Synthesis of poly(vinyl acetate)-b-poly(vinyl chloride) block copolymers by cobalt-mediated radical polymerization (CMRP)

in Polymer Chemistry (2013), 4(5), 1685-1693

The synthesis of poly(vinyl acetate)-b-poly(vinyl chloride) (PVAc-b-PVC) block copolymers by Cobalt-Mediated Radical Polymerization (CMRP) is investigated for the first time in this paper. A PVAc–Co(acac ... [more ▼]

The synthesis of poly(vinyl acetate)-b-poly(vinyl chloride) (PVAc-b-PVC) block copolymers by Cobalt-Mediated Radical Polymerization (CMRP) is investigated for the first time in this paper. A PVAc–Co(acac)2 macroinitiator is prepared by CMRP using the V-70/Co(acac)2 binary system or a preformed alkylcobalt(III) compound. Then, the block copolymerization occurs in the bulk at 40 °C by the addition of VC. The addition of water to the polymerization medium or the slow generation of alkyl radicals during the whole polymerization is beneficial to the process by consuming part of the excess of deactivator (Co(acac)2) that blocks the polymer chains into the dormant form. Dynamic light scattering (DLS) measurements and AFM analyses evidence that the PVAc-b-PVC forms core–shell micelles in a selective solvent of the PVAc block, i.e. methanol, evidencing the blocky structure of the copolymer. PVAc-b-P(VC-co-VAc) copolymers are also successfully prepared by initiating the radical copolymerization of VC and VAc at 40 °C from a PVAc–Co(acac)2 macroinitiator. [less ▲]

SINGLE-MOLECULE AFM STUDY OF ADHESIVE POLYMERS PREPARED BY COBALT-MEDIATED RADICAL POLYMERIZATION AND NITRONE-MEDIATED RADICAL COUPLING

Scientific conference (2012, September 10)

Well-defined poly(vinyl acetate) (PVAc) chains prepared by CMRP (cobalt-mediated radical polymerization) were coupled using an alkyne-functional nitrone via NMRC (nitrone-mediated radical coupling).1 In ... [more ▼]

Well-defined poly(vinyl acetate) (PVAc) chains prepared by CMRP (cobalt-mediated radical polymerization) were coupled using an alkyne-functional nitrone via NMRC (nitrone-mediated radical coupling).1 In all the cases, the coupling efficiencies were close to 90% or higher. The polymers mid-chain functionalized with an alkyne group were then reacted with azide-functionalized atomic force microscopy (AFM) tips via copper-catalyzed azide-alkyne cycloaddition (CuAAC). As a result, polymers having a double-branch architecture were linked to AFM tips via a short linker. The structure and the molecular parameters of the polymers were determined by NMR and GPC, whereas the ‘click’ step onto AFM tips was assessed by performing the same CuAAC reaction onto macroscopic surfaces and characterizing them by ATR FT-IR. The adhesive properties of these double-branched polymers were studied by AFM single-molecule force spectroscopy. By performing approach-retraction cycles in solution upon a glass surface, the interaction between single PVAc chains and the surface was investigated. The effect of the double-branch architecture on the adhesion forces was under focus. Setting a residence time of the tip on the surface before retraction was found to have a beneficial influence on the adhesion forces. Signs of multiple interactions acting in parallel were detected in the experimental force-distance traces. [less ▲]

UNFOLDING SYNTHETIC PEPTIDES BY AFM AT THE SINGLE-MOLECULE LEVEL

Poster (2012, September)

The aim of this study is to investigate the mechanochemical behavior of homopolypeptides able to change their conformation is a stimuli-responsive way. The peptidic secondary structures were studied in ... [more ▼]

The aim of this study is to investigate the mechanochemical behavior of homopolypeptides able to change their conformation is a stimuli-responsive way. The peptidic secondary structures were studied in detail by atomic force microscopy (AFM) at the single-molecule level. Synthetic copolymers containing a polypeptide block were prepared by N-carboxyanhydride amino acid ring-opening polymerization. The polymer chains were grafted as a dilute brush onto gold surfaces and their mechanochemical behavior was then studied by AFM single-molecule force spectroscopy (SMFS). The investigated polypeptide blocks were based on poly(L-glutamic acid), which undergoes a transition from alpha-helix to random coil. This can be induced by external stimuli (pH, ionic strength, temperature) or simply by applying a force. We were able to study the mechanically driven unfolding of the peptide by stretching-release cycles of the biomacromolecule. Stretching the helical peptide resulted in original features in the force-distance traces. Plateaus that are specific for the helical conformation were detected, quantified and discussed. Pulling-relaxing SMFS experiments will eventually lead to a better understanding of the force-induced unfolding of an alpha-helix and the reversibility of the phenomenon. [less ▲]

Mechanochemical Study of Conformational Transitions in a Single Synthetic Peptide Chain

Poster (2012, June 05)

The aim of this study is to investigate the mechanochemical behavior of homopolypeptides able to change their conformation is a stimuli-responsive way. The peptidic secondary structures were studied in ... [more ▼]

The aim of this study is to investigate the mechanochemical behavior of homopolypeptides able to change their conformation is a stimuli-responsive way. The peptidic secondary structures were studied in detail by atomic force microscopy (AFM) at the single-molecule level. Synthetic copolymers containing a polypeptide block were prepared by N-carboxyanhydride amino acid ring-opening polymerization. The polymer chains were grafted as a dilute brush onto gold surfaces via disulfide end-groups. Their mechanochemical behavior was then studied by AFM single-molecule force spectroscopy (SMFS). The investigated polypeptide blocks were based on poly(L-glutamic acid), which undergoes a transition from alpha-helix to random coil. This can be induced by external stimuli (pH, ionic strength, temperature) or simply by applying a force. We were able to study the mechanically driven unfolding of the peptide by stretching-release cycles of the biomacromolecule. Stretching the helical peptide resulted in original features in the force-distance traces. Plateaus that are specific for the helical conformation were detected, quantified and discussed. Pulling-relaxing SMFS experiments eventually led to a better understanding of the force induced unfolding of an alpha-helix and the reversibility of the phenomenon. [less ▲]

Probing recognition processes, forces and motions within single molecules

Scientific conference (2012, May 09)

Molecular biomimetics applied to medical devices

Poster (2012, May 05)

Molecular biomimetics applied to medical devices

Poster (2012, April 18)

Mechanical testing of electrospun PCL fibers

in Acta Biomaterialia (2012), 8(1), 218-224

Poly(ε-caprolactone) (PCL) fibers ranging from 250 to 700 nm in diameter were produced by electrospinning a polymer tetrahydrofuran/N,N-dimethylformamide solution. The mechanical properties of the fibrous ... [more ▼]

Poly(ε-caprolactone) (PCL) fibers ranging from 250 to 700 nm in diameter were produced by electrospinning a polymer tetrahydrofuran/N,N-dimethylformamide solution. The mechanical properties of the fibrous scaffolds and individual fibers were measured by different methods. The Young’s moduli of the scaffolds were determined using macro-tensile testing equipment, whereas single fibers were mechanically tested using a nanoscale three-point bending method, based on atomic force microscopy and force spectroscopy analyses. The modulus obtained by tensile-testing eight different fiber scaffolds was 3.8 ± 0.8 MPa. Assuming that PCL fibers can be described by the bending model of isotropic materials, a Young’s modulus of 3.7 ± 0.7 GPa was determined for single fibers. The difference of three orders of magnitude observed in the moduli of fiber scaffolds vs. single fibers can be explained by the lacunar and random structure of the scaffolds. [less ▲]

Raman spectroscopy and laser desorption mass spectrometry for minimal destructive forensic analysis of black and color inkjet printed documents

in Forensic Science International (2012), 219

Inkjet ink analysis is the best way to discriminate between printed documents, or even though more difficult, to connect an inkjet printed document with a brand or model of printers. Raman spectroscopy ... [more ▼]

Inkjet ink analysis is the best way to discriminate between printed documents, or even though more difficult, to connect an inkjet printed document with a brand or model of printers. Raman spectroscopy and laser desorption mass spectrometry (LDMS) have been demonstrated as powerful tools for dyes and pigments analysis, which are ink components. The aim of this work is to evaluate the aforementioned techniques for inkjet inks analysis in terms of discriminating power, information quality, and nondestructive capability. So, we investigated 10 different inkjet ink cartridges (primary colors and black), 7 from the HP manufacturer and one each from Epson, Canon and Lexmark. This paper demonstrates the capabilities of three methods: Raman spectroscopy, LDMS and MALDI-MS. Raman spectroscopy, as it is preferable to try the nondestructive approach first, is successfully adapted to the analysis of color printed documents in most cases. For analysis of color inkjet inks by LDMS, we show that a MALDI matrix (9- aminoacridine, 9AA) is needed to desorb and to ionize dyes from most inkjet inks (except Epson inks). Therefore, a method was developed to apply the 9AA MALDI matrix directly onto the piece of paper while avoiding analyte spreading. The obtained mass spectra are very discriminating and lead to information about ink additives and paper compositions. Discrimination of black inkjet printed documents is more difficult because of the common use of carbon black as the principal pigment. We show for the first time the possibility to discriminate between two black-printed documents coming from different, as well as from the same, manufacturers. Mass spectra recorded from black inks in positive ion mode LDMS detect polyethylene glycol polymers which have characteristic mass distributions and end groups. Moreover, software has been developed for rapid and objective comparison of the low mass range of these positive mode LDMS spectra which have characteristic unknown peaks. [less ▲]

Stainless steel with robust anibacterial activiy based on a versatile and bio-inspired strategy

Conference (2011, September 01)

The synthesis of a poly(methacrylamide) bearing 3,4-dihydroxyphenylalanine inspired from the chemical composition of mussel adhesives will be presented. This homopolymer is designed to insure a multilayer ... [more ▼]

The synthesis of a poly(methacrylamide) bearing 3,4-dihydroxyphenylalanine inspired from the chemical composition of mussel adhesives will be presented. This homopolymer is designed to insure a multilayer film growth by covalent coupling during the layer-by-layer building with a homopolymer containing amino groups. The film cross-linking is initiated by adequately controlling both the redox state of the polymer and the pH of the solutions. This cross-linking is evidenced by solid-state 13C NMR with the occurrence of a typical signal of imine, traducing the Schiff base formation during film growth. The same coupling reaction is implemented for grafting an antibacterial peptide, Nisin, on a stainless steel substrate. Antibacterial activity against Bacillus subtilis is preserved even after long immersion time, as the result of the peptide covalent anchoring on the surface. All the processing steps, including the synthesis of the polymers and the peptide grafting, are performed in aqueous solutions under mild conditions. [less ▲]