Francesco Della Monica

Poly(lactide-co-ε-caprolactone) copolymers prepared using bis-thioetherphenolate group 4 metal complexes: synthesis, characterization and morphology

Titanium and zirconium complexes 1–3 (1 = (t-BuOS)2Ti(O-i-Pr)2; 2 = (t-BuOS)2Zr(O-t-Bu)2; 3 = (CumOS)2Zr(O-t-Bu)2) supported by two phenolate bidentate ligands (t-BuOS-H = 4,6-di-tert-butyl-2-phenylsulfanylphenol and CumOS-H = 4,6-di-cumyl-2-phenylsulfanylphenol) promoted the copolymerization of L-lactide with e-caprolactone. The reactivity displayed by the two monomers during the copolymerization experiments and the microstructure disclosed by 13C NMR analysis indicated a gradient distribution of the two monomers along the polymer chain. Copolymers with high e-caprolactone content showed a large scale formation of crystalline spherulites prone to perfection of the crystallinity upon thermal annealing at 50 °C. Differently L-lactide rich copolymers revealed a thin film morphology consisting of small rigid domains of L-lactide segments of about 15 nm embedded in a soft matrix of the counterpart. Copolymers with comparable mole fractions of the two monomers were entirely amorphous.

Glycidol: an Hydroxyl-Containing Epoxide Playing the Double Role of Substrate and Catalyst for CO2 Cycloaddition Reactions.

Glycidol is converted into glycerol carbonate (GC) by coupling with CO2 in the presence of tetrabutylammonium bromide (TBAB) under mild reaction conditions (T=60 °C, PCO2 =1 MPa) in excellent yields (99 %) and short reaction time (t=3 h). The unusual reactivity of this substrate compared to other epoxides, such as propylene oxide, under the same reaction conditions is clearly related to the presence of a hydroxyl functionality on the oxirane ring. Density functional theory calculations (DFT) supported by 1 H NMR experiments reveal that the unique behavior of this substrate is a result of the formation of intermolecular hydrogen bonds into a dimeric structure, activating this molecule to nucleophilic attack, and allowing the formation of GC. Furthermore, the glycidol/TBAB catalytic system acts as an efficient organocatalyst for the cycloaddition of CO2 to various oxiranes.

Rational design of nanoparticle/monomer interfaces: a combined computational and experimental study of in situ polymerization of silica based nanocomposites

Interfaces between methylmethacrylate monomers, oligomers and silica nanoparticles (NPs) were explored by molecular dynamics simulations, infrared and solid state nuclear magnetic resonance spectroscopy. This knowledge allowed the control of the structure of the interfaces by employment of MMA macromonomers, and the design of an improved process for in situ polymerizations with a remarkable increase of NP dispersion.

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

The synthesis of four new group 4 metal complexes 1–4 (1 = (t-BuOS)2TiCl2; 2 = (CumOS)2TiCl2; 3 = (t-BuOS)2Zr(CH2Ph)2; 4 = (CumOS)2Zr(CH2Ph)2) bearing two bidentate thioetherphenolate ligands (t-BuOS-H = 4,6-di-tert-butyl-2-phenylsulfanylphenol; CumOS-H = 4,6-bis-(α,α-dimethylbenzyl)-2-phenylsulfanylphenol) has been accomplished. These complexes exhibit fluxional behaviour in solution and this was revealed by VT 1H NMR and supported by density functional theory (DFT) calculations. All these complexes are active catalysts in ethylene polymerization, producing linear polyethylene. Notably, the zirconium complex 3 displays, under proper reaction conditions, very high activity (1422 kgPE molcat−1 bar−1 h−1), which compares well with that of the most active post-metallocene catalysts. Furthermore, propylene polymerization catalyzed by the titanium complex 1 yields atactic polypropylene, whereas the zirconium complexes 3 and 4 selectively produce oligopropylene with Schultz–Flory distribution. NMR analysis of the unsaturated chain ends in the latter samples provides evidence of a regioselective propagation reaction with a large preference for 1,2-monomer insertion. DFT calculations allowed the modelling of the elementary reaction steps, namely, the chain propagation reaction, β-hydrogen elimination and transfer, highlighting the importance of the flexibility and steric hindrance of the ancillary ligands in determining the high activity of the title catalysts.

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

The dichloro titanium complexes (OSSOtBu)TiCl2 (1) and (OSSOCum)TiCl2 (2) bearing o-phenylene-bridged OSSO-type ligands [OSSOtBu-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 C2 symmetric structure, whereas 2 shows an equilibrium between C2- and C1-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 Tm of 122 °C and Mw 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.