Ph. Teyssié

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.

Effect of the emulsion stability on the morphology and porosity of semicrystalline poly l-lactide microparticles prepared by w/o/w double emulsion-evaporation

Two semi-crystalline poly l-lactides of very different molecular weights have been used as coating polymers in microencapsulation by the w/o/w double emulsion-evaporation technique. The purpose of this paper is to focus on the effect of crystallinity, i.e. of the chain microstructure, of the coating polylactide on the primary emulsion stability, the encapsulation efficiency and, ultimately, the external and internal morphology and porosity of the final microparticles. Crystallizable chains have clearly a deleterious effect on the encapsulation efficiency of indigocarmine used as a probe and on the internal morphology of microparticles. Moreover, a substantial increase in the molecular weight of poly l-lactide (from 60 to 840 kDa) forces to dilute the polymer solution in order to prevent an exceedingly high viscosity and leads to less stable primary emulsions and more porous solid microspheres. Microparticles of semi-crystalline poly l-lactide have proved to be not suitable for the sustained drug release. These observations are in sharp contrast to the poly d.l-lactide (Mn = 50 kDa), used as the amorphous counterpart, which meets the criteria for an efficient microencapsulation, particularly when the primary emulsion is stabilized by gelation.

Transition-metal-catalyzed reaction of diazocompounds, efficient synthesis of functionalized ethers by carbene insertion into the hydroxylic bond of alcohols

Abstract An Efficient catalytic synthesis of unsaturated ethers by carbene insertion (with diazoesters as carbene precursors) into the OH bond of unsaturated alcohols is reported. The regioselectivity for the OH insertion is high. However, depending on the catalyst counter-ions and the diazoester alkoxy group, addition to the unsaturated centre can be promoted to some extent, yielding then cyclopropyl and cyclopropenyl carbinols. The mechanistic aspects of the reactions are discussed.

(D, L) Polylactide microspheres as embolic agent

SummaryOwing to their shape, accurately calibrated microspheres appear to be very suitable material for distal embolization. Moreover, the biocompatible (D, L) polyactide (PLA) microspheres possess two other valuable advantages: easy adjustment of their biodegradation rate, and incorporation of chemotherapeutic agents during their production. The authors describe the preparation of these (D, L) PLA microspheres and their clinical applications as a preliminary step to arterial chemoembolization.

Surface analysis of polymers end-capped with metal carboxylates using x-ray photoelectron spectroscopy

Abstract X-ray photoelectron spectroscopy is an efficient tool to determine how the metal carboxylate groups of halato-telechelic polymers are distributed in moving from the surface to the bulk of the host polymer. Depending on the nature and structure of both the polymeric matrix and the metal carboxylate end-groups, the surface layer of bulk halato-telechelic polymers can exhibit a continuum of situations going from a high depletion to an enrichment in metal carboxylates compared to the theoretical composition. When an excess of metal atoms is observed in the surface region, these atoms are present at a depth of a few tens of A below the very surface. Finally, when an excess of Zr or Ti alkoxide is used to neutralize α, ω-dicarboxylic acid polymers, the hydrolysis of the unreacted alkoxide groups do promote the formation of carboxylato metal oxohydroxide aggregates.

Transition metal catalyzed reactions of diazoesters : Cyclopropanation of dienes and trienes

Abstract The regioselectivity of the cyclopropanation of polyenes by cycloaddition of carbenes generated by catalyzed decomposition of diazoesters in the presence of Rh, Pd and Cu catalysts can be controlled to some extent by selecting proper reaction parameters. For a particular diene, the regioselectivity depends both on the catalyst and on the nature of the double-bond (conjugation, substitution). The cyclopropanation of trienes containing both a conjugated diene system and an isolated double bond is reported as an application of these reactions. The practical interest of the present study is further demonstrated by the synthesis of a pyrethroid precursor by the rhodium(II) carboxylates catalyzed-cyclopropanations of 1.1-dichloro-4-methyl-1, 3-pentadiene.

The role of copper(I) complexes in the selective formation of oxazoles from unsaturated nitriles and diazoesters

Abstract The 1,3-dipolar addition of ketocarbenes (generated from diazoesters) to nitriles is promoted at room temperature by palladium acetate and even more efficiently by copper trifluoromethanesulphonate. The reduction of copper(II) to copper(I) is a key step in the catalytic process, as shown by kinetic studies, EPR and polarography.

Polycaprolactone-based block copolymers: 4. Interfacial activity in poly(vinyl chloride) containing polyblends

Abstract The substantial difference in the Tg of poly(vinyl chloride) (PVC) and poly(e-caprolactone) (PCL) offers a sensitive method of locating a polystyrene (PS)-PCL diblock in PVC or in PS/PVC polyblends. When mixed with PVC, these diblocks are dispersed as individual molecules in equilibrium with micelles. The equilibrium position depends on the composition of the diblock; when PCL is the major component, molecular dissolution in PVC is enhanced. A 50 50 PS-PCL diblock, each block of which is of a higher molecular weight than the related homopolymer, is located mainly at the PS/PVC interface, as shown by the essentially unchanged Tg of the PVC matrix and a sub-Tg assigned to the external layer of the PVC phases plasticized by the PCL blocks of the copolymer. Blocks longer than the associated homopolymer chain clearly enhance the mutual anchoring of the PS and PVC phases. Since PS and PVC are intrinsically brittle polymers, their melt blending in the presence of properly designed PS-PCL diblocks gives rise to fragile materials.

Halato-telechelic polymers

SummaryHalato-telechelic polymers (HTP) resulting from the neutralization of carboxy telechelic polymers behave as useful ion-containing model compounds. Carboxy telechelic polybutadiene (