Electrochemically Controlled Switchable Copolymerization of Lactide, Carbon Dioxide, and Epoxides.

Electrochemical redox-control is an emerging strategy for the regulation of polymerization process without the addition of external oxidants and reductants, which enables the control over composition, microstructure and properties of the polymer products. In this paper, based on the chemical selectivity of heterometallic Salen-Co-Mn complexes of different valences, an electrochemically switchable strategy was developed for the copolymerization of lactide (LA), CO2 and epoxides. The switchable redox reactions endowed this system with the capability to easily synthesize a multi-block copolymer of polylactide (PLA) and polycarbonate (PC). Moreover, the multi-block copolymer could be further modified by introducing various monomers with different microstructures and functional groups.

Monomer Controlled Switchable Copolymerization: A Feasible Route for the Functionalization of Poly(lactide).

Switchable polymerization is an attractive strategy to enable the sequential selectivity of multi-block polyesters. Besides, these well-defined multi-block polyesters could enable further modification for wider applications. Herein, based on the reversible insertion of CO2 by Salen-MnIII , a new monomer controlled self-switchable polymerization route was developed. Chemoselective ring opening copolymerization of O-carboxyanhydrides (OCAs) and lactide (LA) was explored without cocatalyst. The sequential conversion of OCAs and LA into the polymer chain could form multi-block polyesters. Based on this strategy, a series of multi-block polyesters with different pendant groups were synthesized. Furthermore, by modifying the propargyl-containing copolymers with quaternary ammonium groups, we have realized antibacterial functionalization of PLA. These results imply the potential application of this strategy for the fabrication of functional polymers for biomedical applications.

A trinuclear salen-Al complex for copolymerization of epoxides and anhydride: mechanistic insight into a cocatalyst-free system.

A rare example of a trinuclear salen-Al complex is reported. Due to the intramolecular interaction, the trinuclear salen-Al complex can catalyze copolymerization with high activity in the absence of any cocatalyst. On the basis of a covalent coordination insertion mechanism, ABC(1)C(2) type tetrablock copolymers were produced using an hydroxyl initiator.

Zinc and Magnesium Complexes Bearing Oxazoline-Derived Ligands and Their Application for Ring Opening Polymerization of Cyclic Esters.

A family of different substituents aza(oxazoline) ligand-based zinc and magnesium complexes were synthesized. These complexes can catalyze ring opening polymerization of ε-caprolactone (ε-CL) and lactide (LA) to produce poly-ε-caprolactone and polylactide with good conversions. Polymerization studies showed that the zinc complexes 1a-4a had moderate activity toward LA and ε-CL polymerization. In situ IR spectroscopy research of zinc complexes showed that the N-donor group-substituted complexes had higher activity than that of the O-ether donor group. The substituted analogies and the flexibility of the amino backbone had a distinct influence on the activity of LA and ε-CL polymerization. The alternates of zinc with magnesium produced complexes 5a-8a, which achieved an obviously increased polymerization activity. Among these magnesium complexes, 7a showed the highest activity in the polymerization of LA. At [M]/[cat] = 1000, the reaction progress was stabilized in 5 min with up to 97% conversion of a monomer at ambient temperature.

Preparation and Thermal Properties of Polycarbonates/esters Catalyzed by Using Dinuclear Salph-Al from Ring-Opening Polymerization of Epoxide Monomers.

A dinuclear Salph-Al complex/bis(triphenylphosphine)iminium chloride catalyst system was synthesized and employed for cyclohexene oxide (CHO) and CO2 copolymerization. The catalyst system had an excellent selectivity of 99 % for carbonate linkages and the resultant poly(cyclohexene carbonate) (PCHC) had a high glass transition temperature (Tg ) of 123.8 °C and a thermal decomposition temperature (5 % weight loss; Td 5 % ) of 265 °C. Furthermore, this catalyst system was active in the polymerization of phthalic anhydride (PA) and epoxides. Poly(CHO-alt-PA) was completely alternating, and had improved thermal properties (Tg =142.7 and Td 5 % =295 °C) compared with PCHC. The Tg values of the polyesters could be adjusted by addition of PO to the CHO/PA reaction system. For the CHO/PO/PA terpolymerization, CHO and PO participated concurrently and proportionally in the chain growth and the obtained terpolyesters had tunable Tg values from 62.8 to 142.7 °C depending on the CHO/PO feed ratio.

Zinc complexes containing asymmetrical N,N,O-tridentate ligands and their application in lactide polymerization.

A series of zinc complexes based on asymmetrical N,N,O-tridentate ligands were prepared via binaphthyl diamine derivatives. These complexes were characterized and employed as catalysts in lactide polymerization. The X-ray diffraction analyses revealed that molecular structures of 1b and 2b were mononuclear complexes with zinc atoms in distorted octahedral geometries. Upon co-catalysis with isopropanol, complex 2a showed the highest activity among these zinc complexes for the ring-opening polymerization of L-lactide, and complex 3a exhibited the highest stereoselectivity for the ring-opening polymerization of rac-lactide affording substantially isotactic polylactide (PLA) with a P(m) of 0.62. The polymerization kinetics using 2a as a catalyst was studied in detail. The kinetics of the polymerization results revealed that the rates of polymerization were first-order both in the monomer and the catalyst, and there was a linear relationship between the L-LA conversion and the number-average molecular weight of PLA with a narrow molecular distribution (1.07-1.17). The activation energy (31.49 kJ mol(-1)) was deduced according to the Arrhenius equation.