren aller unzersetzt fluchtigen Oligomeren die Molekulionen als intensivste Peaks auf, so das–bei strukturell gleichen Polymeren–eine eindeutige Identifizierung von thermischen Abbauprodukten erwartet werden kann. In Abhangigkeit von den Bruckenatomen werden charakteristische Unterschiede in den Intensitaten der durch “α-Spaltung” gebildeten elektronenstosinduzierten Fragmente gefunden. The fragmentation reactions of oligomeric 1,4-phenylenes containing oxygene, sulphur, and disulphide bridges, as well as a number of alternating co-oligomers, were investigated as model compounds to differentiate the thermal and electron impact induced degradation reactions of corresponding polymers in the mass spectrometer. At reduced ionization energy (15eV), the mass spectra of all oligomers, which could be volatilized without degradation, show most intense molecular ions. Thus, an unequivocal detection of thermal degradation products of the isostructural polymers can be expected. Remarkable differences in the abundances of the electron impact fragments formed by “α-cleavage” were observed depending on the bridging groups in the molecules.

Copolyesters containing ethylene terephthalate and p-oxybenzoate units in mole ratios of ca. 80:20, 70:30, 40:60, and 20:80, respectively, were examined by direct pyrolysis–mass spectrometry to obtain information about the thermal stabilities and the sequences distributions of the two types of units as a function of composition. Thermal stability as measured by rate of volatilization increased with increasing oxybenzoate content, as did the amount of char residue formed. The electron impact mass spectrum of the volatile fragments showed the formation of predominantly linear fragments with carboxyl and vinyl end groups. Dimer, trimer, and tetramer fragments containing either or both types of units could be identified and their relative amounts could be estimated from peak intensities. The results were consistent with those expected for random distributions of the two units, i.e., for statistical copolymers.