Effect of the phenyl ring substituent on stereoselectivity in the ring-opening polymerization of the rac-lactide initiated by salen aluminum complexes

Cooperative Heterometallic Catalysts for Lactide Ring-Opening Polymerization: Combining Aluminum with Divalent Metals

While homometallic (salen)Al catalysts display excellent performance in lactide ring-opening polymerization (ROP), heterometallic (salen)Al complexes have yet to be reported. Herein, we describe four heterobimetallic (salen)Al catalysts and show that the choice of the heterometal is key. Cooperative Al/Mg and Al/Zn combinations improved the catalyst activity by a factor of up to 11 compared to the mono-Al analogue, whereas the mono-Mg and mono-Zn analogues were completely inactive. In contrast, Al/Li and Al/Ca heterocombinations stunted the polymerization rate. Kinetic and computational studies suggest that Al/Mg and Al/Zn cooperativity arises from the close intermetallic proximity facilitating chloride bridging (thus enhancing initiation), which promotes a rigid square pyramidal geometry around the Al center and further increases the available monomer coordination sites. This work also translates the use of ab initio molecular dynamics calculations to ROP, introducing a useful method of investigating catalyst flexibility and revealing that ligand strain and molecular rigidity can enhance heterometallic catalyst performance.

Preparation of star-shaped functionalized polylactides by metal porphyrin complexes as both catalysts and cocatalysts

Several aluminum porphyrin complexes as catalysts and a copper porphyrin complex as a cocatalyst were prepared. These complexes were characterized by 1H NMR and elemental analysis. These complexes are used for L-lactide polymerization. The kinetic data of the polymerization using complex 2 as catalyst revealed that the polymeric rates were first-ordered in both the monomer and catalyst. There is a linear relationship between lactide conversion and the number-averaged molecular weight of PLA.

Synthesis of biodegradable and biorenewable polylactides initiated by aluminum complexes bearing m-xylylenediamine derivatives via the ring-opening polymerization of lactides

Aluminum complexes derived from m-xylylenediamine were synthesized and investigated as initiators for l-lactide and rac-lactide polymerization.

Recent progress in the application of group 1, 2 & 13 metal complexes as catalysts for the ring opening polymerization of cyclic esters

This review focuses on recent developments concerned with the use of well-defined main group complexes as (pre-)catalysts for the ROP of cyclic esters to give aliphatic polyesters; factors influencing catalytic activity, selectivity and polymer properties are all discussed.

Nanoporous PLA/(Chitosan Nanoparticle) Composite Fibrous Membranes with Excellent Air Filtration and Antibacterial Performance

Particulate matter (PM) pollution, which usually carries viruses and bacteria, has drawn considerable attention as a major threat to public health. In this present study, an environment-friendly antibacterial Poly(lactic acid)(PLA)/chitosan composite air filter was fabricated using the one-step electrospinning technique. The composite PLA/chitosan fibres show a highly porous structure, in which chitosan nanoparticles (NPs) were found to be uniformly distributed throughout the entire fibre. The morphologies, through-pore size and distribution, air filtration and anti-microbial properties of these filter media were studied. The results showed that it was not the chitosan content but instead the concentration of the spinning solutions that had the greatest effect on the morphologies of the porous fibres. The relative humidity influenced the nanometre-scale pores on the surface of PLA/chitosan fibres. The PLA/chitosan fibrous membranes with a chitosan to PLA mass ratio of 2.5:8 exhibited a high filtration efficiency of 98.99% and a relatively low pressure drop (147.60 Pa) when the air flow rate was 14 cm/s, while these also had high antibacterial activity of 99.4% and 99.5% against Escherichia coli and Staphylococcus aureus, respectively. It took 33 min for the PM2.5 concentration to decrease to 0 μg/m³ from 999 μg/m³ using the PLA/chitosan fibrous membranes, which demonstrates obviously effective air purification performance.