Active Ga-catalysts for the ring opening homo- and copolymerization of cyclic esters, and copolymerization of epoxide and anhydrides.

A series of gallium complexes L12Ga4Me8 (1), L22Ga4Me8 (2), and L32Ga4Me8 (3) was synthesized by reaction of GaMe3 with Schiff base ligands L1-3H2 (L1H2 = 2,4-di-tert-butyl-6-{[(3-hydroxypropyl)imino]methyl}phenol; L2H2 = 2,4-dichloro-6-{[(3-hydroxypropyl)imino]methyl}phenol; L3H2 = 4-tert-butyl-2-{[(3-hydroxypropyl)imino]methyl}phenol) and characterized by 1H, 13C NMR, IR spectroscopy, elemental analysis and single crystal X-ray analysis (1, 2), proving their tetranuclear structure in the solid state. Complexes 1-3 showed good catalytic activity in the ring opening homopolymerization (ROP) and ring opening copolymerization (ROcoP) of lactide (LA) and ε-caprolactone (ε-CL) in the presence of benzyl alcohol (BnOH) in toluene at 100 °C, yielding polymers with the expected average molecular weights (Mn) and narrow molecular weight distributions (MWD), as well as a high isoselectivity for the ROP of rac-lactide (rac-LA), yielding isotactic-enriched PLAs with Pm values up to 0.78. Kinetic studies with complex 1 proved the first order dependence on monomer concentration, while mechanistic studies confirmed the coordination insertion mechanistic (CIM) pathway. Sequential addition of monomers gave well defined diblock copolymers of PCL-b-PLLA and PLLA-b-PCL, proving the living character of the polymerization reactions. The catalysts also showed perfect selectivity for the copolymerization of cyclohexene oxide (CHO) with both succinic anhydride (SA) and maleic anhydride (MA) in the presence of BnOH and produced >99% alternating block copolymers.

Terpolymer Multicompartment Nanofibers as Templates for Hybrid Pt Double Helices.

Hybrid inorganic/block copolymer (BCP) materials have become increasingly relevant for application in heterogeneous catalysis, microelectronics, and nanomedicine. While block copolymer templates are widely used for the formation of inorganic nanostructures, multicompartment templates could give access to more complex shapes and inner structures that are challenging to obtain with traditional processes. Here, we report the formation and characterization of hybrid platinum/polymer helices using multicompartment nanofibers (MCNFs) of polystyrene-block-polybutadiene-block-poly(tert-butyl methacrylate) (PS-b-PB-b-PT) triblock terpolymers as templates. Cross-linking of a PS-b-PB-b-PT helix-on-cylinder morphology resulted in uniform nanofibers with a diameter of 90 nm and a length of several micrometers, as well as an inner PB double helix (diameter 35 nm, pitch 25 nm, core 12 nm). The PB double helix served as template for the sol-gel reaction of H2PtCl6 into hybrid Pt double helices (Pt@MCNFs) as verified by STEM, electron tomography, AFM, and SEM. Carbonization of the Pt hybrids into Pt decorated carbon nanofibers (Pt@C) was followed in situ on a TEM heating state. Gradual heating from 25 to 1000 °C induced fusion of amorphous Pt NPs into larger crystalline Pt NP, which sheds light on the aging of Pt NPs in BCP scaffolds under high temperature conditions. The Pt@MCNFs were further sulfonated and incorporated into a filter to catalyze a model compound in a continuous flow process.

Syntheses, structures and catalytic activity of tetranuclear Mg complexes in the ROP of cyclic esters under industrially relevant conditions.

Four tetranuclear magnesium complexes were synthesized and fully characterized. They are excellent catalysts for the ring-opening polymerization (ROP) of bulk racemic-lactide (rac-LA) and ε-caprolactone (ε-CL) even with low catalyst loading under industrially relevant conditions without additional co-initiators, yielding polymers with high molecular weight (Mn) and moderately controlled molecular weight distribution (MWD). The polymerization activity depends on the steric and electronic properties of the imino(phenolate) ligands. Kinetic studies of the most active catalyst 1 confirmed that the ROP of rac-LA and ε-CL has a first order dependence on monomer concentration. The ROP of rac-LA and ε-CL using 1-4 with BnOH gave polymers with narrow MWD and a close correlation between Mobsn and Mtheon values. Catalyst 1 was also capable of polymerizing technical-grade rac-LA and ε-CL even with large monomer-to-catalyst ratios ([M]0/[C]0) of up to 10 000 : 1 and without any additional co-initiator. The very high turnover frequencies (TOF) of 9600 h-1 (rac-LA) and 24 000 h-1 (ε-CL) prove that 1 belongs to the most active biocompatible, sustainable and nontoxic ROP catalysts under industrially relevant conditions.

Heterolepic ß-Ketoiminate Zinc Phenoxide Complexes as Efficient Catalysts for the Ring Opening Polymerization of Lactide.

Zinc phenoxide complexes L1ZnOAr 1-4 (L1=Me2NC2H4NC(Me)CHC(Me)O) and L2ZnOAr 5-8 (L2=Me2NC3H6NC(Me)CHC(Me)O) with donor-functionalized ß-ketoiminate ligands (L1/2) and OAr substituents (Ar=Ph 1, 5; 2,6-Me2-C6H3 2, 6; 3,5-Me2-C6H3 3, 7; 4-Bu-C6H4 4, 8) with tuneable electronic and steric properties were synthesized and characterized. 1-8 adopt binuclear structures in the solid state except for 5, while they are monomeric in CDCl3 solution. 1-8 are active catalysts for the ring opening polymerization (ROP) of lactide (LA) in CH2Cl2 at ambient temperature and the catalytic activity is controlled by the electronic and steric properties of the OAr substituent, yielding polymers with high average molecular weight (M n) and moderately controlled molecular weight distribution (MWDs). 1 and 5 showed a living polymerization character and kinetic studies on the ROP of L-LA with 1 and 5 proved first order dependencies on the monomer concentration. Homonuclear decoupled 1H-NMR analyses of polylactic acid (PLA) formed with rac-LA proved isotactic enrichment of the PLA microstructure.