Giorgio Montaudo

Evolution of aromatics in the thermal degradation of poly(vinyl chloride): A mechanistic study

Abstract Various aspects of the thermal decomposition, flammability and smoke evolution from PVC have been investigated in an attempt to account for the mechanism of evolution of aromatics from this polymer. The most relevant experimental observations for the understanding of the mechanism of thermal decomposition of PVC were obtained by the method of direct pyrolysis in the mass spectrometer. A number of facts that had partly escaped previous workers was revealed: that in each of the two degradation steps of PVC a family of aromatic hydrocarbons was formed with different structures; that the two families of aromatics are suppressed at considerably different rates by the addition of metal oxides. The selective suppression of aromatics is related to the fact that the two families of aromatics are evolved from linear and from crosslinked polyene chains, respectively. Another conclusion is that the intramolecular cyclization processes in linear and crosslinked polyenes are satisfactorily explained by the cyclization of polyene radicals, whereas mechanisms based solely on Diels-Alder processes meet with several difficulties. The close analogy found with the thermal degradation of polyacetylene supports these conclusions. Another model system is provided by PVC 2 and PVF 2 . These vinylidene polymers do not form alkyl-aromatics, only unsubstituted aromatics are evolved and the thermal degradation occurs in a single stage.

Synthesis and enzymatic degradation of aliphatic copolyesters

Abstract 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.

Application of size exclusion chromatography matrix-assisted laser desorption/ionization time-of-flight to the determination of molecular masses in polydisperse polymers

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.

Primary thermal decomposition processes in aliphatic polyamides

Abstract The primary thermal decomposition processes of a series of aliphatic polyamides were investigated by Direct Chemical Ionization (DCI) and Tandem mass spectrometry. Results show that an intramolecular exchange process is the preferred thermal decomposition mechanism for many of the polyamides. Decomposition through a C-H hydrogen transfer reaction appears to occur as a secondary thermal process, except in the case of nylon 3 because of its particular structure. A quite different decomposition pathway is followed by nylons from adipic acid (nylons 6.6 and 11.6), where specific structural factors make the formation of cyclopentanone preferred. These polymers decompose via a C-H hydrogen transfer to nitrogen with the formation of compounds having amine and/or ketoamide end groups. These primary products further decompose or react with the formation of cyclopentanone and compounds bearing amine and/or Schiff base groups.

Characterization of end groups in nylon 6 by MALDI‐TOF mass spectrometry

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

Simulation of the lanthanide induced shifts : Description of a computer method and its applications to conformational equilibria of simple systems

Abstract A computer method to simulate the observed Lanthanide Induced Shifts (LIS) is described and its applications to the study of the conformational equilibria in solution for simple systems are reported. Starting from structurally rigid systems, it is shown that the LIS simulation process allows mistaken assignment to be corrected by systematic permutation of signals with uncertain assignments. Some examples of structurally flexible systems with an internal rotation angle are studied (2-carbonyl derivatives of furan and thiophene, N-vinylpyrrolidone, cyclopropanecarboxyamides), and the results allow the structures actually present in the conformational equilibrium to be determined. It has been also found that it is possible to estimate the population ratio between s - cis and s - trans conformers in a number of α,β-unsaturated systems.

Conformational preference of ortho-substituted diphenyl ethers and diphenyl thioethers

Abstract NMR data are reported for two series of ortho substituted diphenyl ethers (DPO) and diphenyl thioethers (DPS). The results obtained indicate that in these molecules, in addition to steric hindrance effects, conjugative effects may prove important in determining conformational preferences.

A topological approach to the interaction of lanthanide shift reagents with the carbonyl group : Its relevance to conformational analysis

Abstract A topological approach to the LIS simulation process of compounds bearing the carbonyl functional group is reported. The Lanthanide was always found to complex in the less hindered position, along the sp 2 lone-pair orbital of the O atom. The relevance to chemistry of such an approach is that only chemical significant positions are considered as feasible sites of complexation of the Lanthanide with the substrate, disregarding all other positions. More important, the results obtained have thrown some light on the factors that may influence the equilibria of conformationally mobile systems, in the presence of LSR. The reliability of the method employed has been tested in several disparate carbonyl derivatives.

Chemical reactions which occur in the thermal treatment of polycarbonate/polyethyleneterephthalate blends, investigated by direct pyrolysis mass spectrometry

Abstract The chemical reactions which occur in the thermal treatment of polycarbonate/poly(ethyleneterephthalate) (PC/PET) blends have been investigated by gradual heating (10°C/min) using thermogravimetry and direct pyrolysis into the mass spectrometer. Exchange reactions occur even in the temperature range below 300°C, but the transesterification equilibrium is affected by the evolution of thermal degradation products. Ethylene carbonate was detected in the first decomposition stage (280–380°C), and is evolved together with a series of cyclic compounds containing units of PC and PET in varying ratios. The overall thermal reaction evolves towards the formation of the most thermally stable polymer, i.e. a totally aromatic polyester (polymer III, Table 1), which was found to be the end product of the thermal processes occurring in the system investigated. Several thermal decomposition products, originating from the PC/PET blends in the range 250–600°C, were identified. The compounds detected have masses sufficiently high to be structurally significant, since they contain at least one copolymer repeating unit. The reactions which occur during the thermal treatment of the PC/PET blend are discussed in detail.

Chemical reactions occurring in the thermal treatment of PC/PMMA blends

The chemical reactions occurring in the thermal treatment of bisphenol-A polycarbonate (PC) and poly(methyl methacrylate) (PMMA) blends have been investigated by nuclear magnetic resonance (NMR), mass spectrometry (MS), size exclusion chromatography (SEC), and thermogravimetry (TG). Our results suggest that in the melt-mixing of PC/PMMA blends, at 230°C, no exchange reactions occur and that only the depolymerization reaction of PMMA has been observed. In the presence of an ester-exchange catalyst (SnOBu2), an exchange reaction was found to occur at 230°C, but no trace of PC/PMMA graft copolymer has been observed. Instead, an exchange reaction between the monomer methyl methacrylate (MMA), generated in the unzipping of PMMA chains, and the carbonate groups of PC has been suggested. This is due to the diffusion of MMA at the interface or even into the PC domains, where it can react with PC producing low molar mass PC oligomers bearing methacrylate and methyl carbonate chain ends and leaving the undecomposed PMMA chains unaffected. The TG curves of PC/PMMA blends prepared by mechanical mixing and by casting from THF show two separated degradation steps corresponding to that of homopolymers. This behavior is different from that of a transparent film of PC/PMMA blend, obtained by solvent casting from DCB/CHCl3, which shows a single degradation step indicating that the degradation rate of PC is increased by the presence of PMMA in the blend. The thermal degradation products obtained by DPMS of this blend consist of methyl methacrylate (MMA), cyclic carbonates arising from the degradation of PMMA and PC, respectively, and a series of open chain bisphenol-A carbonate oligomers with methacrylate and methyl carbonate terminal groups. The presence of the latter compounds suggests a thermally activated exchange reaction occurring above 300°C between MMA and PC. The presence of bisphenol-A carbonate oligomers bearing methyl ether end groups, generated by a thermally activated decarboxylation of the methyl carbonate end groups of PC, has also been observed among the pyrolysis products.