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See detailRecyclable shape-memory materials based on photo- or thermo-reversible reactions
Defize, Thomas ULg; Riva, Raphaël ULg; Thomassin, Jean-Michel ULg et al

Poster (2016, February 16)

Shape-memory polymers (SMPs) are remarkable materials able to switch from a stressed deformed state (temporary shape) to their initial relaxed state (permanent shape) by the application of a stimulus ... [more ▼]

Shape-memory polymers (SMPs) are remarkable materials able to switch from a stressed deformed state (temporary shape) to their initial relaxed state (permanent shape) by the application of a stimulus, such as heat or light. Typically, the shape-memory property is generally observed for chemically or physically cross-linked polymers that exhibit an elastomeric behavior above a phase transition, e.g. glass or melting transition. As an example, cross-linked semi-crystalline poly(ε-caprolactone) (PCL) is widely studied for the development of SMPs. As most of SMPs are irreversibly cross-linked material, their reprocessing is impossible preventing any recycling. Thereby, reversible reactions, allowing the formation/cleavage of the network, raise tremendous interest for the development of new SMPs. Recently, we reported the preparation reversibly cross-linked PCL-based SMP using the Diels-Alder (DA) reaction between furan and maleimide end-groups of 4-arm star-shaped PCL, well-known to create reversible bonds. After implementation, this shape-memory material was demonstrated to be recyclable, and was characterized by excellent fixity and recovery before and after recycling experiments. However, the relatively low retro DA temperature of the furan-maleimide adducts led to an inelastic deformation during shape-memory tensile cycles. In order to get rid of this drawback, an alternative approach was investigated. The substitution of the DA reaction by a photo-reversible reaction, typically the photo-induced (2+2) cycloaddition of coumarins, was proposed to prepare cross-linked PCL matrix presenting one-way and two-way memory properties, since photolabile adducts are supposed to be stable during shape-memory tensile cycles. [less ▲]

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See detailComprehensive study of the thermo-reversibility of Diels-Alder based PCL polymer networks
Defize, Thomas ULg; Thomassin, Jean-Michel ULg; Alexandre, Michaël et al

in Polymer (2016), 84

Chemical crosslinking is an efficient tool to improve or impart new properties to conventional polymers. Especially, crosslinking imparts remarkable shapeememory properties to poly-ε-caprolactone (PCL ... [more ▼]

Chemical crosslinking is an efficient tool to improve or impart new properties to conventional polymers. Especially, crosslinking imparts remarkable shapeememory properties to poly-ε-caprolactone (PCL) materials. Nevertheless, the processing of networks is often tricky due to infusibility and insolubility of cross-linked chains. Therefore, the synthesis of PCL networks including thermo-reversible crosslinks based on (retro)-Diels-Alder (DA) reaction were developed to allowpreserving the melt-processing while keeping the required mechanical properties below the melting point. This paper aims at studying in depth, such thermo-dependent network formation and stability. Besides conventional swelling experi- ments, Raman spectroscopy was revealed as a powerful tool to follow the formation of the DA adduct during the crosslinking. In combination with rheological measurements, we were able to determine the most appropriate temperatures to form the network (DA crosslinking) and to process it (retro-DA re- action) without degradation of the material. [less ▲]

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See detailDevelopment of photo- or thermo-reversible cross-linked recyclable shape-memory materials
Defize, Thomas ULg; Riva, Raphaël ULg; Thomassin, Jean-Michel ULg et al

Conference (2015, September 01)

Shape-memory polymers (SMPs) are remarkable materials able to switch from a stressed deformed state (temporary shape) to their initial relaxed state (permanent shape) by the application of a stimulus ... [more ▼]

Shape-memory polymers (SMPs) are remarkable materials able to switch from a stressed deformed state (temporary shape) to their initial relaxed state (permanent shape) by the application of a stimulus, such as heat or light. Typically, the shape-memory property is generally observed for chemically or physically cross-linked polymers that exhibit an elastomeric behavior above a phase transition, e.g. glass or melting transition. As an example, cross-linked semi-crystalline poly(ε-caprolactone) (PCL) is widely studied for the development of SMPs. As most of SMPs are irreversibly cross-linked material, their reprocessing is impossible preventing any recycling. Thereby, reversible reactions, allowing the formation/cleavage of the network, raise tremendous interest for the development of new SMPs. Recently, we reported the preparation reversibly cross-linked PCL-based SMP using the Diels-Alder (DA) reaction between furan and maleimide end-groups of 4-arm star-shaped PCL, well-known to create reversible bonds. After implementation, this shape-memory material was demonstrated to be recyclable, and was characterized by excellent fixity and recovery before and after recycling experiments. However, the relatively low retro DA temperature of the furan-maleimide adducts led to an inelastic deformation during shape-memory tensile cycles. In order to get rid of this drawback, an alternative approach was investigated. The substitution of the DA reaction by a photo-reversible reaction, typically the photo-induced (2+2) cycloaddition of coumarins, was proposed to prepare cross-linked PCL matrix presenting one-way and two-way memory properties, since photolabile adducts are supposed to be stable during shape-memory tensile cycles. [less ▲]

Detailed reference viewed: 69 (5 ULg)
See detailPhoto- and thermo-reversible crosslinked recyclable shape memory materials
Defize, Thomas ULg; Riva, Raphaël ULg; Thomassin, Jean-Michel ULg et al

Poster (2015, July 02)

Shape memory polymers (SMPs) are remarkable materials able to switch from a stressed deformed state (temporary shape) to their initial relaxed state (permanent shape) by the application of a stimulus ... [more ▼]

Shape memory polymers (SMPs) are remarkable materials able to switch from a stressed deformed state (temporary shape) to their initial relaxed state (permanent shape) by the application of a stimulus; such as heat or light. Typically; the shape memory property is generally observed for chemically or physically cross-linked polymers that exhibit an elastomeric behavior above a phase transition; e.g. glass or melting transition. As an example; cross-linked semi-crystalline poly(ε-caprolactone) (PCL) is widely studied for the development of SMPs. As most of SMPs are irreversibly cross-linked material; their reprocessing is impossible preventing any recycling. Thereby; reversible reactions; allowing the formation/cleavage of the network; raise tremendous interest for the development of new SMPs. Recently, we reported the preparation reversibly cross-linked PCL-based SMP using the Diels-Alder (DA) reaction between furan and maleimide end-groups of 4-arm star-shaped PCL, well-known to create reversible bonds. After implementation, this shape memory material was demonstrated to be recyclable, and was characterized by excellent fixity and recovery before and after recycling experiments. However, the relatively low retro DA temperature of the furan-maleimide adducts led to an inelastic deformation during shape memory tensile cycles. In order to get rid of this drawback, an alternative approach was investigated. The substitution of the DA reaction by a photo-reversible reaction, typically the photo-induced (2+2) cycloaddition of coumarins, was proposed to prepare cross-linked PCL matrix presenting one-way and two-way memory properties, since photolabile adducts are supposed to be stable during shape memory tensile cycles. [less ▲]

Detailed reference viewed: 84 (8 ULg)
See detailRecyclable shape-memory materials based on photo or thermo-reversible crosslinking
Defize, Thomas ULg; Riva, Raphaël ULg; Wauters, Céline et al

Poster (2014, November 11)

Shape memory polymers (SMPs) are remarkable materials able to switch from a stressed deformed state (temporary shape) to their initial relaxed state (permanent shape) by the application of a stimulus ... [more ▼]

Shape memory polymers (SMPs) are remarkable materials able to switch from a stressed deformed state (temporary shape) to their initial relaxed state (permanent shape) by the application of a stimulus, such as heat or light. Typically, the shape memory property is generally observed for chemically or physically cross-linked polymers that exhibit an elastomeric behavior above a phase transition, e.g. glass or melting transition. Cross-linked semi-crystalline poly(ε-caprolactone) (PCL) is already widely studied for the development of SMPs. However, the tensile strength of standard PCL-based SMPs remains quite low, limiting their use in some applications. A convenient way to enhance the strength of SMPs relies on the introduction of nanofillers, such as silica nanoparticles, leading to an enhancement of mechanical strength. Moreover, silica nanoparticles can be advantageously used as multifunctional crosslinking nodes, with the purpose to increase the cross-linking density of the material. As most of SMPs are irreversibly cross-linked material, their reprocessing is impossible preventing any recycling. Thereby, reversible reactions, allowing the formation/cleavage of the network, raise tremendous interest in macromolecular engineering. Recently, a reversibly cross-linked 4-arm star-shaped PCL-based SMP was prepared using the Diels-Alder (DA) reaction between furan and maleimide moieties, well-known to create reversible bonds. This shape memory material demonstrated to be implementable, and so recyclable, and was characterized by excellent fixity and recovery before and after recycling experiments. However, the relatively low retro-DA temperature of the furan- maleimide adducts led to an inelastic deformation during shape memory tensile cycles. In order to get rid of this drawback, two alternative approaches were investigated. Firstly, the substitution of the DA reaction by a photo-reversible reaction, typically the photo- induced (2+2) cycloaddition of coumarins, was proposed to crosslink the PCL matrix. The second approach is based on the use of surface functionalized silica nanoparticles as crosslinking nodes with the purpose to increase the crosslinking density of the material. The network formation and cleavage were studied by solid-state NMR and rheology.4 The resulting shape memory materials were characterized by excellent one-way and two-way shape memory properties as demonstrated by dynamical mechanical analysis. [less ▲]

Detailed reference viewed: 57 (3 ULg)
See detailElaboration of degradable PCL-based shape memory materials
Defize, Thomas ULg; Thomassin, Jean-Michel ULg; Alexandre, Michaël et al

Poster (2014, September 02)

Shape memory polymers (SMPs) are smart materials presenting the remarkable property to switch from a temporary shape (stressed) to a permanent shape (relaxed) upon exposure to a stimulus, such as heat or ... [more ▼]

Shape memory polymers (SMPs) are smart materials presenting the remarkable property to switch from a temporary shape (stressed) to a permanent shape (relaxed) upon exposure to a stimulus, such as heat or light. SMPs raised a lot of interest, especially for biomedical applications, for the elaboration of suture wires and stents. In the last few years, biodegradable aliphatic polyesters, typically poly(ɛ-caprolactone) (PCL) and poly(lactide) (PLA) were widely studied for the synthesis of SMPs. This communication aims at reporting a new concept for the synthesis of PCL-based SMPs. In order to meet the increasingly stringent requirements of biomedical applications, a metal-free process is proposed occurring at relatively low temperature, which can be compatible with the presence of a drug during implementation. [less ▲]

Detailed reference viewed: 39 (7 ULg)
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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 (2014), 86(19), 96939700

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 ▲]

Detailed reference viewed: 63 (21 ULg)
See detailComprehensive study of chemically cross-linked PCLs presenting one-way and two-way shape memory properties
Defize, Thomas ULg; Riva, Raphaël ULg; Thomassin, Jean-Michel ULg et al

Poster (2014, May 26)

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. 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. 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 at which DA cycloaddition is largely disfavored, followed by the curing of the blend above the melting temperature to improve the kinetic of DA adduct formation. The shape memory properties of the materials have been studied by cyclic tensile thermomechanical analysis. As cross-linked PCLs are knowned to exhibit one-way and two-way shape memory properties, a comprehensive study of the shape memory of these materials has been carried out. Unfortunately, creep from shape memory cycle to cycle was observed in DMA for the furan/maleimide sample, certainly due to the reversibility of the adduct. In order to limit this creep effect, the substitution of the furan/maleimide adduct by a more stable adduct is required. The anthracene/maleimide system was tested because this adduct is more stable under stress than the furan/maleimide one. This contribution aims at reporting a complete study of one-way and two-way shape memory properties of the PCL cross-linked by anthracene/maleimide adduct. The shape memory properties of this material have been assessed by DMA and DSC experiments. [less ▲]

Detailed reference viewed: 9 (2 ULg)
Peer Reviewed
See detailPolymer architecture revealed by ion mobility - mass spectrometry
Morsa, Denis ULg; Defize, Thomas ULg; Dehareng, Dominique et al

Conference (2014, April)

Detailed reference viewed: 23 (3 ULg)
See detailShape-memory materials based on thermoreversibly cross-linked poly-ε-caprolactones
Defize, Thomas ULg; Riva, Raphaël ULg; Thomassin, Jean-Michel ULg et al

Poster (2013, August 19)

Shape memory polymers (SMPs) are materials that are able to change their shape from a temporary shape to a permanent one by application of a stimulus such as heat or light. SMPs are usually chemically or ... [more ▼]

Shape memory polymers (SMPs) are materials that are able to change their shape from a temporary shape to a permanent one by application of a stimulus such as heat or light. SMPs are usually chemically or physically crosslinked materials that exhibit an elastomeric behaviour above a glass or melting transition temperature. Poly(ε-caprolactone) (PCL) is one of the most widely studied polymers for the development of SMPs. PCL presents several advantages such as a melting transition temperature close to human body temperature, a high biocompatibility, is (bio)degradable and potentially biosourced. So, this polymer is highly relevant for both degradable packaging and also for biomedical devices such as resorbable suture wires or stents. However, after crosslinking, the material can not be reprocessed, preventing any reuse/recycling. The main purpose of this work is to provide a solution to this major drawback, which would then enable, for example, to reshape packaging films after use or to reprocess trimmings remaining after production. Amongst current trends in the design of new polymer and composite materials, organic reactions that are able to create and reversibly disrupt chemical bonds upon an external stimulus (temperature, irradiation,…) are currently gaining more and more attention in macromolecular engineering and are used in various areas such as remendable materials, drug delivery systems, stimulus-degrading materials or recyclable materials. Amongst all the reversible links described in the literature, thermally (4+2) reversible cycloadditions present interesting properties 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. This contribution aims at reporting a new concept for the preparation of well defined and recyclable PCL based reversibly cross-linked SMPs by the formation of reversible carbon-carbon bonds. For this purpose, commercially-available linear and multi-arm star shaped PCL precursors have been selected and selectively functionalized 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 architecture of the PCL precursors as well as 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 ▲]

Detailed reference viewed: 11 (2 ULg)
See detailThermoreversibly cross-linked poly-ε-caprolactones for the elaboration of shape memory materials
Defize, Thomas ULg; Riva, Raphaël ULg; Thomassin, Jean-Michel ULg et al

Poster (2013, April 19)

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 ... [more ▼]

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. For this purpose, commercially-available star-shaped PCL precursors were selected and selectively modified at their chain ends either by a diene (furan) or a dienophile (maleimide). PCL-based shape memory materials were prepared by mixing a stoichiometric amount of diene-bearing and maleimide-bearing PCLs at a temperature which favors cycloreversion. The polymer blend is then cured at 65°C (slightly above PCL melting temperature), with the purpose to increase chains mobility and improve the formation of the adducts. The Diels-Alder kinetics has been followed by Raman spectroscopy and the PCL cross-linking was evidenced by both swelling experiments and rheological measurements. The obtained cross-linked PCL was characterized by shape memory properties with excellent fixity and recovery, as determined by cyclic tensile thermomechanical analysis. [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 ▲]

Detailed reference viewed: 78 (38 ULg)
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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 ▲]

Detailed reference viewed: 65 (22 ULg)