Search

A series of bidentate ligands were examined to improve the catalytic activity of l-lactide ( LA) polymerization by using n-butyl lithium and BnOH. For LA polymerization, n-butyl lithium with tetraisopropyl methylenebis(phosphonate) ( L8 ) showed the greatest catalytic activity but with poor controllability of the polymer molecular weight. The polydispersity indices ( PDIs) could be improved without BnOH addition, but Mn GPC was much different from the Mn Cal . 1H NMR spectra confirmed that the cyclized PLA was obtained, thus implying that active chain-end mechanisms were operative in LA polymerization. [ABSTRACT FROM AUTHOR]

This study synthesized a series of titanium iminophenoxide complexes and investigated their suitability as catalysts for the ring-opening polymerization of L-lactide ( L-LA) and ε-caprolactone (CL). Complexes with bidentate ligands demonstrate higher catalytic activity than their tridentate counterparts since the third coordination atom needs to contend with L-LA and CL. Differences in the geometric framework of bidentate ligands also influence the catalytic activity. Type II ligands ( N, N-trans form of Ti complex) prevent the coordination of monomers to Ti thereby decreasing the initiation rate. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013 [ABSTRACT FROM AUTHOR]

Abstract: A novel calcium complex, [(DAIP)2Ca]2 (where DAIP-H=2-[(2-dimethylamino-ethylimino)methyl]phenol), is prepared in a one flask reaction by condensation of Ca(OMe)2 with DAIP-H in toluene/THF. Experimental results show that in the presence of various alcohols, [(DAIP)2Ca]2 efficiently initiates the ring-opening polymerization of l-lactide in a controlled fashion, yielding polymers with expectative molecular weight and low polydispersity indexes. Furthermore, kinetic studies show a first-order dependency on both [LA] and [BnOH]. [Copyright &y& Elsevier]

A series of titanium (Ti) complexes bearing ONO-tridentate Schiff bases were synthesized and their application to the ring-opening polymerization of L-lactide and ε-caprolactone was studied. Ti complexes bearing ONO-tridentate Schiff bases revealed a greater catalytic activity compared to other previously synthesized Ti complexes bearing multi-dentate phenolate ligands. We hypothesize that using ONO-tridentate Schiff bases as ligands reduces the occupied space and increases the monomer coordination around the Ti center, thereby increasing catalytic activity. The electronic effect of the phenolate group on the polymerization rate was also studied, showing that electron-donating substituents on the ligands could drastically increase polymerization activity. [ABSTRACT FROM AUTHOR]

A series of titanium (Ti) compounds bearing 2,6-bis(o -hydroxyalkyl)pyridine ligands were synthesized and investigated as catalysts for the ring-opening polymerization of ε-caprolactone (CL) and L -lactide (LA). The Ti complexes with electron-withdrawing groups in pyridine rings or steric bulky groups in hydroxymethyl groups reduced the catalytic activity in CL and LA polymerizations, and Me L Ph -TiOPr 2 exhibited the highest catalytic activity ([CL] = 0.5 M, [CL]:[Cat] = 100:8, 60 °C, 7.5 h, conversion = 93%; [LA] = 0.5 M, [LA]:[Cat] = 100:8, 60 °C, 3.5 h, conversion = 98%). The density functional theory calculation results revealed that CL interacted with the ligand through weak hydrogen bonds, and then approached the Ti center. After being attacked by isopropyl oxide, the carbonyl group of CL bonded to the Ti center. After the rearrangement and ring opening of CL ring, CL was converted to poly-ε-caprolactone. Image 1 • Ti compounds bearing 2,6-bis(o -hydroxyalkyl)pyridine ligands were synthesized. • LA and CL polymerizations were investigated. • Me L Ph -TiOPr 2 exhibited the highest catalytic activity. [ABSTRACT FROM AUTHOR]

A series of aluminum complexes bearing heterocyclic amine ligands were synthesized, and their application in ε -caprolactone (CL) and L -Lactide (LA) polymerization and copolymerization were studied. The CL polymerization results revealed that ligands containing the higher electronegativity atom increased the polymerization rate of CL polymerization. Among these Al complexes, NON-AlMe 3 bearing benzofurazan ligand was the best catalyst in CL polymerization ([ NON-AlMe 3 ] = 10 mM, conversion = 94% after 4 min at room temperature). In LA polymerization, the catalytic trend of Al complexes was random, and NCN-AlMe 3 bearing 1-benzylbenzimidazole ligand was the best catalyst ([ NCN-AlMe 3 ] = 10 mM, conversion = 90% after 45 min at 80 °C). The selectivity of the production of a PLA- gradual -PCL copolymer could be controlled by different Al complexes. Our study revealed that the four-coordinated trimethyl Al complexes bearing heterocyclic amine ligands were easily synthesized and constitute an ideal catalyst design in CL polymerization. Image 1 • NON-AlMe 3 was the best catalyst in CL polymerization. • NCN-AlMe 3 was the best catalyst in LA polymerization. • PLA- gradual -PCL copolymer could be controlled by different Al complexes. [ABSTRACT FROM AUTHOR]

• 5-membered ring Mg complexes had higher activity in lactide polymerization. • Mg complexes with thiophene groups revealed the highest catalytic activity. • BnOH approaches LA through the hydrogen bond with phenolate, and then initiates LA. A series of magnesium complexes bearing 2-(arylideneamino)phenolate (forming 5-membered ring Mg complexes) and 2-((arylimino)methyl)phenolate (forming 6-membered ring Mg complexes) ligands were synthesized, and their application in the ring-opening polymerization of L -lactide (LA) was investigated. The Mg complexes with 5-membered rings exhibit a higher polymerization rate and controllability for polylactide production than those with 6-membered rings do (one-fold to three-fold for LA polymerization). The density function theory calculation results revealed that benzyl alcohol approaches LA through the hydrogen bond with phenolate oxygen, and then initiates LA, with the proton transferring to phenolate oxygen to form the LA-OBn adduct. The LA-OBn adduct was activated using the proton present on phenolate oxygen to open the ring of the LA-OBn adduct. Moreover, the LA polymerization using L5ThioMg as a catalyst needs to overcome a 17.7 kcal/mol activation free energy that is lower than that of L6ThioMg (21.0 kcal/mol) [ABSTRACT FROM AUTHOR]

A series of pyridine and polypyridine-zinc complexes were synthesized, and their application in ε-caprolactone and l -lactide polymerization was studied. In ε-caprolactone polymerization, zinc complexes bearing 1,10-phenanthroline derivatives exhibited a higher polymerization rate than did diethyl zinc (2–10 times). In l -lactide polymerization, zinc complexes bearing 1,10-phenanthroline derivatives exhibited a considerably higher polymerization rate than did diethyl zinc (2–220 times). According to density functional theory results, the ortho -hydrogens of polypyridine ligand can co-activate the carbonyl group of monomers with zinc metal center to increase the catalytic activity of zinc catalysts. Image 1 • The polypyridne-zinc complexes were synthesized. • 1,10-Phenanthroline derivatives enhanced the catalytic activity of Zn complexes. • Hydrogens of polypyridine co-activate the carbonyl group of monomers. [ABSTRACT FROM AUTHOR]

Main-group metal-based catalysts have attracted considerable attentions due to their complementary reactivities to transition metals. In searching for the catalytic application of heavy divalent Group 14 derivatives, we came to discover that the benzannulated N -heterocyclic plumbylene (1) could serve as an effective catalyst for ring-opening polymerization of l -lactide (L- LA) at room temperature. In the presence of benzyl alcohol (BnOH), 97% conversion of L- LA was accomplished in 10 min under a catalyst loading of merely 0.3 mol% ([LA]:[1]:[BnOH] = 400:1.2:1.2, [1] = 1.2 mM). Compared to the polymeric plumbylene ([Pb(μ -O i Pr) 2 ∞), the excellent catalytic activity of 1 at ambient temperature may be ascribed to the steric and electronic stabilizations of the Pb2+ center by the organic backbone. Thus, thermal activation is no longer required to expose the Lewis acidic metal center for polymerization. Image 1 • N -Heterocyclic plumbylene is an efficient catalyst in ring-opening polymerization of l -lactide. • 97% conversion of L- LA was accomplished in 10 min under a catalyst loading of merely 0.3 mol%. • N -Heterocyclic plumbylene reveals outstanding controllability in l -lactide polymerization. [ABSTRACT FROM AUTHOR]