Efficient Initiators For Ring-opening Polymerization Research Articles

Zinc complexes supported by (benzimidazolyl)pyridine alcohol ligands as highly efficient initiators for ring-opening polymerization of ε-caprolactone

A series of air-stable zinc complexes (1–3) supported by (benzimidazolyl)pyridine alcohol ligands {tridentate [N,N,O]} has been synthesized and well characterized by FT-IR, 1H and 13C NMR, elemental analysis and single-crystal X-ray diffraction analysis. In combination with methyllithium, these zinc complexes were proved to be highly efficient initiators for the ring-opening polymerization (ROP) of ε-caprolactone (ε-CL). The ROP of ε-CL in the absence or presence of benzyl alcohol, as well as the influences of monomer concentration, reaction temperature and the substituent on the ligand, were investigated in detail.

Aluminum Complexes Containing the C–O–Al–O–C Framework as Efficient Initiators for Ring-Opening Polymerization of ε-Caprolactone

Three aluminum complexes, LAl(OCH2C6H4-2-NH2)2 (2), LAl(9-OC13H9)2 (3), and LAl(OC6H10-4-NH2)2 (4), were synthesized in good yield by reacting one equivalent of LAlH2 (1) (L = HC(CMeNAr)2, Ar = 2,6-iPr2C6H3) with two equivalents of 2-aminobenzyl alcohol, 9-hydroxyfluorene, and trans-4-aminocyclohexanol, respectively. All complexes (2, 3, and 4) contain the C–O–Al–O–C framework. These complexes have been characterized by IR, 1H and 13C NMR, elemental analyses, and single-crystal X-ray structural analysis. Furthermore, the excellent catalytic activities of 2, 3, and 4 for ring-opening polymerization of e-caprolactone in the presence of isopropyl alcohol were investigated.

Zinc complexes coordinated by bipyridine-phenolate ligands as an efficient initiator for ring-opening polymerization of cyclic esters

A series of zinc complexes coordinated by different bipyridine-phenolate (BpyPh) ligands, 2-([2,2′-bipyridin]-6-yl)-4,6-di-tert-butylphenol (BpyPh2,4-tBu-H, 3) and 2-([2,2′-bipyridin]-6-yl)-4-(tert-butyl)phenol (BpyPh4-tBu-H, 4) have been synthesized. The reaction of BpyPh2,4-tBu-H with ZnEt2 gave a six-coordinated complex of [(BpyPh2,4-tBu)2Zn] (5) with the distorted octahedral geometry. However, the dinuclear complexes of [(BpyPh)Zn(μ-OBn)]2 (6 and 7) were formed when benzyl alcohol was added and then can be converted to mononuclear zinc benzylalkoxide species by the increased temperature. The ε-CL and L-LA polymerizations initiated by complex 6 showed the living characteristics of narrow molecular weight distribution (PDIs < 1.15) and the capability of block copolymer synthesis demonstrated by the formation of PCL-b-PVL and PCL-b-PHB. The ring-opening polymerizations of cyclic esters initiated by complex 5, however, was not effective possibly due to the highly steric hindered metal center.

Bisguanidinato and bisamidinato Tin(IV) diolates applicable in ring-opening polymerization

Series of bisamidinato and bisguanidinato tin(IV) diolates prepared from 1,2-diones (3,5-di-tert-butyl-o-benzoquinone, 3,4,5,6-tetrachloro-1,2-benzoquinone, 9,10-phenanthrenedione, acenaphthenequinone, 1,2-diphenylethanedione) and {Cy-NC(n-Bu)N-Cy}2Sn or {pTol-NC[N(SiMe3)2]N-pTol}2Sn, respectively, were used as efficient initiators for ring-opening polymerization of ε-caprolactone. Moderate to good efficiency of selected compounds in trimethylene carbonate polymerization was also observed.

Synthesis and structural determination of zinc complexes based on an anilido-aldimine ligand containing an O-donor pendant arm: zinc alkoxide derivative as an efficient initiator for ring-opening polymerization of cyclic esters

Zinc complexes bearing the anilido-aldiminate AA(OMe) ligand (AA(OMe)-H = (E)-2,6-diisopropyl-N-(2-(((2-methoxyethyl)imino)methyl)phenyl)aniline) were synthesized in a stepwise method and were structurally characterized. The reaction of AA(OMe)-H (1) with one equivalent of diethyl zinc (ZnEt2) furnishes a three-coordinated and mononuclear zinc complex [(AA(OMe))ZnEt] (2). Further reaction of 2 with a stoichiometric amount of benzyl alcohol (BnOH) affords a four-coordinated and dinuclear zinc benzylalkoxide complex [(AA(OMe))Zn(μ-OBn)]2 (3). In the presence of two equivalents of AA(OMe)-H with ZnEt2, a homoleptic and four-coordinated zinc complex [(AA(OMe))2Zn] (4) is formed. The geometry around the zinc centres of 3 and 4 are both distorted tetrahedrals, while 2 adopts a different coordination mode with a slightly distorted trigonal planar geometry. The variable-temperature (1)H NMR studies of 3 illustrate that 3 exhibits a dinuclear structure in solution at low temperature as well as in the solid state. While raising the temperature, it drifts towards dissociation to form a mononuclear zinc benzylalkoxide species, which coexists in solution. The ring-opening polymerizations of ε-caprolactone (ε-CL) and β-butyrolactone (β-BL) catalyzed by complexes 3 and 4 are investigated. The ε-CL and β-BL polymerizations initiated by zinc alkoxide 3 were demonstrated to have living characteristics and to proceed in a controlled manner with narrow polydispersity indices (PDIs < 1.12). An efficient catalytic performance for the β-BL polymerization with a high monomer-to-initiator ratio (1200/1) initiated by 3 has also been reported.

Synthesis, Characterization, and Catalytic Studies of Lithium Complexes: Efficient Initiators for Ring-Opening Polymerization of l-Lactide

The reaction of 2,2‘-ethylidenebis(4,6-di-tert-butylphenol) (EDBP-H2) with nBuLi in tetrahydrofuran (THF), giving [(EDBP-H)Li(THF)3] (1) in high yield. However, the reaction of EDBP-H2 with nBuLi in the presence of benzyl alcohol (BnOH) in diethyl ether or tetrahydrofuran produces compounds [(EDBP-H)Li(BnOH)]2 (2) and [(EDBP-H)Li(BnOH)(THF)2] (3), respectively. Further reaction of 2 with excess of THF produces 3. Alternatively, 3 can also be prepared by the reaction of benzyl alcohol with 1 in toluene. Experimental results show that 2 and 3 efficiently initiate the ring-opening polymerization (ROP) of l-lactide in a controlled fashion, yielding polymers with very narrow polydispersity indexes in a wide range of monomer-to-initiator ratios. Block copolymers, polystyrene-b-poly(l-lactide), have also been prepared from the ring-opening polymerization of l-latide catalyzed by 3 using polystyrene as a macroinitiator.