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International audience; ROP of bulky functional β-lactones mediated by an achiral diamino-bis(phenolate) yttrium catalyst affords syndio-enriched polyhydroxyalkanoates.

International audience; Enhancing thermal stability of polyhydroxyalkanoates for their closed-loop chemistry

International audience; Polydicyclopentadiene (PDCPD) thermoset, as commonly prepared by ring-opening metathesis polymerization (ROMP), features excellent mechanical, thermal and anti-corrosion properties, but lacks ductility and toughness. In situ addition of 2 to 8 wt% of Styrene-Ethylene-Butylene-Styrene (SEBS) thermoplastic during material preparation slightly alters the stiffness while improving its toughness and ductility. Remarkably, 4wt% SEBS increases PDCPD glass transition temperature T g up to 165 °C (i.e. + 7 °C). Calorimetric analyses suggest that addition of SEBS, acting as a plasticizer during molding, reduces the polymerization time of DCPD. This result offers a simple method to adjust PDCPD impact properties and to increase its T g .

International audience; We report here on the ring-opening polymerization (ROP) of racemic beta-thiobutyrolactone (rac-TBL), as the first chemical synthesis of poly(3-thiobutyrolactone) (P3TB), the thioester analogue of the ubiquitous poly(3-hydroxybutyrate) (P3HB). The ROP reactions proceed very fast (TOF >12 000 h(-1) at r.t.) in the presence of various metal-based catalysts. Remarkably, catalyst systems based on non-chiral yttrium complexes stabilized by tetradentate amino alkoxy- or diamino-bis(phenolate) ligands {ONXOR1,R2}(2-) (X=O, N) provide access to cyclic P3TB with either high isoselectivity (P-m up to 0.90) or high syndiotactic bias (P-r up to 0.70). The stereoselectivity can be controlled by manipulation of the substituents on the ligand platform and adequate choice of the reaction solvent and temperature as well. The cyclic polymer topology is evidenced by MALDI-ToF MS, NMR and TGA. Highly isotactic cyclic P3TB is a semi-crystalline material as revealed by DSC.

International audience; α,ω-Bis(trialkoxysilyl) telechelic polyether/polyolefin copolymers were synthesized and evaluated as monocomponent adhesive precursors. The Ru-catalyzed tandem ring-opening insertion-metathesis polymerization (ROIMP) and cross-metathesis (CM) reactions in the presence of a bis(trialkoxysilyl)alkene as chain-transfer agent (CTA) were first explored toward the synthesis of such silyl-modified polymers (SMPs). The one-pot, two-step ROIMP/CM of cyclooctene (COE) and poly(propyleneglycol) diacrylate (PPG(*)) with {(EtO)3Si(CH2)3NHC(O)OCH2CH═}2 (CTAEt) catalyzed by Grubb’s second generation catalyst (Method II) successfully enables the preparation of α,ω-[(EtO)3Si]2-PCOE/PPG(*) alternated copolymers, isolated in 10–100 g. The polyether/polyolefin copolymers were thoroughly characterized by SEC, 1D and 2D NMR, and FTIR spectroscopies and mass spectrometry analyses. The good thermal stability and rheofluidifying profile of the PCOE/PPG* copolymers are maintained following their catalyzed moisture-curing, as revealed by TGA, DSC, and rheology. The corresponding siloxane cross-linked copolymers then demonstrate strain-at-break, elongation-at-break, and wood-adhesion properties greater than those of the benchmarked SMP reference from Bostik, namely, Polyvest E100 (strain-at-break on wood up to 4.0 vs 2.6 MPa, respectively). These characteristics can be tuned according to the PCOE/PPG* ratio and also revealed significantly better than the ones of our previously reported alike siloxane cross-linked PCOE/PPG* copolymers similarly prepared, yet from a one-pot, one-step ROIMP/CM approach (Method I). Such polyolefin/polyether monocomponent SMPs are thus promising adhesive precursors.

International audience; The organocatalyzed ring-opening polymerization (ROP) of various 4-alkoxymethylene-beta-propiolactones (BPL(OR)s; R = CH2CH=H-2 (All), CH2Ph (Bn), (CH2)(3)CH3 (Bu-n), (SiMe2Bu)-Bu-t (TBDMS)) towards the formation of the corresponding poly(hydroxyalkanoate)s (PHAs; poly(BPLOR)s (PBPL(OR)s)) is investigated under mild operating conditions (neat, 60 degrees C), simply using basic organocatalysts of the guanidine (1,5,7-triazabicyclo [4.4.0]dec-5-ene, TBD), amidine (1,8-diazabicyclo[5.4.0]-undec-7-ene, DBU) or phosphazene (2-tert-butylimino-2-diethylamino-1,3-dimethylperhydro-1,3,2diazaphosphorine, BEMP) type. The polymerization proceeds basically at the same rate as the alike organocatalyzed ROP of related beta-lactones (especially the ubiquitous beta-butyrolactone (BL) and alkyl beta-malolactonates (MLA(R)s)), with BEMP being significantly more active than TBD and DBU. Insights into the polymerization mechanisms are gained through detailed 1D/2D NMR spectroscopy and MALDI-ToF mass spectrometry analyses of the resulting PBPL(OR)s and in particular through the identification of the nature of the end-capping groups. Each of the three organobases promotes the polymerization in its own way, as dictated by either its basic, nucleophilic or dual behavior.

International audience; Polyhydroxyalkanoates (PHAs) are biodegradable and biocompatible polyesters with a wide range of applications; in particular, they currently stand as promising alternatives to conventional polyolefin-based "plastics". The introduction of sulfur atoms within the PHAs backbone can endow the resulting polythioesters (PTEs) with differentiated, sometimes enhanced thermal, optical and mechanical properties, thereby widening their versatility and use. Hence, PTEs have been gaining increasing attention over the past half-decade. This review highlights recent advances towards the synthesis of well-defined PTEs by ring-opening polymerization (ROP) of cyclic thioesters - namely thiolactones - as well as of S-carboxyanhydrides and thionolactones; it also covers the ring-opening copolymerization (ROCOP) of cyclic thioanhydrides or thiolactones with epoxides or episulfides. Most of the ROP reactions described are of anionic type, mediated by inorganic, organic or organometallic initiators/catalysts, along with a few enzymatic reactions as well. Emphasis is placed on the reactivity of the thio monomers, in relation to their ring-size ranging from 4- to 5-, 6- and 7-membered cycles, the nature of the catalyst/initiating systems implemented and their efficiency in terms of activity and control over the PTE molar mass, dispersity, topology, and microstructure.

International audience; Polyhydroxyalkanoates (PHAs) are a unique class of polyesters especially due to their chemical diversity imparted by their side-chain substituent that provides a handle to tune their properties, such as their thermal, mechanical and (bio)degradability signature. Here, we report that some functional PHAs, namely PBPLFGs (FG = functional group), were synthesized by the controlled stereoselective ring-opening polymerization (ROP) of racemic 4-substituted-β-propiolactones, namely rac-BPLCH2ZPhs with Z = O, S, CH2OCH2, catalyzed by diamino- or amino-alkoxy-bis(phenolate) yttrium amido complexes (1a–1g) in the presence of isopropanol. Unprecedented syndio-enriched (Pr up to 0.87) PBPLCH2ZPhs of high molar mass (Mn,NMR up to 86 400 g mol−1, ĐM < 1.23) were thus typically prepared under mild operating conditions (toluene, 20 °C). Catalyst systems with smaller “uncrowded” Me or Cl ortho-substituents installed on the yttrium phenolate ligands (1a–1c) typically revealed less active than those with larger bulkier tBu or CMe2Ph groups (1d–1g), regardless of the monomer (TOF1a–1c = 0.48–15 h−1, TOF1d–1g = 450–1840 h−1). Irrespective of the catalyst system, exchanging oxygen with sulphur in BPLCH2ZPhs, with Z = O, S, did not affect the stereochemistry, always affording syndiotactic PBPLCH2ZPhs. On the other hand, either atactic or syndiotactic PBPLCH2CH2OCH2Phs were formed upon tuning the catalyst from 1a–1c or 1d–1g, respectively. The intimate relationship, through “non-covalent” interactions, between the chemical nature of the exocyclic functional side-group on the β-lactone and the stereoelectronic tuning arising from the phenolate ligand ortho-substituents within the yttrium coordination sphere, modulated the stereocontrol of the ROP. The thermal behavior of these original functional PHAs depended closely on their side-chain substituent (Tonsetd = 226 to 272 °C; Tg = −15 to +40 °C).

International audience; Poly(hydroxy acid)s are a family of biocompatible and (bio)degradable polyesters with various outcomes in different domains of application. To date, poly(hydroxy acid)s are best prepared by ring-opening polymerization (ROP) of the corresponding cyclic esters. Using racemic chiral monomers featuring side-chain groups enables to access, providing a stereoselective catalyst/initiator system is implemented, stereoregular functional polymers, thereby improving their physico-chemical properties and ultimately widening their range of uses. Here, we highlight a few important advances in metal-mediated stereoselective ROP of cyclic esters towards the synthesis of (functional) stereoregular poly(hydroxy acid)s that have recently been disclosed, emphasizing on (functional) β- and γ-lactones, diolide and O -carboxyanhydride (OCA) monomers and yttrium-based catalysis. Fine-tuning of the substituents flanked on the catalyst ligand enables reaching poly(hydroxy acid)s with syndiotactic and also isotactic microstructures. The stereocontrol mechanisms at work and their probable origin, relying on steric but also electronic factors imparted in particular by the ligand substituents, are discussed. Taking advantages of such stereoselective ROPs, original copoly(hydroxy acid)s with gradient or alternated patterns then become accessible from the use of mixtures of chemically different, oppositely configurated enantiopure monomers.

International audience; The ring-opening polymerization (ROP) of bio-derived six-membered (substituted) delta-valerolactones, including the 5-Me substituted delta-valerolactone (aka delta-hexalactone (HL)), 2-ethylidene-6-hepten-5-olide (EVL), 2-ethylheptane-5-olide (EHO) and the novel 2-ethylidene-6-heptan-5-olide (MH), is investigated. In comparison to the ubiquitous unsubstituted d-valerolactone (VL), the presence of a substituent on the lactone ring appears to significantly affect the polymerizability of the monomer, whichever the catalyst/initiator system or the operating conditions. Typical Bronsted acids, organocatalysts or Lewis acidic metal complexes revealed hardly active in the ROP of HL, most likely originating from polymerization/depolymerization issues. Better efficiency was achieved from alkali metal complexes, especially using NaOMe (1-2.5 mol%) from which high-to-quantitative HL conversion was reached within 18 h at 60 degrees C. Oligomers ((M) over bar (n, NMR)

Poly(3-hydroxyalkanoate)s (PHAs) are a class of polymers receiving attention because of their potential as renewable, biodegradable and high-technology properties. Unlike most short chain length (scl) PHAs such as poly(3-hydroxybutyrate) (PHB), medium chain length (mcl) PHAs such as poly(3-hydroxyoctanoate) (PHO) exhibit low crystallinity and are elastomeric in character. PHB-b–PEG-b–PHO block copolymers can combine both properties in block copolymer matrix. In this study, we report the synthesis of the block copolymers combining the PHB and PHO blocks. Transamidation reactions of PHB with polyethylene glycol with primary amine yield equimolar amounts and PHB with amine ends. PHO reacts with the modified PHB containing the amine end to give PHB-b–PEG-b–PHO block copolymers. Structural analysis of the products was performed by using 1H–, 13C, heteronuclear single quantum coherence NMR techniques. Thermal and mechanical properties of the block polymers were also evaluated. © 2018, Springer-Verlag GmbH Germany, part of Springer Nature., Bitlis Eren Üniversitesi: 72118496 - 03 Bülent Ecevit Üniversitesi: – 2013 – 72118496 - 02, Acknowledgements This work was supported by the Bülent Ecevit University Research Funds (#BEU – 2013 – 72118496 - 02 and BEU - 2013 – 72118496 - 03). The authors thank to Prof. Dr. Mahmut Köse and Prof. Dr. İbrahim Demirtaş for their valuable discussion about the NMR spectra.

The first functional cross-metathesis (CM) depolymerization of commercial (co)polydienes using a ruthenium catalyst and an acyclic bis(trialkoxysilyl) difunctionalized chain-transfer agent (CTA), [(EtO) 3 Si(CH 2 ) 3 NHC(O)OCH 2 CH ] 2 ( 1 ), towards the synthesis of low viscosity liquid α,ω-bis(trialkoxysilyl) telechelic (co)polydienes is reported. The reactivity of three commercial grades of liquid (co)polydienes ( P1 – P3 , polybutadienes (PBDs) or poly(butadiene- co -isoprene) (P(BD- co -IP))) differing in their end-functionalization, in the amount of 1,2-vinyl and in their dispersity, was explored. Operating conditions for effective production of α,ω-bis(trialkoxysilyl) telechelic PBDs or P(BD- co -IP)s with high chemoselectivity (80–90 wt%) and catalytic productivity (non-optimized TON up to 24 000) were established. The chemoselectivity of this tandem metathesis reaction was assessed in particular through detailed 2D NMR analyses. An original approach combining the CM depolymerization of PBD with the ring-opening functional metathesis polymerization (ROMP) of a cycloolefin in the presence of CTA 1 has also been next implemented affording low viscosity liquid α,ω-bis(trialkoxysilyl) telechelic copolydienes. The viscosity of the (co)polyolefins was investigated by rheological analyses.

Within the general context of nanomedicine, drug delivery systems based on polymers have sparked a rapidly growing interest and raised many efforts to tackle various diseases, among which cancer. Polyester-based nanoparticulate drug delivery systems, including polymer-drug conjugates and amphiphilic block copolymers, represent a major class with promising outcomes, especially for those derived from poly(3-hydroxybutyrate) (PHB). This review describes recent advances in drug delivery systems designed from the self-assembly of synthetic (co)polymers derived from PHB. The various strategies for the synthesis of PHB-conjugates, PHB/poly(ethylene glycol) (PEG) and other PHB-based copolymers are first summarized. Nanoparticles, micelles, microparticles, and hydrogels elaborated from these (co)polymers following various preparation methods, along with their exploitation in the encapsulation and release of various therapeutic agents, are next detailed. Finally, we discuss the synthetic challenges, drug delivery outlooks, and perspectives of PHB-based drug delivery systems. Engineered nano-scaled materials based on PHB self-assembled systems are thus anticipated to emerge as a valuable platform for original drug delivery systems.

International audience; Current polyurethane (PU) industrial and academic research aims at developing non-isocyanate PUs, referred to as NIPUs. Within this context, we report herein the synthesis of original vinylene carbonate (VC) compounds, subsequently used as chain-transfer agents (CTAs) towards the preparation of α,ω-di(VC) telechelic (co)polyolefins from the tandem ring-opening metathesis polymerization (ROMP)/cross-metathesis (CM) of cyclic olefins. Thus, (5-methyl-2-oxo-1,3-dioxol-4-yl)methyl acrylate (VC1), bis((5-methyl-2-oxo-1,3-dioxol-4-yl)methyl) fumarate (VC2), and bis((5-methyl-2-oxo-1,3-dioxol-4-yl)methyl) (E)-hex-3-enedioate (VC3) were synthesized from 4-(hydroxymethyl)-5-methyl-1,3-dioxol-2-one (DMDO-OH). Among these, only VC3 successfully and selectively afforded well-defined α,ω-di(vinylene carbonate) telechelic polyolefins, namely di(VC3)-PCOE and di(VC3)-P(NB-co-CDT), from the ROMP/CM of COE, and norbonene (NB)/trans,trans,cis-1,5,9-cyclododecatriene (CDT), respectively, using Grubbs’ 2nd-generation ruthenium catalyst (G2) under mild operating conditions (CH2Cl2, 40 °C, 3 h). Preliminary investigations on the reactivity of a model VC, namely 4,5-dimethyl-1,3-dioxol-2-one (DMDO), towards nucleophiles such as a primary or secondary amine, promisingly showed the formation of hydroxy-oxazolidone compounds 1 and 2, and oxo-urethane 3 species, respectively. Yet, the ultimate reaction of di(VC3)-PCOE with 2,2′-(ethylenedioxy)bis(ethylamine) (EDR-148) did not give the expected poly(di(hydroxy-oxazolidone)polyolefin) polyaddition type of NIPUs; competing amidation and/or dehydration or urea formation reactions evidenced by detailed NMR, FTIR and MS analyses, were proposed to account for this inefficiency.

Monocomponent alkoxysilyl telechelic rigid polyolefins incorporating soft polyether segments along the backbone are valuable adhesives precursors. Herein, the synthesis of α,ω-bis(trialkoxysilyl) t...

Commercially available poly(propylene glycol) (PPG) and poly(tetrahydrofuran diglycidyl ether) (PTG) α,ω-end-capped with epoxide functions have been chemically modified into α,ω-bis(cyclodithiocarb...

Poly(lactic acid)/poly(lactide) (PLA) is an aliphatic polyester nowadays emerging as the most popular and promising bio-based, sustainable, (bio)degradable, biocompatible and ecological/environmentally friendly “plastic” candidate. PLA is a commercialized viable alternative to the traditional petrochemically derived polymeric materials in many short-time commodity and engineering applications. Whereas polycondensation of lactic acid gives PLA, ring-opening polymerization (ROP) of lactide (LA) is the preferred route towards well-defined PLA. Following the traditional metal-catalyzed ROP, the organocatalyzed ROP (OROP) of LA, enables, under mild and highly selective polymerization conditions, to prepare PLA with predictable/tunable molar mass values and extremely narrow dispersities. Organic activators most typically used in the ROP of LA, most commonly based on commercially available molecules, revolve around single organic initiators, Brønsted/Lewis acids or bases featuring different functional groups including amines and pyridine derivatives, amidines and guanidines, N-heterocyclic carbenes (NHCs), as well as phosphines and phosphazenes, and mono- or multi-component dual catalytic systems involving hydrogen-bond interactions. Recent advances in LA OROP developed over the past decade are thus accordingly addressed, emphasizing polymerization mechanism aspects and monomer activation modes, catalyst development, methodologies, stereocontrol/stereoselectivity, and functional group incorporation. The OROP of O-carboxy anhydrides (OCAs), which similarly to LA produce poly(α-hydroxy acid)s, thus enabling the introduction of functional groups along the polyester backbone, is also covered.

International audience; Yttrium [amino-alkoxy-bis(phenolate)]amido complexes have been used for the ring-opening polymerization (ROP) of racemic alkyl β-malolactonates (4-alkoxycarbonyl-2-oxetanones, rac-MLARs) bearing an allyl (All), benzyl (Bz) or methyl (Me) lateral ester function. The nature of the ortho-substituent on the phenolate rings in the metal ancillary dictated the stereocontrol of the ROP, and consequently the syndiotactic enrichment of the resulting polyesters. ROP promoted by catalysts with halogen (Cl, Br)-disubstituted ligands allowed the first reported synthesis of highly syndiotactic PMLARs (Pr ≥ 0.95); conversely, catalysts bearing bulky alkyl and aryl ortho-substituted ligands proved largely ineffective. All polymers have been characterized by 1H and 13C\1H\ NMR spectroscopy, MALDI-ToF mass spectrometry and DSC analyses. Statistical and thermal analyses enabled the rationalization of the chain-end control mechanism. Whereas the stereocontrol of the polymerization obeyed a Markov first-order (Mk1) model for the ROP of rac-MLABz and rac-MLAAll, the ROP of rac-MLAMe led to a chain end-control of Markov second-order type (Mk2). DFT computations suggest that the high stereocontrol ability featured by catalysts bearing Cl- and Br-substituted ligands does not likely originate from halogen bonding between the halogen substituent and the growing polyester chain

International audience; Amphiphilic polycarbonate-poly(hydroxyalkanoate) diblock copolymers, namely, poly(trimethylene carbonate) (PTMC)-b-poly(β-malic acid) (PMLA), are reported for the first time. The synthetic strategy relies on commercially available catalysts and initiator. The controlled ring-opening polymerization (ROP) of trimethylene carbonate (TMC) catalyzed by the organic guanidine base 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), associated with iPrOH as an initiator, provided iPrO-PTMC-OH, which served as a macroinitiator in the controlled ROP of benzyl β-malolactonate (MLABe) catalyzed by the neodymium triflate salt (Nd(OTf)3 ). The resulting hydrophobic iPrO-PTMC-b-PMLABe-OH copolymers were then hydrogenolyzed into the parent iPrO-PTMC-b-PMLA-OH copolymers. A range of well-defined copolymers, featuring different sizes of segments (Mn,NMR up to 9300 g mol(-1) ; ÐM =1.28-1.40), were thus isolated in gram quantities, as evidenced by NMR spectroscopy, size exclusion chromatography, thermogravimetric analysis, differential scanning calorimetry, and contact angle analyses. Subsequently, PTMC-b-PMLA copolymers with different hydrophilic weight fractions (11-75 %) self-assembled in phosphate-buffered saline upon nanoprecipitation into well-defined nano-objects with Dh =61-176 nm, a polydispersity index \textless0.25, and a negative surface charge, as characterized by dynamic light scattering and zeta-potential analyses. In addition, these nanoparticles demonstrated no significant effect on cell viability at low concentrations, and a very low cytotoxicity at high concentrations only for PTMC-b-PMLA copolymers exhibiting hydrophilic fractions over 47 %, thus illustrating the potential of these copolymers as promising nanoparticles

International audience; Polyhydroxyalkanoates (PHAs) are biocompatible and biodegradable polyesters widely used for biomedical applications. Amphiphilic triblock copolymers with a PHB hydrophobic segment recently demonstrated attractive advantages such as high colloidal stability and low critical micellar concentration (CMC) values for the elaboration of drug delivery systems. Our approach aims at associating PHB with a fully biodegradable hydrophilic block to access new self-assembled systems with unique potential. Well-defined alpha,omega-dihydroxy telechelic PHA-based hydrophobic triblock copolymers with tunable segments length were synthesized by the controlled ring-opening polymerization (ROP) of benzyl beta-malolactonate, using polyhydroxybutyrate (PHB) diol/Nd(OTf)(3) as the catalytic system. Remarkably, the reaction proceeds with the selective oxygen-acyl bond cleavage of the beta-lactone. The corresponding amphiphilic copolymers were then obtained by hydrogenolysis. These copolymers are the only examples of fully biodegradable PHA-PHB-PHA triblock copolymers. The hydrophilic weight fraction of the copolymers was tuned from 7 to 83% upon modulating the monomer loading thus affording the ability to next access different self-assembling architectures.

International audience; Band-selective (bs) HSQC, improving spectral resolution by restriction of the heteronuclear dimension without inducing spectral folding, has been recently used for polymer tacticity determination. Herein is reported an evaluation of various bs-HSQC and bs-HMBC sequences, first from a methodological point of view (selectivity, dependence to INEPT interpulse delay or relaxation delay), using the cyclic peptide cyclosporin selected as a model compound, and then from an applicative approach, comparing tacticity determined from bs-HSQC and bs-HMBC experiments to the one obtained from 1D 13C(1H) on poly(3-hydroxyalkanoate)s samples. For HSQC sequences, the 13 selectivity scheme consisting in substituting a 13 broadband refocalization by a selective one revealed itself problematic, with unwanted aliased signals, whereas the insertion of double pulsed field gradients spin-echo (DPFGSE) or the use of opposite sign gradients bracketing a selective refocalization gave satisfactory results. Determination of the probability of syndiotactic enchainments, Ps, by bs-HSQC is fully consistent and no precision loss was observed when decreasing acquisition time (37 min vs. 106 min for 1D 13[1H]). Bs-HMBC, although not straightforwardly applicable for tacticity determination, could provide (after a calibration step) an alternative for compounds of which only 13 carbonyl signals are resolved enough for discriminating between syndiotactic and isotactic configurations. © 2018 by the authors.

International audience; Origins of stereoselectivity in ROP of racemic chiral cyclic esters promoted by achiral yttrium complexes, resulting in the formation of highly heterotactic polylactide, and highly syndiotactic or, more uniquely, highly isotactic poly(3-hydroxybutyrate)s, are discussed. A close interplay between the nature of the cyclic ester, most particularly of the exocyclic functional chain installed on the chiral center of β-lactones, and the ortho-substituents installed on the phenolate rings of the ligand, results in various determining secondary interactions of steric and also electronic nature.

International audience; Silyl-modified polymers (SMPs) are alkoxysilyl functionalized polymers of high importance both academically and industrially. SMPs are being developed for coating, adhesive, sealant and elastomer applications. In this paper, emphasis is placed first on the different chemical modification approaches available to tackle the synthesis of SMPs by in situ functionalization (ISF) and post-polymerization functionalization (PPF) routes, with their pros and cons being underlined. Recent progress and modern trends towards alkoxysilyl telechelic polyenes and polyolefins by olefin metathesis strategies are next discussed. The state-of-the-art of alkoxysilyl functionalized polymers, especially of telechelic ones, delineated according to the latter two main synthetic pathways, is then covered along with their subsequent curing, and is illustrated by selected examples including, in particular, polyenes, polyolefins and some other selected relevant polymers.

International audience; Expanding on our strategy to design telechelic polyolefins through the catalyzed ring-opening metathesis polymerization/cross metathesis/ring-closing metathesis polymerization of cyclic olefins using bifunctional symmetric alkene chain transfer agents (CTAs), we have now explored the metathesis of cyclooctene (COE), 1,5,9-cyclododecatriene (CDT), and norbornene (NB), using azlactone (AZL)-functional CTAs, toward the synthesis of original AZL telechelic polyolefins. The monofunctional 2-vinyl-4,4-dimethylazlactone predominantly gives, as anticipated, (isomerized) monofunctional and/or difunctional PCOEs. On the other hand, the new symmetric AZL-based CTAs 1–3, namely, (E)-2,2′-(ethene-1,2-diyl)bis(4,4-dimethyloxazol-5(4H)-one) (1), (E)-2,2′-(but-2-ene-1,4-diyl)bis(4,4-dimethyloxazol-5(4H)-one) (2), and (E)-2,2′-(but-2-ene-1,4-diyl)bis(3-oxa-1-azaspiro[4.5]dec-1-en-4-one) (3), selectively give α,ω-di(AZL) telechelic PCOEs, along with minor amounts of cyclic PCOE. The synthesis of related AZL telechelic CDT and NB copolymers has also been implemented through such a tandem metathesis approach. Subsequently, the inherent AZL reactivity toward (di)amines has been evidenced using a triethylene glycol diamine, in first the model reaction with CTA 3 and next upon reacting with the new α,ω-di(CTA 3)-P(NB-co-CDT) copolymers, thereby enabling the preparation of original polyolefins/polyamides

International audience; The sequential and random ring-opening polymns. (ROP) of racemic-trans-cyclohexene carbonate (rac-CHC) or enantiopure trans-(R,R)-cyclohexene carbonate ((R,R)-CHC) with L-lactide (LLA) or trimethylene carbonate (TMC) have been performed. Catalytic systems based on zinc diaminophenolate [(NNO)ZnEt] ((NNO)- = 2,4-di-tert-butyl-6-\[(2'-dimethylaminoethyl)methylamino]methyl\phenolate)) or tris[N,N-bis(trimethysilyl)amide]yttrium (Y[N(SiMe3)2]3) complexes, or a guanidine-type organocatalyst (1,5,7-triazabicyclo[4.4.0]dec-5-ene, TBD), combined to an alc. (BnOH or iPrOH) as initiator/chain-transfer agent were used. Well-defined diblock P(rac-CHC)-b-PLLA and P((R,R)-CHC)-b-PLLA and random P(rac-CHC)-co-PLLA and P(rac-CHC)-co-PTMC copolymers were thus synthesized with molar mass values up to Mn,NMR = ca. 34 000 g mol-1 and rather narrow dispersity values (DM = 1.2-1.7). 1H and 13C\1H\ NMR characterizations of the copolymers revealed the presence of -OBn or -OiPr chain-end groups, thereby supporting the active role of exogenous alc. as initiator. No decarboxylation reaction was ever obsd. during any copolymn., thus providing PCHC/PLLA and PCHC/PTMC copolymers void of ether defects. Thermal anal. of the copolymers assessed by DSC and TGA confirmed their block or random structure. The block PCHC-b-PLA and the random PCHC-co-PLLA and PCHC-co-PTMC copolymers represent the first examples of such copolymers synthesized by ring-opening copolymn. of the two comonomers. The latter PCHC-co-PTMC copolymers randomly combining CHC and TMC units are the first examples ever reported

International audience; The diaminophenolate and β-diketiminate zinc complexes [(NNO)ZnEt] ((NNO)− = 2,4-di-tert-butyl-6-{[(2′-dimethylaminoethyl)-methylamino]methyl}phenolate)) and [(BDIiPr)Zn{N(SiMe3)2}] (BDIiPr = CH(CMeNC6H3-2,6-iPr2)2), respectively, the Lewis acidic triflate salt Al(OTf)3, and the guanidine TBD (= 1,5,7-triazabicyclo[4.4.0]dec-5-ene), combined to a protic source as initiator, typically benzyl alcohol (BnOH), enabled the successful copolymerization of ethylene carbonate (EC) with various cyclic esters such as β-butyrolactone (BL), δ-valerolactone (VL), ε-caprolactone (CL) or L-lactide (LLA). The random copolymerizations proceeded smoothly under mild operating conditions, preferentially from [(NNO)ZnEt]/BnOH at 60 °C in toluene within a few hours, affording the corresponding copolymers void of ether units, with Mn,SEC values in the range ca. 6000–93 350 g mol−1 and with unimodal, moderately broad dispersity values (ĐM = 1.3–2.1). Under the same experimental conditions, the homopolymerization of EC did not proceed. The first EC/BL random copolymers were thus synthesized with up to 26 mol% of EC inserted within the polyester, while the second example of P(EC-co-VL) was isolated. P(EC-co-VL), P(EC-co-CL), and P(EC-co-LLA) copolymers were prepared with higher than previously reported EC content, namely 23, 37, and 17 mol% vs. 10, 31, and 4 mol%, respectively. In contrast to other catalyst systems, the Al(OTf)3/BnOH system promoted CO2 elimination from the copolymers, thereby leading to ether defects. Microstructural analysis of the copolymers by 13C{1H} NMR spectroscopy revealed the presence of signals previously never described and possibly arising from consecutive EC units within the random copolymers. Thermal transition temperatures measured by DSC further supported the random nature of these copolymers.

International audience; The synthesis of low viscosity liquid α,ω-bis(trialkoxysilyl) telechelic copolyolefins (DF) via ring-opening metathesis polymerization (ROMP)/cross metathesis (CM) is reported. Copolymerization of a norbornene-based olefin (NB-OLF = norbornene (NB), ethylidene norbornene (ENB), methyl 5-norbornene-2-carboxylate (NBCOOMe), methyl 5-oxanorbornene-2-carboxylate (oxaNBCOOMe), or dicyclopentadiene (DCPD)) with a monocycloolefin (mOLF = cyclooctene (COE), 1,5-cyclooctadiene (COD), or 1,5,9-cyclododecatriene (CDT)) was carried out at 40 °C (except for DCPD at 23 °C) in CH2Cl2 for 24 h, using Grubbs' 2nd generation catalyst (G2) and the bis(trialkoxysilyl)-functionalized symmetric acyclic alkene (RO)3Si(CH2)3NHC(O)OCH2CHCHCH2OC(O)NH(CH2)3Si(OR)3 (R = Me or Et) as the chain-transfer agent (CTA). The catalytic productivity (turnover numbers, TONs, up to 50 000 mol(comonomers) mol(Ru)-1 and 1250 mol(CTA 1) mol(Ru)-1) and selectivity (>85 wt%; only minor amounts of cyclic non-functionalized copolymers (CNFs) formed) toward the formation of the corresponding DFs were quite high, as evidenced by fractionation experiments and detailed 1D and 2D 1H and 13C NMR spectroscopy and SEC analyses. The thermal and rheological properties of the random copolymers, assessed by DSC and viscosimetric analyses, could be tuned according to the nature and the ratio of the comonomers. At 23 °C, P(NBCOOMe-co-COE) and P(oxaNBCOOMe-co-COE) synthesized from a 50:50 ratio of comonomers displayed the lowest viscosity. Such silyl-modified polyolefins (SMPOs) are thus foreseen in possible industrial applications as one-component adhesives.

International audience; Polymer diols are a class of polymeric building blocks of high interest for the synthesis of complex macromolecular edifices. Rare-earth borohydride complexes are known as efficient initiators for the ring-opening polymerization (ROP) of cyclic esters, directly affording α,ω-dihydroxy-telechelic polyesters. Here, were report the direct synthesis of poly(benzyl β-malolactonate) (PMLABe) diols, from the ROP of racemic (benzyl β-malolactonate) (rac-MLABe), a valuable and renewable monomer, initiated by the homoleptic [Ln(BH4)3(thf)3] (Ln=La, Nd, and Sm) complexes. These initiators enabled the controlled ROP of this β-lactone, affording well-defined syndiotactic-enriched (Pr≈0.83) PMLABes (Mn up to 21 300 g mol−1, ÐM≈1.5) as evidenced by size exclusion chromatography, 1H and 13C NMR spectroscopy, and MALDI-ToF mass spectrometry analyses. The first and second insertions of rac-MLABe, as assessed by DFT calculations, revealed more favorable stationary front-side than migratory back-side insertions, the thermodynamically and kinetically competitive ROP on two distinct arms with that on a one arm-only, and the thermodynamically slightly favored formation of syndiotactic-enriched PMLABes.

International audience; Alternating copolymers constitute an attractive class of materials. It was shown previously that highly alternated poly(β-hydroxyalkanoate)s (PHAs) can be prepared by ring-opening polymerization (ROP) of mixtures of two different enantiomerically pure 4-alkyl-β-propiolactones. However, the approach could not be extended to PHAs with chemically tunable functional groups, which is highly desirable to access original advanced materials. Reported herein is the first highly syndioselective and controlled ROP of racemic allyl and benzyl β-malolactonates (MLAR; R=allyl, benzyl) using an yttrium complex supported by a tetradentate dichloro-substituted bis(phenolate) ligand. This highly active catalyst allows the nearly perfect alternating copolymerization of MLAAllyl and MLABenzyl. Hydrogenolysis of the benzyloxycarbonyl or functionalization of the allyl pendant groups opens a route towards a new class of functional alternating copolymers.

International audience; Poly (-benzyl malolactonate) (PMLABe) is an aliphatic renewable, biocompatible, biodegradable, hydrophobic polyester of the poly(hydroxyalkanoate) (PHA) family. Along with the hydrophilic parent poly(-malic acid) (PMLA), PMLABe and PMLA have been studied as materials for biomedical applications. Herein, advances on the synthesis of benzyl -malolactonate (MLABe) and the related alkyl -malolactonates (MLARs), PMLABe homopolymers and copolymers, are reviewed. Focus is placed on the ring-opening polymerization (ROP) of MLABe and on copolymers of MLABe, with relevant data on the performances of the initiating systems and on the PMLABes molecular characteristics, along with detailed mechanistic insights, being reported.

International audience; The present work reports the investigation of the biocompatibility, opsonisation and cell uptake by human primary macrophages and HepaRG cells of nanoparticles (NPs) formulated from poly(β-malic acid)-b-poly(β-hydroxybutyrate) (PMLA-b-PHB) and poly(β-malic acid)-b-poly(trimethylene carbonate) (PMLA-b-PTMC) diblock copolymers, namely PMLA800-b-PHB7300, PMLA4500-b-PHB4400, PMLA2500-b-PTMC2800 and PMLA4300-b-PTMC1400. NPs derived from PMLA-b-PHB and PMLA-b-PTMC do not trigger lactate dehydrogenase release and do not activate the secretion of pro-inflammatory cytokines demonstrating the excellent biocompatibility of these copolymers derived nano-objects. Using a protein adsorption assay, we demonstrate that the binding of plasma proteins is very low for PMLA-b-PHB-based nano-objects, and higher for those prepared from PMLA-b-PTMC copolymers. Moreover, a more efficient uptake by macrophages and HepaRG cells is observed for NPs formulated from PMLA-b-PHB copolymers compared to that of PMLA-b-PTMC-based NPs. Interestingly, the uptake in HepaRG cells of NPs formulated from PMLA800-b-PHB7300 is much higher than that of NPs based on PMLA4500-b-PHB4400. In addition, the cell internalization of PMLA800-b-PHB7300 based-NPs, probably through endocytosis, is strongly increased by serum pre-coating in HepaRG cells but not in macrophages. Together, these data strongly suggest that the binding of a specific subset of plasmatic proteins onto the PMLA800-b-PHB7300-based NPs favors the HepaRG cell uptake while reducing that of macrophages.

International audience; The synthesis of multi-arm poly([R]-3-hydroxybutyrate) (PHB)-based triblock copolymers (poly([R]-3-hydroxybutyrate)-b-poly(N-isopropylacrylamide)-b-[[poly(methyl ether methacrylate)-g-poly(ethylene glycol)]-co-[poly(methacrylate)-g-poly(propylene glycol)]], PHB-b-PNIPAAM-b-(PPEGMEMA-co-PPPGMA), and their subsequent self-assembly into thermo-responsive hydrogels is described. Atom transfer radical polymerization (ATRP) of N-isopropylacrylamide (NIPAAM) followed by poly(ethylene glycol) methyl ether methacrylate (PEGMEMA) and poly(propylene glycol) methacrylate (PPGMA) was achieved from bromoesterified multi-arm PHB macroinitiators. The composition of the resulting copolymers was investigated by 1H and 13C J-MOD NMR spectroscopy as well as size-exclusion chromatography (SEC), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The copolymers featuring different architectures and distinct hydrophilic/hydrophobic contents were found to self-assemble into thermo-responsive gels in aqueous solution. Rheological studies indicated that the linear one-arm PHB-based copolymer tend to form a micellar solution, whereas the two- and four-arm PHB-based copolymers afforded gels with enhanced mechanical properties and solid-like behavior. These investigations are the first to correlate the gelation properties to the arm number of a PHB-based copolymer. All copolymers revealed a double thermo-responsive behavior due to the NIPAAM and PPGMA blocks, thus allowing first the copolymer self-assembly at room temperature, and then the delivery of a drug at body temperature (37 °C). The non-significant toxic response of the gels, as assessed by the cell viability of the CCD-112CoN human fibroblast cell line with different concentrations of the triblock copolymers ranging from 0.03 to 1 mg mL−1, suggest that these PHB-based thermo-responsive gels are promising candidate biomaterials for drug-delivery applications.

International audience; The ring-opening metathesis polymerization/cross-metathesis (ROMP/CM) of cyclooctene (COE) using bis(trialkoxysilyl)alkenes as chain-transfer agents (CTAs) and Ru catalysts to afford difunctionalized polyolefins is reported. The formation of alpha,omega-bis(trialkoxysilyl) telechelic polycycloolefins (DF) with controlled molar mass values takes place quite selectively (>90 wt%), along with minor amounts of cyclic non-functionalized polymers (CNF), as evidenced by NMR, MALDI-ToF MS, SEC analyses and fractionation experiments. The nature of the CTA and catalyst influenced much the efficiency and selectivity of the reaction. (MeO)(3)SiCH2CH=CHCH2Si(OMe)(3) (2) and (MeO)(3)Si(CH2)(3)NHC(O)OCH2CH=CHCH2OC(O)NH (CH2)(3)Si(OMe)(3) (5) proved to be the most efficient CTAs in terms of reactivity, catalyst productivity and selectivity towards DF. Diurethane CTA 5 is easily prepared, and can also be conveniently generated in situ during the ROMP/CM. Grubbs' 2nd-generation catalyst (G2) and Hoveyda-Grubbs's catalyst (HG2) afforded the best compromise in terms of selectivity and productivity, with turnover numbers of up to 95 000 mol(COE) mol(Ru)(-1) and 5000 mol(CTA) mol(Ru)(-1).

The controlled ring-opening polymerization of racemic allyl-β-butyrolactone (rac-BLallyl) in toluene or in bulk, catalyzed by the discrete β-diiminate zinc amido [(BDIiPr)Zn(N(SiMe3)2)] (1) or {amino-methoxy-bis(phenolate)}yttrium amido [(ONOOtBu)Y(N(SiHMe2)2)(THF)] (2) complexes, in association with an alcohol, gave poly(β-hydroxyalkanoate)s (PHAs) with allylic side chains. These PHAsallyl exhibit either a slightly isotactic-enriched (Pm = 0.61) or highly syndiotactic-enriched (Pr = 0.82) backbone structure, respectively, with high molar mass (Mn up to 21,100 g mol−1) and narrow molar mass distribution values (1.05 < Mw/Mn < 1.28), as evidenced by detailed 13C NMR and size exclusion chromatography analyses. Postpolymerization rhodium-catalyzed hydroboration of the resulting PHAsallyl with pinacolborane quantitatively afforded the corresponding PHAsboron. Introduction of boron into the pendant chains did not alter neither the structure of the polymer backbone nor the macromolecular features (Mn, Mw/Mn, and stereoregularity). However, differential scanning calorimetry analyses revealed a significant increase of the glass transition temperature on modifying the allyl for the boron function in these PHAs.

International audience; Allyl complexes based on group IIIb metals (Sc, Y, La) and lanthanides are reviewed. The diversity, synthesis, and main structural and reactivity features of discrete, well-defined homoleptic and pseudo-homoleptic neutral, anionic and cationic bis-, tris- and tetra(allyl)-lanthanide complexes, as well as heteroleptic allyl-lanthanidocenes and allyl-lanthanide complexes supported by non-Cp ligands are covered. Brief comments on the catalytic performances of some key compounds in polymerization processes are also provided.

α,ω-Dihydroxy-telechelic poly(trimethylenecarbonate), HO-PTMC-OH, is synthesized from the controlled "immortal" ring-opening polymerization (ROP) of trimethylene carbonate under mild conditions (bulk, 60 °C), using ZnEt(2) or, more efficiently, [(BDI)Zn(N(SiMe(3) )(2) )] (BDI = CH(CMeNC(6) H(3) -2,6-iPr(2) )(2) ) as catalyst precursor, in the presence of a diol HO-R-OH (R = (CH(2) )(2) or CH(2) C(6) H(4) CH(2) ; 0.5-10 equiv. vs Zn) acting both as co-initiator and chain transfer agent. Alternatively, HO-PTMC-OH is prepared upon hydrogenolysis of HO-PTMC-OCH(2) Ph, initially prepared from the ROP of TMC using the [(BDI)Zn(N(SiMe(3) )(2) )]/PhCH(2) OH system, under smooth operating conditions using Pd/charcoal. Well-defined dihydroxy-functionalized PTMCs of molar mass ranging from $\overline M _{\rm n}$ = 2 000 to 109 500 g · mol(-1) were thus quantitatively obtained and fully characterized by NMR, MALDI-TOF-MS and SEC analyses. The versatility of this "immortal" ROP allows the preparation of alike α,ω-functional polyester such as linear HO-poly(lactide)-OH, as well as star polymers such as the glycerol-based PTM-OH(3) .

The ring-opening polymerization (ROP) of trimethylene carbonate (TMC) was evaluated in bulk at 60―110°C using various catalyst systems based on bio-friendly metals, including the metal bis(trimethylsilylamides) Mg[N(SiMe 3 ) 2 ] 2 , Ca[N-(SiMe 3 ) 2 ] 2 (THF) 2 , Y[N(SiMe 3 ) 2 ] 3 , (BDI)Fe[N-(SiMe 3 ) 2 ] [BDI=CH(CMeNC 6 H 3 -2,6-i-Pr 2 ) 2 ], Fe[N-(SiMe 3 ) 2 ] 2 , Fe[N(SiMe 3 ) 2 ] 3 , Zn[N(SiMe 3 ) 2 ] 2 , (BDI)Zn[N(SiMe 3 ) 2 ] and ZnEt 2 , associated with an alcohol such as isopropyl or benzyl alcohol. The actual metal alkoxide initiating species has been formed in situ prior to the addition of TMC. Introduction of the alcohol component in excess leads to the "immortal" ring-opening polymerization (ROP) of TMC. According to such an "immortal" ROP process of TMC, whichever the metal species, as many as 200 polycarbonate chains could be successfully grown from a unique metal center in a well controlled ROP process. The best performances were obtained using the discrete (BDI)Zn[N(SiMe 3 ) 2 ] precursor. Under optimized conditions, as many as 50,000 equivalents of TMC could be fully converted from as little as 20 ppm of this metallic precursor, allowing the preparation of a polytrimethylene carbonate (PTMC) with a molar mass as high as 185,200 g mol ―1 with a relatively narrow molar mass distribution (M w /M n = 1.68). A double monomer feed experiment carried out with the (BDI)Zn[N-(SiMe 3 ) 2 ]/BnOH initiating system proved the "living" character of the polymerization. Characterization of the PTMCs by NMR and size exclusion chromatography (SEC) showed well-defined α-hydroxy-ω-alkoxycarbonate telechelic polymers, highlighting the controlled character of this "living and immortal" ROP process. Using the (BDI)Zn[N-(SiMe 3 ) 2 ] precursor, varying the alcohol (ROH) to 2-butanol, 3-buten-2-ol or 4-(trifluoromethyl)benzyl alcohol, revealed the versatility of this approach, allowing the preparation of accordingly end-functionalized HO-PTMC-OR polymers. The very low initial loading of metal catalyst considerably limits the potential toxicity and thus allows such polycarbonates to be used in the biomedical field.

The mechanisms of polymerization of e-caprolactone (CL) initiated by either the rare-earth hydride [Cp 2 Eu(H)] or the borohydrides [Cp 2 Eu(BH 4 )] or [(N 2 NN')Eu(BH 4 )] were studied at the DFT level (Cp=η 5 C 5 H 5 ; N 2 NN'= (2-C 5 H 4 N)CH 2 (CH 2 -CH 2 NMe) 2 ). For all compounds the reaction proceeds in two steps: a hydride transfer from the rare earth initiator to the carbonyl carbon of the lactone, followed by ring-opening of the monomer. In the last step a difference is observed between the hydride and borohydride complexes, because for the latter the ring-opening is induced by an additional B-H bond cleavage leading to a terminal -CH 2 OBH 2 group. This corresponds to the reduction by BH 3 of the carbonyl group of CL. Upon reaction of [Cp 2 Eu(H)] with CL, the alkoxy-aldehyde complex produced, [Cp2Eu{O(CH2)5C(O)H}], is the first-formed initiating species. In contrast, for the reaction of CL with the borohydride complexes [(L x )Eu(BH 4 )] (L x = Cp 2 or N 2 NN'), an aliphatic alkoxide with a terminal -CH 2 OBH 2 group, [(L x )Eu{O(CH 2 ) 6 OBH 2 }] is formed and subsequently propagates the polymerization. The present DFT investigations are fully compatible with previously reported mechanistic studies of experimental systems.

Lewis base free hydrido complexes of yttrium and lutetium supported by bulky cyclohexyl- substituted guanidinato ligands, [Ln(mu-H){(Me3Si)(2)NC(NCy)(2)}(2)](2) (Ln = Y, Lu), were synthesized and characterized. Single-crystal X-ray diffraction studies revealed dimeric structures. H-1 NMR spectroscopy shows that complex [Y(mu-H){(Me3Si)(2)NC(NCy)(2)}(2)](2) retains its dimeric structure in C6D6 solution. Scrambling of the hydrido complexes [Ln(mu-H){(Me3Si)(2)NC(NCy)(2)}(2)](2) (Ln = Y, Lu) in C6D6 resulted in an equilibrium mixture containing the heterodimetallic species [{(Me3Si)(2)NC(NCy)(2)}(2)Y(mu-H)(2)-Lu{(Me3Si)(2)NC(NCy)(2)}(2)], indicating the dissociation of dimers and the presence of monomeric species in solution. Both compounds initiate the polymerization of ethylene: the activity of the cyclohexyl- substituted yttrium complex, [Y(mu-H){(Me3Si)(2)NC(NCy)(2)}(2)](2), is much lower than that of the isopropyl-substituted analogue, [Y(mu-H){(Me3Si)(2)NC(NiPr)(2)}(2))(2), while in the case of lutetium the activities of [Ln(mu-H){(Me3Si)(2)NC(NR)(2)}(2)](2) (R = iPr, Cy) are similar. Complexes [Ln(mu-H){(Me3Si)(2)NC(NR)(2)}(2)](2) (Ln = Y, Lu; R = iPr, Cy) were shown to catalyze efficiently the hydrosilylation of 1-nonene with PhSiH3 (at a 1:1 substrates mol ratio) to give the terminal silane PhSiH2(n-C9H19) exclusively. If the hydrosilylation reaction is carried out in the presence of a twofold molar excess of 1-nonene, double addition takes place and leads to the formation of tertiary silane PhSiH(n-C9H19)2, which was obtained in 96% yield. The hydrido complexes [Ln(mu-H){(Me3Si)(2)NC(NiPr)(2)}(2)](2) (Ln = Y, Lu) efficiently initiate the ring-opening polymerization of epsilon-caprolactone to give polymers with molar mass up to 80000. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008).

Metal-based catalysts and initiators have played a pivotal role in the ring-opening polymerization (ROP) of cyclic esters, thanks to their high activity and remarkable ability to control precisely the architectures of the resulting polyesters in terms of molar mass, dispersity, microstructure, or tacticity. Today, after two decades of extensive research, the field is slowly reaching maturity. However, several challenges remain, while original concepts have emerged around new types or new applications of catalysis. This Review is not intended to comprehensively cover all of these aspects. Rather, it provides a personal overview of the very recent progress achieved in some selected, important aspects of ROP catalysis-stereocontrol and switchable catalysis. Hence, the first part addresses the development of new metal-based catalysts for the isoselective ROP of racemic lactide towards stereoblock copolymers, and the use of syndioselective ROP metal catalysts to control the monomer sequence in copolymers. A second part covers the development of ROP catalysts-primarily metal-based catalysts, but also organocatalysts-that can be externally regulated by the use of chemical or photo stimuli to switch them between two states with different catalytic abilities. Current challenges and opportunities are highlighted.

International audience; Metal-based catalysts and initiators have played a pivotal role in the ring-opening polymerization (ROP) of cyclic esters, thanks to their high activity and remarkable ability to control precisely the architectures of the resulting polyesters in terms of molar mass, dispersity, microstructure, or tacticity. Today, after two decades of extensive research, the field is slowly reaching maturity. However, several challenges remain, while original concepts have emerged around new types or new applications of catalysis. This Review is not intended to comprehensively cover all of these aspects. Rather, it provides a personal overview of the very recent progress achieved in some selected, important aspects of ROP catalysis-stereocontrol and switchable catalysis. Hence, the first part addresses the development of new metal-based catalysts for the isoselective ROP of racemic lactide towards stereoblock copolymers, and the use of syndioselective ROP metal catalysts to control the monomer sequence in copolymers. A second part covers the development of ROP catalysts-primarily metal-based catalysts, but also organocatalysts-that can be externally regulated by the use of chemical or photo stimuli to switch them between two states with different catalytic abilities. Current challenges and opportunities are highlighted.

International audience; The (iminophosphoranyl)(thiophosphoranyl)methanide {CH(PPh2=NSiMe3)(PPh2=S)}(-) ligand has been used for the synthesis of divalent and trivalent rare-earth borohydride complexes. The salt metathesis of the potassium reagent [K{CH(PPh2=NSiMe3)(PPh2=S)}]2 with [Yb(BH4)2(THF)2] resulted in the divalent monoborohydride ytterbium complex [{CH(PPh2=NSiMe3)(PPh2=S)}Yb(BH4)(THF)2]. The 2D (31)P/(171)Yb HMQC-NMR spectrum clearly showed the coupling between both nuclei. The trivalent bisborohydrides [{CH(PPh2=NSiMe3)(PPh2=S)}Ln(BH4)2(THF)] (Ln = Y, Sm, Tb, Dy, Er, Yb and Lu) were obtained by reaction of [K{CH(PPh2=NSiMe3)(PPh2=S)}]2 with [Ln(BH4)3(THF)3]. All new compounds were characterized by single X-ray diffraction. The divalent and trivalent compounds were next used as initiators in the ring-opening polymerization (ROP) of ε-caprolactone (CL) and trimethylene carbonate (TMC). All complexes afforded a generally well-controlled ROP of both of these cyclic esters. High molar mass poly(ε-caprolactone) diols (Mn,NMR < 101,300 g mol(-1), ĐM = 1.44), and α,ω-dihydroxy and α-hydroxy,ω-formate telechelic poly(trimethylene carbonate)s (Mn,NMR < 20,000 g mol(-1), ĐM = 1.61) were thus synthesized under mild operating conditions.

International audience; Ring-opening polymn. (ROP) of racemic-benzyl β-malolactonate (MLABe) initiated by an alc. such as 1,3-propanediol (PPD) or 2-hydroxymethyl-1,3-propanediol (TMM), and catalyzed by a metal triflate M(OTf)3 with M = Nd, Bi, proceeded under mild operating conditions (in bulk at 60 °C). The functionality of the alc. dictates the topol. of the resulting hydroxy telechelic PMLABe. The ROP promoted by the neodymium-based catalytic system afforded a satisfactory activity and control in terms of molar mass and dispersity values (Mn,NMR up to 7000 g mol-1, DM \textless 1.35). Mechanistic insights revealed that ring-opening of MLABe took place through the selective oxygen-acyl bond cleavage without undesirable side reactions such as transesterification or crotonisation, as evidenced by NMR and mass spectrometry analyses of the recovered polyesters. The structure of the corresponding α,ω-hydroxy telechelic PMLABes was ascertained by 1H and 13C\1H\ NMR, SEC, and MALDI-ToF mass spectrometry analyses. In comparison, methane and trifluoromethane sulfonic acids did not allow the formation of well-defined PMLABe diols. Differences in the behavior of MLABe and the related β-butyrolactone are highlighted. The present Nd(OTf)3/PPD or TMM catalytic ROP of MLABe thus represents a valuable direct synthesis of PMLABe diols and triols, resp., without requiring chem. modification of a preformed PMLABe precursor.

International audience; The ring-opening polymerization (ROP) of trans-1,4-cyclohexadiene carbonate (CHDC) has been investigated computationally and experimentally. DFT computations indicate that ring-opening of CHDC is thermodynamically possible, yet to a lesser extent than that of trans-cyclohexene carbonate (CHC). Effective homopolymerizations of rac-CHDC and simultaneous or sequential copolymerizations of rac-CHDC with rac-CHC and L-LA were achieved with a diaminophenolate zinc-based complex ([(NNO)ZnEt]) or a guanidine (TBD) associated with an alcohol. These ROP reactions, which confirmed the lower reactivity of rac-CHDC vs. rac-CHC, especially in homopolymerization, proceeded without any decarboxylation. Quite uniquely, highly syndiotactic PCHDC was obtained from ROP of rac-CHDC with both the zinc- and TBD-based catalysts, as revealed by 13C{1H} NMR studies. The prepared homopolymers and block or random copolymers were characterized by 1H, 13C{1H} NMR, MALDI-ToF MS, SEC and DSC techniques.

International audience; Polyhydroxyalkanoate-based diblock copolymers, poly(β-malic acid)-b-poly(3-hydroxybutyrate) (PMLA-b-PHB), featuring different sizes of segments have been synthesized, for the first time, in two steps and in grams quantity. First, the controlled sequential ring-opening polymn. of β-butyrolactone (BL, in bulk) followed by benzyl β-malolactonate (MLABe, in toluene) has been achieved with 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) to afford well-defined poly(benzyl β-malolactonate)-b-poly(3-hydroxybutyrate) (PMLABe-b-PHB) copolymers. A subsequent hydrogenolysis of β-benzyloxycarbonyl units afforded the corresponding PMLA-b-PHB amphiphilic copolymers, as evidenced by 1H, 13C\1H\ and DOSY NMR, SEC, TGA, DSC and contact angle analyses. Next, PMLA-b-PHB copolymers featuring different hydrophilic wt. fractions (10-65%) self-assembled in PBS upon nanopptn. Nano-objects with narrow size distributions (Dh = 17-180 nm; 0.19 \textless PDI \textless 0.30) and exhibiting a neg. surface charge (-32 to -52 mV) were obtained as characterized by DLS, zeta potential, and TEM analyses. Using HepaRG and SK-MEL-28 cells, cytotoxicity studies evidenced no effect on cell viability at low concns. (\textless 88 μg mL-1) while high concns. (88-320 μg mL-1) induced a mild toxicity. Also, high concns. of nanoparticles (ca. 180 μg mL-1) slightly reduced DNA replication while apoptosis measured with DEVD-AMC caspase activity remained unaffected, thus suggesting a moderate cytostatic effect of the nanoparticles without induction of cell death. Furthermore, HepaRG cells were found to efficiently uptake PMLA-b-PHB-based nanoparticles. All these results demonstrated that PMLA-b-PHB copolymers are promising candidates as drug-delivery systems.