Binary Copolymerization of p-Methylstyrene with Butadiene and Isoprene Catalyzed by Titanium Compounds Showing Different Stereoselectivity

Micro(nano)plastics from synthetic oligomers persisting in Mediterranean seawater: Comprehensive NMR analysis, concerns and origins

The presence in seawater of low-molecular-weight polyethylene (PE) and polydimethylsiloxane (PDMS), synthetic polymers with high chemical resistance, has been demonstrated in this study for the first time by developing a novel methodology for their recovery and quantification from surface seawater. These synthetic polymer debris (SPD) with very low molecular weights and sizes in the nano- and micro-metre range have escaped conventional analytical methods. SPD have been easily recovered from water samples (2 L) through filtration with a nitrocellulose membrane filter with a pore size of 0.45 μm. Dissolving the filter in acetone allowed the isolation of the particulates by centrifugation followed by drying. The isolated SPD were analysed by 1H nuclear magnetic resonance spectroscopy (1H NMR), identifying PE and PDMS. These polymers are thus persisting on seawater because of their low density and the ponderal concentrations were quantified in mg/m3. This method was used in an actual case study in which 120 surface seawater samples were collected during two sampling campaigns in the Mediterranean Sea (from the Gulf of Salerno to the Gulf of Policastro in South Italy). The developed analytical protocol allowed achieving unprecedented simplicity, rapidity and sensitivity. The 1H and 13C NMR structural analysis of the PE debris indicates the presence of oxidised polymer chains with very low molecular weights. Additionally, the origin of those low molecular weight polymers was investigated by analysing influents and effluents from a wastewater treatment plant (WWTP) in Salerno as a hot spot for the release of SPD: the analysis indicates the presence of low molecular weight polymers compatible with wax-PE, widely used for coating applications, food industry, cosmetics and detergents. Moreover, the origin of PDMS debris found in surface seawater can be ascribed to silicone-based antifoamers and emulsifiers.

3,4-Enhanced Polymerization of Isoprene Catalyzed by Side-Arm Tridentate Iminopyridine Iron Complex with High Activity: Optimization via Response Surface Methodology

3,4-Enhanced polymerization of isoprene catalyzed by late transition metal with high activity remains one of the great challenges in synthetic rubber chemistry. Herein, a library of [N, N, X] tridentate iminopyridine iron chloride pre-catalysts (Fe 1-4) with the side arm were synthesized and confirmed by the element analysis and HRMS. All the iron compounds served as highly efficient pre-catalysts for 3,4-enhanced (up to 62%) isoprene polymerization when 500 equivalent MAOs were utilized as co-catalysts, delivering the corresponding high-performance polyisoprenes. Furthermore, optimization via single factor and response surface method, it was observed that the highest activity was obtained by complex Fe 2 with 4.0889 × 10⁷ g·mol(Fe)^-1·h^-1 under the following conditions: Al/Fe = 683; IP/Fe = 7095; t = 0.52 min.

Isospecific Polymerization of Halide- and Amino-Substituted Styrenes Using a Bis(phenolate) Titanium Catalyst

Isospecific polymerization of polar styrenes is a challenge of polymer science. Particularly challenging are monomers bearing electron-withdrawing substituents or bulky substituents. Here, we report the coordination polymerization of halide- and amino-functionalized styrenes including para-fluorostyrene (pFS), para-chlorostyrene (pClS), para-bromostyrene (pBrS), and para-(N,N-diethylamino)styrene (DMAS) using 2,2′-sulfur-bridged bis(phenolate) titanium precursor (1). The combination of 1 and [Ph3C][B(C6F5)4] and AliBu3 provides crystalline poly(pFS)s with perfect isotacticity (mmmm > 95%) and high molecular weights (≤16.0 × 104 g mol−1). Upon activation with a large excess of DMAO, 1 reaches polymerization activity of 5.58 × 105 g molTi−1 h−1 producing isotactic poly(pFS)s featuring higher molecular weights (≤39.6 × 104 g mol−1). The distinguished performance of the 1/DMAO system has been extended to the polymerization of pClS and pBrS, both usually involve halogen abstraction during the polymerization, to produce isotactic and high molecular weight (Mn = 32.2 × 104 vs. 13.7 × 104 g mol−1) polymers in good activities (2.18 × 105 vs. 1.31 × 105 g molTi−1 h−1). Surprisingly, 1/DMAO is nearly inactive for DMAS polymerization, on contrary, the system 1/[Ph3C][B(C6F5)4]/AliBu3 displays isoselectivity (mmmm > 95%) albeit in a moderate activity.

[OSSO]-Type Chromium(III) Complexes for the Reaction of CO2 with Epoxides

In this work, four new mononuclear Cr(III) complexes (2-5) bearing bis-thioether-diphenolate, [OSSO]-type ligands, were synthesized and characterized. These complexes in combination with bis(triphenylphosphine)iminium chloride (PPNCl) promoted the coupling of CO2 with epoxides. Depending on the type of substrate and the conditions, the reaction results in the selective formation of either polycarbonate or cyclic carbonate. For example, the reactions in the presence of complex 2 led to the exclusive formation of poly(cyclohexene carbonate, PCHC) from cyclohexene oxide (CHO) (TOF up to 39 h-1 , at T=45-100 °C, time=24 h, pCO2 =20 bar, epoxide/2 (mol/mol)=1000, and PPNCl/2=0.5-2.0 mol %). Under the same conditions and PPNCl/2=0.5-5.0 mol %, the reactions of CO2 with styrene oxide (SO), epichlorohydrin (ECH), 1,2 epoxydodecane (EDD), and allyl glycidyl ether (AGE) have shown selective conversion to the corresponding cyclic carbonates (TOF up to 41 h-1 ).

Metal Complexes Bearing Sulfur-Containing Ligands as Catalysts in the Reaction of CO2 with Epoxides

Coupling of CO2 with epoxides is a green emerging alternative for the synthesis of cyclic organic carbonates (COC) and aliphatic polycarbonates (APC). The scope of this work is to provide a comprehensive overview of metal complexes having sulfur-containing ligands as homogeneous catalytic systems able to efficiently promote this transformation with a concise discussion of the most significant results. The crucial role of sulfur as the hemilabile ligand and its influence on the catalytic activity are highlighted as well.

A Novel [OSSO]-Type Chromium(III) Complex as a Versatile Catalyst for Copolymerization of Carbon Dioxide with Epoxides

A new chromium(III) complex, bearing a bis-thioether-diphenolate [OSSO]-type ligand, was found to be an efficient catalyst in the copolymerization of CO₂ and epoxides to achieve poly(propylene carbonate), poly(cyclohexene carbonate), poly(hexene carbonate) and poly(styrene carbonate), as well as poly(propylene carbonate)(cyclohexene carbonate) and poly(propylene carbonate)(hexene carbonate) terpolymers.

Carbazolyl-Substituted [OSSO]-Type Zirconium(IV) Complex as a Precatalyst for the Oligomerization and Polymerization of α-Olefins

The dibenzyl zirconium(IV) complex (4) incorporating with a carbazolyl(Cbz)-substituted [OSSO]-type bis(phenolate) ligand was synthesized. Upon activation with dried modified methylaluminoxane (dMMAO), precatalyst 4 at relatively low catalyst loadings was found to promote the 1,2-regioselective oligomerization of 1-hexene to produce the corresponding vinylidene-ended oligomers with moderate turnover frequencies (TOFs) up to 2080 h−1. The 13C NMR analysis of the resulting oligomers revealed the formation of dimer-enriched oligo(1-hexene)s in 39–62% distributions. The precatalyst 4 with dried methylaluminoxane (dMAO) also exhibited good performance in the polymerization of styrene yielding isotactic polystyrenes ([mm] > 99%) with quite large molecular weights (Mw < 508,100 g mol−1) and relatively high catalytic activity (up to 2810 g mmol(4)−1 h−1).

Phenylene-Bridged OSSO-Type Titanium Complexes in the Polymerization of Ethylene and Propylene

The dichloro titanium complexes (OSSO tBu)TiCl2 (1) and (OSSOCum)TiCl2 (2) bearing o-phenylene-bridged OSSO-type ligands [OSSO tBu-H = 6,6'-((1,2-phenylenebis(sulfanediyl))bis(methylene))bis(2,4-di-tert-butyphenol) and OSSOCum-H = 6,6'-((1,2-phenylenebis(sulfanediyl))bis(methylene))bis(2,4-bis(2-phenylpropan-2-yl)phenol)] were prepared and characterized. The X-ray structure of 1 revealed that Ti atom has an octahedral coordination geometry with an fac-fac wrapping of the [OSSO] ligand. In solution at 25 °C, 1 mainly retains the C 2 symmetric structure, whereas 2 shows an equilibrium between C 2- and C 1-symmetric stereoisomers. Activation of 2 with (Ph3C)[B(C6F5)4] led to a highly active catalytic system with an activity of 238 kgPE·molcat -1·bar-1·h-1; linear polyethylene with a T m of 122 °C and M w of 107 kDa were obtained under these conditions. Catalyst 1 displayed the moderate activity of 59 kgPE·molcat -1·bar-1·h-1. Gel permeation chromatography analysis revealed the formation of high-molecular-weight polyethylenes with very large distributions of the molecular weights, indicating a low control of the polymerization process, probably becaue of the presence of different active species in solution. Density functional theory investigation provides a rational for the relative high-molecular-weight polymers obtained with these complexes. The precatalyst 2 was also active in propylene polymerization producing atactic oligomers terminated with unsaturated end groups.

Aerobic Oxidation and Oxidative Esterification of 5-Hydroxymethylfurfural by Gold Nanoparticles Supported on Nanoporous Polymer Host Matrix

The aerobic oxidation and oxidative esterification of 5-hydroxymethylfurfural (HMF) catalyzed by gold nanoparticles (AuNPs) supported on a semicrystalline nanoporous multiblock copolymer matrix consisting of syndiotactic poly(styrene)-cis-1,4-poly(butadiene) (sPSB) have been investigated. Depending on the reaction parameters (support nanoporosity, presence of water, solvent, temperature, cocatalyst, oxygen pressure), the conversion of HMF can be finely addressed to the formation of the desired oxidation product, such as 2,5-diformylfuran (DFF), 5-formylfuran-2-carboxylic acid (FFCA), methyl 5-(hydroxymethyl)furan-2-carboxylate (MHMFC), dimethyl furan-2,5-dicarboxylate (DMFC), and furan-2,5-dicarboxylic acid (FDCA), under optimized reaction conditions. The AuNP-sPSB catalyst is highly effective and selective because the polymer support acts as a conveyor and concentrator of the reactants toward the catalytic sites.

Synthesis and structural characterization of zirconium complexes supported by tridentate pyrrolide-imino ligands with pendant N-, O- and S-donor groups and their application in ethylene polymerization

Zirconium complexes supported by pyrrolide-imino ligands been synthesized and their catalytic behavior in ethylene polymerization has been investigated.

Convenient synthesis of versatile syndiotactic polystyrene materials containing pendant alkenyl groups with a scandium catalyst system

The syndioselective copolymerization of styrene with five alkenyl functionalized styrenic monomers, with the use of a scandium catalyst, produced a new family of versatile syndiotactic polystyrene materials with pendant alkenyl groups.

Engineering of Syndiotactic and Isotactic Polystyrene-Based Copolymers via Stereoselective Catalytic Polymerization

This contribution presents an updated overview of the different copolymers containing stereoregular polystyrene blocks. Special emphasis is placed on syndiospecific and isospecific copolymerization of styrene with co-monomers (ethylene and α-olefins, conjugated and non-conjugated dienes, styrene derivatives, etc.). The catalytic systems involved are described and the polymerization mechanisms are discussed. Alternative approaches (simultaneous, living, chain-transfer and graft copolymerization) and the resulting detailed structures and characteristics of the copolymers are also reported.

Synthesis of novel copolymers based on p-methylstyrene, N,N-butylvinylimidazolium and polybenzimidazole as highly conductive anion exchange membranes for fuel cell application

A series of copolymers based N,N-butylvinylimidazolium, p-methylstyrene and polybenzimidazole as anion exchange membrane materials VIBx/PMSy/PBIz.

Influences of Alkyl and Aryl Substituents on Iminopyridine Fe(II)- and Co(II)-Catalyzed Isoprene Polymerization

A series of alkyl- and aryl-substituted iminopyridine Fe(II) complexes 1a⁻7a and Co(II) complexes 2b, 3b, 5b, and 6b were synthesized. The activator effect, influence of temperature, and, particularly, the alkyl and aryl substituents' effect on catalytic activity, polymer molecular weight, and regio-/stereoselectivity were investigated when these complexes were applied in isoprene polymerization. All of the Fe(II) complexes afforded polyisoprene with high molecular weight and moderate cis-1,4 selectivity. In contrast, the Co(II) complexes produced polymers with low molecular weight and relatively high cis-1,4 selectivity. In the iminopyridine Fe(II) system, the alkyl and aryl substituents' effect exhibits significant variation on the isoprene polymerization. In the iminopyridine Co(II) system, there is little influence observed on isoprene polymerization by alkyl and aryl substituents.

Stereoselective copolymerization of amino-functionalized styrene with butadiene using a half-sandwich scandium complex

Stereoselective copolymerization of amino-functionalized styrene with butadiene was conducted and the influence of amino groups on the copolymerization performance was investigated.

Styrene–isoprene and styrene–1,3-pentadiene copolymerisation catalyzed by titanium [OSSO]-type catalysts

Titanium [OSSO]-type catalysts promote the copolymerization of styrene with isoprene and 1,3-pentadiene giving copolymers in a wide range of compositions.

Polymerization of ethylene and propylene promoted by group 4 metal complexes bearing thioetherphenolate ligands

New group 4 complexes with OS ligands promote the polymerization of ethylene and propylene giving linear polyethylene and atactic polypropylene or oligopropene, respectively.

Nanostructured ethylene–styrene copolymers

A judicious choice of a polyinsertion catalyst and monomer feed composition allows the one-pot synthesis of ethylene–styrene copolymers with an unprecedented structure, containing an isotactic polystyrene (iPS) block joined to an isotactic ethylene-alt-styrene sequence (iP(E-alt-S)).