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Emanuele Paternò (Palermo, 1847-1935) si laureò a Palermo nel 1871, nello stesso anno divenne professore a Torino, l'anno successivo venne chiamato a Palermo, e successe poi a Cannizzaro nella Cattedra di Chimica Generale di Roma. Celebri sono le sue ricerche pionieristiche (1869) sul carbonio tetraedrico. Paternò passò poi ad occuparsi di crioscopia (1885), applicando tale metodo alla determinazione delle masse molecolari. Gli studi successivi (1889-1910) sullo stato colloidale furono di grande avanguardia in campo europeo, rivelando alcune proprietà di base dei colloidi. Egli poté dimostrare che si tratta di soluzioni in cui le molecole formano degli aggregati molecolari (micelle). La conclusione pioneristica che Paternò trasse da queste osservazioni fu che "la proprietà colloidale di una sostanza non è una proprietà intrinseca inerente alla molecola dei corpi, ma è una proprietà relativa che si manifesta in presenza di un solvente e di un altro no".

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.

Poly{2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride−1,3-phenylendiamine} copolymer (ULTEM) was subjected to thermoaging in an attempt to determine the structure of the species formed during oxidative degradation. The oxidative process was followed as a function of exposure time by using MALDI−TOF MS. Thermal oxidation produces charring after only 15 min and the formation of insoluble residue amounts to 50% after 180 min at 350°C. Highly valuable structural information (including the end groups) was extracted from the MALDI spectra of the thermally oxidized ULTEM soluble samples. Oxidized specimens contained acetophenone, phenylacetic acid, phenols, benzoic acid, bisphenol A, phthalimide, and phthalic anhydride end groups. The mechanisms accounting for their formation involve several reactions: (i) cleavage of the diphenyl ether units; (ii) oxidative degradation of the isopropylidene bridge of BPA units; (iii) thermal cleavage of phenylphthalimide units.

Poly(ester amide)s from dimethyl sebacate or sebacic acid and 2-aminoethanol or 4-amino-1-butanol were characterized by post-source decay matrix-assisted laser desorption/ionization time-of-flight (PSD-MALDI-TOF) and time-of-flight/time-of-flight tandem mass spectrometry (MALDI-TOF/TOF-MS/MS). Sodiated oligomers were selected as precursor ions for dissociation studies. PSD analysis was performed on dimethyl sebacate, dicarboxylic, carboxylic and amino alcohol, and diamino alcohol terminated oligomers. PSD-MALDI-TOF mass spectra yielded information on the fragmentation mechanisms of the poly(ester amide) chains, showing that the main cleavages proceed through a beta-hydrogen transfer rearrangement. MALDI-TOF/TOF-MS/MS provided structural information concerning ester/amide sequences in the polymer chains. As expected, together with the ions appearing in the PSD-MALDI mass spectrum, several new abundant fragment ions in the low-mass range are present in MALDI-TOF/TOF-MS/MS spectra. These new product ions proved to be diagnostic and made it possible to establish the presence of random sequences of ester and amide bonds in the poly(ester amide)s samples.

Ny6-Ny6,10 and Ny6-Ny4,6 copolyamides prepd. by a facile melt mixing at 290-310 °C of carboxyl terminated Nylon6 (Ny6-COOH) with Ny6,10 or Ny4,6, were characterized by MALDI, 13C NMR, and DSC anal. The results, from one side show how facile is the high yield synthesis of random copolyamides via the melt mixing of the corresponding polyamides. What makes the synthesis so facile is the use of a carboxyl terminated polyamide (Ny6-COOH) to attack the other polyamide (Ny4,6 or Ny6,10), as described herewith. The DSC data acquired provide a clear picture of the process. The second relevant point is about the sequence anal. of the copolyamides, made using their 13C NMR spectra. The sequence has been derived directly from chain statistics principles, avoiding the use of inadequate procedures. To our knowledge, this is the first time as far as condensation copolymers are concerned. Interesting, the sequence anal. of our copolyamides has been also performed independently, by extg. pertinent information from their MALDI spectra. The results have been found in excellent agreement with those from 13C NMR data.

A series of aliphatic copolyesters was obtained from (R,S)-β-butyrolactone and two isomeric hydroxy acids, 6-hydroxyhexanoic and (R,S)-2-hydroxyhexanoic acids. The reactions were conducted in bulk without catalyst. Electrospray ionization tandem mass spectrometry (ESI-MSn) was used for molecular characterization of these copolyester oligomers. The mass spectra of the copolyesters studied have enabled identification of their molecular structures including chemical nature of the end groups (hydroxyl and carboxylate). The compositions of the oligocopolyesters and their sequence distributions were determined based on measurement of the relative intensities of the individual oligocopolyester peaks in the ESI mass spectra. The mass spectra (MS1) provided information on composition and sequence distribution, and small deviations from Bernoulli statistics were detected. The arrangement of co-monomer structural units along the oligopolyester chains was verified by MS/MS experiments and investigation of the fragmentation pathways. Copyright © 2004 John Wiley & Sons, Ltd.

Several isothermal degradation experiments on poly(ethylene terephthalate) (PET) were conducted in the temperature range of 270–370 °C, in order to simulate the reactions that take place during the processing of PET under inert atmosphere (N 2 ). The structural characterisation of the reaction products was performed by MALDI mass spectrometry and by NMR analysis. The results indicate the formation of cyclic oligomers that decompose at higher temperature. Vinyl ester terminated oligomers could not be detected by MALDI and also by 1 H and 13 C NMR, whereas the formation of anhydride containing oligomers is well apparent. Formation of acetaldehyde in PET samples processed at various temperatures was detected by 1 H NMR. We have also included in the present study a set of experiments where 0.5%w p -TsOH·H 2 O was added to PET. Our results show that the addition of small amounts of p -TsOH·H 2 O to PET, heated at 270 and 285 °C, induces a strong hydrolytic reaction with consequent increase of carboxyl terminated polyester chains.

Matrix-assisted laser desorption ionization mass spectrometry (MALDI) is an excellent method to use in detg. the structure of the mols. produced in the photo-oxidative degrdn. of nylon 6 at 60 °C in air. The MALDI spectra of photo-oxidized nylon 6 (Ny6) show the presence of over 40 compds., as compared to only 3 in the blank Ny6 sample. The extremely favorable event here is that the MALDI spectra present so many new well-resolved peaks, which provide information on the structure and end groups of the oxidn. products. The structural anal. of the photo-oxidn. products provided by the MALDI spectra allowed us to draw a detailed map of the photo-oxidn. mechanisms of Ny6 (Schemes 1-4). The presence of the majority of the oligomers listed in Table 1 had not been revealed before. Our results extend and modify the currently accepted picture for the photo-oxidn. mechanisms of Ny6. In fact, our results confirm previous insights that the hydrogen abstraction and subsequent formation of a hydroperoxide intermediate actually occur but also reveal that Norrish I and Norrish II chain-cleavage reactions play an important role in the photo-oxidn. process of Ny6. This essential feature of the process had been missed in previous studies focused on UV and IR techniques. The peculiarity of our approach consists of using a high-sensitivity and nonaveraging technique such as mass spectrometry, which allows the detection and monitoring of each new oligomers formed during the oxidn. process. This is a remarkable result, and it should be expected that future MALDI studies may have an impact on the current views of photo-oxidn. processes of other polymer systems

A study on the sequence and composition of copolyamides formed by activated exchange reactions occurring in the melt mixing of Ny6,10 and Ny6,6 is reported. Equimolar mixtures of Ny6,10, Ny6,6, and carboxyl-terminated Ny6,6 (Ny6,6-COOH) samples were melt mixed at different temperatures (290-310 C) for different times (10-180 min). The determination of copolyamides formation, sequence, and composition proved to be unfeasible with 13C NMR spectroscopy. On the other hand, matrix-assisted laser desorption ionization-time-of-flight (MALDI-TOF) mass spectra allowed the detection of the copolyamides formation and the determination of their sequence and composition. The results can be reconciled within the overall scheme of exchange reaction occurring through active chain ends. In fact, the composition of the copolyamides formed by the exchange of Ny6,6-COOH/Ny6,10 mixtures showed a higher amount of Ny6,6 units, with respect to the initial blends composition, and a higher value of the Ny6,6 average block length, at the beginning of the reaction (10 min). The composition of the copolyamides was found to be equal to the feed composition (50/50), after 30 min of heating, with a random distribution of sequences. The composition and the sequence distributions of the copolyamides remained unaffected even at a higher heating time (180 min) although some degradation reactions also occurred. Instead, the exchange reaction of a mixture of high molar mass Ny6,6 and Ny6,10 both containing a very low amount of carboxylic chain ends produced a segmented copolyamides even at high heating time (150 min). The Ny6,6/Ny6,10 copolyamides were also characterized by differential scanning calorimetry (DSC) and by wide-angle X-ray spectroscopy (WAXS)

Progress in the study of thermal and thermoxidative decomposition processes of poly(bisphenol a carbonate) (PC) was obtained by Matrix assisted laser description ionization time of flight (MALDI-TOF) and FAB mass spectroscopic techniques. PC samples were subjected to thermal degradation (under inert atmosphere) heating at 300, 350, 400 and 450 °C. The MALDI mass spectra of the pyrolysis residues obtained at 300 °C showed only a progressive reduction of the abundance of cyclic oligomers and an increase of the molar mass of the PC sample most likely due to post-condensation polymerisation reactions. At 350 °C the occurrence of an extensive hydrolysis reaction producing phenol groups was observed. PC chains terminated with phenol groups together with chains bearing phenyl and isopropenyl end groups were observed at 400 °C. Condensed aromatic compounds such as xanthones were also detected in the MALDI spectra of PC samples heated at 400 °C, and they became the most intense species at 450 °C. The FAB-MS spectrum of the pyrolysis residue obtained at 400 °C subjected to a selective and exhaustive aminolysis reaction showed the presence of compounds containing several consecutive xanthone units. These units undergo cross-linking processes, leading to a graphite-like charred residue (insoluble), as the temperature increases. The thermoxidative degradation of PC carried out heating the samples in air at 300 °C for 30, 60, 90, 120, 150 and 180 min produced a reduction of the PC molar mass. The MALDI mass spectra of thermally oxidised PC samples at 300 °C for 90 and 180 min showed the presence of PC chains terminated with methyl-ketone, phenyl and phenol groups, most likely formed by the oxidative degradation of the isopropilidene bridge of bisphenol A units. The presence of dehydrogenated structures containing biphenyl linkage may account for the insoluble residue produced in these conditions.

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.

Thermal oxidation products of poly(bisphenol A carbonate) (PC) generated by heating at 300 and 350 °C, respectively, under atmospheric air, were detected by an hyphenated SEC/MALDI technique. The SEC curves of the thermal oxidised samples showed extensive degradation as a function of heating time, up to the formation of very low mass oligomers. Oxidised PC samples were subjected to SEC fractionation by collecting several fractions which were analysed “ off-line ” by MALDI-TOF. The MALDI spectra of the SEC fractions of the thermal oxidised PC samples showed the presence of polymer chains containing acetophenone, phenyl substituted acetone, phenols, benzyl-alcohol and biphenyl terminal groups. 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.

A series of high molar mass aliphatic homo- and copolyesters was obtained from 1,4-butanediol and dimethylesters of succinic, adipic and sebacic acids. These materials were characterised by 1 H-NMR, SEC, DSC, X-ray and viscometry. Good filmability was achieved for all the polyesters. Film samples were subjected to enzymatic attack and the relative normalised weight loss rates were compared. The results indicate that the copolyesters have reduced crystallinity with respect to the homopolyesters, and that the rate of enzymatic degradation is increased when the sample crystallinity decreases. Furthermore, it was observed that structural changes in the repeat unit of the copolyesters affect the rate of enzymatic degradation, independent of sample crystallinity. Instead, molar mass changes in the polymer investigated do not affect the rate of enzymatic degradation.

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 determination of molecular mass (MM) data for polydisperse polymers by size exclusion chromatography matrix assisted laser desorption/ionization time-of-flight (SEC/MALDI-TOF) involves the fractionation of samples through an analytical SEC. Selected fractions are then analysed by MALDI-TOF and the mass spectra of these nearly monodisperse samples allow the determination of Mn and Mw averages. To test the reliability of the molecular mass estimates by the SEC/MALDI-TOF method, a sample of polymethylmethacrylate (PMMA), two samples of polydimethylsiloxane (PDMS), and four samples of copolyesters, all polydisperse, were analysed. The results show that the molecular mass values of PMMA fractions obtained by MALDI-TOF are coincident with those obtained using the SEC calibration plots obtained with anionic PMMA standards. In the case of the two polydimethylsiloxanes (PDMS1 and PDMS2: linear and cyclic, respectively), two slightly differing SEC calibration plots were obtained, reflecting the different structures of the polymer chains of the two samples. The SEC traces of four copolyesters were obtained in tetrahydrofuran and CHCl3. Data on MM, MM distribution solvent effects and copolymer composition are reported. © 1998 John Wiley & Sons, Ltd.

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.

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).

Nylon 6 (Ny6) and Bisphenol A polycarbonate (PC) are immiscible and form biphasic blends. To improve the compatibility of Ny6 and PC several ABA and AB Ny6/PC block copolymers were synthesized, and their compatibilizing behavior on the blends were tested. Block copolymers were prepared by reacting monoamino- or diamino-terminated Ny6 homopolymers with high molecular weight PC at 130°C in anhydrous DMSO. The reaction of diamino- and monoamino-terminated Ny6 with polycarbonate produces block copolymers of the type PC-Ny6-PC (ABA) and PC-Ny6 (AB), respectively, plus a certain amount of unconverted PC degradated to lower molecular weights. To separate the block copolymer from the unconverted PC, a selective fractionation with tetrahydrofuran (THF) and trifluoroethanol (TFE) was carried out. Three different fractions were obtained: THF-soluble fraction, TFE-soluble fraction, and the TFE-insoluble fraction. The scanning electron microscopy (SEM) analysis of a 75/25 (wt/wt) Ny6/PC blend added with 2% of ABA or AB block copolymers, showed the presence of smaller PC particles more adherent to the polyamide matrix, with respect to the same blend nonadded, which is clearly biphasic. The size of the PC particles decreases from ABA to AB compatibilized blends and the adhesion with the matrix is increases in the same way. © 1996 John Wiley & Sons, Inc.

The synthesis and NMR characterization of some poly(ether ketone)/poly(ether sulfone) (PEK/PES) alternating copolymers together with a series of sequential homopolymers containing CO, O, S and SO 2 bridging groups, all obtained by electrophilic condensation reactions using phosphorus pentoxide/methanesulfonic acid as dehydrating agent, is here reported. Properties of such polymers are compared with those of their model compounds from which it can be inferred that both proton and carbon chemical shifts are very sensitive to the electronic environment generated by the O, S, CO and SO 2 bridges. Differential scanning calorimetry indicates that our polymers are essentially amorphous irrespective of the bridging sequence. From viscosity measurements the molecular weights of these copolymers are judged to be very low.

The thermal degradation processes of two sulfur polymers, poly(xylylene sulfide) (PXM) and poly(xylylene disulfide) (PXD), were investigated in parallel by direct pyrolysis mass spectrometry (DPMS) and flash pyrolysis GC/MS (Py-GC/MS). Thermogravimetric data showed that these polymers decompose with two separate steps in the temperature ranges of 250-280 and 600-650 degrees C, leaving a high amount of residue (about 50% at 800 degrees C). The pyrolysis products detected by DPMS in the first degradation step of PXM and PXD were terminated by three types of end groups, -CH3, -CH2SH, and -CH=S, originating from thermal cleavage reactions involving a series of homolytic chain scissions followed by hydrogen transfer reactions, generating several oligomers containing some intact xylylene sulfide repeating units. The presence of pyrolysis compounds containing some stilbene-like units in the first degradation step has also been observed. Their formation has been accounted for with a parallel cleavage involving the elimination of H2S from the PXM main chains. These unsaturated units can undergo cross-linking at higher temperatures, producing the high amount of char residue observed. The thermal degradation compounds detected by DPMS in the second decomposition step at about 600-650 degrees C were constituted of condensed aromatic molecules containing dihydrofenanthrene and fenanthrene units. These compounds might be generated from the polymer chains containing stilbene units, by isomerization and dehydrogenation reactions. The pyrolysis products obtained in the Py-GC/MS of PXM and PXD at 610 degrees C are almost identical. The relative abundance in the pyrolysate and the spectral properties of the main pyrolysis products were found to be in generally good agreement with those obtained by DPMS. Polycyclic aromatic hydrocarbons (PAHs) were also detected by Py-GC/MS but in minor amounts with respect to DPMS. This apparent discrepancy was due to the simultaneous detection of PAHs together with all pyrolysis products in the Py-GC/MS, whereas in DPMS they were detected in the second thermal degradation step without the greatest part of pyrolysis compounds generated in the first degradation step. The results obtained by DPMS and PSI-GC/MS experiments showed complementary data for the degradation of PXM and PXD and, therefore, allowed the unequivocal formulation of the thermal degradation mechanism for these sulfur-containing polymers.

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.

A calibration procedure is introduced, which allows one to obtain absolute mass values in matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) spectra of polymeric materials, thus avoiding ambiguous mass assignments, The method consists in combining the observed times of flight in a function denoted as 'modified sum of squares' (SS2) and in finding the point of minimum for SS2. The procedure takes advantage of the finding that SS2 possesses an extremum property, i.e. it takes its minimum at theta, the mass of the first oligomer appearing in the MALDI-TOF spectrum, The method was tested by recording the MALDI-TOF spectrum of an aminolyzed Nylon 6 and of a glycolized poly(butyleneadipate) (PEA) sample. Nylon 6 was found to be made of a series of oligomers bearing diaminohexamethylene (DAHM) terminal groups. PEA is made of a series of oligomers with butyleneglycol end-groups. The intense peaks seen in the mass spectra are due to sodium-cationized ions, whereas the less-intense peaks are due to potassium-cationized ions. The function SS2 was built for the two samples and a point of minimum was found at the point theta=817.6 for Nylon 6 and at the point theta=713,6 for PBA. This finding allowed the interpretation of the mass spectra.

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.

New poly(aryl ether ketone) and poly(aryl ether sulfone) monodisperse model oligomers were synthesized in good yield via nucleophilic reactions. They were characterized by means of 1 H and 13 C NMR spectroscopy, and all chemical shifts were assigned to the corresponding nuclei. Both proton and carbon chemical shifts are very sensitive to the electronic environment generated by the O, CO and SO 2 bridges, but in all oligomers, nuclei with similar electronic environments are very close to each other no matter what the sequence or the length of the oligomer is. Only quaternary carbons are more sensitive to the nature of the bridging groups, and therefore their chemical shifts can be of utility in sequencing the polymers

The thermal degradation Processes which occur in poly(phenylenesulfide) (PPS) have been studied by direct pyrolysis-mass spectrometry (DPMS). The structure of the compounds evolved in the overall temperature range of PPS decomposition (400–700°C) suggests the occurrence of several thermal decomposition steps. At the onset of the thermal degradation (430–450°C) this polymer decomposes with the formation of cyclic oligomers, generated by a simple cylization mechanism either initiated at the—SH end groups or by the exchange between the inner sulfur atoms along the polymer chain. At higher temperature (> 500°C) another decomposition reaction takes over with the formation of aromatic linear thiols. The formation of thiodibenzofuran units by a subsequent dehydrogenation reaction occurs in the temperature range of 550–650°C; in fact, pyrolysis products with a quasi-ladder structure have also been detected. Ultimately, above 600°C, extrusion of sulfur from the pyrolysis residue occurs with the maximum evolution at the end of decomposition (about 700°C). It appears, therefore, that the residue obtained at high temperature tends to have a crosslinked graphite-like structure from which the bonded sulfur is extruded. © 1994 John Wiley & Sons, Inc.

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.

The mechanisms of thermal degradation of poly(ether-ketone) (PEK) and four poly(ether-ketone)/poly(ether-sulfone) copolymers (PEK/PES) have been investigated by direct pyrolysis-mass spectrometry (DPMS). Several families of pyrolysis compounds with H, OH and CHO end-groups have been identified in the pyrolysis mass spectra of PEK. All these pyrolysis compounds can arise from degradation mechanisms involving cleavages of the bridged groups (diphenyl ether and dibenzophenone units). Our data show that the main degradation products of PEK are aldehydes, most likely formed by an intramolecular thermal cleavage of benzophenone units. Compounds containing dibenzofuran units have also been observed in the DCI mass spectrum of PEK. The thermal decomposition of a low molecular weight PEK sample occurs in two stages with the maxima of decomposition at 390°C and 490°C, respectively. This fact indicates the occurrence of an end-group initiated thermal decomposition in the early degradation stage which is not present in the case of the high molecular weight PEK sample. The pyrolysis of PEK does not produce compounds containing biphenyl units, indicating that extrusion of carbonyls or recominbation processes are not involved. The thermal degradation compounds of the PEK/PES copolymers originate from the thermal cleavage of the bridge groups (diphenyl ether, benzophenone and diphenyl sulfone). The pyrolysis mass spectra of 1:1 (alt.), 1:1 (random), 3:1 and 1:3 PEK/PES copolymers appear essentially identical (apart for obvious differences in peak intensities), indicating that the molecular rearrangements (SO2 extrusion, transesterification, cleavage of bridges) which occur at higher temperatures and/or in the pyrolysis processes are able to randomize the distribution of comonomer units originally present in the copolymers. Differences in peak intensities have been found to reflect almost quantitatively the molar composition of the copolymers.

An almost pure poly(4-hydroxybutyrate) (P(4HB)) sample (i.e., a P(3HB-co-4HB) copolymer containing only 3% of 3HB units) was obtained by microbial synthesis. The thermal degradation of this material was investigated using thermogravimetry, direct pyrolysis mass spectrometry and abo by preparative pyrolysis and subsequent NMR analysis of the pyrolyzate. Previous studies on P(3HB-co-4HB) copolyesters have reported that the thermal degradation process occurs by a β-CH hydrogen transfer, similar to the well-known case of P(3HB). However, the latter work did not distinguish between the thermal degradation fate of 3HB and 4HB units. Our indings indicate that the thermal

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 low molecular weight compounds formed by partial ozonolysis of poly(isoprene) and poly(chloroprene) were analyzed by fast atom bombardment mass spectrometry (FABMS). In the poly(chloroprene) case, the ozonized mixtures were treated with piperidine before the MS analysis to transform in amide end groups the reactive acyl chlorides formed by the cleavage of double bonds along the main chain. Only one family of compounds having carboxyl and ketone or carboxyl and amide end groups were obtained from the ozonolysis of poly(isoprene) and poly(chloroprene), respectively. The assigned structures were confirmed by FAB-MS analysis of the GPC separation fractions [poly(chloroprene)] or by FAB-MS of the KOH-doped ozonolysis mixtures [poly(isoprene)]. It has been also ascertained, by GPC experiments, that poly(chloroprene) decomposes more rapidly than poly(isoprene) and poly(butadiene).

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 production-system language OPS5 implemented in LISP with the MEA strategy and the RETE match algorithm is used for developing the Expert System (ES) IONIA. This is an ES for the prediction of thermal degradation processes, temperature of thermal degradation and degradation products of condensation polymers. The prediction is based on the structure of the polymers. The prototype for polyurethanes and polyureas is outlined as an example of how the system is functioning. The knowledge base used, both the chemical rules and the meta-rules, are discussed. The system makes an enhancement and change of the knowledge base possible. The advantages of IONIA in practical applications are presented.

The development of a “hybrid” software system for the interpretation of pyrolysis mass spectra of condensation polymers is presented. Pyrolysis mass spectra acquired with various ionization techniques and ionization energies are used. The spectral interpretation algorithms are based on library search and retrieval using heuristics. The library, which is actually a data base, organizes information in hierarchical and encoded form on name, type, structural units, pyrolysis products and pyrolysis mass spectra of the polymers. The various stages of interpretation are outlined.

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.