Cédric Hervieu

Covalent adaptable networks (CANs) are predominantly developed as bulk thermoset matrices, while their use as dynamically crosslinked functional phases within melt-processed thermoplastics remains largely unexplored. Here, phosphorus-containing CANs (P-CANs) with systematically varied molecular architectures are employed as macromolecular additives in polyamide 6 (PA6) to establish relationships between network structure, dynamic response, dispersion, retention, and melt processability. Transitioning from a rigid small-molecule-derived network to flexible polyphosphonate architectures shifted the glass-transition temperature from 160 to –5 °C and markedly altered stress relaxation and deformation under processing conditions. These architecture-dependent differences translated directly into thermoplastic integration: the rigid P-CAN formed larger phosphorus-rich domains and exhibited greater phosphorus retention, whereas the most flexible network appeared more uniformly dispersed, lowered processing resistance, and promoted shear-thinning behavior. The resulting balance between dispersion and retention enabled kilogram-scale twin-screw compounding and continuous film extrusion of homogeneous PA6 composites containing 5–10 wt % flexible P-CAN. Despite low final phosphorus contents (∼0.25–0.60 wt %), incorporation of the P-CANs increased limiting oxygen index, promoted char formation, and reduced microscale heat release. These results demonstrate that CAN molecular architecture provides a tunable design parameter for controlling the integration and functional performance of dynamically crosslinked polymeric additives in melt-processed thermoplastics.

Thermosets underpin many structural, coating, adhesive and electronic applications, but their permanent crosslinked architectures make damage repair, reshaping and end-of-life recycling intrinsically difficult. At the same time, many epoxy thermosets require flame retardancy, creating a design challenge in which dynamicity and fire safety are typically introduced through separate molecular components. Here we report β-amino phosphine oxide junctions as a multifunctional dynamic motif that simultaneously enables thermally activated network rearrangement and intrinsic phosphorus-based flame retardancy in epoxy covalent adaptable networks. Di- (DVPPO)and trifunctional (TVPO)vinyl phosphine oxides were covalently incorporated into epoxy–piperazine networks through a controlled aza-Michael addition, establishing reversible aza-Michael/retro-aza-Michael chemistry from vinyl phosphine oxide Michael acceptors in polymer networks while providing a practical formulation window distinct from rapidly reacting β-amino ester systems. The resulting materials undergo stress relaxation, pressure-assisted healing of surface damage, and repeated thermomechanical reconstruction over five reprocessing cycles while retaining useful thermal and mechanical performance. At 6 wt% phosphorus, the DVPPO-based network retains a UL-94 V-0 classification after five reprocessing cycles, whereas the TVPO-based network gives the largest initial peak heat-release-rate reduction. Coupled cone calorimetry, DEP-MS and SEM–EDX analyses show that molecular architecture controls the dominant fire-retardant pathway: DVPPO promotes phosphorus volatilization and gas-phase flame inhibition, while TVPO favors phosphorus retention and condensed-phase char protection. These results establish β-amino phosphine oxides as dynamic phosphorus junctions for designing repairable, reprocessable, and fire-safe thermosets from a single molecular platform.

Thermosetting polymers are widely employed in high-performance applications owing to their excellent mechanical properties, thermal stability, and chemical resistance. However, their permanently crosslinked architecture severely limits recyclability, while their intrinsic flammability remains a major concern for safety-critical applications. Herein, hybrid epoxy–amino ester covalent adaptable networks (CANs), incorporating phosphorus-containing polyelectrolyte complex (PEC) micro-particles, are developed to simultaneously address these two challenges. The developed networks undergo thermally activated rearrangement and can be thermomechanically reprocessed while retaining an overall crosslinked architecture. The aqueous, organic-solvent-free preparation of PEC from comparatively low-hazard ingredients provides an environmentally preferable route to a phosphorus–nitrogen flame-retardant additive. PEC preserves the overall curing behavior and dynamic network properties. The moderate increase in apparent curing activation energy from 44 to 51 kJ mol⁻¹ indicates a limited kinetic influence that does not require modification of the curing procedure. The resulting materials show stable glass transition temperatures, efficient stress relaxation, and retained thermal properties after one thermomechanical reprocessing cycle. An optimized phosphorus loading of 3 wt% enables the material to achieve a UL-94 V-0 classification, while maintaining its flame-retardant performance after one thermomechanical reprocessing cycle. In contrast, formulations containing commercial ammonium polyphosphate (APP), used as a practical commercial reference under the present processing conditions, did not achieve a UL-94 V-0 classification even at 4 wt% phosphorus. Carbon-fiber-reinforced composites fabricated using the developed matrix exhibited high flexural strength, although PEC incorporation reduced the flexural modulus relative to the phosphorus-free composite, demonstrating the feasibility of using the developed CAN as a composite matrix.

Thermosetting polymers are widely employed in high-performance applications owing to their excellent mechanical properties, thermal stability, and chemical resistance. However, their permanently crosslinked architecture severely limits recyclability, while their intrinsic flammability remains a major concern for safety-critical applications. Herein, hybrid epoxy–amino ester covalent adaptable networks (CANs), incorporating phosphorus-containing polyelectrolyte complex (PEC) micro-particles, are developed to simultaneously address these two challenges. The hybrid network combines associative transesterification and dissociative retro Aza-Michael addition exchange reactions, enabling efficient thermomechanical reprocessing while preserving the crosslinked architecture. The incorporation of PEC, prepared through a simple aqueous process from poly(allylamine hydrochloride) and sodium polyphosphate, provides an environmentally friendly phosphorus-nitrogen flame-retardant additive without altering the curing behavior or dynamic network properties. The resulting materials exhibit stable glass transition temperatures, efficient stress relaxation, and excellent retention of thermal properties after recycling. An optimized phosphorus loading of 3 wt% enables the material to achieve a UL-94 V-0 classification, while maintaining its flame-retardant performance after thermomechanical recycling. In contrast, equivalent formulations containing commercial ammonium polyphosphate (APP) flame retardant failed to achieve a UL-94 V-0 classification, even at 4 wt% phosphorus, demonstrating the superior flame-retardant efficiency of PEC. Finally, carbon-fiber-reinforced composites fabricated using the developed matrix demonstrate excellent flexural properties, highlighting the potential of these recyclable flame-retardant CANs for sustainable structural applications.

Covalent adaptable networks (CANs) are predominantly employed as bulk polymer matrices, while their potential as dynamically crosslinked functional additive phases within conventional thermoplastics remains largely unexplored. Here, phosphorus-containing CANs (P-CANs) with systematically varied molecular architectures are employed as durable functional additives for polyamide 6 (PA6), enabling network architecture to be related to additive dispersion, retention, melt processability, and functional performance. Transitioning from a rigid, small-molecule-derived network to flexible polyphosphonate-based architectures tunes the glass transition temperature from 160 to -5 °C and markedly alters network dynamics and dispersion during melt processing. The rigid P-CAN forms larger phosphorus-rich domains in PA6, whereas the most flexible architecture exhibits substantially more homogeneous dispersion, reduced processing resistance, and pronounced shear-thinning behavior. This balance enables translation from laboratory-scale screening to pilot-scale twin-screw compounding and continuous extrusion of uniform PA6 films containing 5–10 wt% CANFR15. Despite low final phosphorus contents of only ~0.25–0.60 wt%, P-CAN incorporation increases the limiting oxygen index of PA6 from 25.8% to as high as 33.0%, promotes char formation, and reduces peak heat release measured in microscale combustion calorimetry. Embedding phosphorus within the CAN architecture additionally suppresses its extraction relative to conventional phosphorus-containing additive flame retardants under accelerated solvent-leaching conditions. These results establish molecular architecture as a key design parameter for balancing network rigidity, additive dispersion and retention, functional performance, and melt processability, while demonstrating P-CANs as a promising class of durable macromolecular additives for scalable thermoplastic processing.

This work presents the demonstration of phosphonamidate-derived covalent adaptable networks (CANs), offering a promising strategy to overcome the traditional trade-off between sustainability and fire safety in thermoset materials. We introduce phosphonamidate-based curing agents that integrate epoxy curing, intrinsic flame retardancy, and dynamic bond exchange within a single molecular design. These curing agents enable the formation of epoxy-based CANs that can be reprocessed multiple times without loss of performance, enabled by an efficient trans-phosphonamidate exchange mechanism at the P-O bond. The phosphonamidate structure further promotes faster bond exchange relative to other phosphorylated networks, facilitating dynamic network rearrangement. Beyond recyclability, the intrinsic phosphorus-nitrogen framework provides excellent fire resistance, achieving UL-94 V-0 ratings at only 2 wt % phosphorus loading while significantly reducing peak heat release. Importantly, the flame-retardant performance remains stable after repeated recycling, demonstrating the robustness of this approach. Thermal and mechanical analyses reveal tunable glass-transition temperatures, high thermal stability, and durable performance over five recycling cycles. To demonstrate application potential, carbon-fiber-reinforced composites were fabricated, confirming that these CAN systems can be processed into high-performance structural materials. Overall, phosphonamidate hardeners provide a versatile platform for thermoset resins and composites requiring recyclability, fire safety, and structural performance.

An efficient asymmetric remote arylation of C(sp³)−H bonds under photoredox conditions is described here. The reaction features the addition radicals to a double bond followed by a site‐selective radical translocation (1,n‐hydrogen atom transfer) as well as a stereocontrolled aryl migration via sulfinyl‐Smiles rearrangement furnishing a wide range of chiral α‐arylated amides with up to >99 : 1 er. Mechanistic studies indicate that the sulfinamide group governs the stereochemistry of the product with the aryl migration being the rate determining step preceded by a kinetically favored 1,n‐HAT process.

An efficient asymmetric remote arylation of C(sp³)−H bonds under photoredox conditions is described here. The reaction features the addition radicals to a double bond followed by a site‐selective radical translocation (1,n‐hydrogen atom transfer) as well as a stereocontrolled aryl migration via sulfinyl‐Smiles rearrangement furnishing a wide range of chiral α‐arylated amides with up to >99 : 1 er. Mechanistic studies indicate that the sulfinamide group governs the stereochemistry of the product with the aryl migration being the rate determining step preceded by a kinetically favored 1,n‐HAT process.

Two- or one-electron-mediated difunctionalizations of internal alkenes represent straightforward approaches to assemble molecular complexity by the simultaneous formation of two contiguous Csp³ stereocentres. Although racemic versions have been extensively explored, asymmetric variants, especially those involving open-shell C-centred radical species, are much more limited both in number and scope. Here we describe enantioenriched arylsulfinylamides as all-in-one reagents for the efficient asymmetric, intermolecular aminoarylation of alkenes. Under mild photoredox conditions, nitrogen addition of the arylsulfinylamide onto the double bond, followed by 1,4-translocation of the aromatic ring, produce, in a single operation, the corresponding aminoarylation adducts in enantiomerically enriched form. The sulfinyl group acts here as a traceless chiral auxiliary, as it is eliminated in situ under the mild reaction conditions. Optically pure β,β-diarylethylamines, aryl-α,β-ethylenediamines and α-aryl-β-aminoalcohols, prominent motifs in pharmaceuticals, bioactive natural products and ligands for transition metals, are thereby accessible with excellent levels of regio-, relative and absolute stereocontrol.