References of "Defize, Thomas"
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See detailPolymer topology revealed by ion mobility coupled with mass spectrometry
Morsa, Denis ULg; Defize, Thomas ULg; Dehareng, Dominique ULg et al

in Analytical Chemistry (in press)

Hyperbranched and star shaped polymers have raised tremendous interests because of their unusual structural and photochemical properties which provide them potent applications in various domains, namely ... [more ▼]

Hyperbranched and star shaped polymers have raised tremendous interests because of their unusual structural and photochemical properties which provide them potent applications in various domains, namely in the biomedical field. In this context, the development of adequate tools aiming to probe particular three-dimensional features of such polymers is of crucial importance. In this present work, ion mobility coupled with mass spectrometry was used to experimentally derive structural information related to cationized linear and star-shaped poly-ε-caprolactones as a function of their charge state and chain length. Two major conformations were observed and identified using theoretical modeling: (1) near spherical conformations whose size is invariant with the polymer topology for long and lightly charged chains and (2) elongated conformations whose size varies with the polymer topology for short and highly charged chains. These conformations were further confirmed by collisional activation experiments based on the ejection thresholds of the coordinated cations that vary according to the elongation amplitude of the polymer chains. Finally, a comparison between solution and gas-phase conformations highlights a compaction of the structure with a loss of specific chain arrangements during the ionization and desolvation steps of the electrospray process, fueling the long-time debated question related to the preservation of the analyte structure during the transfer into the mass spectrometer. [less ▲]

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See detailCrosslinking of star-shape PCLs through Diels-Alder reactions for the preparation of shape memory polymers
Defize, Thomas ULg; Riva, Raphaël ULg; Thomassin, Jean-Michel ULg et al

Poster (2012, May 10)

Poly(ε-caprolactone) (PCL), a semi-crystalline polymer, is one of the most widely studied polymers for the development of shape memory materials when chemically cross-linked. PCL presents several ... [more ▼]

Poly(ε-caprolactone) (PCL), a semi-crystalline polymer, is one of the most widely studied polymers for the development of shape memory materials when chemically cross-linked. PCL presents several advantages such as a melting transition temperature close to human body temperature, a high biocompatibility and is (bio)degradable. So, this polymer is highly relevant for both biomedical devices such as stents or resorbable suture wires and also for degradable packaging. However, after cross-linking, the material can not be reprocessed, preventing any reuse/recycling of the material. One of the purposes of this work is to find a solution to this major drawback, which would then allow, for example, to reshape packaging films after use or to recycle trimmings remaining after fabrication. Amongst current trends in the design of new polymer and composite materials, the use of organic reactions that are able to create and reversibly disrupt chemical bonds upon an external stimulus (temperature, irradiation,…) is currently gaining more and more attention as it can lead to applications in various areas such as remendable materials, drug delivery systems, stimulus-degrading materials or recyclable materials. This contribution aims at reporting a new concept for the preparation of well defined and recyclable PCL based reversibly cross-linked shape memory polymer by the formation of reversible carbon-carbon bonds. Amongst all the reversible links described in the literature, thermally (4+2) reversible cycloadditions present interesting features such as the creation of robust bonds and well defined reversibility conditions. As an example, the application of furan/maleimide adducts as covalent link, which cycloreversion is largely favored in the range of temperature (90-120°C), is widely reported. For this purpose, commercially-available star-shaped PCL precursors have been selected and selectively modified at their chain ends either by a diene (furan, anthracene) or a dienophile (maleimide). Typically, PCL-based shape memory materials have been prepared by mixing a stoichiometric amount of diene-bearing and maleimide-bearing PCLs in a twin-screw mini-extruder at a temperature which favors cycloreversion. The polymer blend is then cured at 65°C (just above PCL melting temperature), with the purpose to increase chains mobility and improve the formation of the adducts. Cross-linked PCLs were obtained, as evidenced by swelling experiments. The shape memory properties of the materials have been studied by cyclic tensile thermomechanical analysis. The influence of the nature of the Diels-Alder moieties on the cross-linking rate and on the shape memory properties has been studied. Reversibility of the network formation in the case of furan, used as diene, has been assessed by rheology and by recycling experiment. [less ▲]

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See detailMultifunctional poly( ε-caprolactone)-forming networks by Diels–Alder cycloaddition: effect of the adduct on the shape-memory properties
Defize, Thomas ULg; Riva, Raphaël ULg; Jérôme, Christine ULg et al

in Macromolecular Chemistry and Physics (2012), 213(2), 187-197

Star-shaped poly(e-caprolactone)s are functionalized by various dienes (furan and anthracene) and a dienophile (maleimide), and the kinetics of network formation by melt-blending is compared for both ... [more ▼]

Star-shaped poly(e-caprolactone)s are functionalized by various dienes (furan and anthracene) and a dienophile (maleimide), and the kinetics of network formation by melt-blending is compared for both Diels–Alder adducts. When curing at 60 °C, the anthracene–maleimide network forms more rapidly and gives rise to a more crosslinked material than with the furan–maleimide adduct. Shape-memory properties of the networks are compared in terms of Diels–Alder adduct stability. Both materials exhibit excellent fixity and recovery ratios, but the relatively low retro Diels–Alder temperature of the furan–maleimide adduct perturbs the mechanical stability of the network during cyclic tensile testing between 0 and 60 °C, whereas the anthracene–maleimide adduct is shown to be stable up to 150 °C. [less ▲]

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See detailThermo-reversible reactions for the preparation of smart materials: recyclable covalently-crosslinked shape memory polymers
Defize, Thomas ULg; Riva, Raphaël ULg; Thomassin, Jean-Michel ULg et al

in Macromolecular Symposia (2011), 309/310(1), 154-161

[4+2] thermoreversible Diels-Alder cycloaddition has been used to crosslink star-shaped poly(ε-caprolactone) in order to produce networks based on strong carbon-carbon covalent bondings. Depending on the ... [more ▼]

[4+2] thermoreversible Diels-Alder cycloaddition has been used to crosslink star-shaped poly(ε-caprolactone) in order to produce networks based on strong carbon-carbon covalent bondings. Depending on the nature of the Diels-Alder reactants, these bonds can be thermoreversibly broken, allowing re-processing of the polymer matrix. [less ▲]

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See detailThermoreversibly crosslinked poly(ε-caprolactone) as recyclable shape-memory polymer network
Defize, Thomas ULg; Riva, Raphaël ULg; Raquez, Jean-Marie et al

in Macromolecular Rapid Communications (2011), 32(16), 1264-1269

A new concept to build shape memory polymers (SMP) combining outstanding fixity and recovery ratios (both above 99% after only one training cycle) typical of chemically crosslinked SMPs with ... [more ▼]

A new concept to build shape memory polymers (SMP) combining outstanding fixity and recovery ratios (both above 99% after only one training cycle) typical of chemically crosslinked SMPs with reprocessability restricted to physically crosslinked SMPs is demonstrated by covalently bonding, through thermoreversible Diels–Alder (DA) adducts, star-shaped poly(epsilon-caprolactones) (PCL) end-functionalized by furan and maleimide moieties. A PCL network is easily prepared by melt-blending complementary end-functional star polymers in retro DA regime, then by curing at lower temperature to favour the DA cycloaddition. Such covalent network can be reprocessed when heated again at the retro DA temperature. The resulting SMP shows still excellent shape memory properties attesting for its good recyclability. [less ▲]

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