Fanny Bonnet

Unprecedented dual behaviour of a half-sandwich scandium-based initiator for both highly selective isoprene and styrene polymerisation

Highly cis-1,4 polymerisation of isoprene and syndiospecific polymerisation of styrene were conducted using the same borohydrido half-sandwich scandium pre-initiator.

Isoprene–Styrene Chain Shuttling Copolymerization Mediated by a Lanthanide Half-Sandwich Complex and a Lanthanidocene: Straightforward Access to a New Type of Thermoplastic Elastomers†

A lanthanide half-sandwich complex and a ansa lanthanidocene have been assessed for isoprene-styrene chain shuttling copolymerization with n-butylethylmagnesium (BEM). In the presence of 1 equiv BEM, a fully amorphous multiblock microstructure of soft and hard segments is achieved. The microstructure consists of poly(isoprene-co-styrene) blocks, with hard blocks rich in styrene and soft blocks rich in isoprene. The composition of the blocks and the resulting glass transition temperatures (Tg ) can be easily modified by changing the feed and/or the relative amount of the catalysts, highlighting a new class of thermoplastic elastomers (TPEs) with tunable transition temperatures. The materials self-organize into nanostructures in the solid state.

Non-hindered ansasamarocenes, versatile catalysts for diene/olefin/polar monomer copolymerisations. What is really the active species?

Abstract Catalytic systems containing an ansabiscyclopentadienyllanthanide core and lithium and/or magnesium salts are obtained by reaction of the chloride precursors with allyllithium. These allyl complexes lead to the same active species which polymerises 1,3-dienes, copolymerises 1,3-dienes and α-olefin or α,ω-dienes or allows the controlled diblock polyisoprene/polycaprolactone copolymerisation. The exact nature of this active species and of the allyl precursors is investigated here.

A Joint Experimental/Theoretical Investigation of the Statistical Olefin/Conjugated Diene Copolymerization Catalyzed by a Hemi-Lanthanidocene [(Cp*)(BH4)LnR]

Statistical copolymerization of ethylene and isoprene was achieved by using a borohydrido half-lanthanidocene complex. Under copolymerization conditions, activation of [(Cp*)(BH(4))(2)Nd(thf)(2)] (Cp*=η(5)-C(5)Me(5)) by an appropriate alkylating agent affords trans-1,4-poly-isoprene-co-ethylene. Analysis of the microstructure of the copolymer revealed the presence of successive short sequences of ethylene/ethylene, trans-1,4-isoprene/ethylene, and trans-1,4-isoprene/trans-1,4-isoprene. A small amount of 1,2-insertion of isoprene was observed, and no cyclic structures within the chain were characterized. Test runs showed that these catalysts are unable to copolymerize α-olefins (such as hex-1-ene) with isoprene. The probable initial steps in the copolymerization have been computed at the DFT level of theory. Analysis of the energy profile provides insight into the catalysts activity and selectivity. Our theoretical results highlight the key role played by the allyl intermediate, in which diene insertion, and to a lesser extent olefin insertion, is the rate-determining step of the process. These results also illustrate the coordination behavior of the allyl ligand during the insertion of an incoming monomer, which directly inserts, after pre-coordination to the metal center, into the η(3)-allyl ligand without inducing an η(3) to η(1) haptotropic shift. Finally, the inactivity of this family of catalysts towards the copolymerization of hex-1-ene was rationalized on the basis of the free-energy profile of the copolymerization.

New Viscoelastic Materials Obtained by Insertion of an α-Olefin in a trans-Polyisoprene Chain with a Single-Component Organolanthanide Catalyst

Copolymerisation of isoprene with C 6 -C 18 a-olefins by a single component organolanthanide catalyst affords poly(trans-1,4-isoprene) containing 6-10% of inserted olefin. The mechanical properties of highly crystalline transpolyisoprene are dratically modified after insertion of the alkyl chains, leading to quasi-amorphous viscoelastic materials.

The first rare earth organometallic complex of 1,4,7-trithiacyclononane: a precursor to unique cationic ethylene and α-olefin polymerisation catalysts supported by an all-sulfur donor ligand

[Sc([9]aneS3)(CH2SiMe3)3], the first rare earth organometallic complex of 1,4,7-trithiacyclonane, is a precursor to ethylene and alpha-olefin polymerisation catalysts upon activation with BAr(F)3 or [CPh3][BAr(F)4](Ar(F) = C6F5); these are the first cationic rare earth organometallic catalysts supported by an all-sulfur donor ligand.

Lanthanide mono(borohydride) complexes of diamide-diamine donor ligands: novel single site catalysts for the polymerisation of methyl methacrylate

Samarium chloride and borohydride complexes of the diamide-diamine ligands (2-C5H4N)CH2N(CH2CH2NR)2(R = SiMe3 or mesityl) are described; the borohydride compounds are the first polydentate amide-supported single component lanthanide catalysts for the controlled polymerisation of polar monomers, and also represent the first lanthanide borohydride complex for the polymerisation of methyl methacrylate.

Organolanthanides, catalysts for specific olefin-diene copolymerization : access to new materials

Abstract Non-hindered ansa dicyclopentadienylallyl complexes of samarium, [(CMe2C5H4)2Sm(allyl)]n, and (CMe2C5H4)2Sm(allyl)L (L=THF or allylLi) polymerize isoprene without an aluminum cocatalyst. The polymerizations are highly stereospecific, affording nearly quantitatively 1–4 trans polyisoprene. In the presence of linear 1-olefins, copolymers are formed, with 6–10% of olefin inserted; the 1–4 trans structure of the polyisoprene chain is not altered, and only one olefin molecule is inserted between two polyisoprene fragments. In the common initiator of these three catalytic systems, the (CMe2C5H4)2Sm(allyl) moiety, only one vacant site would be available. As a consequence of the presence of the alkyl aliphatic chain, the viscoelastic behaviour of the branched copolymers markedly differs from that of trans 1–4 polyisoprene: an important loss of crystallinity and a dramatic decrease of the Young modulus are observed; the copolymers show elastomeric properties.

Diene/polar monomer copolymers, compatibilisers for polar/non-polar polymer blends. A controlled block copolymerisation with a single-site component samarocene initiator

A well-controlled two-step process, the polymerisation of isoprene or isoprene/hex-1-ene copolymerisation followed by e-caprolactone polymerisation, affords trans-polyisoprene or (trans-polyisoprene/hex-1-ene copolymer)–poly(e-caprolactone) diblocks of various lengths. The single component initiator is an allylsamarocene compound. An atomic force microscopy study shows that these copolymers are efficient compatibilisers for poly(e-caprolactone) and polyisoprene blends. Poly(e-caprolactone) chain growth from Sm–polyisoprene chain.

Continuous cyclo-polymerisation of L-lactide by reactive extrusion using atoxic metal-based catalysts: easy access to well-defined polylactide macrocycles

The bulk polymerisation of L-lactide was assessed using the alkaline-earth and lanthanide borohydride complexes Mg(BH4)2 (1), Ca(BH4)2(THF)2 (2) and Ln(BH4)3(THF)3 with Ln = Nd (3), Sm (4) and La (5). All five catalysts display good activities, with up to 77% conversion in 20 min with 5. Lanthanide-based catalysts 3, 4 and 5, which were found to lead to the highest conversions, were tested in reactive extrusion polymerisation conditions in a twin-screw micro-extruder. High activities were also observed in theses experimental conditions, affording up to 73% conversion in only 20 min with lanthanum-based catalyst 5. More interestingly, the polylactides formed display a macrocyclic structure with molecular weights up to 30 000 g mol−1 along with relatively narrow dispersities (1.23–1.79). The macrocycles are formed via intramolecular transesterification reactions taking place during the ring opening polymerisation. Furthermore, the reactive extrusion polymerisations operate at a temperature as low as 130 °C, this monomer usually being polymerized at 185 °C. This is the first example of a cyclic polyester obtained directly via a continuous process.