Jean-Pierre Couvercelle

Organo-catalyzed synthesis of aliphatic polycarbonates in solvent-free conditions

A new efficient and expeditious route to the synthesis of aliphatic polycarbonates, in solvent-free conditions and using 1-n-butyl-3-methylimidazolium-2-carboxylate (BMIM-2-CO2) as a catalyst precursor, is described. The protocol consists of a two-step polymerization process involving the transesterification of dimethyl carbonate (DMC) with linear alkane diols and leading to high molecular weight homopolymers. The reaction went to completion quantitatively with the liberation of methanol as the only by-product. The in situ formation of N-heterocyclic carbene species resulting from BMIM-2-CO2 decarboxylation is suggested to be a key feature of the condensation process. The protocol was then applied to the copolymerization of diverse diols leading to the synthesis of polycarbonates with average segment lengths and random sequences.

1-n-Butyl-3-methylimidazolium-2-carboxylate: a versatile precatalyst for the ring-opening polymerization of ε-caprolactone and rac-lactide under solvent-free conditions

Summary The ring-opening polymerization of ε-caprolactone (ε-CL) and rac-lactide (rac-LA) under solvent-free conditions and using 1-n-butyl-3-methylimidazolium-2-carboxylate (BMIM-2-CO2) as precatalyst is described. Linear and star-branched polyesters were synthesized by successive use of benzyl alcohol, ethylene glycol, glycerol and pentaerythritol as initiator alcohols, and the products were fully characterized by 1H and 13C{1H} NMR spectroscopy, gel permeation chromatography (GPC), and differential scanning calorimetry (DSC). BMIM-2-CO2 acts as an N-heterocyclic carbene precursor, resulting from in situ decarboxylation, either by heating under vacuo (method A) or by addition of NaBPh4 (method B). Possible catalytic and deactivation mechanisms are proposed.

Characterizations of Thermoplastic Block Elastomers Based on Polybutadiene and ε -Caprolactone

A broad series of tri- and multiblock copolymers based on linear and branched oligomers of polybutadiene as central blocks and polycaprolactone (PCL) as block extremities are characterized by SEC, DSC, DMA, Dynamical Rheology and DRX. DSC analyses reveal phase separation between the two amorphous PB and PCL phases. By thermal analysis, the glass transition temperature of PCL is only detected for materials containing at least 80% w/w of PCL. This is attributed to the small length of the polyester blocks for copolymers containing less than 80% w/w of PCL. The increase of fusion heat with increasing PCL content in the copolymers is correlated to the greater ability of PCL chains to rearrange as HTPB amount decrease in the material. Regarding the evolution of the melting temperature of the various copolymers, the characterization by DMA and dynamical rheology confirms the behaviour observed by DSC. Mechanical and rheological properties (i.e., storage modulus and complex viscosities) were studied and reveal that the behavior of the copolymers depends on both the rate of PCL chains and on the nature of the elastomeric block.

In Vitro Release of Local Anaesthetic and Anti-Inflammatory Drugs from Crosslinked Collagen Based Device

The drug delivery systems that are the object of this article take the form of a hydrophilic matrix (collagen or crosslinked collagen) containing a drug. These devices can be used as The model active agents, were chosen from the range of local anaesthetics (lidocaine hydrochloride), anti-inflammatory (diclofenac sodium salt) and antioxydant (caffeic acid). Whatever the drug affinity for water, in the first time of the experiments, the release appears to be systematically delayed when the matrix is crosslinked. For lidocaine hydrochloride based systems, as the amount of drug increases in the matrix, the high gap concentration between the matrix and the buffer solution promote the diffusion and a Fickian behavior is observed on the release curves. Depending on the chemical nature of the drug and its solubility, several interactions between the drug and the collagen matrix can be considered. A new drug delivery system containing caffeic acid as the anti-inflammatory and antioxydant molecule could be tested. This new system was able to release 95% of the drug in 5 h and the global release rate depends on the initial drug concentration in the device.

Chain-extending of Hydroxytelechelic Polybutadiene: Synthesis and Characterization

Extension of hydroxytelechelic polybutadiene oligomers ( 3200 g/mol) is performed in mild conditions, in order to avoid backbone modifications, using succinic anhydride or methylenedicyclohexyl diisocyanate. The two routes present significative extension of the initial oligomers. Extension through the anhydride route, in the presence of DCC and DMAP, leads to new hydroxytelechelic oligomers ( 8000 g/mol). Extension through the diisocyanate route, catalyzed by DBTL at 65°C leads to hydroxytelechelic oligomers of higher average molecular weight ( 20000 g/mol). New materials are characterized by FTIR/1H-NMR and changes in their Tg according to , are discussed. The influence of reaction time on the length of the macromolecular chains is also studied.

New approach for synthesis of poly(ethylglyoxylate) using Maghnite-H+, an Algerian proton exchanged montmorillonite clay, as an eco-catalyst

ABSTRACT In this works, we have explored a new method for a green synthesis of poly(ethylglyoxylate) (PEtG). This method consists on using a montmorillonite clay called “Maghnite-H+” as an eco-catalyst to replace triethylamine which is toxic. Cationic polymerization experiments are performed in bulk conditions at three temperatures (−40°C, 25°C, 80°C) and in THF solutions at room temperature (25°C). At 25°C, an optimum ratio of 5 wt% of catalyst leads to molar masses up to 22000 g/mol in THF solutions. Polymerizations in bulk conditions lead to slightly lower masses than experiments conducted in THF solutions. However, bulk polymerization of ethyleglyoxylate remains a preferable method in order to avoid the use of a solvent and therefore to stay in the context of green chemistry. The structure of obtained polymers are characterized and confirmed by 1H and 13C NMR. Thermogravimetric Analysis (TGA) shows an enhanced thermal stability for end-capped PEtG compared to non-terminated PEtG. The best conversion rate (92%) is observed in bulk conditions at 25°C for a reaction time of 48h. An activation energy could be calculated from bulk experiments (Ea = 6.9 kJ/mol). An interesting advantage of Maghnite-H+ is an easy recoverage by a simple filtration from the polymer solution.

Aqueous chemical grafting of modified-PEG onto maghemite nanoparticles: Influence of grafting conditions

Abstract The synthesis of maghemite nanoparticles coated with triethoxysilanemonomethylether- PEG (Si-mPEG), is presented in aqueous conditions, by the “grafting to” process. This procedure is performed in one step, starting from anchored polymer and native nanoparticles. The maghemite nanoparticles obtained were first identified by XRD and the average diameter is about 10 nm according to the Nitrogen adsorption, XRD and TEM techniques. The nature of the catalysts (acetic acid, triethylamine, NH4OH and dibutyl-tin-dilaurate) used for the establishment of the covalent bond between the γ-Fe2O3 particles and the SimPEG, as well as the influence of the temperature and the reaction time, were evaluated on the grafting rate of the particles in water by TGA and FTIR techniques. Using the size exclusion chromatography, SEC technique, we showed that the monomethoxy-PEG was resistant to mild acidic up to strong basic conditions. The best ratio “time/amount of polymer” for the highest grafting rate was the use of tinbased organometallic compound (DBTL) at 80 °C during 48 h. In these conditions, a grafting rate of 54 % is achieved.

Synthesis of poly(butadiene)-poly(ε-caprolactone) multiblocks based on hydroxyl telechelic poly(butadiene): composition and kinetic study

Abstract Thermoplastic block copolymers based on poly(butadiene) and poly(ε- caprolactone) were synthesised from the ring opening polymerization of ε- caprolactone onto a polybutadiene macroinitiator. The lithium alkoxide macroinitiator results from BuLi addition on hydroxy telechelic polybutadiene (HTPB R45®) chain ends. The reaction is fast (about 5 min) and quantitative, leading to well defined copolymers with PCL/PBHT ratio varying from 45/55 and 18/82. Average molar masses range from 10 000g/mol to 26 000g/mol with PDI about 1.6. 1H NRM was used to follow the polymerization kinetic and 13CNMR was used to determine the chemical link between the blocks.