Filippo Samperi

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.

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.

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.

Further studies on the thermal decomposition processes in polycarbonates

Abstract The thermal decomposition mechanisms of poly(trimethylene carbonate), poly(neopentylene carbonate), poly(2-phenyltrimethylene carbonate) and poly(p-xylylene carbonate) have been investigated by EI/CI direct pyrolysis mass spectrometry and by desorption chemical ionization (DCI) mass spectrometry. The results indicate that all four polycarbonates decompose by an intramolecular exchange, an ionic process that produces cyclic carbonates as pyrolysis products. Other thermal processes (Reactions 1c-li, Scheme 1) also occur during the pyrolysis, and are all explained on the basis of well-established ionic reactions (Scheme 1).

Thermal Oxidation Products of Nylon 6 Determined by MALDI‐TOF Mass Spectrometry

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.

Analysis of poly(bisphenol A carbonate) by size exclusion chromatography/matrix‐assisted laser desorption/ionization. 1. End group and molar mass determination

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.

Synthesis of AB and ABA block copolymers as compatibilizers in nylon 6/polycarbonate blends

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.

Thermal decomposition processes in polycarbonates

Abstract The thermal decomposition mechanisms of some polycarbonates have been studied by direct pyrolysis mass spectrometry. The results indicate that aliphatic polycarbonates decompose by intramolecular exchange processes which produce cyclic compounds as primary pyrolysis products. Aliphatic-aromatic polycarbonates yield cyclic compounds containing various ratios of bisphenol A (BPA) and aliphatic carbonates. Poly(ethylene-co-BPA carbonate) decomposes to produce ethylene carbonate and BPA polycarbonate. The latter further decomposes at higher temperature to yield cyclic oligomers. Alt-copoly(resorcinol-co-BPA carbonate) undergoes ester-exchange rearrangement to produce cyclic resorcinol carbonate oligomers and BPA polycarbonate.

A Click Chemistry-Based “Grafting Through” Approach to the Synthesis of a Biorelevant Polymer Brush

A new biorelevant polymer brush showing a polybenzofulvene backbone was synthesized by a “grafting through” approach based on click chemistry and spontaneous polymerization reactions. The easy polymerization of the relatively complex monomer (6-MOEG-9-TM-BF3k) suggests the existence of a particularly efficient recognition process capable of pre-organizing the monomer molecules for the spontaneous polymerization. 13C-NMR spectroscopy as well as UV-vis and fluorescence spectroscopy suggested for poly-6-MOEG-9-TM-BF3k the features of a vinyl (1,2) π-stacked polymer. The new polybenzofulvene derivative was found to interact with water at room temperature to give clear water solutions, but TEM analysis demonstrated the presence of macromolecular aggregates showing dimensions larger than those suggested by SEC-MALS analysis for the isolated macromolecules. DLS studies confirmed the presence of objects showing average dimensions in the range of 200–300 nm and suggested thermoresponsive colloidal properties for poly-6-MOEG-9-TM-BF3kmacromolecules. Finally, owing to its favourable absorption/emission properties and water solubility, the interaction of poly-6-MOEG-9-TM-BF3k with live cells was studied by fluorescence microscopy experiments, which revealed that the polymer brush was unable to enter live cells and alter cell morphology.