Aluminium complexes of phenoxy-azo ligands in the catalysis of -lactide polymerisation.

Fourteen new phenoxy-azo aluminium complexes comprising two series, namely, dimethyl{phenoxy-azo}aluminium complexes 1a-7a and monomethyl{phenoxy-azo}aluminium complexes 1b-7b, were successfully synthesised and characterised. The molecular structure of complex 4a, determined using X-ray diffraction analysis, displayed a distorted tetrahedral geometry. The H NMR spectrum of complex 5b revealed fluxional behaviour caused by isomeric transformation that occurs in the solution at room temperature.

Titanium Complexes of Salicylbenzoxazole and Salicylbenzothiazole Ligands for the Ring-Opening Polymerization of ε-Caprolactone and Substituted ε-Caprolactones and Their Copolymerizations.

Two series of titanium complexes, including salicylbenzoxazole titanium complexes (-) and salicylbenzothiazole titanium complexes (-), were successfully synthesized and characterized by NMR spectroscopy, elemental analysis, and X-ray diffraction crystallography (for and ). The H NMR spectra of complexes and reveal fluxional behavior in solution at room temperature, and the activation parameters were determined by lineshape analysis of variable-temperature (VT) NMR spectra in toluene-: for , Δ = 73.0 ± 1.

Titanium complexes of pyrrolylaldiminate ligands and their exploitation for the ring-opening polymerization of cyclic esters.

A series of six-coordinate titanium complexes 1-6 supported by pyrrolylaldiminate ligands were prepared via the reaction of 2 equivalents of ligands and Ti(OPr) in toluene at 70 °C. The X-ray structure of 2 revealed that the two ligands were κ-coordinated to the titanium center with the two pyrrole nitrogen atoms in trans positions and the two imine nitrogen atoms in cis positions. All complexes were active initiators for the ring-opening polymerization (ROP) of rac-lactide (rac-LA), ε-caprolactone (ε-CL), and three substituted ε-caprolactones (γ-methyl-ε-caprolactone (γMeCL), γ-ethyl-ε-caprolactone (γEtCL), and γ-phenyl-ε-caprolactone (γPhCL)).

Aluminium complexes containing salicylbenzothiazole ligands and their application in the ring-opening polymerisation of rac-lactide and ε-caprolactone.

Two series of aluminium complexes bearing salicylbenzothiazole ligands, namely four-coordinate aluminium complexes (1a-7a) and five-coordinate aluminium complexes (1b-7b), were synthesized and characterized by NMR spectroscopy, elemental analysis and X-ray diffraction crystallography (for 5a and 1b). Their application in the ring-opening polymerisation of rac-lactide and ε-caprolactone was studied with the aim of drawing comparisons to closely related aluminium salicylbenzoxazole complexes investigated previously. In the presence of benzyl alcohol, all complexes were active initiators and polymerisations were all well controlled and living.

Aluminum complexes containing salicylbenzoxazole ligands and their application in the ring-opening polymerization of rac-lactide and ε-caprolactone.

Two series of four-coordinate aluminum () and five-coordinate aluminum () complexes were successfully synthesized via the reactions between the corresponding salicylbenzoxazole ligands and 1 or 0.5 equivalents of AlMe3, respectively. The synthesized aluminum complexes were characterized by (1)H and (13)C NMR spectroscopy and elemental analysis.

Comparing a series of 8-quinolinolato complexes of aluminium, titanium and zinc as initiators for the ring-opening polymerization of rac-lactide.

The preparation and characterization of a series of 8-hydroxyquinoline ligands and their complexes with Ti(IV), Al(III) and Zn(II) centres is presented. The complexes are characterized using NMR spectroscopy, elemental analysis and, in some cases, by single crystal X-ray diffraction experiments. The complexes are compared as initiators for the ring-opening polymerization of racemic-lactide; all the complexes show moderate/good rates and high levels of polymerization control.

Monomethylaluminum and dimethylaluminum pyrrolylaldiminates for the ring-opening polymerization of rac-lactide: effects of ligand structure and coordination geometry.

Two series of aluminum alkyl complexes supported by pyrrolylaldiminate ligands, LAlMe2 (1a-7a) and L2AlMe (1b-7b), were successfully synthesized and characterized by NMR spectroscopy and elemental analysis. Reactions of trimethylaluminum with the corresponding pyrrolylaldiminate ligands in the molar ratios of 1 : 1 and 1 : 2 yielded dimethylaluminum pyrrolylaldiminates (1a-7a) and monomethylaluminum pyrrolylaldiminates (1b-7b), respectively, in good yields. The structure of 3b, determined by single-crystal X-ray diffraction, displayed a distorted trigonal bipyramidal geometry with the τ value of 0.

Electrical conductivity response of poly(phenylene-vinylene)/zeolite composites exposed to ammonium nitrate.

Poly(p-phenylenevinylene) (PPV) was chemically synthesized via the polymerization of p-xylene-bis(tetrahydrothiophenium chloride) monomer and doped with H(2)SO(4). To improve the electrical conductivity sensitivity of the conductive polymer, Zeolites Y (Si/Al = 5.1, 30, 60, 80) were added into the conductive polymer matrix.

Study of ligand substituent effects on the rate and stereoselectivity of lactide polymerization using aluminum salen-type initiators.

A series of aluminum salen-type complexes [where salen is N,N'-bis(salicylaldimine)-1,2-ethylenediamine] bearing ligands that differ in their steric and electronic properties have been synthesized and investigated for the polymerization of rac-lactide. X-ray crystal structures on key precatalysts reveal metal coordination geometries intermediate between trigonal bipyramidal and square-based pyramidal. Both the phenoxy substituents and the backbone linker have a significant influence over the polymerization.

Remarkable stereocontrol in the polymerization of racemic lactide using aluminum initiators supported by tetradentate aminophenoxide ligands.

A new family of aluminum complexes bearing tetradentate bis(aminophenoxide) ligands is reported and shown to initiate the living ring-opening polymerization of rac-lactide. The microstructures of the polylactide products are found to be highly dependent upon the ancillary ligand substituents, ranging from highly isotactic (Pm = 0.79) to very highly heterotactic (Pr = 0.