Paola Rizzarelli

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.

Thermal degradation of poly(ethylene oxide–propylene oxide–ethylene oxide) triblock copolymer: comparative study by SEC/NMR, SEC/MALDI-TOF-MS and SPME/GC-MS

By comparing size exclusion chromatography/matrix assisted laser desorption ionisation (SEC/MALDI) and SEC/NMR spectra from virgin poly(ethylene oxide-propylene oxide-ethylene oxide) triblock copol ...

Modern mass spectrometry in the characterization and degradation of biodegradable polymers.

In the last decades, the solid-waste management related to the extensively growing production of plastic materials, in concert with their durability, have stimulated increasing interest in biodegradable polymers. At present, a variety of biodegradable polymers has already been introduced onto the market and can now be competitive with non biodegradable thermoplastics in different fields (packaging, biomedical, textile, etc.). However, a significant economical effort is still directed in tailoring structural properties in order to further broaden the range of applications without impairing biodegradation. Improving the performance of biodegradable materials requires a good characterization of both physico-chemical and mechanical parameters. Polymer analysis can involve many different features including detailed characterization of chemical structures and compositions as well as average molecular mass determination. It is of outstanding importance in troubleshooting of a polymer manufacturing process and for quality control, especially in biomedical applications. This review describes recent trends in the structural characterization of biodegradable materials by modern mass spectrometry (MS). It provides an overview of the analytical tools used to evaluate their degradation. Several successful applications of MALDI-TOF MS (matrix assisted laser desorption ionization time of flight) and ESI MS (electrospray mass spectrometry) for the determination of the structural architecture of biodegradable macromolecules, including their topology, composition, chemical structure of the end groups have been reported. However, MS methodologies have been recently applied to evaluate the biodegradation of polymeric materials. ESI MS represents the most useful technique for characterizing water-soluble polymers possessing different end group structures, with the advantage of being easily interfaced with solution-based separation techniques such as high-performance liquid chromatography (HPLC).

Matrix-assisted laser desorption/ionisation time-of-flight characterisation of biodegradable aliphatic copolyesters

Matrix-assisted laser desorption/ionisation time-of-flight (MALDI-TOF) and the off-line size exclusion chromatography matrix-assisted laser desorption/ionisation (SEC/MALDI) method has been applied to the structural characterisation and the molar mass (MM) determination of a series of biodegradable copolyesters synthesised by high temperature melt polycondensation reaction, and of two commercial copolyesters with the trade name Bionolle. The MALDI-TOF spectra of these copolymers showed the presence of cyclic oligomers in the lower mass region, in accord with expectations from polycondensation kinetics, and the presence of all linear species expected from their method of synthesis. The presence of unexpected linear species with olefin and carboxyl as end groups suggested the occurrence of undesirable thermal degradation processes during the melt polycondensation reaction. The absolute average molar masses obtained by the SEC-MALDI method turned out to be lower, by a factor of about two for succinate/adipate copolymers, and by a factor of three for succinate/sebacate copolymers, with respect to those computed by using polystyrene standards in SEC. Furthermore, the MALDI-TOF spectra of SEC fractions allowed not only the detection of linear and cyclic oligomers contained in these samples, but also the simultaneous determination of the average molar mass of both cyclic and linear oligomers. Due to the smaller hydrodynamic volume of cyclic chains with respect to linear ones, the ratio (M( cycle)/M( linear))( Ve) at a fixed elution volume was found to be 1.25, in good agreement with the theoretical value of 1.24. Copyright 2000 John Wiley & Sons, Ltd.

Testing a fluorinated compound as a protective material for calcarenite

Abstract A polyfluorinated compound was studied as a material for the specific protection of calcarenite. Water capillary absorption and vapour permeability measurements were carried out in order to evaluate efficiency as a protective agent. Particular attention was given to characterising its resistance against bio-deterioration induced by microorganisms such as blue and green algae. Chemical surface modifications were induced by UV-irradiation in a specially designed climatic chamber and were investigated through comparative tests on untreated and artificially weathered samples using X-ray photoelectron spectroscopy (XPS). This paper discusses the potential use of the compound studied as a specific coating material for the protection of calcarenite.

Structural characterization of synthetic poly(ester amide) from sebacic acid and 4-amino-1-butanol by matrix-assisted laser desorption ionization time-of-flight/ time-of-flight tandem mass spectrometry

Matrix-assisted laser desorption/ionization time-of-flight/time-of-flight tandem mass spectrometry (MALDI-TOF/TOF-MS/MS) was employed to analyze a poly(ester amide) sample (PEA-Bu) from the melt condensation of sebacic acid and 4-amino-1-butanol. In particular, we investigated the fragmentation pathways, the ester/amide bond sequences and the structure of species derived from side reactions during the synthesis. MALDI-TOF/TOF-MS/MS analysis was performed on cyclic species and linear oligomers terminated by dicarboxyl groups, carboxyl and hydroxyl groups and diamino alcohol groups. The sodium adducts of these oligomers were selected as precursor ions. Different end groups do not influence the fragmentation of sodiated poly(ester amide) oligomers and similar series of product ions were observed in the MALDI-TOF/TOF-MS/MS spectra. According to the structures of the most abundant product ions identified, the main cleavages proceed through a beta-hydrogen-transfer rearrangement, leading to the selective scission of the --O--CH2-- bonds. Abundant product ions originating from --CH2--CH2-- (beta-gamma) bond cleavage in the sebacate moiety were also detected. Their formation should be promoted by the presence of an alpha,beta-unsaturated ester or amide end group. MALDI-TOF/TOF-MS/MS provided structural information concerning the ester/amide sequences in the polymer chains. In the MALDI-TOF/TOF-MS/MS spectra acquired, using argon as the collision gas, of cyclic species and linear oligomers terminated by diamino alcohol groups, product ions in the low-mass range, undetected in the mass spectra acquired using air as the collision gas, 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) sample. Furthermore, MALDI-TOF/TOF-MS/MS provided useful information to clarify the structures of precursor ions derived from side reactions during the synthesis.

Functionalization of aliphatic polyesters by nitroxide radical coupling

Functionalized poly(butylene succinate) (PBS) samples were prepared by a post-polymerization method based on the coupling reaction between TEMPO derivatives bearing different functionalities and PBS macroradicals generated by H-abstraction using a peroxide. 4-Benzoyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl (BzO-TEMPO) and 4-(1-naphthoate)-2,2,6,6-tetramethylpiperidine-1-oxyl (NfO-TEMPO), a pro-fluorescent nitroxide, were successfully grafted on PBS, as revealed by MALDI TOF MS and UV-Vis spectroscopy. The functionalization degrees were accurately determined by UV-Vis analysis and confirmed by 1H-NMR spectroscopy. The grafting site was identified by combining theoretical calculations with experimental evidence. This evidence was collected by both EPR analysis of a functionalized sample subjected to controlled heating in the EPR cavity, and by 1H-NMR spectroscopy. Our functionalization method, which was also tested for poly(lactic acid) (PLA), preserves the original polymer structure. This avoids the crosslinking-branching side reaction, which generally affects the free radical treatment of biodegradable aliphatic polyesters. In addition, using a pro-fluorescent nitroxide to form functionalized samples is a significant step towards unambiguously demonstrating the radical grafting on these types of polymer. It also proves that well-defined fluorescently labeled biodegradable polyesters can be tailored.

Direct electrospray ionization mass spectrometry quantitative analysis of sebacic and terephthalic acids in biodegradable polymers.

A direct, rapid, and easy electrospray ionization mass spectrometry (ESI-MS) method to determine concentrations of sebacic acid (SA) and terephthalic acid (TA) residues in biodegradable copolymers was developed. Copolyester samples were synthesized from 1,4-butanediol and sebacic and terephthalic acids by melt polymerization. Extraction of monomers was performed in methanol. Their concentrations were determined by direct infusion ESI-MS, without chromatographic separation, using 1,12-dodecanedioic acid (DDA) as an internal standard. Calibration curves were obtained by plotting the ratio of the areas of the peaks relative to monomers and DDA standard as a function of their concentration ratio. We validated the method by determining the concentration of TA residue using both the ESI-MS protocol and high-performance liquid chromatography (HPLC) analysis with UV detection. The linearity range and the detection limit of this assay were 0.1-5.0 and 0.01 ppm for SA and 0.1-6.0 and 0.03 ppm for TA. This assay represents a useful alternative to conventional methods currently employed for acid quantification, resulting advantageous for its speed and high sensitivity.

Matrix-assisted laser desorption ionization time-of-flight/time-of-flight tandem mass spectra of biodegradable polybutylenesuccinate.

RATIONALE Matrix-Assisted Laser Desorption/Ionization Time-Of-Flight/Time-Of-Flight Tandem Mass Spectrometry (MALDI-TOF MS/MS) was employed to analyze five poly(butylene succinate) (PBSu) oligomers and to investigate their fragmentation pathways. METHODS MALDI-TOF MS/MS analysis was performed on cyclic and linear oligomers terminated by dicarboxyl groups, carboxyl and hydroxyl groups, hydroxyl and olefin groups, and dihydroxyl groups. The sodium adduct ions of these oligomers were selected as precursor ions. Experiments were carried out with and without argon as the collision gas. RESULTS A β-hydrogen transfer rearrangement, leading to the selective cleavage of the -O-CH2- bonds, and cleavage of the -CH2-CO- bonds, the ester bonds, and the -CH2-CH2- bonds in the diol moiety were observed. Two fragmentation mechanisms, correlated to the end-group structure of the precursor ions, were also proposed. The detection of cyclic anhydrides was related to the presence of succinic acid terminal groups. The formation of microcyclic oligoesters probably occurred via an intramolecular transesterification mechanism involving a hydroxyl end group. CONCLUSIONS A β-hydrogen transfer rearrangement has been proposed as the main fragmentation mechanism occurring in PBSu without using the collision gas. Cleavages of almost all types of bonds take place in the MALDI CID experiments. According to the structures of the most abundant product ions, six fragmentation pathways have been proposed when using argon as the collision gas. Two fragmentation mechanisms were suggested as being correlated to the end-group structure of the precursor ions.

Fluorinated Phosphoric Ester-Based Protective Material for Limestone-Made Ancient Monuments, Buildings, and Artifacts: An X-ray Photoelectron Spectroscopy Study

In this study, fluorinated phosphoric esters are evaluated as protective material for limestone from water-driven alteration processes. Hypotheses as to their molecular arrangement are also provided. The surface composition of limestone after treatment with a commercially available fluorinated phosphoric ester material was evaluated by X-ray photoelectron spectroscopy (XPS). Results were then compared with those obtained for the treated limestone after accelerated aging tests. In the limestone that had not been subjected to aging processes an XPS determined thickness of the protective coating equivalent to 95 ± 18 Å was observed. This fell to 49 ± 10 Å in the limestone examined after intensive aging tests. However, low surface wettability (θ = 135° ± 4) was seen to be maintained.