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See detailMacromolecular engineering of aliphatic polyesters based on macrocyclic units
Lecomte, Philippe ULg; Li, Haiying; Riva, Raphaël ULg et al

Poster (2007, August 31)

The last decades have witnessed a steadily increasing progress in the macromolecular engineering of the main families of synthetic polymers. Ring-shaped copolymers show a unique topology due to the ... [more ▼]

The last decades have witnessed a steadily increasing progress in the macromolecular engineering of the main families of synthetic polymers. Ring-shaped copolymers show a unique topology due to the absence of any chain-end and exhibit distinct properties from their linear counterparts, such as glass transition temperature, order-disorder transition, reduced viscosity, lower hydrodynamic volumes. This communication aims at reporting on a novel route to biodegradable cyclic polyesters. Our strategy is based on the work of Prof. Kricheldorf who initiated the ring-opening polymerization of ε-caprolactone by cyclic tin dialkoxides, e.g., 2,2-dibutyl-2-stanna-1,3-dioxepane (DSDOP) in order to obtain “living” macrocyclic PCL, still containing two endocyclic tin-oxygen bonds. In this work, the resumption of polymerization by a few units of ε-caprolactone substituted by an acrylic unit, e.g., 1-(2-oxooxepan-3-yl)ethyl prop-2-enoate, followed by intramolecular photo-cross-linking of pendant unsaturations and finally by hydrolysis gave rise to macrocyclic PCL. As a rule, this strategy is very well-suited for the synthesis of high molecular weight PCL. Moreover, tin alkoxides were kept untouched after the cross-linking step and remained thus available for further macromolecular engineering. The process was extended to the synthesis of other architectures such as sun-shaped, two-tail tadpole-shaped, eight-shaped and symmetrical four-tail eight-shaped copolyesters. [less ▲]

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See detailMacromolecular engineering of aliphatic polyesters by click chemistry
Lecomte, Philippe ULg

Scientific conference (2009, September 10)

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See detailMacromolecular engineering of aliphatic polyesters by ring-opening polymerization
Lecomte, Philippe ULg; Jérôme, Christine ULg; Jérôme, Robert ULg

Conference (2008, September 09)

During the past few years, a steadily increasing attention was paid to the synthesis of biodegradable and biocompatible aliphatic polyesters because of potential applications as biomaterials or as ... [more ▼]

During the past few years, a steadily increasing attention was paid to the synthesis of biodegradable and biocompatible aliphatic polyesters because of potential applications as biomaterials or as environmentally friendly thermoplastics. The first purpose of this work is to show that the modification of these aliphatic polyesters by pendant functional groups is an efficient tool to tailor the main properties, including biodegradation rate, bioadhesion, hydrophilicity, degree of crystallinity. The strategies implemented for the synthesis of aliphatic polyesters bearing pendant functional groups rely on the synthesis of g-substituted e-caprolactones followed by their ring-opening polymerization and on the chemical modification of duly functionalized aliphatic polyesters.The second part of the lecture will be dedicated to some recent examples dealing with the use of functional caprolactones to prepare various architectures such as star-shaped copolymers, graft copolymers, macrocycles and networks. [less ▲]

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See detailMacromolecular engineering of biodegradable polyesters by ring-opening polymerization and 'Click' chemistry
Lecomte, Philippe ULg; Riva, Raphaël ULg; Jérôme, Christine ULg et al

in Macromolecular Rapid Communications (2008), 29(12-13), 982-997

Biodegradability makes aliphatic polyesters valuable candidates for biomaterials and environmentally friendly thermoplastics. Nevertheless, their chemical modification, which is mandatory for a series of ... [more ▼]

Biodegradability makes aliphatic polyesters valuable candidates for biomaterials and environmentally friendly thermoplastics. Nevertheless, their chemical modification, which is mandatory for a series of potential applications, is usually a problem because it must be carried out under very mild conditions in order to prevent degradation by hydrolysis and/or transesterification from occurring. In this review, the copper(i) -catalyzed azide-alkyne cycloaddition, which is a click reaction, is shown to be very efficient to bypass these problems and to tailor the macromolecular architecture and functionality of those polyesters without facing undesired degradation reactions. [less ▲]

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See detailMacromolecular engineering of cyclic aliphatic polyesters
Li, Haiying

Doctoral thesis (2007)

This works aims at reporting a novel strategy that combines the controlled ring-opening polymerization of lactones initiated by a cyclic tin(IV) dialkoxide and intramolecular cyclization by photo-cross ... [more ▼]

This works aims at reporting a novel strategy that combines the controlled ring-opening polymerization of lactones initiated by a cyclic tin(IV) dialkoxide and intramolecular cyclization by photo-cross-linking of pendant unsaturations next to the propagating sites. No linear species is ever involved in the polymerization, which allows higher molecular weight macrocycles to be prepared with high efficiency. Moreover, the synthetic route is very flexible to the point where macrocyclic polyesters with more complex although well-defined architectures, such as tadpole-shaped and sun-shaped copolyesters, can be tailored. Synthesis of well-defined star- and eight-shaped polyesters and twin tadpole-shaped amphiphilic copolymers has also been explored by using a spirocyclic tin(IV) alkoxide as an initiator. [less ▲]

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See detailMacromolecular engineering of cyclic aliphatic polyesters by ring-opening polymerization
Lecomte, Philippe ULg; Riva, Raphaël ULg; Li, Haiying et al

Conference (2006, September 24)

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See detailMacromolecular engineering of cyclic aliphatic polyesters by ring-opening polymerization and "click" chemistry
Lecomte, Philippe ULg; Li, Haiying; Riva, Raphaël ULg et al

Conference (2007, September 04)

The last decades have witnessed a steadily increasing progress in the macromolecular engineering of the main families of synthetic polymers. Ring-shaped copolymers show a unique topology due to the ... [more ▼]

The last decades have witnessed a steadily increasing progress in the macromolecular engineering of the main families of synthetic polymers. Ring-shaped copolymers show a unique topology due to the absence of any chain-end and exhibit distinct properties from their linear counterparts, such as glass transition temperature, order-disorder transition, reduced viscosity, lower hydrodynamic volumes. This communication aims at reporting on a novel route to biodegradable cyclic polyesters. Our strategy is based on the work of Prof. Kricheldorf who initiated the ring-opening polymerization of ε-caprolactone by cyclic tin dialkoxides, e.g., 2,2-dibutyl-2-stanna-1,3-dioxepane (DSDOP) in order to obtain “living” macrocyclic PCL, still containing two endocyclic tin-oxygen bonds. In this work, the resumption of polymerization by a few units of ε-caprolactone substituted by an acrylic unit, e.g., 1-(2-oxooxepan-3-yl)ethyl prop- 2-enoate, followed by intramolecular photo-crosslinking of pendant unsaturations and finally by hydrolysis gave rise to macrocyclic PCL. As a rule, this strategy is very well-suited for the synthesis of high molecular weight PCL. Moreover, tin alkoxides were kept untouched after the cross-linking step and remained thus available for further macromolecular engineering. The process was extended to the synthesis of other architectures such as sun-shaped, two-tail tadpoleshaped, and eight-shaped copolyesters. The second part of the lecture, it will be shown that the copper(I)-catalyzed Huisgen’s [3+2] cycloaddition, which is the most popular “Click" reaction, is very efficient to graft alkynes, duly substituted by functional groups or chains, onto aliphatic copolyesters bearing pendant azides. Interestingly enough, mild conditions were found and no degradation was observed during the “click” derivatization of copolyesters of PCL. The “click” reactions of alkynes onto pendant azides of copolyesters of PLA, by far more sensitive than PCL, was also successfully carried out without any detectable degradation. ”Click” chemistry is very versatile because this reaction was successfully implemented to graft functional groups or chains directly onto ω-azido-ε-caprolactone, without any ring-opening of the lactone, in order to make available a new range of functional caprolactones. Finally, the “click” grafting of PEO onto the tails of tadpole-shaped copolymers will be shown to be a route to amphiphilic copolymers with an original architecture. [less ▲]

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See detailMacromolecular engineering of lactone-based (co)polymers for biomedical applications
Dubois, Philippe ULg; Grandfils, Christian ULg; Jérôme, Robert ULg et al

in Polymer Chemistry (1991), 32 (1)

Ring-opening polymerization of epsilon-caprolactone and lactides by aluminum alkoxides allows aliphatic polyesters to be tailored at will and fitted to requirements for biomedical applications ... [more ▼]

Ring-opening polymerization of epsilon-caprolactone and lactides by aluminum alkoxides allows aliphatic polyesters to be tailored at will and fitted to requirements for biomedical applications, particularly for controlled drug delivery systems. Variation in molecular weight controls the effective life time of microspheres or implants in vivo. Block copolymerization leads to microphase separated materials and opportunity to modify the overall release kinetics and to get, for instance, a zero-order. Macromonomers and dimacromonomers are ideal precursors for physically and chemically stabilized hydrogels, respectively. Dimacromonomers can actually generate amphiphilic networks. [less ▲]

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See detailMacromolecular engineering of lactones and lactides. 24. Controlled synthesis of (R,S)-β-butyrolactone-b-ε-caprolactone block copolymers by anionic and coordination polymerization
Kurcok, Piotr; Dubois, Philippe ULg; Sikorska, Wanda et al

in Macromolecules (1997), 30(19), 5591-5595

Block copolymers of (R,S)-β-butyrolactone and ε-caprolactone have been synthesized by combining the anionic polymerization of the first monomer with the coordinative ring-opening polymerization of the ... [more ▼]

Block copolymers of (R,S)-β-butyrolactone and ε-caprolactone have been synthesized by combining the anionic polymerization of the first monomer with the coordinative ring-opening polymerization of the second one. The copolymerization yield is close to 100% and the final molecular weight of each sequence can be predicted from the initial monomer-to-initiator molar ratio. The molecular weight distribution of copolymers obtained is quite narrow (Mw/Mn ≤ 1.3). According to NMR and DSC analysis, the polybutyrolactone block is atactic and totally amorphous, in contrast to the polycaprolactone block which is semicrystalline. A partial miscibility of the two blocks in the amorphous phase has however been detected. Thermal and enzymatic degradations of the block copolymers have been investigated. The enzymatic degradation rate promoted by the lipase form Rhizopus arrhizus strongly depends on the copolyester composition and increases with the β-butyrolactone content. [less ▲]

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See detailMacromolecular engineering of poly(ε-caprolactone) based on macrocyclic units
Lecomte, Philippe ULg; Li, Haiying; Riva, Raphaël ULg et al

Poster (2007, May 24)

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See detailMacromolecular engineering of polylactones and polylactides. 11. Synthesis and use of alkylaluminium dialkoxides and dithiolates as promoters of hydroxy telechelic poly(epsilon-capprolactone) and alph,omega-dihydroxy triblock copolymers containing outer polyester blocks
Dubois, Philippe; Degée, Philippe; Jérôme, Robert ULg et al

in Macromolecules (1993), 26(11), 2730-2735

Diethylaluminum dialkoxides (Et2AlOXOAlEt2, where X is either an aliphatic radical or a polymer chain) and related dithiolates have been investigated as potential initiators for the ring-opening ... [more ▼]

Diethylaluminum dialkoxides (Et2AlOXOAlEt2, where X is either an aliphatic radical or a polymer chain) and related dithiolates have been investigated as potential initiators for the ring-opening polymerization of ε-caprolactone. Hydroxy telechelic poly(ε-caprolactone) and alpha,omega-dihydroxypoly(ε-caprolactone-b-X-b-ε-caprolactone) have been accordingly prepared and characterized. A hydroxy group is selectively attached at both ends as demonstrated by IR and H-1 NMR spectroscopies and confirmed by titration of the derivatized alpha,omega-dicarboxylic acid (co)polymers. Polymerization of epsilon-caprolactone is living and yields linear polyester chains of a predictable molecular weight and of quite a narrow molecular weight distribution. [less ▲]

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See detailMacromolecular engineering of polylactones and polylactides. 12. Study of the depolymerizatin reactions of poly(ε-caprolactone with functional aluminum alkoxide end groups
Dubois, Philippe; Barakat, Ibrahim; Jérôme, Robert ULg et al

in Macromolecules (1993), 26(17), 4407-4412

Ring-opening polymerization of epsilon-caprolactone has been initiated with functional aluminum alkoxides in toluene at 25-degrees-C. Degradation of ''living'' polyester chains by transesterification ... [more ▼]

Ring-opening polymerization of epsilon-caprolactone has been initiated with functional aluminum alkoxides in toluene at 25-degrees-C. Degradation of ''living'' polyester chains by transesterification reactions has been studied in relation to temperature, solvent polarity, average molecular weight, and structure of the initiator, i.e., the nature of the functional group and the number of alkoxides per Al atom. Degradation products, particularly cyclic oligomers, have been isolated by supercritical fluid extraction (SFE) and characterized by GC-MS. The effect of Lewis bases on transesterification reactions has been investigated and discussed in reference to the ''coordination-insertion'' mechanism. [less ▲]

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See detailMacromolecular engineering of polylactones and polylactides. 14. A 13C and 27Al NMR study of the effect of γ-butyrolactone on the structure of aluminum isopropoxide in toluene
Ropson, Nathalie; Dubois, Philippe; Jérôme, Robert ULg et al

in Macromolecules (1993), 26(24), 6378-6385

Solutions of Al isopropoxide in toluene have been investigated by C-13 and Al-27 NMR spectroscopy. Since Al(OiPr)3 is currently used as an initiator for the living polymerization of epsilon-caprolactone ... [more ▼]

Solutions of Al isopropoxide in toluene have been investigated by C-13 and Al-27 NMR spectroscopy. Since Al(OiPr)3 is currently used as an initiator for the living polymerization of epsilon-caprolactone, special attention has been paid to the effect of the monomer on the coordinative structure of Al(OiPr3) in toluene. Gamma-butyrolactone (BL) has been chosen as a nonpolymerizable model, representative of epsilon-caprolactone. The NMR spectra have been recorded at various concentrations of gamma-butyrolactone and temperatures. As a rule, Al(OiPr)3 is coordinatively aggregated in toluene in such a way that tetrameric and trimeric species are in equilibrium. Upon the addition of BL, this equilibrium is shifted toward the formation of an octahedric [Al(OiPr)3.3BL] mixed tetramer coexisting with [Al(OiPr)3]4 tetramers, the external tetrahedric Al atoms of which are coordinated with extra BL molecules. In the presence of a large excess of BL, only the mixed tetramer persists, which suggests that the single [Al(OiPr)3.3M] species would be the actual initiator for the ring-opening polymerization of cyclic monomers M, such as epsilon-caprolactone, lactides, glycolide, and cyclic anhydrides. [less ▲]

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See detailMacromolecular engineering of polylactones and polylactides. 17. Cryometric andviscosimetric analysis of the species active in the ring-opening polymerization of lactones, lactides, and cyclic anhydrides as initiated by aluminum triisopropoxide
Ropson, Nathalie; Dubois, Philippe; Jérôme, Robert ULg et al

in Macromolecules (1994), 27(27), 5950-5956

Al((OPr)-Pr-i)(3), which is one of the most efficient initiators for the living ring-opening polymerization (ROP) of lactones, lactides, and cyclic anhydrides, is known to be coordinatively associated in ... [more ▼]

Al((OPr)-Pr-i)(3), which is one of the most efficient initiators for the living ring-opening polymerization (ROP) of lactones, lactides, and cyclic anhydrides, is known to be coordinatively associated in apolar solvents. In the present study, the effect of cyclic monomers on the coordinative structure of Al((OPr)-Pr-i)(3) in benzene was investigated by cryometry. gamma-Butyrolactone (gamma-BL), a nonpolymerizable lactone, was first studied as a model monomer. The cryometric Job diagram for the gamma-BL/Al((OPr)-Pr-i)(3) system in benzene established formation of a trisolvated six-coordinate [Al((OPr)-Pr-i)(3).3 gamma-BL] complex. This is in perfect agreement with the hexacoordinated Al atoms as reported by Al-27 NMR. The extension of the cryometric study to a polymerizable lactone, e.g., delta-valerolactone (delta-VL), confirmed that the single [Al((OPr)-Pr-i)(3).3M] species is the actual initiator for the ring-opening polymerization. Al-27 NMR shows that the same conclusion holds when other cyclic monomers, such as lactides and glutaric anhydride, are considered. The induction period of time that is usually observed in the ROP of lactones, lactides, and cyclic anhydrides may now be attributed to the dissociation of the Al((OPr)-Pr-i)(3) aggregates upon the addition of the cyclic monomer. Toluene solutions of living poly(epsilon-CL) and polylactide chains as initiated by Al((OPr)-Pr-i)(3) were also investigated by viscosimetry. The mean association degree ((DA)) over bar of the living chains was calculated from the intrinsic viscosity compared to the value measured for the parent hydrolyzed and purified polyester. [less ▲]

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See detailMacromolecular engineering of polylactones and polylactides. 18. Synthesis of star-branched aliphatic polyesters bearing various functinal end groups
Tian, Dong; Dubois, Philippe; Jérôme, Robert ULg et al

in Macromolecules (1994), 27(15), 4134-4144

Three-arm star-branched aliphatic polyesters have been synthesized by an appropriate termination reaction of the living chains prepared by ring-opening polymerization with aluminum alkoxides. The use of ... [more ▼]

Three-arm star-branched aliphatic polyesters have been synthesized by an appropriate termination reaction of the living chains prepared by ring-opening polymerization with aluminum alkoxides. The use of functional aluminum alkoxides, Et2AlOCH2X with X = CH2CH2CH=CH2 and (CH2)10Br, has led to X functional end-capped star-branched polyesters. Trimesic acid trichloride has proved to be an efficient termination agent for the living poly(epsilon-caprolactone) [PCL] chains ended with a reactive aluminum alkoxide group. A quantitative end functionalization has been reported for bromide and 1-pentene end-capped star-branched PCL. The bromide end groups have been converted into azido end groups, which have been subsequently reduced to the expected primary amine end-capped star-branched PCL by catalytic transfer hydrogenation in DMF. In contrast to living PCL, reaction of trimesic acid chloride with the aluminum alkoxide end group of living poly(L,L)lactide [P(L,L)LA] and living poly(epsilon-caprolactone-b-(L,L)lactide) [P(CL-b-(L,L)LA] chains has produced star-branched polyesters within a very poor yield. This result is more likely due to a steric effect of the methyl group in a-position of the terminal aluminum alkoxide. This drawback has been overcome to some extent by initiating the living polymerization of (L,L)LA with primary amine end-capped star-branched PCL in the presence of triethylaluminum. Formation of a hydroxyl end-capped star-branched poly(epsilon-caprolactone-b-(L,L)lactide) diblock copolymer has accordingly been reported. [less ▲]

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See detailMacromolecular engineering of polylactones and polylactides. 19. Kinetics of ring-opening polymerization of epsilon-caprolactone initiated with functional aluminum alkoxides
Dubois, Philippe ULg; Ropson, Nathalie; Jérôme, Robert ULg et al

in Macromolecules (1996), 29(6), 1965-1975

End-functional aliphatic polyesters have been synthesized by ring-opening polymerization (ROP) of epsilon-caprolactone (epsilon-CL) and lactides (LA). Polymerization initiated with any of the functional ... [more ▼]

End-functional aliphatic polyesters have been synthesized by ring-opening polymerization (ROP) of epsilon-caprolactone (epsilon-CL) and lactides (LA). Polymerization initiated with any of the functional aluminum alkoxides of the general structure Et(3-p)Al(OCH(2)X)(p), where p = 1 and 3, obeys a living ''coordination-insertion'' mechanism, under suitable conditions (temperature, concentration, and solvent), with the formation of alpha-functional chains of a predictable molecular weight. A kinetic study has emphasized the importance of the cyclic monomer (epsilon-CL or LA) and the key role of the initiator structure: the number of functional alkoxides per aluminum and the nature of the functional group (X = CH2Br, (CH2)(2)CH=CH2, (CH2)(2)NEt(2)). Activation enthalpy and entropy have been calculated for the epsilon-CL polymerization initiated by several aluminum alkoxides at various temperatures. The effects of solvent (toluene or tetrahydrofuran) and purification of the aluminum monoalkoxides by distillation under reduced pressure have also been considered. [less ▲]

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See detailMacromolecular engineering of polylactones and polylactides. 20. Effect of monomer, solvent, and initiator on the ring-opening polymerization as initiated with aluminum alkoxides
Ropson, Nathalie; Dubois, Philippe ULg; Jérôme, Robert ULg et al

in Macromolecules (1995), 28(23), 7589-7598

Structure and coordinative association of the propagating species have been studied by H-1, Al-27, and C-13 NMR and viscosimetry in case of epsilon-caprolactone (E-CL) and lactides (LA) polymerization ... [more ▼]

Structure and coordinative association of the propagating species have been studied by H-1, Al-27, and C-13 NMR and viscosimetry in case of epsilon-caprolactone (E-CL) and lactides (LA) polymerization initiated by aluminum alkoxides. In toluene, aluminum triisopropoxide, a commonly used initiator, forms tetrameric (A(4)) and/or trimeric (A(3)) aggregates, which are dissociated upon the addition of the cyclic monomer. Actually, LA is responsible for the complete deaggregation of both A(3) and A(4) into single species (A(1)) trisolvated by the monomer (Al coordination number, CN = 6), whereas A(3) is selectively deaggregated by epsilon-CL. This behavior is consistent with the higher stability of A(4) compared to A(3). Whatever the monomer, three chains are initiated by the active A(1) species. When conversion of epsilon-CL is complete, the active aluminum trialkoxide sites are solvated by one (CN = 4) and more probably three (CN = 6) carbonyl groups of the attached poly-epsilon-caprolactone chains. At the complete LA conversion, only one carbonyl group of the polylactide chains is coordinated to Al (CN = 4). In THF, there is a competition between monomer and solvent for coordination to Al, which explains why polymerization is slower in THF than in toluene. In both toluene and THF, diethylaluminum monoalkoxide forms cyclic trimers that are solvated by the monomer (epsilon-CL) at least on the NMR time scale. Nevertheless, a fractional kinetic order in initiator is observed which gives credit to a fast reversible dissociation of the epsilon-CL-solvated trimers. [less ▲]

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See detailMacromolecular engineering of polylactones and polylactides. 21. Controlled synthesis of low molecular weight polylactide macromonomers
Barakat, Ibrahim; Dubois, Philippe ULg; Grandfils, Christian ULg et al

in Journal of Polymer Science. Part A, Polymer Chemistry (1996), 34(3), 497-502

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