Ph. Dubois

Macromolecular engineering of polylactones and polylactides I. End-functionalization of poly ~- caprolactone

SummaryAluminum alkoxides carrying functional alkoxy groups are effective initiators for theɛ-caprolactone polymerization in toluene and tetrahydrofuran. The coordination-insertion type of polymerization is living and yields exclusively linear polyesters of a predictable molecular weight with a narrow molecular weight distribution within the period of time required for the total monomer conversion. The functional group associated to the active alkoxy group of the initiator is selectively attached to one chain-end, and the second end-group is systematically a hydroxyl function resulting from the hydrolysis of the living growing site. Asymmetric telechelic polyesters are thus obtained in a perfectly controlled way, including macromonomers. Beside (meth)acrylic double bond, the functional end-group derived from the initiator can be, for instance, an unsaturation, a halogen and a tert-amine. Coupling the asymmetric telechelic polymer via the OH end-group (or the precursor Al alkoxide end-group) is a direct way to the related symmetric telechelic of a twofold increased molecular weight.

Healing by the Joule effect of electrically conductive poly(ester-urethane)/carbon nanotube nanocomposites

Recent demands for polymers with autonomous self-healing properties are being constantly raised due to the need for high-performance and reliable materials. So far, the advances in this field are limited to the production of self-healing materials requiring a high energy input. Therefore there is an urgent need to develop self-healing polymer systems, in which healing can be easily and specifically induced by external stimuli for economical and viable applications. In the current work we demonstrate, for the first time to our knowledge, the possibility to heal local macroscopic damage by a confined temperature increase arising from the Joule effect. The damage healing is promoted by the resistance to an electrical current at the crack tip. This new concept is studied on thermo-reversible and electrically conductive poly(ester-urethane)/carbon nanotube nanocomposites derived from thermo-reversible Diels–Alder reactions between furfuryl- and maleimide-functionalized poly(e-caprolactone) (PCL)-based precursors. Electrically conductive materials are then obtained after incorporating multi-walled carbon nanotubes into the thermo-reversible networks using reactive extrusion. Under mild electrical conditions, temperature in the range of the retro-Diels–Alder reaction can be obtained near the damaged site. The obtained results reveal the potential of this new approach for healing materials locally while maintaining the overall material properties.

Osteoconductive and bioresorbable composites based on poly(L,L-lactide) and pseudowollastonite: from synthesis and interfacial compatibilization to in vitro bioactivity and in vivo osseointegration studies.

This contribution reports on the elaboration of novel bioresorbable composites consisting of pseudowollastonite (psW) (a silicate-based polycrystalline ceramic (α-CaSiO(3))) and poly(L,L-lactide) as a valuable polymeric candidate in bone-guided regeneration. These composites were prepared by direct melt-blending to avoid the use of organic solvents harmful for biomedical applications. Amphiphilic poly(ethylene oxide-b-L,L-lactide) diblock copolymers synthesized by ring-opening polymerization were added to psW-based composites to modulate the bioactivity of the composites. The bioactivity of the composites was first evaluated by monitoring the release of bioactive Ca(2+) and (SiO(4))(4-) ions as well as the concomitant formation of hydroxyapatite on the material surface after soaking them in physiological fluid. Subsequently, the composites were studied in vitro to evaluate their cytotoxicity in the presence of SaOS-2 osteoblastic cells and in vivo to assess their osteoconductivity in an orthotopic rat tibia model. This study provides a first insight into the use of direct melt-blended psW-poly(L,L-lactide) composites for bone-regeneration applications.

Control over molar mass, dispersity, end-groups and kinetics in cyclopolymerization of ortho-phthalaldehyde: adapted choice of a phosphazene organocatalyst

The use of different phosphazene bases as catalysts has been investigated in the polymerization of ortho-phthalaldehyde (PA) in the presence of an alcohol used as the initiator. Among the catalysts considered (P1-t-Bu, P2-t-Bu and P4-t-Bu) only the less active one (P1-t-Bu) allows a very good control of the PA polymerization in terms of mass parameters (Mn, Mw and molar mass dispersity) and end-group fidelity. To confirm the structure and the mass range of the newly synthesized PPA, mass spectrometry and gel permeation chromatography have been selected as main characterization techniques. By comparison with the state-of-the-art, the kinetics of polymerization has also been significantly improved by reducing the polymerization time from several hours to a few minutes. The judicious choice of catalyst also allowed expanding the macromolecular engineering by preparing in a one-step procedure a defined and controlled polyphthalaldehyde-block-polyethylene oxide amphiphilic diblock copolymer.

Fire and Gas Barrier Properties of Poly(styrene-co-acrylonitrile) Nanocomposites Using Polycaprolactone/Clay Nanohybrid Based-Masterbatch

Exfoliated nanocomposites are prepared by dispersion of poly(-caprolactone) (PCL) grafted montmorillonite nanohybrids used as masterbatches in poly(styrene-co-acrylonitrile) (SAN). The PCL-grafted clay nanohybrids with high inorganic content are synthesized by in situ intercalative ring-opening polymerization of -caprolactone between silicate layers organomodified by alkylammonium cations bearing two hydroxyl functions. The polymerization is initiated by tin alcoholate species derived from the exchange reaction of tin(II) bis(2-ethylhexanoate) with the hydroxyl groups borne by the ammonium cations that organomodified the clay. These highly filled PCL nanocomposites (25 wt% in inorganics) are dispersed as masterbatches in commercial poly(styrene-co-acrylonitrile) by melt blending. SAN-based nanocomposites containing 3 wt% of inorganics are accordingly prepared. The direct blend of SAN/organomodified clay is also prepared for sake of comparison. The clay dispersion is characterized by wide-angle X-ray diffraction (WAXD), atomic force microscopy (AFM), and solid state NMR spectroscopy measurements. The thermal properties are studied by thermogravimetric analysis. The flame retardancy and gas barrier resistance properties of nanocomposites are discussed both as a function of the clay dispersion and of the matrix/clay interaction.

Macromolecular engineering of polylactones and polylactides: 13. Synthesis of telechelic polyesters by coupling reactions☆

Abstract Aromatic diisocyanates, such as phenylene-1,4-diisocyanate have proved to be very effective coupling agents of α-X functional ω-hydroxy poly-e-caprolactone (PCL). Very high yields (> 98%) have been observed in the presence of triethylamine, in tetrahydrofuran. Accordingly α,ω-X functional PCL of a two-fold molecular weight have been obtained and characterized by size exclusion chromatography and nuclear magnetic resonance spectroscopy. More interestingly, the same coupling reactions have been successfully carried out when applied to the precursor living polyester (XCH2OPCLOAlEt2) rather than to the chains recovered after hydrolysis of the living propagating sites. Terephthalic acid chloride has been the most efficient coupling agent and, in the presence of pyridine, has yielded quantitatively the expected α,ω-functional polyesters.

Thermogravimetry as a Method for Investigating the Thermal Stability of Polymer Composites

Thermogravimetry was used to investigate the effects of different inorganic functional fillers on the heat resistance of polymer matrices. The kinetic parameters of thermal oxidative degradation were shown to depend on the polymer, the chemical composition of the filler surface, the filler concentration, and the processing method, which determines the distribution of filler particles in the polymer matrix. Magnetic fillers (carbonyl iron, and hexaferrites of different structural types) were shown to be chemically active fillers, increasing the heat resistance of siliconorganic polymers. Their stabilizing effect is due to blocking of the end silanol groups and macroradicals by the surface of the filler and non-chain inhibition of thermal oxidative degradation. In the case of fiber-forming polymers (UHMWPE, PVOH and PAN), most magnetic fillers are chemically inert, but at concentrations of 30–50 vol% they increase the heat resistance of the composite. Addition of carbon black increased the heat resistance of the thermoplastic matrix. The dependence of the thermal degradation onset temperature on the kaolin concentration in the polyolefin matrix exhibited a maximum. Analysis of the experimental results demonstrated the operating temperature ranges for different composites, and their maximum operating temperature.

SAXS analysis of the morphology of biocompatible and biodegradable poly(ε-caprolactone-b-glycolide) copolymers☆

Abstract Poly(e-caprolacrone-b-glycolide) diblock copolyesters have been synthesized by the sequential polymerization of e-caprolactone and glycolide as initiated by aluminium alkoxides. Copolymerization is typically “living” and yields copolyesters of perfectly controlled molecular weight and composition. Diblock molecular weight (MnPGA + MnPCL) ranges from 5700 to 42000 and the ϱ = Mn PCL Mn PGA ratio varies from 1.5 to 13.1. Due to the inherent insolubility of the polyglycolide (PGA) segment in common organic solvent, the diblock copolyesters form stable non-aqueous colloidal dispersions e.g., in toluene, the stability of which results from the soluble poly(e-caprolactone) (PCL) block. Combining all the experimental observations (PCS, TEM, WAXS, SAXS, AFM), a micelle model has been proposed which consists of a polyglycolide core surrounded with a corona of polycaprolactone (PCL). Both constituents are semi crystalline. From SAXS observations, the PGA core is better described by two concentric spheres. The internal sphere of a 5–6.7 nm diameter would essentially contain crystalline PGA. The diameter of the external sphere, DPGA, is in the range from 6.2 to 9.6 nm, at least for the investigated diblock copolymers. As a rule, this diameter increases as ϱ decreases at constant molecular weight and as the diblock molecular weight increases at constant ϱ. A scattering peak (weak) is observed in the range from 10.8 to 15.5 nm and the Bragg distance is close μDPGA, where μ is equal to (1+ 3 ϱ 2 ) 1 3 . From steric considerations, μ is the ratio between the diameter of the micelle and the diameter of the PGA core, so that this peak has been assigned to the characteristic intermicellar distance. At very small angles, several additional peaks are the signature of a hyperstructure which is possibly lamellar.

Chapter 21 – Pathways to Biodegradable Flame Retardant Polymer (Nano)Composites

The realization of special formulations of biopolymers characterized by flame retardancy significantly enlarges their potential for utilization in engineering sectors while reducing the environmental impact. The production of nanocomposites using nanofillers of different morphologies, associated or not associated with traditional flame retardants (FR), is undeniably one of the most promising ways considered to improve the flame retardancy of biopolymers. The chapter presents current researches, results, and trends in the field of bionanocomposites (BNCs) characterized by improved fire resistance, with a special mention for polylactic acid (PLA), an aliphatic polyester that is derived from renewable resources and which is environmentally biodegradable. The chapter highlights the main developments in FR systems during the last decade using various nanofillers (clays, carbon nanotubes, graphite derivatives, etc.) and attempts in the formulation of innovative intumescent formulations. Furthermore, selected results are presented in relation to the characterization of novel BNCs with special end-use properties (flame retardancy) designed for the production of PLA fibers.

Smart acrylic coatings containing silica particles for corrosion protection of aluminum and other metals

Abstract: Polymer-based films and hybrid films based on an organic matrix filled with inorganic particles have been applied to solid substrates for protective and functional purposes. This chapter examines the preparation, through a sol–gel approach, of new hybrid nanocomposites that are based on an acrylic copolymer and on the formulation of silica nanoparticles. Also discussed are the barrier properties of these coatings when in a NaCl solution, which were assessed using electrochemical impedance spectroscopy (EIS) and correlated with chemical structure, morphology, physicochemical properties and thermal behavior, and the corrosion properties of coatings based on hybrid materials.