Search

Block copolymers based on ethylene (E) and butadiene (B) were prepared using the ansa-bis(fluorenyl) complex {Me

International audience; Monocationic complexes of yttrium with various bis-alkyl and bis-allyl ligands Y(CH2SiMe2Ph)2(THF)4][B(C6F5)4], [Y(CH2C6H4NMe2)2(THF)2][B(C6F5)4], and [Y[1,3-(SiMe3)2C3H3]2(THF)2][B(C6F5)4] have been prepared by protonolysis of the corresponding homoleptic tris-alkyl or -allyl complexes using the anilinium borate salt [PhNMe2H][B(C6F5)4]. The resulting ion-pair complexes have been isolated and characterized by different techniques such as elemental analysis, 1H, 13C, and 89Y NMR, and EXAFS for the allyl cationic complex [Y[1,3-(SiMe3)2C3H3]2(THF)2][B(C6F5)4]. More specifically, a 1H-coupled 89Y INEPT sequence has been developed in order to quantify the metal/alkyl ligand stoichiometry of both synthesized neutral tris-alkyl and cationic bis-alkyl yttrium complexes. The activity of the cationic complexes toward ethylene and isoprene homopolymerization has been assessed. In presence of TiBA, polyethylene was produced with activities ranging from 6 to 26 kgPE molY–1 h–1 bar–1. The molar mass of the yielded polymers shows a bimodal distribution. Under similar conditions, polyisoprene was produced up to full conversion of the monomer. The microstructure of the yielded polyisoprene displayed mainly cis-1,4-units (ca. 60–70%) and 3,4-units (ca. 20–30%). Only a few percent of trans-1,4 units was revealed.

International audience; A one-pot synthesis method for various α-vinyl,ω-methoxysilyl polyethylene oligomers with well-defined lengths and high end-group functionalities and crystallinities is presented. This method relies on the combination of catalyzed chain growth of ethylene in the presence of a di(alkenyl)magnesium chain transfer agent and a neodymocene complex, followed by efficient deactivation using a variety of silane reagents: trimethoxymethylsilane, trimethoxyvinylsilane and tetramethoxysilane. Further condensation of the ω-methoxysilyl groups of these polymers in active medium (toluene/acetic acid mixture) leads to complex architectures such as comb-like structures or star-like structures that combine high vinyl functionality at extremities with a high crystallinity.

The organocatalytic synthesis of vinylene carbonates from benzoins and acyloins was studied using diphenyl carbonate as a carbonyl source. A range of N-Heterocyclic Carbene (NHC) precursors were screened and it was found that imidazolium salts were the most active for this transformation. The reaction occurs at 90°C under solvent-free conditions. A wide range of vinylene carbonates (symmetrical and unsymmetrical, aromatic or aliphatic), including some derived from natural products, were prepared with 20-99% isolated yields (24 examples). The reaction was also developed using thermomorphic polyethylene-supported organocatalysts as recoverable and recyclable species. The use of such species facilitates the workup and allows the synthesis of vinylene carbonates on the preparative scale (> 30 g after 5 runs).

International audience; A range of thermomorphic polyethylene-supported organocatalysts is prepared from N-alkyl imidazoles and polyethylene iodide (PE) with good yields (85–92%) and high funtionality (98–99%). The catalytic activity of these species is studied for the ring opening of epoxidized methyl oleate with CO2 to give the corresponding cyclic carbonate. The reaction is carried out at 100 °C to fully exploit the thermomorphic behavior of the organocatalysts. The optimized conditions (neat, 100 °C, and 20 bar of CO2) are applied to a range of epoxidized fatty acids, including an epoxidized rapeseed oil, to give the corresponding carbonates with good yields (75–96%). The catalyst recycling is also studied, and no significant loss of activity is observed after ten runs. The fatty carbonates are important intermediates for the preparation of non-isocyanate polyurethanes (NIPUs).

International audience; A range of dialkenylmagnesium compounds ([CH2═CH(CH2)n]2Mg; n = 1–6) were synthesized and used as chain transfer agents (CTA) with either (C5Me5)2NdCl2Li(OEt2)2 (1) or [Me2Si(C13H8)2Nd(BH4)2Li(thf)]2 (2) neodymium precursors for the polymerization of ethylene. In all cases, the systems followed a controlled coordinative chain transfer polymerization mechanism. The intramolecular insertion of the vinyl group on the CTA in growing chains is possible and led to the formation of cyclopentyl, cyclohexyl, and possibly cycloheptyl chain ends. While the production of cyclopentyl- or cyclohexyl-capped polyethylene chains can be quantitative (n = 2–5), the integrity of this double bond can also be kept if n is higher than 6. In comparison to 1/CTA catalytic systems, 2/CTA catalytic systems showed a higher propensity to produce cycloalkyl chain ends. This was ascribed to the lower steric demand around the active site, as shown by DFT calculations. In addition, the formation of bis(cyclopentylmethyl)magnesium from dipentenylmagnesium using a catalytic amount of 2 was shown.

International audience; Mid and near infrared (MIR and NIR) spectroscopy associated with the partial least squares (PLS) method makes it possible to rapidly characterize the composition of linear low-density polyethylene (LLDPE) in a large range of 1-hexene content from 0 to 21 mol%. LLDPEs are produced using zirconocene catalysts activated with methylaluminoxane. PLS regression methods for MIR and NIR are constructed from this series of LLDPEs to quantify the 1-hexene content in unknown copolymers. In this case, the PLS regression method aims to correlate the 1-hexene content in the copolymers with their IR spectra. Multivariate calibration models are constructed by the PLS algorithm on pretreated data of MIR and NIR analyses. They are tested and validated by comparing results obtained by NMR and the PLS analyses for four unknown ethylene-1-hexene copolymers.

International audience; An innovative method based on thermogravimetric analysis combined with gas chromatography and mass spectrometry, TGA-IST16-GC-MS, was developed for measuring the comonomer type and the comonomer content in a series of linear low-density polyethylene (LLDPE). LLDPE such as copolymers of ethylene and octene or ethylene and hexene were synthetized using the Et(Ind)2ZrCl2 / MAO zirconium-metallocene catalyst. Their characterization with TGA-IST16-GC-MS system were compared to the one of polyethylene prepared under similar conditions and used as reference. TGA-IST16-GC-MS allowed discriminating the comonomer type (hexene or octene) and content. Combining the versatility of thermal analysis and the accuracy and sensitivity of mass spectrometry, this original method proved to be very useful for routine characterization of LLDPE. It has the advantage of being quicker and more easily performed that traditional means of obtaining copolymer compositions such as nuclear magnetic resonance (NMR), or chromatographic methods such as TREF.

International audience

Summary Morphology and particle size distribution (PSD) of high density polyethylene (HDPE) produced in slurry and gas phase ethylene homopolymerisations have been analysed in connection with the catalytic activity of silica supported (n-BuCp)2ZrCl2/Methylaluminoxane (MAO) catalysts. It has been shown that the silica dehydroxylation temperature affects the catalytic activity of these silica supported catalysts in ethylene homopolymerisation which, in turn, affects the polymer morphology and PSD. Thick fibrous HDPE is observed in all the polymer samples produced via slurry phase process, whereas, the gas phase process HDPE samples did not show such fibrous structures. PSD of the polymers replicate the PSD of silica support and shifts towards larger particle size with increase in productivity which is related to silica dehydroxylation temperature.

Thymine (Thy) or 2,6-diamino-1,3,5-triazine (DAT) end-groups were efficiently installed on well-defined polyethylenes (PEs) synthesized by catalyzed chain growth (CCG) polymerization. Mono- and bifunctional low-molar mass PEs (1200–1500 g·mol–1) formed lamellar morphologies with long-range order upon cooling from the melt due to microphase segregation of polar supramolecular units and apolar PE chains. Crystallization of Thy functions into rigid planes at 180 °C induced very long-range lamellar order in Thy-functionalized PEs and dramatically suppressed PE crystallization (from 67% to 19%). DAT-functionalized PEs, whose end-groups do not crystallize, showed slightly reduced PE crystallinity (62%) and less long-range order, since assembly was instead driven by PE crystallization. Mechanical analysis of the bifunctional PEs demonstrated high moduli roughly proportional to PE crystallinity but low strains at break due to the absence of chain entanglements and/or tie chains between crystalline lamellae. This ...

Monofunctional or telechelic polyethylenes (PEs) carrying phosphonic acid end groups are obtained from functional PE produced by catalyzed chain growth (CCG) on magnesium. CCG is first used to produce iodo-end-functionalized PE (PE-I) that is efficiently turned into phosphonate end-functionalized PE (PE-P(O)(OEt)2 ) in the presence of triethylphosphite through the Michaelis-Arbuzov reaction. A simple treatment of the resulting PE-P(O)(OEt)2 with bromotrimethylsilane leads to the targeted phosphonic acid end-functionalized PE (PE-P(O)(OH)2 ) for the first time. Vinyl-end-functionalized analogs (Vin-PE-P(O)(OEt)2 ) are produced using vinyl-end-functionalized PE-I (Vin-PE-I) recently obtained through CCG. A cross-metathesis reaction is then employed to couple Vin-PE-P(O)(OEt)2 and produce after treatment with bromotrimethylsilane the corresponding unprecedented α-ω-(diphosphonic acid) telechelic PE ((OH)2 (O)P-PE-P(O)(OH)2 ).

International audience; Coordinative chain transfer copolymerization of ethylene and styrene was successfully achieved using an ansa-bisfluorenyl neodymium complex, a dialkylmagnesium as a chain transfer agent and di-n-butylether (Bu2O) as a co-solvent. Under these conditions, a controlled chain growth was observed during the polymerization. Chain-end functionalization was performed and it revealed that both styryl and alkyl terminated chains shuttle between neodymium and magnesium. The analysis of the microstructure revealed that up to 3 mol% of styrene can be incorporated into the polymer. A computational mechanistic study at the DFT level was performed to characterize insertion selectivities and it further revealed the role of magnesium species in assisting β-H elimination.

Di(1-(propyl)-2,2,5,5-tetramethyl-1-aza-2,5-disilacylopentane)magnesium was synthesized and used as chain transfer agent for the ethylene polymerization in the presence of a neodymocene precursor. The polymerization was shown to be governed by a catalyzed chain growth process (CCG) on magnesium, allowing the quantitative formation of ammonium or amine functionalized polyethylene (PE) chains. The structure of these chains was shown by 1H and 13C NMR analyses. MALDI-ToF mass spectrometry was successfully used to confirm the structure predicted by the CCG mechanism. The additional formation of telechelic PE chains carrying an ammonium and either a diethyldithiocarbamate or an iodo moiety as end groups was shown after a simple deactivation of the polymerization medium with disulfiram or molecular iodine, respectively.

This work highlights a medium pressure and temperature radical polymerization process in organic solvents for the synthesis of ethylene–vinyl acetate copolymers (EVA). Organic solvents play a crucial role in copolymerization yields, copolymer molar masses, chemical composition, and branching degree. THF and dimethylcarbonate (DMC) were selected, yielding EVA copolymers exhibiting molar masses from 1000 up to 35000 g mol–1 and vinyl acetate contents between 4 and 32 mol %. In the case of DMC, an additional transfer agent (propanal) was required to reach the molar-mass range targeted for the specific application of EVA copolymers as cold flow improver (CFI): an essential diesel fuel additive.

The determination of the xylene soluble fraction in high impact polypropylene is used to estimate the rubber content in the polymer material. In analytical laboratories, the soluble fraction is measured by a solvent extraction using gravimetric methods according to ASTM5492 or ISO6427. These methods require large quantity of polymers, large volume of solvent and long extraction times. It is therefore highly desirable to develop other laboratory methodologies for this task; preferably methodologies that employ existing laboratory equipment. It is found that the SEC method proposed here yields estimates of rubber contents very close to those found using standardized technics but in much shorter times. This article is protected by copyright. All rights reserved

Summary A range of crystalline copolymers of ethylene with α-olefins (propene, hexene, octene and octadecene) were prepared using the complexes Et(Ind)2ZrCl2 and (nBuCp)2ZrCl2 activated with MAO. The average composition of the copolymers was measured using 1H- and 13C-NMR. Then the samples were characterized by High Temperature SEC and DSC. These investigations showed that polymers are homogeneous in composition and consequently were suitable to be used as standards for TREF. This work provided calibrations curves for TREF that can be used on a wide range of α-olefin contents. Finally, these calibrations curves were used to characterize heterogeneous copolymers of ethylene/hexene synthesized using a conventional Ziegler-Natta catalyst.

International audience

Homoleptic benzyl derivatives of titanium and zirconium have been grafted onto silica that was dehydroxylated at 200 and 700 °C, thereby affording bi-grafted and mono-grafted single-site species, respectively, as shown by a combination of experimental techniques (IR, MAS NMR, EXAFS, and elemental analysis) and theoretical calculations. Marked differences between these compounds and their neopentyl analogues are discussed and rationalized by using DFT. These differences were assigned to the selectivity of the grafting process, which, depending on the structure of the molecular precursors, led to different outcomes in terms of the mono- versus bi-grafted species for the same surface concentration of silanol species. The benzylzirconium derivatives were active towards ethylene polymerization in the absence of an activator and the bi-grafted species displayed higher activity than their mono-grafted analogues. In contrast, the benzyltitanium and neopentylzirconium counterparts were not active under similar reaction conditions.

Copolyamides of PA 66/6 lithium 5-sulfoisophthalic acid (LiSIPA) containing up to 40 mol % of LiSIPA were prepared in a 1L-pilot reactor operating at high pressures and high temperatures. Interestingly, the presence of lithium sulfonate moieties highly impacted the glass transition temperature of the polyamide. The Tg increased from 59 °C for PA 66 to 155 °C for a copolymer containing about 40 mol % of LiSIPA. 1,3-Dihexylbenzenedicarboxamide and lithium p-toluenesulfonate were synthesized as model compounds to investigate the interaction of lithium sulfonate moieties and amide functions. Infrared spectroscopy using ATR technology performed on mixture of both compounds showed that the carbonyl group of amide functions interacts with the lithium cation of lithium sulfonate moieties. Similar SO and CO adsorption bands were observed in copolyamides PA 66/6LiSIPA and in mixture of model compounds, which strongly suggest the formation in the copolyamides of physical cross-linking points centered on lithium cations coordinated by carbonyl groups of amide functions. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

In the current contribution it is demonstrated - for the first time - that poly(ethylene) (M(n) = 1,400 as well as 2,800 g · mol(-1) , PDI = 1.2) can be readily equipped with highly reactive cyclopentadienyl (Cp) end groups. The Cp terminal poly(ethylene) can subsequently be reacted in an efficient hetero Diels-Alder (HDA) reaction with macromolecules (poly(isobornyl acrylate) (M(n) = 4,600 g · mol(-1) , PDI = 1.10) and poly(styrene) (M(n) = 6,300 g · mol(-1) , PDI = 1.13) featuring strongly electron withdrawing thiocarbonyl thio end groups, prepared via reversible addition fragmentation chain transfer (RAFT) polymerization employing benzylpyridin-2-yldithioformate (BPDF) as transfer agent. The resulting block copolymers have been analyzed via high-temperature size exclusion chromatography (SEC) as well as nuclear magnetic resonance (NMR) spectroscopy. The current system allows for the removal of the excess of the non-poly(ethylene) containing segment via filtration of the poly(ethylene)-containing block copolymer. However, the reaction temperatures need to be judiciously selected. Characterization of the generated block copolymers at elevated temperatures can lead - depending on the block copolymer type - to the occurrence of retro Diels-Alder processes. The present study thus demonstrates that RAFT-HDA ligation can be effectively employed for the generation of block copolymers containing poly(ethylene) segments.

Polyethylene (PE), alkoxyamine- and thiol-terminated PEs (PE-TEMPO and PE-SH, respectively) can be converted to macroradicals using a peroxide, a thermal cleavage of the alkoxyamine and a hydrogen transfer reaction of the thiol, respectively. The addition of these macroradicals to multiwalled carbon nanotubes (MWCNTs) were compared by performing grafting reactions at 160 degrees C in 1,3-dichlorobenzene as solvent. Raman spectroscopy was utilized to follow the introduction of PE on the MWCNTs' surface while thermogravimetric and elemental analysis indicated the extent of this grafting. The grafting ratio was found to be in the range of 19-36 wt %. PE-functionalized MWCNTs were imaged by transmission elec-tronic microscopy showing a PE layer with various thicknesses covering the surface of nanotubes. It was found that higher levels of grafting were obtained using PE-2,2,6,6-tetramethyl-piperidinyl-1-oxy and PE-SH rather than a radical grafting reaction in which dicumyl peroxide, PE, and MWCNTs were reacted. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 957-965, 2011

Poly(styrene) macromercaptanes (Mn = 1900, 3600, and 6100 g mol-1, PDI ≈ 1.2) derived from thiocarbonyl thio capped polymers prepared via reversible addition fragmentation chain transfer polymerization were employed to initiate the ring opening polymerization (ROP) of D,L-lactide under conditions of organo-catalyis employing 4,4-dimethylaminopyridine. Poly(styrene)-block-poly(lactide) polymers of number average molecular weights up to 25,000 g mol-1 (PDI ≈ 1.2 to 1.6) were obtained and characterized via multiple detection size exclusion chromatography (SEC) using refractive index as well as UV detection. In addition, diffusion ordered nuclear magnetic resonance and liquid chromatography at critical conditions (of both polystyrene as well as poly(lactide) were employed to assess the copolymers' structure. Furthermore, it was demonstrated that polyethylenes capped with a thiol moiety can also be readily chain extended in a ROP employing D,L-lactide, evidenced via NMR and high temperature SEC. This study indicates that the direct use of macromercaptantes is indeed a methodology to switch from a radical to a ROP process. © 2010 Wiley Periodicals, Inc.

A new synthetic strategy, the combination of living polymerization of ylides and ring-opening polymerization (ROP), was successfully used to obtain well-defined polymethylene-b-poly(epsilon-caprolactone) (PM-b-PCL) diblock copolymers. Two hydroxyl-terminated polymethylenes (PM-OH, M-n = 1800 g mol(-1) (PDI = 1.18) and M-n = 6400 g mol(-1) (PDI = 1.14)) were prepared using living polymerization of dimethylsulfoxonium methylides. Then, such polymers were successfully transformed to PM-b-PCL diblock copolymers by using stannous octoate as a catalyst for ROP of c-caprolactone. The GPC traces and H-1 NMR of PM-b-PCL diblock copolymers indicated the successful extension of PCL segment (M-n of PM-b-PCL = 5200-10,300 g mol(-1); PDI = 1.06-1.13). The thermal properties of the double crystalline diblock copolymers were investigated by differential scanning calorimetry (DSC). The results indicated that the incorporation of crystalline segments of PCL chain effectively influence the crystalline process of PM segments. The low-density polyethylene (LDPE)/PCL and LDPE/polycarbonate (PC) blends were prepared using PM-b-PCL as compatibilizer, respectively. The scanning electron microscopy (SEM) observation on the cryofractured surface of such blend polymers indicates that the PM-b-PCL diblock copolymers are effective compatibilizers for LDPE/PCL and LDPE/PC blends. Porous films were fabricated via the breath-figure method using different concentration of PM-b-PCL diblock copolymers in CH2Cl2 under a static humid condition. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 511-517, 2011

Synthesis of well-defined and highly thiol-end-functionalized polyethylene (PE-SH) was performed using olefin polymerization by coordination chemistry and robust functionalization chemistries. Using a Nd-based catalyst in combination with n-butyloctylmagnesium (BOMg), dipolyethylenylmagnesium compounds (PE-Mg-PE) were first prepared by catalyzed polyethylene chain growth on magnesium. Taking advantage of the reactivity of the carbon−magnesium bonds so formed, several functionalization strategies were assessed with the main aim of producing the targeted PE-SH in the simplest and most efficient way. In particular, polysulfurs and thiothiocarbonylated-end-functionalized polyethylenes were successfully obtained and reduced by lithium aluminum hydride (LiAlH4) to give the desired PE with up to 90% thiol chain end functionality.

The role of certain morphological properties of different silica used as supports for metallocene catalysts was investigated in order to quantify their eventual influence on the kinetics of ethylene polymerisation in heptane slurry, as well as on the polymer properties. It was shown that there is no clear link between porosity and observed activity with some highly porous silica producing relatively inactive supported catalysts. It was further shown that within a batch of silica, the particle size had a significant impact on observed kinetics. While it appears that there is possibly some diffusion resistance encountered in the larger particles, it was also shown that prolonged contact between the support and the alkylating agent could increase reaction rates in the larger particles.

Metallocene borohydride complexes {(Me2Si(C13H8)2)Nd(μ-BH4)[(μ-BH4)Li(THF)]}2 (1) and (Me2Si(2,7-tBu2C13H6)2)Nd(BH4)(μ-BH4)Li(ether)3 (2) were prepared by reaction of the dilithium salts of silylene-bridged bis(fluorenyl) ligands with the borohydride precursor Nd(BH4)3(THF)3. The solid state structures of dimeric 1 and monomeric 2 ate complexes were established by X-ray diffraction studies. We showed that these complexes used in combination with (nBu)(nOct)Mg are highly efficient for cyclocopolymerization of ethylene with butadiene leading to a new class of elastomers. Catalyst 1/(nBu)(nOct)Mg provided elastomers with a polyethylene skeleton incorporating unsaturated groups (trans double bond and pendant vinyl units) and 1,2-cyclohexane rings. These rings are formed via an intramolecular cyclization which occurs with a high trans selectivity. The investigation of catalyst 2/(nBu)(nOct)Mg has revealed that the tertio-butyl substitution in positions 2 and 7 of fluorenyl ligands influenced the microstructure...

A new class of well-defined activating supports for olefin polymerization was obtained via the surface organometallic chemistry approach. High activities in slurry polymerization of ethylene along with industrial-grade physical properties of the resulting polyethylene were obtained when these activators were combined with metallocene complexes in the presence of triisobutylaluminium.

Polyolefins account for more than half of worldwide production of thermoplastics. The majority is used as commodity polymers but they may also provide the starting backbones for original architectures. Most polyolefins are obtained by catalytic polymerization and this powerful technique may be used to produce polyolefins incorporating interesting functional groups that can serve as initiating sites for other successively applied polymerization techniques. This review describes the state of the art in strategies employing catalytic olefin polymerization followed by a living or controlled polymerization. The latter methodologies are classified according to the living/controlled polymerization technique used including anionic polymerization, nitroxide-mediated radical polymerization (NMRP), atom transfer radical polymerization (ATRP) and reversible addition-fragmentation chain transfer (RAFT).

International audience

A Lewis acid surfactant combined catalyst (LASC) was tentatively used in a cationic polymerization in miniemulsion of p-methoxystyrene (pMOS). In a first part, the initiating potential of trisdodecyl sulfate ytterbium (Yb(DS)3, 0.25H2O) was evidenced in the solution polymerization of pMOS initiated by the corresponding chlorinated adduct pMOS−HCl. Miniemulsion polymerizations of pMOS performed using the same initiating system gave rise to oligomers, but experimental conditions chosen could not evidence the expected LASC-mediated cationic polymerization process. Further studies showed that LASC is located at the interface and acts only as a surfactant together with SDS. The polymerization occurred due to the hydrolysis of pMOS−HCl. The resulting acidification of the water phase leads to the transformation of SDS into its sulfuric acid form acting as an inisurf according to an interfacial cationic polymerization process. Latex particles of pMOS incorporating narrowly distributed low molar mass chains were o...

Well-defined, crystalline, low molar mass polyethylene PEx (where x is the molar mass 1300 and 2200 g mol–1) bearing thymine (Thy) or 2,6-diaminotriazine (DAT) end groups have been synthesized from amino-terminated PE. Either double-layer or monolayer solid-state morphologies were attained depending on the nature of the end-group(s). PE1300-NH2, PE1300-DAT, and the equimolar blend PE1300-Thy/DAT-PE1300 all organized into double-layer structures composed of extended PE chains sandwiched between H-bonding chain-ends. The double-layered morphology arose from the microphase separation of the polar end-groups and the nonpolar PE chains and was frozen by the crystallization of the PE domains. The regularity of the PE lamellar stacking was higher for the stronger and more directional associated pair Thy/DAT compared with samples of either PE-NH2 or PE-DAT. For PE1300-Thy, the mesoscopic organization was driven by the crystallization of Thy domains prior to crystallization of the PE chains, forcing the small prop...

International audience

The synthesis of lanthanide(III) alkoxides has been described as a series of reactions for which the control of product purity is difficult. The possibility of using amide complexes, in the presence of alcohol, to produce alkoxides was investigated in homogeneous and heterogeneous media. The polymerization of e-caprolactone with alkoxides formed in situ was performed with and without excess alcohol. The latter system was efficient since the polymers were obtained in a short time period, with a well-controlled molecular weight and low polydispersity. The alcohol functionalized all the polymer chains.

Nitrogen-based organolanthanide complexes: (Siam)3Ln (Ln=Yb, 1a, Sm, 1b), (C5H4CMe2)2Sm(Siam), 2, (COT)SmN(SiMe3)2, 4 (Siam=PhC(NSiMe3)2, COT=C8H8), are very efficient towards polymerisation of e-caprolactone. Mechanistic studies on the basis of NMR experiments show that the complexes 1a, 1b and 2 behave as real catalysts, while 4 is the precursor of a heterogeneous initiator. The hapticity of the nitrogen ligand may be related to the formation of cyclic oligomers. © 2000 Academie des sciences / Editions scientifiques et medicales Elsevier SAS organolanthanide / e-caprolactone / polymerisation

International audience; The cationic uranium amide compound [U($Cp^{∗}$$)_{2}$(N$Me_{2}$)(THF)][B$Ph_{4}$] 1 (($Cp^{∗}$ = $\eta$-$C_{5}$$Me_{5}$, THF = tetrahydrofuran) was transformed into the heterocyclic metallacycle |(($Cp^{∗}$$)_{2}$U(O(C$H_{2}$$)_{4}$N$Me_{2}$((C$H_{2}$$)_{4}$O)B$Ph_{4}$| ·0.5THF 2 in the presence of a catalytic amount of the free amine N$R_2$H (R = Me, Et). Treatment of 1 with $^{t}Bu$NC afforded the isocyanide adduct [U($Cp^{∗}$$)_{2}$(N$Me_{2}$)(CN$^{t}Bu$$)_{2}$][B$Ph_{4}$] whereas reactions with MeCN, C$O_2$ and CO gave the insertion compounds [U($Cp^{∗}$$)_{2}$(NC{Me}{N$Me_{2}$})(THF)][B$Ph_{4}$] 5, [U(($Cp^{∗}$$)_{2}$ ($O_{2}$CN$Me_{2}$)(THF)][B$Ph_{4}$] 6 and [U(($Cp^{∗}$$)_{2}$($\eta_{2}$-CON$Me_{2}$)(THF)][B$Ph_{4}$] 7. The crystal structure of a THF solvate of 4 has been determined.

Summary 2 laboratory-scale reactor systems suitable for gas phase, and for solution or slurry polymerisations are discussed. The underlying concept behind the design and use of these reactors is that they can be used to understand the impact of conditions specific to different time scales and/or length scales inherent to large reactors that are difficult to recreate at the laboratory scale. For instance the fixed bed gas phase reactor is used to study the influence of different relative gas/solid velocities on the evolution of the molecular weight distribution of the nascent polymer. It is shown that in certain conditions, changing the heat transfer characteristics does not change the observed yield, but will impact the polymer properties. In the case of the solution reactor, the concept is to design and use a reactor to study the activation of unsupported metallocenes. Here it is shown that different metallocenes have very different activation profiles to a point where a stopped flow reactor might not be the ideal tool for their study.

International audience; Polyethylenes and azide-terminated polyethylenes can be converted to macroradicals and nitrenes, respectively followed by addition reactions onto the unsaturated system of graphite oxide sheets. For the first time, the addition of these macroradicals to graphite oxide sheets was compared by performing grafting reactions at 190 degrees C in 1,2,4-trichlorobenzene as a solvent and at 100 degrees C followed by a solvothermal reduction at 150 degrees C in a solvent mixture of 1,4-dioxane and 1,2-dichlorobenzene. Dispersion of PE coated graphite oxide in a DMF-heptane mixture was utilised to follow the introduction of polyethylene onto the GO sheet surface while the thermogravimetric analysis indicated the extent of this grafting. The grafting ratio was found to be in the 1.5 wt% range and despite this low grafting content, the amount of grafted PE was high enough to dramatically improve the affinity of GO with the heptane phase in the DMF-heptane (50/50 v/v) mixture. Polyethylene functionalised GO was imaged by scanning electron microscopy showing a significant difference in morphology between the two grafting paths. It was found that a higher level of grafting was obtained using a radical grafting reaction in the presence of benzoyl peroxide rather than the thermal cleavage of PE-N-3 onto GO while a similar grafting content was obtained with the thermal cleavage of PE-N-3 onto GO grafted trimethoxy(7-octen-1-yl)silane.

International audience; Enhanced spin capturing polymerization (ESCP)-a recent and versatile technique in the field of controlled radical polymerization-achieves control over molecular weights and the synthesis of complex copolymer structures for a wide range of monomers. In the present work, the use of ESCP was extended to the radical polymerization of ethylene under mild conditions (low temperature and medium ethylene pressure) using a nitrone as spin trapping agent. It was demonstrated that the evolution of polyethylene (PE) molecular weight can be accurately described by classical ESCP kinetic equations. A PE bearing a midchain alkoxyamine function was thus obtained with high selectivity (90%). A more complex structure was produced from the radical polymerization of ethylene in the presence of a midchain alkoxyamine-functionalized polystyrene (PS) synthesized by ESCP in the form of ABA triblock copolymer (where A is polystyrene and B polyethylene).

International audience; Thiol end functionalized polyethylenes (PE-SH, Mn around 1000 g mol−1, Đ \textless 1.3) were used as nucleophiles in thia-Michael additions with different acrylic molecules. It was found that under commonly used practical conditions the addition to methacrylates was very difficult, whereas addition to acrylates was very efficient. First, block copolymers based on PE and poly(methyl methacrylate) (PMMA) were targeted by reaction of PE-SH with PMMA obtained by catalytic chain transfer polymerization (CCTP). The reaction however failed and detailed model experiments using butanethiol and a dimer of MMA showed that the solubilization temperature of PE-SH was an impediment to the success of the reaction. The lack of reactivity towards PMMA obtained by CCTP and methacrylate functions was advantageously used to react molecules containing both an acrylate and a methacrylate group in the presence of tributyl phosphine (PBu3) to produce methacrylate-type PE macromonomers. The presence of a hydroxyl function on 3-(acryloyloxy)-2-hydroxypropyl methacrylate induced side trans-esterification reactions catalyzed by PBu3. This was overcome by using the hydroxyl free 2-(acryloyloxy) ethyl methacrylate. With the latter, the desired PE macromonomer exhibited a functionality as high as 85%. Alternatively, 2-isocyanatoethyl methacrylate could also be reacted with PE-SH to produce a highly functionalized methacrylate type PE macromonomer (functionality 89%). Eventually, the efficiency of the thia-Michael addition of PE-SH onto poly(ethylene glycol) acrylate (PEG-acrylate) was used to synthesize the PE-b-PEG block copolymer.

International audience; A poly(glycidyl methacrylate) (PGMA) synthesized by RAFT polymerization was spin-coated onto a silicon substrate to yield, after annealing and rinsing unreacted chains, covalently attached epoxy-containing PGMA pseudo-brushes. A tailor-made ω-amino-poly(ethylene) (Mn = 1040 g mol−1, PDI = 1.3) was then grafted in melt at 130 °C for 24 h by reaction between amine chain-ends and surface-tethered epoxy groups. After discarding unreacted poly(ethylene) chains by sonication and Soxhlet rinsing, the resulting poly(ethylene) brushes were characterized by scanning probe microscopy, water contact angle and neutron reflectivity measurements. The grafting of poly(ethylene) brushes to silicon substrates has thus been demonstrated for the first time and resulted in nanostructured grafted layers with homogeneous surface coverage.

Neutral NiII complexes, classically used for catalytic ethylene polymerization, can play an additional role as radical initiators of the homo- and copolymerizations of (meth)acrylates and styrene. Benefiting from this duality, the copolymerization of ethylene and various (meth)acrylates or styrene was successfully performed. Multiblock copolymers containing sequences of both ethylene and (meth)acrylates were prepared for the first time from an original dual radical/catalytic mechanism.

International audience; Synthesis of highly end-functionalized polyethylene chains was accomplished using both coordination chemistry and radical mediated thiol?ene chemistry. A vinyl end-terminated polyethylene (Mn =1440 g·mol?1, PDI = 1.8) with a functionalization rate of 100% was synthesized using a P,O-chelated catalyst [Ni\Ph2PC(COOEt)═C(C6H5)O\Ph(PPh3)]. Thiol?ene reactions were subsequently undertaken between vinyl-terminated polyethylene and the thiol-containing molecules thioglycolic acid, 2-mercaptoethanol, 1-thioglycerol, chloropropanethiol, and methyl thioglycolate. A range of end-functionalized polyethylenes was thus prepared using simple reaction conditions and exhibiting degrees of functionalization higher than 93%.

International audience; Nickel complexes [(X,O)NiR(PPh(3))] (X = N or P), designed for the polymerization of ethylene, were found to be efficient for the homo- and copolymerization of butylacrylate (BuA), methylmethacrylate (MMA), and styrene. Their role as a radical initiator was demonstrated from the calculation of the copolymerization reactivity ratios. It was shown that the efficiency of the radical initiation is improved by the addition of PPh3 to the nickel complexes as well as by increasing the temperature. The dual role of a nickel complex as radical initiator and catalyst was exploited to succeed in the copolymerization of ethylene with BuA and MMA. Multiblock copolymers containing sequences of both ethylene and polar monomers were thus prepared for the first time by a dual radical/catalytic mechanism.

International audience; Copolymers of ethylene with methyl methacrylate (EMMA) and butyl acrylate (EBA), which are of different average chemical composition and block lengths according to NMR analysis, were analyzed by size exclusion chromatography (SEC), differential scanning calorimetry (DSC), Crystallization Analysis Fractionation (CRYSTAF), and high performance liquid chromatography at high temperature (HT-HPLC). With CRYSTAF and DSC crystallizing fractions were detected only in some samples. HT-HPLC fractionated all the samples irrespective of their crystallinity. Homopolymers, PMMA and PE were also found in the copolymer samples of EMMA. EMMA and EBA were separated in HPLC according to the content of polar comonomer. A linear correlation between the MMA content and elution volume could not be established due to the presence of homopolymers as admixtures. In such a case the average chemical composition obtained by NMR does not correspond to the real chemical composition of the copolymers. Unlike EMMA the EBA samples eluted in single peaks, which was used for evaluation of their chemical composition distribution. The comparison of results obtained by fractionation via CRYSTAF and HT-HPLC clearly demonstrates the advantages of the chromatographic approach to study the chemical heterogeneity of olefin based copolymers.