A lanthanide half-sandwich complex and a ansa lanthanidocene have been assessed for isoprene-styr... more A lanthanide half-sandwich complex and a ansa lanthanidocene have been assessed for isoprene-styrene chain shuttling copolymerization with n-butylethylmagnesium (BEM). In the presence of 1 equiv. BEM, a fully amorphous multiblock microstructure of soft and hard segments is achieved. The microstructure consists of poly(isoprene-co-styrene) blocks, with hard blocks rich in styrene and soft blocks rich in isoprene. The composition of the blocks and the resulting glass transition temperatures (T g ) can be easily modified by changing the feed and/or the relative amount of the catalysts, highlighting a new class of thermoplastic elastomers (TPEs) with tunable transition temperatures. The materials self-organize into nanostructures at the solid state.
Coordinative chain transfer polymerization (CCTP) is a reversible group transfer polymerization i... more Coordinative chain transfer polymerization (CCTP) is a reversible group transfer polymerization involving a transition metal catalyst and a main group metal alkyl. CCTP affords well controlled polymerizations of olefins and conjugated dienes with catalyst economy and good potentialities for polymer end-functionalization. New concepts have recently emerged in this field, affording unprecedented control over both microstructure and architecture of the resulting polymers and copolymers. These concepts are presented and discussed in this perspective.
Reviews in Environmental Science and Bio/Technology, 2009
Polyesters are widely used for biomedical applications such as drug delivery systems and resorbab... more Polyesters are widely used for biomedical applications such as drug delivery systems and resorbable implants. The degradation kinetic of these biopolymers can be tailored by the introduction of functional groups in their backbone, leading to a modification of their morphology and hydrophilicity. This is usually realized via long multistep reaction pathways. This contribution describes the emergence of one-step procedures for this purpose including enzymatic and Lewis acid catalyzed polycondensation as well as coordinative ring opening polymerization.
The pseudoanionic character of the polymerisation of dienes by lanthanide catalysts has been asse... more The pseudoanionic character of the polymerisation of dienes by lanthanide catalysts has been assessed from microwave experiments. The microwave activation of isoprene polymerisation with Nd(BH 4 ) 3 (THF) 3 / Mg(Bu) 2 and Nd(BH 4 ) 3 (THF) 3 / Al(Et) 3 leads to a modification of the reactivity, the selectivity being only slightly modified. An explanation of the observed effect is proposed based on our current knowledge of the catalytic mechanism and by considering the alkylated complex as a ion pair. The bimetallic active species are thought to evolute toward a transition state where ion pairing is much more loose due to negative charge delocalisation, resulting in an enhancement in polarity during the reaction progress. The formation of a highly stabilising polymetallic specie involving tetraaluminate groups is advanced in order to explain the difference in reactivity observed between both catalytic systems. Finally, a "depolymerisation" effect of microwave irradiation in course of reaction is observed at high temperature.
The microstructural analysis of 1,4-cis-and 1,4-trans-polymyrcene was conducted by means of thoro... more The microstructural analysis of 1,4-cis-and 1,4-trans-polymyrcene was conducted by means of thorough investigations at a very high field NMR (21.1T, 900 MHz). A set of 1D and 2D experiments helped to entirely assign the resonances of the spectra for both stereoisomers. A simple method to distinguish between each stereoisomer by NMR spectroscopy is finally provided.
Syndiotactic polystyrene (sPS) is a promising material that has been commercialized and widely st... more Syndiotactic polystyrene (sPS) is a promising material that has been commercialized and widely studied by the academic community. Several drawbacks can however restrict its practical use: its brittleness, in areas where mechanical properties are important, the lack of polar groups, for adhesion and compatibility with other polymers, and the need to process sPS at high temperatures. These drawbacks can be overcome by the introduction of relevant functional groups into sPS. We present in this review the various strategies reported for the functionalization of syndiotactic polystyrene: statistical and sequential block copolymerization, chain transfer and chain end functionalization, polymerization of substituted styrenic monomers and chemical modification of sPS.
An important topic in polymer science seeks to improve the performances of polymer blends using n... more An important topic in polymer science seeks to improve the performances of polymer blends using nanoscale phase segregation. Here, blends between polystyrene and polycaprolactone are realised by a chemical route. The non-interfering character of the radical polymerisation of styrene and the lanthanide halide initiated ring-opening polymerisation of caprolactone is assessed. The molecular weights range from 2000 to 3500 for polycaprolactone and up to 140 000 for polystyrene, with reasonnable polydispersity indexes. From microcalorimetry measurements, it is shown that polystyrene and low molecular weight polycaprolactone are immiscible. The morphology of the blends between the two immiscible polymers studied by atomic force microscopy is consistent with nanometer-scale phase segregation.
The structure of organomineral coatings on glass fibres surface is a function of numerous paramet... more The structure of organomineral coatings on glass fibres surface is a function of numerous parameters. Among them, the molecular parameters of organosilane coupling agents in aqueous solution are of great importance . The understanding of hydrolysis and condensation mechanisms, the influence of the pH, temperature, concentration and the nature of the organic ligand are keys for the control of the structure . It is now well accepted that the structure resulting from the deposition from an aqueous solution of 1,4 γ -aminopropyltriethoxysilane consists in a threedimensional graded cross-linked network . The crosslinking density increases as the glass surface is reached and the outer layers are thought to be physisorbed. The situation still remains uncertain in the case of more complex industrial sizings, although it is assumed that the silane migrates to the interface providing an interfacial region which is similar to that obtained from the pure coupling agents solutions . The silane may act as a surfactant for the colloidal polymer particles in the sizing emulsion. The evolution of the structure in the course of a thermohydrolytic treatment has not been discussed so far, although changes in the mechanical behaviour of the fibres [8-10] and in the mechanical properties and the structure of interfacial zones in composites materials have been reported. The first steps of interfacial zones formation can be described by the dissolution of the outer physisorbed layers of the structure in the reacting comonomers, and the consecutive diffusion in the preformed inorganic-organic network . An attempt to apply general concepts from the chemistry of hybrid materials to the formation and properties of glass-fibers sizings and glass fibers-polymer interfaces can thus be proposed by considering the simultaneous reactions of organic and inorganic components. Apart from an analogy between the sizing treatment of glass fibers and the strengthening of silica glass by means of hybrid inorganic-organic coatings , the application of concepts from the chemistry of hybrid materials in the field of glass fibers sizings and their interfaces with a polymer has remained to our knowledge purely conceptual, suffering from a lack of experimental data. In fact, due to the geometry of these systems, the dimensions involved and the necessity to perform in situ measurements, the experimentation still remains difficult. In the early eighties, Miller [l4] developped a technique based on dynamical mechanical analysis which enables to characterize coatings directly on glass fibers strands.
Dedicated to the memory of John Osborn, on the occasion of this meeting organized thanks to the o... more Dedicated to the memory of John Osborn, on the occasion of this meeting organized thanks to the organizing committee from Strasbourg University, where he spread his brilliant and clever knowledge of organometallic chemistry and catalysis.
A series of ruthenium(II) complexes with the general formula [Ru(η5-C5H5) (η6-substituted arene)]... more A series of ruthenium(II) complexes with the general formula [Ru(η5-C5H5) (η6-substituted arene)]+[PF6]− (substituted arene = 2-phenylpyridine (1), dibenzosuberone (2) and toluene (3)), in combination with isopropyl alcohol were used for the polymerization of ɛ-caprolactone. The polymerization was found to be quantitative and controlled, with PDI in the range 1.1–1.3. By means of MALDI-ToF analyses, functionalization studies with d,l-lactide and NMR monitoring techniques, it has been found that the polymerization proceeds via a living Activated Monomer mechanism (AM) involving an η6–η4 change of the coordination mode of the arene. These experimental results were corroborated by DFT studies. The growth of several polymer chains per ruthenium atom highlights interesting potentialities for molecular weight control and catalyst economy. The stability of the ruthenium complexes allows their recovery at the end of the polymerization, which can be viewed as a further advance in a green chemistry frame.Change in the coordination mode of the arene ligand upon ɛ-caprolactone interaction during an Activated Monomer mechanism promoted by ruthenium(II) mixed metallocenes.► First Ru(II) mixed metallocene catalysts for living Activated Monomer mechanism. ► Innovative polymerization mechanism based on arene η6–η4 slippage. ► DFT studies performed for the first time for a ROP via Activated Monomer mechanism. ► Recovery of the ruthenium catalytic complexes at the end of reaction. ► Growing of several polymer chains per metal: catalyst economy for green chemistry.
In order to extrapolate the tensile strength of glass fibres at short gauge lengths corresponding... more In order to extrapolate the tensile strength of glass fibres at short gauge lengths corresponding for instance to the mean fragment length in a fragmentation test, four types of extrapolation techniques are reviewed. The ability of these models to describe the tensile strength of fibres is checked on E-glass fibres exhibiting multiple modes of failure. It is showed that Weibull unimodal statistics as well as bimodal CDF model lead to underestimated results. The double box approach provides values having a physical meaning but remain phenomenological. The need of a modeling taking into account a trimodality is emphasised.
New bis(phenolate)amine-supported neodymium borohydride complexes and their previously reported s... more New bis(phenolate)amine-supported neodymium borohydride complexes and their previously reported samarium analogues were tested as catalysts for the polymerisation of styrene and isoprene. Pr). X-ray structures of 1'-Nd and 2-Nd were determined and are presented. The neodymium borohydride complexes 1-Nd to 3-Nd and their samarium analogues Sm(O 2 N L )(BH 4 )(THF) (L = py (1-Sm), OMe (2-Sm), NMe 2 (3-Sm), Pr (4-Sm)) were tested as catalysts for the polymerisation of isoprene and styrene in the presence of nbutylethylmagnesium (Mg( n Bu)(Et)). All complexes were found to be active for the polymerisation of isoprene in these conditions, leading to polyisoprene up to 95.1% trans-1,4 stereoregular. They were also found to be active for the polymerisation of styrene leading to atactic polystyrene in all cases. Interestingly, samarium-based complexes were found to be more active than the neodymium ones toward this latter monomer, in sharp contrast to what is usually observed with rare earth borohydride complexes. The structure of both transpolyisoprenes and polystyrenes obtained were studied in detail by MALDI-ToF analysis in order to better understand the polymerisation mechanisms. The coordinative chain transfer polymerisation (CCTP) of both monomers was further conducted using Mg( n Bu)(Et) as transfer agent. Finally, the statistical copolymerisation of isoprene and styrene was examined using these catalytic systems, leading to the formation of poly[(trans-1,4-isoprene)-costyrene] with up to 39 % of styrene moieties inserted in a highly trans-1,4-stereoregular polyisoprene.
A lanthanide half-sandwich complex and a ansa lanthanidocene have been assessed for isoprene-styr... more A lanthanide half-sandwich complex and a ansa lanthanidocene have been assessed for isoprene-styrene chain shuttling copolymerization with n-butylethylmagnesium (BEM). In the presence of 1 equiv. BEM, a fully amorphous multiblock microstructure of soft and hard segments is achieved. The microstructure consists of poly(isoprene-co-styrene) blocks, with hard blocks rich in styrene and soft blocks rich in isoprene. The composition of the blocks and the resulting glass transition temperatures (T g ) can be easily modified by changing the feed and/or the relative amount of the catalysts, highlighting a new class of thermoplastic elastomers (TPEs) with tunable transition temperatures. The materials self-organize into nanostructures at the solid state.
Coordinative chain transfer polymerization (CCTP) is a reversible group transfer polymerization i... more Coordinative chain transfer polymerization (CCTP) is a reversible group transfer polymerization involving a transition metal catalyst and a main group metal alkyl. CCTP affords well controlled polymerizations of olefins and conjugated dienes with catalyst economy and good potentialities for polymer end-functionalization. New concepts have recently emerged in this field, affording unprecedented control over both microstructure and architecture of the resulting polymers and copolymers. These concepts are presented and discussed in this perspective.
Reviews in Environmental Science and Bio/Technology, 2009
Polyesters are widely used for biomedical applications such as drug delivery systems and resorbab... more Polyesters are widely used for biomedical applications such as drug delivery systems and resorbable implants. The degradation kinetic of these biopolymers can be tailored by the introduction of functional groups in their backbone, leading to a modification of their morphology and hydrophilicity. This is usually realized via long multistep reaction pathways. This contribution describes the emergence of one-step procedures for this purpose including enzymatic and Lewis acid catalyzed polycondensation as well as coordinative ring opening polymerization.
The pseudoanionic character of the polymerisation of dienes by lanthanide catalysts has been asse... more The pseudoanionic character of the polymerisation of dienes by lanthanide catalysts has been assessed from microwave experiments. The microwave activation of isoprene polymerisation with Nd(BH 4 ) 3 (THF) 3 / Mg(Bu) 2 and Nd(BH 4 ) 3 (THF) 3 / Al(Et) 3 leads to a modification of the reactivity, the selectivity being only slightly modified. An explanation of the observed effect is proposed based on our current knowledge of the catalytic mechanism and by considering the alkylated complex as a ion pair. The bimetallic active species are thought to evolute toward a transition state where ion pairing is much more loose due to negative charge delocalisation, resulting in an enhancement in polarity during the reaction progress. The formation of a highly stabilising polymetallic specie involving tetraaluminate groups is advanced in order to explain the difference in reactivity observed between both catalytic systems. Finally, a "depolymerisation" effect of microwave irradiation in course of reaction is observed at high temperature.
The microstructural analysis of 1,4-cis-and 1,4-trans-polymyrcene was conducted by means of thoro... more The microstructural analysis of 1,4-cis-and 1,4-trans-polymyrcene was conducted by means of thorough investigations at a very high field NMR (21.1T, 900 MHz). A set of 1D and 2D experiments helped to entirely assign the resonances of the spectra for both stereoisomers. A simple method to distinguish between each stereoisomer by NMR spectroscopy is finally provided.
Syndiotactic polystyrene (sPS) is a promising material that has been commercialized and widely st... more Syndiotactic polystyrene (sPS) is a promising material that has been commercialized and widely studied by the academic community. Several drawbacks can however restrict its practical use: its brittleness, in areas where mechanical properties are important, the lack of polar groups, for adhesion and compatibility with other polymers, and the need to process sPS at high temperatures. These drawbacks can be overcome by the introduction of relevant functional groups into sPS. We present in this review the various strategies reported for the functionalization of syndiotactic polystyrene: statistical and sequential block copolymerization, chain transfer and chain end functionalization, polymerization of substituted styrenic monomers and chemical modification of sPS.
An important topic in polymer science seeks to improve the performances of polymer blends using n... more An important topic in polymer science seeks to improve the performances of polymer blends using nanoscale phase segregation. Here, blends between polystyrene and polycaprolactone are realised by a chemical route. The non-interfering character of the radical polymerisation of styrene and the lanthanide halide initiated ring-opening polymerisation of caprolactone is assessed. The molecular weights range from 2000 to 3500 for polycaprolactone and up to 140 000 for polystyrene, with reasonnable polydispersity indexes. From microcalorimetry measurements, it is shown that polystyrene and low molecular weight polycaprolactone are immiscible. The morphology of the blends between the two immiscible polymers studied by atomic force microscopy is consistent with nanometer-scale phase segregation.
The structure of organomineral coatings on glass fibres surface is a function of numerous paramet... more The structure of organomineral coatings on glass fibres surface is a function of numerous parameters. Among them, the molecular parameters of organosilane coupling agents in aqueous solution are of great importance . The understanding of hydrolysis and condensation mechanisms, the influence of the pH, temperature, concentration and the nature of the organic ligand are keys for the control of the structure . It is now well accepted that the structure resulting from the deposition from an aqueous solution of 1,4 γ -aminopropyltriethoxysilane consists in a threedimensional graded cross-linked network . The crosslinking density increases as the glass surface is reached and the outer layers are thought to be physisorbed. The situation still remains uncertain in the case of more complex industrial sizings, although it is assumed that the silane migrates to the interface providing an interfacial region which is similar to that obtained from the pure coupling agents solutions . The silane may act as a surfactant for the colloidal polymer particles in the sizing emulsion. The evolution of the structure in the course of a thermohydrolytic treatment has not been discussed so far, although changes in the mechanical behaviour of the fibres [8-10] and in the mechanical properties and the structure of interfacial zones in composites materials have been reported. The first steps of interfacial zones formation can be described by the dissolution of the outer physisorbed layers of the structure in the reacting comonomers, and the consecutive diffusion in the preformed inorganic-organic network . An attempt to apply general concepts from the chemistry of hybrid materials to the formation and properties of glass-fibers sizings and glass fibers-polymer interfaces can thus be proposed by considering the simultaneous reactions of organic and inorganic components. Apart from an analogy between the sizing treatment of glass fibers and the strengthening of silica glass by means of hybrid inorganic-organic coatings , the application of concepts from the chemistry of hybrid materials in the field of glass fibers sizings and their interfaces with a polymer has remained to our knowledge purely conceptual, suffering from a lack of experimental data. In fact, due to the geometry of these systems, the dimensions involved and the necessity to perform in situ measurements, the experimentation still remains difficult. In the early eighties, Miller [l4] developped a technique based on dynamical mechanical analysis which enables to characterize coatings directly on glass fibers strands.
Dedicated to the memory of John Osborn, on the occasion of this meeting organized thanks to the o... more Dedicated to the memory of John Osborn, on the occasion of this meeting organized thanks to the organizing committee from Strasbourg University, where he spread his brilliant and clever knowledge of organometallic chemistry and catalysis.
A series of ruthenium(II) complexes with the general formula [Ru(η5-C5H5) (η6-substituted arene)]... more A series of ruthenium(II) complexes with the general formula [Ru(η5-C5H5) (η6-substituted arene)]+[PF6]− (substituted arene = 2-phenylpyridine (1), dibenzosuberone (2) and toluene (3)), in combination with isopropyl alcohol were used for the polymerization of ɛ-caprolactone. The polymerization was found to be quantitative and controlled, with PDI in the range 1.1–1.3. By means of MALDI-ToF analyses, functionalization studies with d,l-lactide and NMR monitoring techniques, it has been found that the polymerization proceeds via a living Activated Monomer mechanism (AM) involving an η6–η4 change of the coordination mode of the arene. These experimental results were corroborated by DFT studies. The growth of several polymer chains per ruthenium atom highlights interesting potentialities for molecular weight control and catalyst economy. The stability of the ruthenium complexes allows their recovery at the end of the polymerization, which can be viewed as a further advance in a green chemistry frame.Change in the coordination mode of the arene ligand upon ɛ-caprolactone interaction during an Activated Monomer mechanism promoted by ruthenium(II) mixed metallocenes.► First Ru(II) mixed metallocene catalysts for living Activated Monomer mechanism. ► Innovative polymerization mechanism based on arene η6–η4 slippage. ► DFT studies performed for the first time for a ROP via Activated Monomer mechanism. ► Recovery of the ruthenium catalytic complexes at the end of reaction. ► Growing of several polymer chains per metal: catalyst economy for green chemistry.
In order to extrapolate the tensile strength of glass fibres at short gauge lengths corresponding... more In order to extrapolate the tensile strength of glass fibres at short gauge lengths corresponding for instance to the mean fragment length in a fragmentation test, four types of extrapolation techniques are reviewed. The ability of these models to describe the tensile strength of fibres is checked on E-glass fibres exhibiting multiple modes of failure. It is showed that Weibull unimodal statistics as well as bimodal CDF model lead to underestimated results. The double box approach provides values having a physical meaning but remain phenomenological. The need of a modeling taking into account a trimodality is emphasised.
New bis(phenolate)amine-supported neodymium borohydride complexes and their previously reported s... more New bis(phenolate)amine-supported neodymium borohydride complexes and their previously reported samarium analogues were tested as catalysts for the polymerisation of styrene and isoprene. Pr). X-ray structures of 1'-Nd and 2-Nd were determined and are presented. The neodymium borohydride complexes 1-Nd to 3-Nd and their samarium analogues Sm(O 2 N L )(BH 4 )(THF) (L = py (1-Sm), OMe (2-Sm), NMe 2 (3-Sm), Pr (4-Sm)) were tested as catalysts for the polymerisation of isoprene and styrene in the presence of nbutylethylmagnesium (Mg( n Bu)(Et)). All complexes were found to be active for the polymerisation of isoprene in these conditions, leading to polyisoprene up to 95.1% trans-1,4 stereoregular. They were also found to be active for the polymerisation of styrene leading to atactic polystyrene in all cases. Interestingly, samarium-based complexes were found to be more active than the neodymium ones toward this latter monomer, in sharp contrast to what is usually observed with rare earth borohydride complexes. The structure of both transpolyisoprenes and polystyrenes obtained were studied in detail by MALDI-ToF analysis in order to better understand the polymerisation mechanisms. The coordinative chain transfer polymerisation (CCTP) of both monomers was further conducted using Mg( n Bu)(Et) as transfer agent. Finally, the statistical copolymerisation of isoprene and styrene was examined using these catalytic systems, leading to the formation of poly[(trans-1,4-isoprene)-costyrene] with up to 39 % of styrene moieties inserted in a highly trans-1,4-stereoregular polyisoprene.
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