Lactide Lactone Chain Shuttling Copolymerization Mediated by an Aminobisphenolate Supported Aluminum Complex and Al(OiPr)3: Access to New Polylactide Based Block Copolymers.

The chain shuttling ring-opening copolymerization of l-lactide with ε-caprolactone has been achieved using two aluminum catalysts presenting different selectivities and benzyl alcohol as chain transfer agent. A newly synthesized aminobisphenolate supported aluminum complex affords the synthesis of lactone rich poly(l-lactide-co-lactone) statistical copolymeric blocks, while Al(OiPr)3 produces semicrystalline poly(l-lactide) rich blocks. Transalkoxylation is shown to operate efficiently. The crystalline ratios and glass transition temperatures of these new classes of polylactide based block copolymers can be tuned by adjusting the catalysts and the comonomers ratio.

A one pot one step combined radical and ring-opening route for the dual functionalization of starch in aqueous medium.

Starch based materials are attractive bio-based alternative to fully synthetic polymers. Native starch has however limited thermoprocessability and properties and must be modified. In order to improve the properties of starch-graft-poly(butyl-acrylate-co-styrene) copolymers via a process as green as possible, we report herein a new method for the dual functionalization of the polysaccharide via a one pot one step reaction in aqueous medium combining free radical polymerizations and ring-opening chemistry. Poly(butyl acrylate) or poly(butyl acrylate-co-styrene) (ca. 60 000 g/mol) and oligo(ε-caprolactone) were grafted on starch with a grafting percentage up to 75 %. The copolymers show two glass transition temperatures: one around 55-60 °C related to starch and a second attributed to the grafted vinyl polymers, from -46 °C to 20 °C depending on butyl acrylate/styrene ratio. The resulting dual functionalized materials exhibit excellent mechanical properties, with elongation at break in the range 20-210 %, while single functionalized starch shows less than 5 %.

Preparation of Glass Fabric/Poly(l-lactide) Composites by Thermoplastic Resin Transfer Molding.

This study reports the first example of the production of polylactide composites prepared by Thermoplastic Resin Transfer Molding (T-RTM) via in situ bulk polymerization of l-lactide (l-LA) after injection in a closed mold containing glass fabrics. Tin octoate Sn(Oct)2 was used as the catalyst and first evaluated at the lab-scale in the experimental conditions required in the tank and in the mold of the RTM device. The reactions were then upscaled in the RTM in the absence of reinforcement to ensure the feasibility of the process (transfer and polymerization). Finally, poly-l-lactide (PLLA)-based composites with glass fabrics as the reinforcement were obtained. The resulting PLLA matrices exhibited conversions up to 99% along with high molar masses of up to 78,000 g·mol-1 when the polymerization was carried out under dynamic vacuum (vacuum-assisted RTM, VARTM). Moreover, a good impregnation of the glass fabrics by the matrix was observed by optical microscopy.

Mixed Allyl Rare-Earth Borohydride Complexes: Synthesis, Structure, and Application in (Co-)Polymerization Catalysis of Cyclic Esters.

A series of new trivalent rare-earth allyl-borohydride complexes with the formula [RE(BH4 )2 (C3 H5 )(thf)x ] (RE=Sc (1), x=2; RE=Y (2) and La (3), x=3) were synthesized by reaction of the corresponding rare-earth trisborohydrides [RE(BH4 )3 (thf)x ] with half an equivalent of bis(allyl)magnesium. The complexes were fully characterized by determining their X-ray structure. Similar to their previously described Nd (4) and Sm (5) analogues, these complexes display a monomeric structure with two terminal trihapto BH4 groups, one π-η3 allyl ligand, three THF molecules for complexes 2 and 3, and two THF molecules for complex 1. The catalytic behavior of complexes 1-5 toward the ring-opening polymerization (ROP) of l-lactide (l-LA) and ϵ-caprolactone (ϵ-CL) was assessed. The Nd complex featured the best activity toward l-LA (turnover frequency (TOF)=1300 h-1 ) and the order was Nd>La>Sm>Y>Sc. Complexes 1-3 were found very active for the ROP of ϵ-CL (TOF=166 000 h-1 ), which is in line with the already established exceptionnally high performance of complexes 4 and 5. With both monomers, it was shown that the borohydride moiety was the preferentially initiating group, rather than the allyl one. The random copolymerization of l-LA and ϵ-CL was performed with complexes 1-5, in the absence or in the presence of benzyl alcohol as a chain-transfer agent, affording copolymers with ϵ-caprolactone up to 62 % inserted. The copolymers synthesized display a variety of microstructures, that is, blocky, random, or quasi-alternating.

Isoprene polymerization mediated by vanadium-[ONNO] complexes.

A series of vanadium complexes bearing dianionic tetradentate amine-bisphenolate [ONNO] ligands, V([double bond, length as m-dash]O)X[ONNO(Me)] (X = Cl (1); O(i)Pr (2)), VCl2[ONNO(Me)] (3) and V(O(i)Pr)2[ONNO(R)] (R = Me (4), (t)Bu (5), Cl (6)), displaying various electronic and steric properties have been prepared. The molecular structures of two of these complexes, namely V[ONNO(R)](O(i)Pr)2 with R = (t)Bu (5) or Cl (6), are reported. Activated with dialkylmagnesium, all complexes lead to modest isoprene homo-polymerization activities at 50 °C. Quantitative polymerizations were observed using 4 and 6 as pre-catalysts combined with Al(i)Bu3. The resulting polyisoprene microstructure was composed of ca. 70% 3,4 enchainments, the remaining 30% 1,4 enchainments being a mixture of cis and trans stereoisomers. 6 leads to a more active catalyst than 4. ß-Hydride abstraction occurs during the reaction.

Bis(phenolate)amine-supported lanthanide borohydride complexes for styrene and trans-1,4-isoprene (co-)polymerisations.

New bis(phenolate)amine-supported neodymium borohydride complexes and their previously reported samarium analogues were tested as catalysts for the polymerisation of styrene and isoprene. Reaction of Na2O2N(L) (L = py, OMe, NMe2) with Nd(BH4)3(THF)3 afforded the borohydride complexes Nd(O2N(L))(BH4)(THF) (L = py (1-Nd), OMe (2-Nd), NMe2 (3-Nd)). Complex 1-Nd has shown a propensity to form phenolate-O-bridged dimer [Nd(µ-O2N(py))(BH4)]2 (1'-Nd) as previously observed with the samarium analogues Sm(O2N(L))(BH4)(THF) (L = py or Pr). X-ray structures of 1'-Nd and 2-Nd were determined and are presented. The neodymium borohydride complexes 1-Nd to 3-Nd and their samarium analogues Sm(O2N(L))(BH4)(THF)x (L = py (1-Sm), OMe (2-Sm), NMe2 (3-Sm), Pr (4-Sm)) were tested as catalysts for the polymerisation of isoprene and styrene in the presence of n-butylethylmagnesium (Mg((n)Bu)(Et)). All complexes were found to be active for the polymerisation of isoprene in these conditions, leading to polyisoprene up to 95.1% trans-1,4 stereoregular. They were also found to be active for the polymerisation of styrene leading to atactic polystyrene in all cases. Interestingly, samarium-based complexes were found to be more active than the neodymium ones toward this latter monomer, in sharp contrast to what is usually observed with rare earth borohydride complexes. The structure of both trans-polyisoprenes and polystyrenes obtained were studied in detail by MALDI-ToF analysis in order to better understand the polymerisation mechanisms. The coordinative chain transfer polymerisation (CCTP) of both monomers was further conducted using Mg((n)Bu)(Et) as transfer agent. Finally, the statistical copolymerisation of isoprene and styrene was examined using these catalytic systems, leading to the formation of poly[(trans-1,4-isoprene)-co-styrene] with up to 39% of styrene moieties inserted in a highly trans-1,4-stereoregular polyisoprene.

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.

Uranium(IV) amido-borohydrides as highly active diene polymerisation catalysts.

The synthesis and structural characterisation of the uranium(IV) amido-borohydrides (N'')2U{κ(2)-N(SiMe3)SiMe2CH2BBN-H} and U{κ(2)-N(SiMe3)SiMe2CH2BBN-H}2, and their activity as pre-catalysts for the polymerisation of isoprene are described.

Tuning the catalytic properties of rare earth borohydrides for the polymerisation of isoprene.

Previous results obtained for the cis-polymerisation of isoprene with scandium half-sandwich complex Cp*Sc(BH(4))(2)(THF) 1a were extended to its neodymium analog. The X-ray structure of the already reported neodymium monomer compound Cp*Nd(BH(4))(2)(THF)(2) 1b is presented. Cp*Nd(BH(4))(2)(THF)(2)/[CPh(3)][B(C(6)F(5))(4)]/Al((i)Bu)(3) catalytic system was found to be very active and stereoselective towards isoprene polymerisation, leading to highly 1,4-cis polyisoprene up to 92%. The effect on isoprene polymerisation of the addition of a NHC molecule to Cp*Ln(BH(4))(2)(THF)(n) pre-catalyst (Cp* = η(5)-C(5)Me(5), Ln = Sc, n = 1, 1a; Nd, n = 2, 1b; Sm, n = 2, 1c) or to a trisborohydride Ln(BH(4))(3)(THF)(n) (Ln = Sc, n = 1.5, 2a; Nd, n = 3, 2b; Sm, n = 3, 2c) was also studied. Several NHC ligands were assessed: the classical [1-C{(N(t)BuCH)}(2)] (L(1)) and functional N-heterocyclic carbenes, two amino-tethered HNBu(t)CH(2)CH(2)[1-C{N(CHCH)NR}] (HL(2-R)) (R = (t)Bu, Mes (Mes = 2,4,6-Me(3)-C(6)H(2))) and the hydroxyl-tethered HOCMe(2)CH(2)[1-C{N(CHCH)N(i)Pr}] (HL(3)). Neodymium-based complex (L(2-tBu))Nd(BH(4))(2)(THF)(2) 3 could be isolated and characterized. With some of the catalytic combinations tested, the introduction of the NHC ligand in the coordination sphere of the complex induces a switch of the stereoselectivity of the resulting polymer. Scandium complex 2a, which produces mainly 1,4-cis polyisoprene when associated to a borate activator and aluminum alkyl, leads to 1,4-trans polymer up to 94% regular when HL(2-tBu) carbene is added to the same reaction mixture. This result is the only example of highly trans-polyisoprene synthesized with a scandium based catalyst. Coordination of the carbene moiety to the rare earth centre is confirmed by NMR studies on paramagnetic neodymium pre-catalysts.

Synthesis and structure of divalent thulium borohydrides, and their application in ε-caprolactone polymerisation.

The new divalent thulium compound [Tm(BH(4))(2)(DME)(2)] could be prepared by reduction of [Tm(BH(4))(3)(THF)(3)] or from TmI(2) and KBH(4). It was used as a precursor to the divalent [(Tp(tBu,Me))Tm(BH(4))(THF)] by reaction with potassium tris(2-tBu-4-Me)pyrazolylborate (KTp(tBu,Me)). Both Tm(II) compounds were found active as ε-caprolactone polymerisation catalysts.

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 catalyst's 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.

Synthesis of samarium(II) borohydrides and their behaviour as initiators in styrene and epsilon-caprolactone polymerisation.

The bisborohydrido samarium compound Sm(BH(4))(2)(THF)(2) (1) was prepared in high yield by comproportionation between Sm and 2 equivalents of Sm(BH(4))(3)(THF)(3). Reaction of 1 with KCp* (Cp* = C(5)Me(5)) afforded the half-sandwich Cp*Sm(BH(4))(THF)(2) (2). The (1)H NMR borohydride resonances of both complexes, observed at very high field, are typical of divalent Sm compounds. X-Ray single crystal analysis revealed polymeric and dimeric molecular arrangements for 1 and 2, respectively. Complex 1 was found moderately active towards styrene polymerisation when activated with Al((i)Bu)(3), or with a borate/Al combination, whereas 2 showed no activity. Ring-opening polymerisation of epsilon-caprolactone could be performed rapidly at room temperature with both initiators. Complex 2 leads to narrow polydispersities and higher activity. Two different mechanisms, by monoelectronic transfer or by insertion into the Sm-(BH(4)) bond can be proposed.

A DFT study of conjugated dienes polymerisation catalyzed by [Cp*ScR]+: insights into the propensity for cis-1,4 insertion.

Calculation of the free energy profile for 1,4 butadiene polymerisation catalyzed by [Cp*ScR](+) highlights the kinetic preference for cis-1,4 over trans-1,4 insertions. The main differences between cis and trans configuration rely on the thermodynamics and the geometry of the precursor diene adduct.

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.

Lanthanide borohydride complexes supported by diaminobis(phenoxide) ligands for the polymerization of epsilon-caprolactone and L- and rac-lactide.

Reaction of Na2O2NN' [H2O2NN' = (2-C5H4N)CH2N[2-HO-3,5-C6H2(t)Bu2]2] with M(BH4)3(THF)3 afforded the dimeric, rare-earth borohydride compounds [M(O2NN')(mu-BH4)(THF)n]2 [M = Y(III), n = 0.5 (1-Y); M = NdIII, n = 1 (1-Nd); M = SmIII, n = 0 (1-Sm)]. For comparison the chloride analogues [M(O2NN')(mu-Cl)(THF)n]2 (2-M; M = La(III) or Sm(III), n = 0; M = Nd(III), n = 1) and the corresponding pyridine adducts [M(O2NN')(mu-X)(py)]2 [X = BH4 (3-M) or Cl (4-M); M = La(III), Nd(III), or Sm(III)] were prepared and structurally characterized for 4-La. Compounds 1-M initiated the ring-opening polymerization of epsilon-caprolactone. The best molecular weight control (suppression of chain transfer) for all three monomers was found for the samarium system 1-Sm. The most effective heterotactic enrichment (Pr) in the polymerization of rac-lactide was found for 1-Y (P(r) = 87%). Compound 1-Nd catalyzed the block copolymerization of epsilon-caprolactone and L- and rac-lactide provided that epsilon-caprolactone was added first. Attempted block polymerization by the addition of L-lactide first, or random copolymerization of a ca. 1:1 mixture of epsilon-caprolactone and L-lactide, gave only a poly(L-lactide) homopolymer.

The first rare earth organometallic complex of 1,4,7-trithiacyclononane: a precursor to unique cationic ethylene and alpha-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.

Organometallic early lanthanide clusters: syntheses and X-ray structures of new monocyclopentadienyl complexes.

The reaction of Ln(BH(4))(3)(THF)(3) or LnCl(3)(THF)(3) with 1 equiv of KCp*' ligand (Cp' = C(5)Me(4)n-Pr) afforded the new monocyclopentadienyl complexes Cp*'LnX(2)(THF)(n) (X = BH(4), Ln = Sm, n = 1, 1a, Ln = Nd, n = 2, 1b; X = Cl, Ln = Sm, n = 1, 3a) and [Cp*'LnX(2)](n') (X = BH(4), n' = 6, Ln = Sm, 2a, Ln = Nd, 2b; X = Cl, Ln = Nd, 4b). All these compounds were characterized by elemental analysis and (1)H NMR. Crystals of mixed borohydrido/chloro-bridged [Cp*'(6)Ln(6)(BH(4))(12-x))Cl(x)(THF)(n')] (x = 10, n' = 4, Ln = Sm, 2a', Ln = Nd, 2b'; x = 5, n = 2, Ln = Sm, 2a' ') were also isolated. Compounds 2a, 2b, 2a', 2b', and 2a'' were structurally characterized; they all exhibit a hexameric structure in the solid state containing the [Cp*(3)Ln(3)X(5)(THF)] building block. The easy clustering of THF adducts first isolated is illustrative of the well-known bridging ability of the BH(4) group. Hexameric 2a was found to be unstable in the presence of THF vapors; this may be correlated to the opening of unsymmetrical borohydride bridges observed in the molecular structure.

Genuine heteroleptic complexes of early rare-earth metals: synthesis, X-ray structure, and their use for stereospecific isoprene polymerization catalysis.

Genuine heteroleptic neodymium and samarium complexes of formula [Cp*'Ln[(p-tol)NN](BH4)] (Cp*' = C5Me4(nPr), (p-tol)NN = (p-tol)NC(Me)CHC(Me)N(p-tol), Ln = Sm: 1a, Ln = Nd: 1b) have been synthesized for the first time. These unprecedented homologues of early lanthanocenes are prepared by a metathetic reaction between their monocyclopentadienylbisborohydrido precursors with the corresponding potassium diketiminate. Both complexes were obtained in good yields and were characterized by 1H NMR spectroscopy and elemental analysis. Complex 1 a has an non-solvated dimeric structure, as indicated by its crystallographic data. The chloroneodymium analogue [Cp*'Nd[(p-tol)NN](Cl)] (2b) was only obtained as a part of a mixture. Analysis of crystals of 2b by X-ray diffraction revealed a molecular structure very similar to that of 1a. Preliminary isoprene polymerization experiments were carried out with 1 b in the presence of an alkylmagnesium coactivator. The resulting bimetallic Nd/Mg system behaves as an efficient and highly stereospecific catalyst with the synthesis of trans-1,4-polyisoprene with more than 98% regularity. The control of the polymer structure is related to the steric hindrance around the lanthanide atom.