Ranlong Duan

Bimetallic salen–aluminum complexes: synthesis, characterization and their reactivity with rac-lactide and ε-caprolactone

A series of bimetallic Schiff-base ligands were synthesized and used to prepare aluminum complexes. All the complexes were characterized by 1H, 13C NMR and elemental analysis. These complexes were used as catalysts in the rac-lactide and e-caprolactone polymerization. Isotactic enriched polylactides were obtained by using these complexes. All polymerizations were living with the narrow molar mass distributions. The Mn(obsd) of the isolated polymers was in good agreement with Mn(calcd). Kinetic studies showed that the polymerizations were first-ordered with respect to both lactide and caprolactone monomers. The more bulky substituents with more steric hindrance of the complexes had relatively poor activity. The increasing temperature had a positive effect as the polymerization rate increased with increasing temperature.

Synthesis and characterization of half-salen complexes and their application in the polymerization of lactide and epsilon-caprolactone

A series of half-salen ligands and their aluminum Al(III) complexes that contained different substituents were designed and synthesized. All the ligands and their complexes were characterized by 1H, 13C NMR and elemental analysis. The complexes can be used as catalysts to produce polylactide and poly-e-caprolactone. All polymerizations were living with narrow molar mass distributions. The Mn(obsd) values of the isolated polymers were in good agreement with Mn(calcd). The polymerization rate of the electrophilic substituted complex was higher than the non-electrophilic substituted analogues. The more bulky substituents with more steric hindrance of the complexes showed relatively low polymerizing activity. The aluminum complexes showed a moderate stereo-selectivity to the ring opening polymerization of rac-lactide to give isotactic enriched polylactide.

Magnesium complexes bearing N,N-bidentate phenanthrene derivatives for the stereoselective ring-opening polymerization of rac-lactides

Three unreported magnesium complexes (1: R = C6H5, 2: R = 2,6-Et2C6H3, 3: R = 2-tBuC6H4) bearing N,N-bidentate phenanthrene derivatives derived from Schiff bases were synthesized. These complexes were characterized using 1H and 13C NMR spectroscopy and elemental analyses and employed for rac-lactide and L-lactide polymerization. Complex 1 showed the highest activity among these Mg complexes for the ring-opening polymerization (ROP) of L-lactide, and complex 3 showed the highest stereoselectivity for the ROP of rac-lactide, achieving partially heterotactic polylactide (PLA) with a Pr of 0.76. The polymerization kinetics utilizing 2 as a catalyst were researched in detail. The kinetics of the polymerization data revealed that the rate of polymerization was first-order with respect to monomer, and had an order of 0.97 with respect to catalyst. There was a linear relationship between the L-lactide conversion and the number-average molecular weight of PLA.

Bimetallic Schiff-base aluminum complexes based on pentaerythrityl tetramine and their stereoselective polymerization of racemic lactide

A series of Schiff base aluminum(III) complexes with bimetallic active centers are synthesized. Their catalytic properties in the solution polymerization of racemic lactide (rac-LA) are examined. The modifications in the auxiliary ligand exhibited a dramatic influence on the catalytic performance. Among these complexes, 3a has the highest stereoselectivity (Pm = 0.91) owing to the bulky tert-butyl groups on the salicylaldehyde. Kinetic studies indicate that the polymerizations are both first-ordered with respect to the monomer and catalyst. Other factors that influence the polymerization such as the polymerization time and the temperature, as well as the monomer concentration, are discussed in detail.

Bimetallic Schiff base complexes for stereoselective polymerisation of racemic-lactide and copolymerisation of racemic-lactide with ε-caprolactone

Three pairs of bimetallic Schiff base aluminum complexes (1a–6a) with different tetraamine backbone bridging parts and bulky silyl-substituted moieties on salicylidene were synthesized. Using these complexes as catalysts for ring opening polymerisation (ROP) of racemic-lactide (rac-LA), systematical stereoselectivity and kinetic studies on ROP of rac-LA were carried out. The Gibbs free energy difference between homo-propagation and cross-propagation (ΔG≠) calculated by activation entropy and enthalpy showed that bulky substituents at the 3-position enhanced the stereoselectivity. And the kinetic study results indicated that bulkier substituents with more steric hindrance reduced the ROP reactivity. Moreover, these complexes could also be used for copolymerisation of rac-LA and e-caprolactone (e-CL). Copolymers of poly(LA-co-CL) with various monomer ratios were synthesized. Kinetic research on copolymerisation as well as microstructure analysis demonstrated that poly (LA-co-CL) achieved by these complexes were tapered block copolymers.

Titanium complexes with octahedral geometry chelated by salen ligands adopting β-cis configuration for the ring-opening polymerisation of lactide

Four titanium complexes based on salen ligands were prepared and employed for the ring-opening polymerisation of lactide. X-ray diffraction analysis revealed that the titanium atom was in a distorted octahedral geometry and the quadridentate ligand adopted β-cis geometry in complex 1.

Synergistic effect of PLA–PBAT–PLA tri-block copolymers with two molecular weights as compatibilizers on the mechanical and rheological properties of PLA/PBAT blends

Two types of polylactide–poly(butylene adipate-co-terephthalate)–polylactide (PLA–PBAT–PLA) tri-block copolymers with different molecular weights (CP1 and CP2) were synthesized as compatibilizers for PLA/PBAT blends. Synergistic effects of CP1 and CP2 on the mechanical and rheological properties of the blends have been studied in detail. The addition of small amounts of CP1 and CP2 remarkably increased the elongation at the break point. 0.5 and 0.5 wt% of CP1 and CP2 led to an increase of elongation by over eightfold. Thermal, morphological and rheological analyses showed that addition of CP1 and CP2 increased the miscibility and interfacial bonding strength between PLA and PBAT, in addition to decreasing the melt viscosity. It was thought that the low-molecular-weight compatibilizer CP1 with high mobility would have a positive effect during the transportation of the high-molecular-weight CP2 from the matrix to the interface. In addition, CP2 played a key role in improving the interaction at the interface.

Hemi-salen aluminum catalysts bearing N, N, O-tridentate type binaphthyl-Schiff-base ligands for the living ring-opening polymerisation of lactide

Four hemi-salen aluminum complexes based on tridentate N, N, O-type binaphthyl-Schiff-base derivatives (1: R = iPr; R1 = H; 2: R = iPr; R1 = Cl; 3: R = 2-adamantyl; R1 = H; 4: R = 2-adamantyl; R1 = tBu) were prepared. These complexes were characterized by 1H, 13C NMR spectroscopy and elemental analysis, these four complexes were employed for ring-opening polymerisation of L-lactide and rac-lactide. Complex 2, which was based on pro-ligand L2 with smaller steric hindrance and electron-withdrawing substituents, displayed the highest activity for ROP of L-lactide among these complexes, and complex 4, which was supported by pro-ligand L4 with the biggest steric hindrance, showed the highest stereoselectivity for the ROP of rac-lactide with partially isotactic polylactide with a Pm of 0.65. Kinetic studies revealed the ROP of L-lactide initiated by complex 3 had first-order dependency on [LA] as well as [Al].

Highly stereoselective bimetallic complexes for lactide and ε-caprolactone polymerization

A series of Schiff-base compounds containing bimetallic ligands and two aluminum centers have been synthesized and characterized by 1H, 13C NMR and elemental analysis. These compounds could be successfully used as catalysts for the polymerization of rac-lactide and e-caprolactone. The polylactides (PLAs) prepared with these compounds were highly isotactic enriched (Pm = 0.97). The nature and steric hindrance of the ligands coordinated to the central metal ions remarkably influenced the polymer properties. Kinetic studies revealed that the polymerization was first order with respect to each of these compounds and lactide/caprolactone monomers. All the polymerizations were living, with good molecular weight control and relatively narrow molar mass distributions.

Preparation of biocompatible, biodegradable and sustainable polylactides catalyzed by aluminum complexes bearing unsymmetrical dinaphthalene-imine derivatives via ring-opening polymerization of lactides

A number of half-salen aluminum complexes bearing unsymmetrical [ONN]-type ligands were prepared from tridentate dinaphthalene-imine derivatives. These complexes were characterized by 1H and 13C NMR spectroscopy, elemental analysis and single crystal X-ray diffraction analysis. These complexes were employed for rac-lactide and L-lactide polymerization. Upon activation with isopropanol, complex (S)-B6 (R1 = R2 = R4 = H; R3 = F) showed the highest activity (a monomer conversion of 94.6%) amid these aluminum complexes for the ring-opening polymerization of L-lactide; and complex (S)-B2 (R1 = R2 = R3 = H; R4 = tBu) showed the highest stereoselectivity for the ring-opening polymerization of rac-lactide, obtaining a polylactide (PLA) with a Pm of 0.69. The polymerization kinetics utilizing (S)-B6 as a catalyst were researched in detail. The data on the polymerization kinetics revealed that the rate of polymerization was first-order with respect to the monomer and the catalyst. There was a linear relationship between the L-lactide conversion and the number-average molecular weight of PLA.