Chiral Salan Aluminium Ethyl Complexes and Their Application in Lactide Polymerization

Synthetic routes to aluminium ethyl complexes supported by chiral tetradentate phenoxyamine (salan-type) ligands [Al(OC6H2(R-6-R-4)CH2)(2){CH3N(C6H10)NCH3}-C2H5] 7: R = H ; 5, 8: R = Cl; 6, 9: R = CH3) are reported. Enantiornerically pure salan ligands 1-3 with (R,R) configurations at their cyclohexane rings afforded the complexes 4, 5, and 6 as mixtures of two diastereoisomers (a and b). Each diastereoisomer a was, as determined by X-ray analysis, monomeric with a five-coordinated aluminium central core in the solid state, adopting a cis-(O,O) and cis-(Me,Me) ligand geometry. From the results of variable-temperature (VT) H-1 NMR in the temperature range of 220-335 K, H-1-H-1 NOESY at 220 K, and diffusion-ordered spectroscopy (DOSY), it is concluded that each diastereoisomer b is also monomeric with a five-coordinated aluminium central core.

Polymerization of Lactide Using Achiral Bis(pyrrolidene) Schiff Base Aluminum Complexes

A series of aluminum ethyls and isopropoxides based on a bis(pyrrolidene) Schiff base ligand framework has been prepared and characterized. NMR studies of the dissolved complexes indicate that they adopt a symmetric structure with a monomeric, five-coordinated aluminum center core. The aluminum ethyls used as catalysts in the presence of 2-propanol as initiator and the aluminum isopropoxides were applied for lactide polymerization in toluene to test their activities and stereoselectivities. All polymerizations are living, as evidenced by the narrow polydispersities and the good fit between calculated and found number-average molecular weights of the isolated polymers. All of these aluminum complexes polymerized (S,S)-lactide to highly isotactic PLA without epimerization of the monomer, furnished isotactic-biased polymer from rac-lactide, and gave atactic polymer from meso-lactide.

The Surface Modification of Hydroxyapatite Nanoparticles by the Ring Opening Polymerization of gamma-Benzyl-L-glutamate N-carboxyanhydride

The surface modification of hydroxyapatite (HA) nanoparticles by the ring opening polymerization (ROP) of gamma-benzyl-L-glutamate N-carboxyanhydride (BLG-NCA) was proposed to prepare the poly(gamma-benzyl-L-glutamate) (PBLG)-grafted HA nanoparticles (PBLG-g-HA) for the first time. HA nanoparticles were firstly treated by 3-aminopropylthriethoxysilane (APS) and then the terminal amino groups of the modified HA particles initiated the ROP of BLG-NCA to obtain PBLG-g-HA. The process was monitored by XPS and FT-IR. The surface grafting amounts of PBLG on HA ranging from 12.1 to 43.1% were characterized by thermal gravimetric analysis (TGA). The powder X-ray diffraction (XRD) analysis confirmed that the ROP only underwent on the surface of HA nanoparticles without changing its bulk properties. The SEM measurement showed that the PBLG-g-HA hybrid could form an interpenetrating net structure in the self-assembly process.

Effects of polymerization conditions on hydrophilic groups in aromatic polyamide thin films

For polyamide used in reverse osmosis (RO) membranes, the content of pendant acid groups is critical to its performance. In this work, FTIR was used to analyze the acid contents in the polyamide films prepared via interfacial polymerization of trimesic acid trichloride (TMC) in hexane and 1,3-phenylenediamine (MPDA) in water, and the effects of reaction conditions, including monomer concentrations, time, and temperature, were studied. It was found that more pendant acid groups are present in the polyramide film at higher TMC concentrations or lower MPDA concentrations, and longer reaction times and lower temperatures also favor the formation of the free acids. These results can be explained by the monomer diffusion in the interfacial polymerization process. This work may help the design and fabrication of RO membranes with different hydrophilicity and target performance.