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A stereoselective, solvent-free ring-opening polymerisation (ROP) of lactide (LA) in supercritical carbon dioxide (scCO2) is reported for the first time. The key aim is to exploit scCO2 to lower the temperature of traditional melt polymerisations, lowering the energy requirement and leading to cleaner polymeric materials. We have utilised a zirconium amine-trisphenolate initiator-stereoselective catalyst [(iPrO)Zr(OPh(tBu)2-CH2)3N] to yield highly heterotactic poly(lactide) (PLA) homopolymer (Pr = 0.74–0.84) from rac-LA, demonstrating control of the PLA microstructure in scCO2. In addition, high monomer conversion (86–93%) was achieved in short reaction time (1 h), affording poly(lactide) with a very low degree of transesterification and narrow molecular weight distribution. Most importantly, all the reactions were performed at only 80 °C, almost 100 °C lower than the conventional melt process (typically performed at 130–180 °C), representing a very significant potential energy saving. [ABSTRACT FROM AUTHOR]

A new way to combine two different polymerisation reactions, using a single catalyst, results in efficient block polymer synthesis. The selective polymerisation of mixtures of l-lactide-O-carboxyanhydride and cyclohexene oxide, using a di-zinc catalyst in a one-pot procedure, allows the preparation of poly(l-lactide-b-cyclohexene carbonate). The catalysis near quantitatively recycles the carbon dioxide released during polyester formation into the subsequent polycarbonate block, with an atom economy of up to of 91%. [ABSTRACT FROM AUTHOR]

A range of ligands based upon 2-(aminomethyl)piperidine have been successfully complexed to Mg(ii), Zn(ii) and group IV metal centres. These complexes have been characterised both in solution and solid state with different coordination geometries realised dependant on the nature of the ligand. For the Mg(ii) and Zn(ii) complexes, M(1–2)2, were isolated and analysed by DOSY NMR spectroscopy. These ligands also furnished diastereomeric group IV complexes, M(1–2)2(OiPr)2. Group IV salalen and salan complexes, M(4–5)(OR)2 were also found to be diastereomeric in nature, with either β-cis or α-cis geometriesrespectively. The tridentate ligand, 6H2, yielded five coordinate complexes with both Ti(iv) and Zr(iv). All complexes were screened for the ring opening polymerisation of rac-lactide under both solvent and melt conditions. For the Mg(ii) and Zn(ii) complexes, good activity was observed with Zn(1–2)2 demonstrating immortal polymerisation characteristics. [ABSTRACT FROM AUTHOR]

Unsymmetrical amine tris(phenolate) ligands have been prepared and complexed to Zr(IV). In the solidstate dimeric species are observed, which persist in solution. The complexes show interesting coordination chemistry and the nature of which is discussed. These complexes are analogues of a highly stereoselective C3-symmetric Zr(IV) amine tris(phenolate) alkoxide and have been prepared, characterised and trialled for the ring-opening of rac-lactide providing insight into the effect of symmetry and ligand steric bulk on selectivity. The polymerisations have been investigated in solution and under the industrially preferred melt conditions (130 °C). The rate law for the ROP has been determined - with Zr2(1)2(OiPr)2, a pseudo first order dependency was seen, however for Zr2(2)2(OiPr)2 this changed to a half order dependency in initiator. [ABSTRACT FROM AUTHOR]

The synthesis, solid-state and solution structure of a magnesium amine bis(phenolate) complex [Mg{(O-2,4-tBu2C6H2-6-CH2N(Me)CH2}2(C6H5CH3)1.5]24-Mg is reported. The complex was prepared by combining MgBu2 with an equimolar amount of the parent bis(aminophenol) at ambient temperature in toluene. In the solid-state, the complex exists as a dimer. Each Mg centre is five-coordinate – bonding to one μ1[sbnd]O, two μ2[sbnd]O and two N moieties. NMR spectroscopy indicates that the solid-state structure is maintained in solution. Complex 4-Mg was investigated as a catalyst for ring opening polymerisation (ROP) of ε-caprolactone and L-lactide at both ambient and elevated temperatures, but was shown to be inactive, presumably as a direct result of the high steric bulk of the amine bis(phenolate) ligand. [ABSTRACT FROM AUTHOR]

The synthesis and structural characterization of an unusual trinuclear barium aminebis(phenolate) complex are reported along with its application as an initiator for the ring-opening polymerization of ϵ-caprolactone and L-lactide. [ABSTRACT FROM AUTHOR]

Here a zirconium amine tris(phenolate) is used as the initiator for the production of polylactide for biomedical applications, as a replacement for a tin initiator (usually tin octanoate). The ring opening polymerization (ROP) was carried out in the melt at 130 °C. The zirconium-catalyzed PLA (PLA-Zr) required 30 min, resulting in a polydispersity index (PDI) of 1.17, compared to 1 h and PDI = 1.77 for tin-catalyzed PLA (PLA-Sn). PLA-Zr and PLA-Sn supported osteosarcoma cell (MG63) culture to the same extent (cell number, morphology, extracellular matrix production and osteogenic function) until day 14 when the PLA-Zr showed increased cell number, overall extracellular matrix production and osteogenic function. To conclude, the reduction in reaction time, controllable microstructure and biologically benign nature of the zirconium amine tris(phenolate) initiator shows that it is a more effective initiator for ROP of polylactide for biomedical applications. [ABSTRACT FROM AUTHOR]