A New Life For Nitrile-Butadiene Rubber: Co-Harnessing Metathesis And Condensation For Reincorporation Into Bio-Based Materials.

Efficient plastic recycling processes are crucial for the production of value-added products or intermediates. Here, we present a multicatalytic route that allows the degradation of nitrile-butadiene rubber, cross-metathesis of the formed oligomers, and polymerization of the resulting dicarboxylic acids with bio-based diols, providing direct access to unsaturated polyesters. This one-pot approach combines the use of commercially available catalysts that are active and selective under mild conditions to synthesize renewable copolymers without the need to isolate intermediates.

One-Pot Catalysis: A Privileged Approach for Sustainable Polymers?

Almost all aspects of daily life involve polymers in some form or the other. However, polymer production is largely based on finite feedstocks. These limitations combined with environmental concerns force us to rethink the strategies for the synthesis of these materials. As an abundant and renewable resource, biomass is composed of a very diverse range of molecules that deserve to be valorized. The development of new methods for transforming biomass into resources suitable for polymer production remains a crucial hurdle on the road to a more sustainable chemical economy. The main challenge is to design efficient and selective transformations of abundant and inexpensive raw materials into innovative polymers. For the chemical industry to meet these challenges, process intensification must play an important role in developing cleaner and more energy-efficient technologies while aiming for safer and more sustainable processes. Catalysis is an important tool to support more sustainable plastics production by being ideally efficient, practical, and versatile. In this regard, the creation of sustainable polymers through one-pot catalysis represents an exciting frontier in materials science.In this Account, we describe some of the published advances for achieving one-pot synthesis of biobased monomers and the resulting (co)polymers. These studies demonstrate that one-pot reactions can produce sustainable materials for a wide range of applications. We show that these new multistep "one-pot" approaches are very promising from an academic and industrial point of view. These synthetic schemes have indeed allowed us to investigate the formation of new polyesters, polypeptides, and poly(meth)acrylates by different polymerization mechanisms. We discuss their efficiency by highlighting their ability to perform multiple (quantitative) synthetic transformations and bond formation steps while bypassing multiple purification procedures at the same time. While enabling the development of novel polymeric structures, we demonstrate that these one-pot procedures can also contribute to reducing the environmental footprint.In light of the growing concerns for sustainable development, these procedures may therefore allow, in the near future, one to prepare sustainable polymeric materials with advanced properties through extremely simplified routes from renewable feedstocks. Among these materials, block and alternating copolymers are unique structures that can exhibit a wide range of properties. While their multistep synthesis remains a demanding process, the one-pot synthesis of these polymers is much more scalable and can create multiblock or alternating copolymers with a wide range of potential sequences. These approaches then give access to materials whose structure and functionality can be designed to suit the need.

Dissociation of N2 on a Si(111)-7x7 Surface at Room Temperature.

We demonstrate that the strong N2 bond can be efficiently dissociated at low pressure and ambient temperature on a Si(111)-7x7 surface. The reaction was experimentally investigated by scanning tunnelling microscopy and X-ray photoemission spectroscopy. Experimental and density functional theory results suggest that relatively low thermal energy collision of N2 with the surface can facilitate electron transfer from the Si(111)-7x7 surface to the π*-antibonding orbitals of N2 that significantly weaken the N2 bond. This activated N2 triple bond dissociation on the surface leads to the formation of a Si3 N interface.

Controlling polymer stereochemistry in ring-opening polymerization: a decade of advances shaping the future of biodegradable polyesters.

This review highlights recent developments in the field of biodegradable polymeric materials intended to replace non-degradable conventional plastics, focusing on studies from the last ten years involving the stereoselective ring-opening polymerization of cyclic esters. This encompasses exciting advances in both catalyst design and monomer scope. Notably, the last decade has seen the emergence of metal-free stereocontrolled ROP for instance, as well as the synthesis and stereocontrolled polymerization of new types of chiral monomers. This study will emphasize recent stereoselective polymerization catalysts and chiral monomers and will focus on stereocontrol quantification, the mechanisms of stereocontrol and their differentiation if reported and studied for a specific catalyst system.

2,5-Furandicarboxylic Acid: An Intriguing Precursor for Monomer and Polymer Synthesis.

The most versatile furanic building block for chemical and polymer applications is 2,5-furandicarboxylic acid. However, the classical 2,5-furandicarboxylic acid production methodology has been found to have significant drawbacks that hinder industrial-scale production. This review highlights new alternative methods to synthesize 2,5-furandicarboxylic acid that are both more advantageous and attractive than conventional oxidation of 5-hydroxymethylfurfural. This review also focuses on the use of 2,5-furandicarboxylic acid as a polymer precursor and the various potential applications that arise from these furan-based materials.

Highly Efficient Synthesis of Poly(silylether)s: Access to Degradable Polymers from Renewable Resources.

The design of new materials with tunable properties and intrinsic recyclability, derived from biomass under mild conditions, stands as a gold standard in polymer chemistry. Reported herein are platinum complexes which catalyze the formation of poly(silylether)s (PSEs) at low catalyst loadings. These polymers are directly obtained from dual-functional biobased building blocks such as 5-hydroxymethylfurfural (HMF) or vanillin, coupled with various dihydrosilanes. Access to different types of copolymer architectures (statistical or alternating) is highlighted by several synthetic strategies. The materials obtained were then characterized as low Tg materials (ranging from -60 to 29 °C), stable upon heating (T-5% up to 301 °C) and resistant towards uncatalyzed methanolysis. Additionally, quantitative chemical recycling of several PSEs could be triggered by acid-catalyzed hydrolysis or methanolysis. These results emphasize the interest of biobased poly(silylether)s as sustainable materials with high recycling potential.

Access to Highly Stereodefined 1,4-cis-Polydienes by a [Ni/Mg] Orthogonal Tandem Catalytic Polymerization.

A [Ni/Mg]-catalyzed orthogonal tandem polymerization has been developed starting from enol phosphates. Initial investigations conducted on branched 1,3-dienes as monomers enabled identification of a Mg-initiated polymerization process leading to 1,4-cis-polydienes. When aryl enol phosphates are used as monomers, the [Ni/Mg]-catalyzed tandem polymerization affords 1,4-cis-polydienes with selectivities up to 99%. Elastomeric or crystalline materials were obtained by simple structural modifications of the monomeric unit. This tandem approach appears as a straightforward and efficient way to enforce diversity and selectivity in diene polymerization while retaining a fair degree of control, just as observed for stepwise systems that are accessible through established time- and manpower-consuming synthetic procedures.

Production and Polymerization of Biobased Acrylates and Analogs.

To prepare biobased polymers, particular attention must be paid to the obtention of the monomers from which they are derived. (Meth)acrylates and their analogs constitute such a class of monomers that have been extensively studied due to the wide range of polymers accessible from them. This review therefore aims to highlight the progresses made in the production and polymerization of (meth)acrylates and their analogs. Acrylic acid production from biomass is close to commercialization, as three different high-potential intermediates are identified: glycerol, lactic acid, and 3-hydroxypropionic acid. Biobased methacrylic acid is less common, but several promising options are available, such as the decarboxylation of itaconic acid or the dehydration of 2-hydroxyisobutyric acid. Itaconic acid is also a vinylic monomer of great interest, and polymers derived from it have already found commercial applications. Methylene butyrolactones are promising monomers, obtained from bioresources via three different intermediates: levulinic, succinic, or itaconic acid. Although expensive, methylene butyrolactones have a strong potential for the production of high-performance polymers. Finally, ß-substituted acrylic monomers, such as cinnamic, fumaric, muconic, or crotonic acid, are also examined, as they provide an original access to biobased materials from various renewable raw materials, such as protein waste, lignin, or wastewater.

Multicatalytic Transformation of (Meth)acrylic Acids: a One-Pot Approach to Biobased Poly(meth)acrylates.

Shifting from petrochemical feedstocks to renewable resources can address some of the environmental issues associated with petrochemical extraction and make plastics production sustainable. Therefore, there is a growing interest in selective methods for transforming abundant renewable feedstocks into monomers suitable for polymer production. Reported herein are one-pot catalytic systems, that are active, productive, and selective under mild conditions for the synthesis of copolymers from renewable materials. Each system allows for anhydride formation, alcohol acylation and/or acid esterification, as well as polymerization of the formed (meth)acrylates, providing direct access to a new library of unique poly(meth)acrylates.

Polymerization of rac-Lactide Using Achiral Iron Complexes: Access to Thermally Stable Stereocomplexes.

Enantiopure poly(lactic acid) (PLA) can form stereocomplexes when enantiomeric PLA chains are mixed in equivalent amounts. Such materials provide interesting features that might be suitable for numerous applications. Despite several advantages, the main drawback of PLA is its narrow window of processing, thus limiting its use for industrial applications. Reported herein are achiral iron complexes, that are highly active, productive, and stereoselective under mild reaction conditions for the ring-opening polymerization of lactide. The corresponding catalytic systems enable the production of stereoblock polymers with high molecular weights, allowing the formation of thermally stable and industrially relevant stereocomplexes.

Mechanistic Aspects of the Polymerization of Lactide Using a Highly Efficient Aluminum(III) Catalytic System.

We report here a unique example of an in situ generated aluminum initiator stabilized by a C2-symmetric salen ligand which shows a hitherto unknown high activity for the ROP of rac-lactide at room temperature. Using a simple and robust catalyst system, which is prepared from a salen complex and an onium salt, this convenient route employs readily available reagents that afford polylactide in good yields with narrow polydispersity indices, without the need for time-consuming and expensive processes that are typically required for catalyst preparation and purification. In line with the experimental evidence, DFT studies reveal that initiation and propagation proceed via an external alkoxide attack on the coordinated monomer.

Real-Time Control of the Enantioselectivity of a Supramolecular Catalyst Allows Selecting the Configuration of Consecutively Formed Stereogenic Centers.

The enantiomeric state of a supramolecular copper catalyst can be switched in situ in ca. five seconds. The dynamic property of the catalyst is provided by the non-covalent nature of the helical assemblies supporting the copper centers. These assemblies are formed by mixing an achiral benzene-1,3,5-tricarboxamide (BTA) phosphine ligand (for copper coordination) and both enantiomers of a chiral phosphine-free BTA co-monomer (for chirality amplification). The enantioselectivity of the hydrosilylation reaction is fixed by the BTA enantiomer in excess, which can be altered by simple BTA addition. As a result of the complete and fast stereochemical switch, any combination of the enantiomers was obtained during the conversion of a mixture of two substrates.

Tandem catalysis: a new approach to polymers.

The creation of polymers by tandem catalysis represents an exciting frontier in materials science. Tandem catalysis is one of the strategies used by Nature for building macromolecules. Living organisms generally synthesize macromolecules by in vivo enzyme-catalyzed chain growth polymerization reactions using activated monomers that have been formed within cells during complex metabolic processes. However, these biological processes rely on highly complex biocatalysts, thus limiting their industrial applications. In order to obtain polymers by tandem catalysis, homogeneous and enzyme catalysts have played a leading role in the last two decades. In the following feature article, we will describe selected published efforts to achieve these research goals.

Acid-Catalyzed Activation and Condensation of the =C5H Bond of Furfural on Aldehydes, an Entry Point to Biobased Monomers.

Furfural is an industrially relevant biobased chemical platform. Unlike classical furan, or C-alkylated furans, which have been previously described in the current literature, the =C5H bond of furfural is unreactive. As a result, on a large scale, C=C and C=O bond hydrogenation/hydrogenolysis is mainly performed, with furfuryl alcohol and methyl tetrahydrofuran being the two main downstream chemicals. Here, we show that the derivatization of the -CHO group of furfural restores the reactivity of its =C5H bond, thus permitting its double condensation on various alkyl aldehydes. Overcoming the recalcitrance of the =C5H bond of furfural has opened an access to a biobased monomer, whose potential have been investigated in the fabrication of renewably-sourced poly(silylether). By means of a combined theoretical-experimental study, a reactivity scale for furfural and its protected derivatives against carbonylated compounds has been established using an electrophilicity descriptor, a means to predict the molecular diversity and complexity this pathway may support, and also to de-risk any project related to this topic. Finally, by using performance criteria for industrial operations in the field of fuels and commodities, we discussed the industrial potential of this work in terms of cost, E-factor, reactor productivity and catalyst consumption.

Replacing tin in lactide polymerization: design of highly active germanium-based catalysts.

Most germane: Hexacoordinate germanium(IV) species exhibit unprecedented activities, yet controlled behavior, as initiators for the ring-opening polymerization of rac-lactide to form polylactide polymers.

Polymeric encapsulation of a ruthenium(ii) polypyridyl complex: from synthesis to in vivo studies against high-grade epithelial ovarian cancer.

The in vitro to in vivo translation of metal-based cytotoxic drugs has proven to be a significant hurdle in their establishment as effective anti-cancer alternatives. Various nano-delivery systems, such as polymeric nanoparticles, have been explored to address the pharmacokinetic limitations associated with the use of these complexes. However, these systems often suffer from poor stability or involve complex synthetic procedures. To circumvent these problems, we report here a simple, one-pot procedure for the preparation of covalently-attached Ru-polylactide nanoparticles. This methodology relies on the ring-opening polymerization of lactide initiated by a calcium alkoxide derivative formed from calcium bis(trimethylsilyl amide) and a hydroxyl-bearing ruthenium complex. This procedure proceeds with high efficiency (near-quantitative incorporation of Ru in the polymer) and enables the preparation of polymers with varying molecular weights (2000-11000 Da) and high drug loadings (up to 68% w/w). These polymers were formulated as narrowly dispersed nanoparticles (110 nm) that exhibited a slow and predictable release of the ruthenium payload. Unlike standard encapsulation methods routinely used, the release kinetics of these nanoparticles is controlled and may be adjusted on demand, by tuning the size of the polymer chain. In terms of cytotoxicity, the nanoparticles were assessed in the ovarian cancer cell line A2780 and displayed potency comparable to cisplatin and the free drug, in the low micromolar range. Interestingly, the activity was maintained when tested in a cisplatin-resistant cell line, suggesting a possible orthogonal mechanism of action. Additionally, the internalization in tumour cells was found to be significantly higher than the free ruthenium complex (>200 times in some cases), clearly showcasing the added benefit in the drug's cellular permeation and accumulation of the drug. Finally, the in vivo performance was evaluated for the first time in mice. The experiments showed that the intravenously injected nanoparticles were well tolerated and were able to significantly improve the pharmacokinetics and biodistribution of the parent drug. Not only was the nanosystem able to promote an 18-fold increase in tumour accumulation, but it also allowed a considerable reduction of drug accumulation in vital organs, achieving, for example, reduction levels of 90% and 97% in the brain and lungs respectively. In summary, this simple and efficient one-pot procedure enables the generation of stable and predictable nanoparticles capable of improving the cellular penetration and systemic accumulation of the Ru drug in the tumour. Altogether, these results showcase the potential of covalently-loaded ruthenium polylactide nanoparticles and pave the way for its exploitation and application as a viable tool in the treatment of ovarian cancer.

Exploring electronic versus steric effects in stereoselective ring-opening polymerization of lactide and ß-butyrolactone with amino-alkoxy-bis(phenolate)-yttrium complexes.

A series of methoxy-amino-bis(phenol)s (ONOO(R(1),R(2)))H(2) possessing on the phenol rings R(1) ortho substituents with variable steric and electronic properties (R(1)=CMe(2)Ph, 1; CMe(2)tBu, 3; CMe(2)(4-CF(3)C(6)H(4)), 5; CPh(3), 9; Cl, 10) has been synthesized and further reacted with [Y{N(SiHMe(2))(2)}(3)](THF)(2) to give cleanly the corresponding yttrium compounds [Y(ONOO(R(1),R(2))){N(SiHMe(2))(2)}(thf)(n)] (Y-x); the solid-state structures of Y-3 and Y-10 have been determined. These amido complexes have been used as initiators for the ring-opening polymerization (ROP) of rac-lactide (LA) and rac-ß-butyrolactone (BBL) to provide heterotactically enriched poly(lactic acid)s (PLAs) and syndiotactically enriched poly(3-hydroxybutyrate)s (PHBs), respectively, by means of a chain-end control mechanism. Most of these polymerizations proceeded in a controlled fashion, giving polymers with narrow polydispersities and experimental molecular weights in good agreement with calculated values. The nature of the R(1) ortho substituents has a profound impact on the rates and, more spectacularly, on the stereocontrol of the polymerizations. The heterotactic stereocontrol in the ROP of rac-LA appears to be governed essentially by steric considerations; the larger the substituent, the higher the heterotacticity: R(1)=Cl (P(r)=0.56)≪CMe(3) (P(r)=0.80)≪CMe(2)Ph (P(r)=0.90)

Metal-catalyzed synthesis of alternating copolymers.

The creation of polymers with a high degree of sequence and/or stereocontrol represents an exciting frontier in materials science. In order to obtain alternating polymers, coordination polymerization using well-defined metal complexes has played a leading role in the last two decades. In the following paper, we will describe selected published efforts to achieve these research goals using discrete, structurally well-characterized metal complexes.

Supported neodymium catalysts for isoprene and rac-ß-butyrolactone polymerization: modulation of reactivity by controlled grafting.

A series of hybrid materials, bearing neodymium silylamide initiating groups, have been shown to mediate isoprene polymerization when combined with alkyl aluminum activators [methylaluminoxane, AlEt(2)Cl, Al(iBu)(3)]. The surface species nature and relative distribution were correlated with isoprene polymerization activity and selectivity. This approach to stereocontrol modulation has been extended to racemic ß-butyrolactone isoselective ring opening polymerization.

Stereocontrolled ring-opening polymerization of cyclic esters: synthesis of new polyester microstructures.

Synthesis of aliphatic polyesters has been studied intensively due to their biocompatible and biodegradable properties and their potential applications in medical and agricultural fields. There has been particular emphasis over the past decade on the synthesis of discrete, well-characterized complexes that are active polymerization initiators for the ring-opening polymerization (ROP) of lactide (LA) and beta-butyrolactone (BBL) to give, respectively, poly(lactide) (PLA) and poly(3-hydroxybutyrate) (PHB). These recent advances in catalyst design have led to a variety of polyester microstructures. This tutorial review focuses on the use of metal-based complexes for the stereoselective ROP of rac-LA and rac-BBL.