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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; Chemistry, Catalysis, Polymers and Processes (C2P2), 43 Bd du 11 Novembre 1918, 69616 Villeurbanne, France metallocene • d 0 metal complexes • butadiene • polymerization • speciation • ion pairing • reactivity • DFT

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.

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 SiO 2 /MgCl 2-bisupported Ziegler−Natta-type catalyst is studied in gas-phase ethylene/1-butene copolymerization. With a minimal amount of alkylaluminum required to activate the catalyst, polymerization kinetics is profoundly affected by the dosage of it. High dosage of alkylaluminum retards the polymerization but does not kill the catalyst. Through a comprehensive characterization on the samples by differential scanning calorimetry, crystallization elution fractionation, thermal gradient interaction chromatography, cross-fractiona-tion chromatography, and nuclear magnetic resonance, it has been shown that alkylaluminum also alters the short-chain branching distribution (SCBD) of the copolymer but barely affects the total comonomer incorporation. It is proposed that alkylaluminum alters the active species from producing statistical copolymer chains to producing block polymer chains with C4-enriched and C4-scattered segments. It provides an example of a bimetallic structure of active species as well as an approach to tailor SCBD between a statistical copolymer and block copolymer bearing C4-enriched and C4-scattered segments.

International audience; The reactivity of a phenoxy-imine-ether system (FI)TiCl3/MAO was studied toward selective ethylene trimerization. This system was shown to either trimerize or polymerize ethylene depending on the reaction temperature. Its selectivity switches from a significant production of the trimerization product, 1-hexene (85 wt %, 520-450 kg1-hexene gTi-1 h-1) between 30 and 40 °C, to a moderate polyethylene formation (70-80 wt %, 60-70 kgpolyethylene gTi-1 h-1) at higher reaction temperature (T > 60 °C). Polymerization was investigated based on an original "polymer-to-catalyst" strategy aiming at identifying the active species responsible for this side reaction. Using DSC, SEC and high temperature 13 C NMR analyses, polyethylenes were found to exhibit high molar masses (> 10 5 g mol-1) and a low 1-hexene content (< 1 mol %) at any temperature. Kinetic studies support that trimerization and polymerization species are generated from the catalyst precursor at 40 °C but a parallel process may occur at higher temperature. The increase dispersity to 4.6 at 80 °C suggests a change from single to multisite catalysis. The poor comonomer incorporation ability of the active species is reminiscent of a molecular Ziegler Natta or a bulky postmetallocene catalyst.

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; Copolymers of ethylene and butadiene were prepared using the ansa-bisfluorenyl Me2Si(C13H8)2NdR complex in combination with dialkylmagnesium as a chain transfer agent. Thorough kinetic studies and computational mechanistic investigations of this copolymerization reaction were performed. Combined with detailed analyses of the polymer microstructure and chain-ends, these studies demonstrate that the entitled copolymerization operates according to a living coordinative chain transfer copol-ymerization of ethylene and butadiene. Besides, in addition to the formation of the previously described 1,2-cyclohexane inner chain cyclic motif, the presence of bicyclic 1,5-decalin units via the formation of transient vinylcyclohexyl-methyl chain-end is discussed in the present communication. The non-accumulation of the vinylcyclohexane motif within the chains is explained by the reversibility of its formation, as interpreted with the help of DFT calculations, or by its rapid conversion into decalin motif after one ethylene insertion. Finally, this study also illustrates the ability of the fluorenyl ligand to adjust its binding mode on demand in order to avoid inhibition of catalyst.

International audience; While the introduction of polymers in aerogels strongly enhances their toughness, truly elastic monolithic aerogels able to restore their dimensions upon extensive compression are still challenging to synthesize. In this context hydrophobic semi-crystalline polymers with low glass transition temperatures that combine both stiffness and flexibility have only recently gained attention. We show that polyethylene aerogels with low density combining chemical crosslinking and high crystallinity display high moduli and excellent mechanical resilience. In order to maximize the crystallinity of these aerogels while maintaining a high crosslinking density, we synthesized polyethylene networks with well-defined segments by hydrosilylation-crosslinking of telechelic, vinyl-functionalized oligomers obtained from recent advances in catalyzed chain growth polymerization. Recoverable deformations both above and below the melting temperature of polyethylene affords remarkable shape-memory properties.

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

Accurately measuring mol. kinetics of catalytic olefin polymn. has been a challenging objective. Many methods have been proposed in the literature, but all of them have drawback(s)​. In this paper, we introduce a labeling method to count active sites employing Me propargyl ether (MPE) as the quench-​labeling agent. It is com. available, does not react with Al-​alkyl species, and has a labeling efficiency close to 100​%. The labeling reaction was evidenced by a mechanistic study on the reaction between the model system Cp2ZrMe2/MAO (Cp = cyclopentadienyl) and MPE that it may occur through a coordination-​insertion mechanism without noticeable multiple insertions. The method was benchmarked by studying a MgCl2-​supported Ziegler-​Natta catalyst in 1-​hexene polymn. The fraction of the active transition metal χ* is found to be

International audience; The synthesis and characterization of silica-grafted monopodal and bipodal aluminum hydrides has been achieved starting from 200 °C- and 700 °C-annealed silica and [AlH3(NMe2Et)]. The mechanism by which aluminum trishydride reacts with isolated and vicinal silanols, assisted by the amine, has been investigated computationally at the ωB97XD-DFT level.

Leaching of (n-BuCp)2ZrCl2/MAO catalyst from silica supports has been studied in slurry phase ethylene homopolymerisation by changing i) the polymerization protocol, ii) aluminum alkyl scavengers and iii) by adding butylated hydroxytoluene (BHT-H) along with aluminum alkyl scavengers. The impact of these three variations on the ethylene polymerization kinetics of the said metallocene/MAO/silica catalyst is also analyzed. The obtained results show that (n-BuCp)2ZrCl2/MAO does not leach from the silica support if pre-contact between the heterogeneous catalyst and aluminum alkyl scavenger is avoided. Furthermore, the addition of equimolar amounts of BHT-H and triisobutylaluminum (TIBA) into the reaction milieu generates Al(i-Bu)BHT2 which appears to be a non-interacting scavenger leading to no catalyst leaching (and therefore, no reactor fouling). This observation has been made by pre-contacting and avoiding the pre-contact between the silica supported (n-BuCp)2ZrCl2/MAO catalyst and the reaction mixture containing equimolar amounts of BHT-H and TIBA followed by the analysis of reactor conditions as well as the obtained polyethylene morphology. Molecular and physical properties of HDPE remain very similar by changing the polymerization protocol or the aluminum alkyl scavenger or by using BHT-H.

The multistep synthesis of a polyethylene-supported iridium(III)-(N-heterocyclic carbene) hydrogen/deuterium exchange catalyst was performed starting from an iodo-polyethylene obtained via catalyzed polyethylene chain growth (CCG) on magnesium. Unique thermomorphic polyethylene properties give the possibility to perform catalytic hydrogen/deuterium exchange reactions at 100 °C in the homogeneous phase with simple catalyst separation as a precipitate at room temperature. The catalytic activity of the polymer-supported catalyst was compared with that of its monomeric analogue. The catalytic studies showed that the supported catalyst exhibits similar profiles and turnover numbers as homogeneous counterparts without deactivation.

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.

International audience

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.

The size of a silica supported metallocene/MAO (methylaluminoxane) catalyst plays an important role in determining its productivity during ethylene polymerization. From a chemical engineering point of view, this size dependency of catalytic activity of supported metallocenes is mathematically connected with the different levels of mass-transfer resistance in big and small catalyst particles but no experimental evidence has been provided to date. The results of this systematic experimental study clearly demonstrate that the intraparticle monomer diffusion resistance is high in bigger catalyst particles during initial instants of ethylene polymerization and diminishes with the polymer particle growth. Two different silica supported metallocene/MAO catalysts provided the same results while highlighting the fact that catalyst chemistry should be carefully considered while studying complex chemical engineering problems. © 2017 American Institute of Chemical Engineers AIChE J, 63: 4476–4490, 2017

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

This paper reports the principal discoveries which have played a major role in the polyolefin field and have positioned polyolefins as the most produced plastics. The early development of polyolefins covering the production of LDPE (Low density polyethylene) at ICI (Imperial Chemical Industries) and the discovery of Phillips or Ziegler-Natta catalysts are highlighted in the first section. In the second part, the impact of the implementation of molecular catalysts on the research in polyolefins is discussed together with the most recent advances leading to high-performance tailor-made resins.

Fluorinated activating supports (AS) for metallocene complexes were prepared via treatment of silica with AlEt3 or AlEt2F followed by pyrolysis and combustion steps, and a subsequent fluorination step when AlEt3 was used. This new family of activators appears to be universal for metallocene complexes leading to catalysts displaying high activities in ethylene polymerization without the addition of MAO. A productivity of 3200 g gAS–1 was obtained in 1 h with the catalyst rac-Et(Ind)2ZrCl2/AS8/Al(iBu)3 at 80 °C under 10 bar of ethylene. An isotactic polypropylene with a melting transition at 145 °C was prepared using rac-Me2Si(2-Me-benz(e)Ind)2ZrCl2 activated by AS9 and Al(iBu)3. The spherical particle morphology of polyolefins was particularly adapted to slurry processes employed in industry.

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.

International audience; Ethylene/butadiene copolymerization can be performed by neodymocene catalysts in the presence of an alkylating/chain transfer agent. A variety of polymerization activities and copolymer microstructures can be obtained depending on the neodymocene ligands. For a set of four catalysts, namely (C5Me5)2NdR, [Me2Si(3-Me3SiC5H3)2]NdR, [Me2Si(C5H4)(C13H8)]NdR and [Me2Si(C13H8)2]NdR, we report a DFT mechanistic study of this copolymerization reaction performed in the presence of dialkylmagnesium. Based on the modeling strategy developed for the ethylene homopolymerization catalyzed by (C5Me5)2NdR in the presence of MgR2, our model is able to account for the following: (i) the formation of Nd/Mg heterobimetallic complexes as intermediates, (ii) the overall differential activity of the catalysts, (iii) the copolymerization reactivity indexes, and (iv) the specific microstructure of the resulting copolymers, including branching and cyclization. The analysis of the reaction mechanisms and the energy profiles thus relates ligand structure, catalyst activity, and polymer microstructure and sets the basis for further catalyst developments.

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; Ethylene polymerizations were performed in toluene using the neodymocene complex (C5Me5)2NdCl2Li(OEt2)2 or {(Me2Si(C13H8)2)Nd(μ-BH4)[(μ-BH4)Li(THF)]}2 in combination with n-butyl-n-octylmagnesium used as both alkylating and chain transfer agent. The kinetics were followed for various [Mg]/[Nd] ratios, at different polymerization temperatures, with or without ether as a cosolvent. These systems allowed us to (i) efficiently obtain narrowly distributed and targeted molar masses, (ii) characterize three phases during the course of polymerization, (iii) estimate the propagation activation energy (17 kcal mol–1), (iv) identify the parameters that control chain transfer, and (v) demonstrate enhanced polymerization rates and molar mass distribution control in the presence of ether as cosolvent. This experimental set of data is supported by a computational investigation at the DFT level that rationalizes the chain transfer mechanism and the specific microsolvation effects in the presence of cosolvents at the molecular scale. This joint experimental/computational investigation offers the basis for further catalyst developments in the field of coordinative chain transfer polymerization (CCTP).

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...

In slurry and gas phase catalytic ethylene polymerization processes, aluminum alkyl (AlR3) compounds are usually present inside the reactor and their role either as co-catalyst or scavenger is of considerable importance. Silica supported metallocene/methyl aluminoxane (MAO) catalysts show specific interactions with AlR3 compounds. Therefore, this study shows an attempt to analyze and compare the effect of concentration as well as type of commonly used AlR3 on slurry phase ethylene homopolymerization kinetics of silica supported (n-BuCp)2ZrCl2/MAO catalyst. The obtained results indicate that the lower the concentration of smaller AlR3 compounds, the higher the instantaneous catalytic activity. Concerning the polymer particle size distributions, a rise in fines generation has been observed with increasing AlR3 content inside the reactor. Finally, it has been shown that the addition of 2,6-di-tert-butyl-4-methylphenol (a substituted phenol) into the reactor containing AlR3 reduces the influence of AlR3 compounds on the reaction kinetics of silica supported metallocene/MAO catalysts. Polyethylene properties remain similar in all the studied scenarios. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45670.

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.

Despite the fact that the very early stages (several tens of seconds) of catalysed olefin polymerisation processes appear negligibly short with respect to the residence time of most industrial reactors, they are critical in terms of catalyst activation, obtaining good particle morphology, and avoiding irreparable problems caused by particle overheating. The different types of reactors that have been used over the course of the past few years are discussed in this feature article. It is shown that despite the difficulties encountered in finding the perfect experimental tool for this purpose, different configurations of stopped flow reactors can be used successfully to explore different aspects of what happens to the catalyst (supported and molecular) during these critical moments of polymerisation. © 2012 Canadian Society for Chemical Engineering

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).